151
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Xie Y, Cao HY, Zhou Y, Chen S, Xiang H, Gong XG. Oxygen Vacancy Induced Flat Phonon Mode at FeSe /SrTiO3 interface. Sci Rep 2015; 5:10011. [PMID: 26067548 PMCID: PMC4464289 DOI: 10.1038/srep10011] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2015] [Accepted: 03/25/2015] [Indexed: 11/09/2022] Open
Abstract
A high-frequency optical phonon mode of SrTiO3 (STO) was found to assist the high-temperature superconductivity observed recently at the interface between monolayer FeSe and STO substrate. However, the origin of this mode is not clear. Through first-principles calculations, we find that there is a novel polar phonon mode on the surface layers of the STO substrate, which does not exist in the STO crystals. The oxygen vacancies near the FeSe/STO interface drives the dispersion of this phonon mode to be flat and lowers its energy, whereas the charge transfer between STO substrate and FeSe monolayer further reduces its energy to 81 meV. This energy is in good agreement with the experimental value fitted by Lee et al. for the phonon mode responsible for the observed replica band separations and the increased superconducting gap. The oxygen-vacancy-induced flat and polar phonon mode provides clues for understanding the origin of high Tc superconductivity at the FeSe/STO interface.
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Affiliation(s)
- Yun Xie
- State Key Laboratory of Surface Physics, Key Laboratory for Computational Physical Sciences (MOE), Collaborative Innovation Center of Advanced Microstructure, Department of Physics, Fudan University, Shanghai 200433, China
| | - Hai-Yuan Cao
- State Key Laboratory of Surface Physics, Key Laboratory for Computational Physical Sciences (MOE), Collaborative Innovation Center of Advanced Microstructure, Department of Physics, Fudan University, Shanghai 200433, China
| | - Yang Zhou
- State Key Laboratory of Surface Physics, Key Laboratory for Computational Physical Sciences (MOE), Collaborative Innovation Center of Advanced Microstructure, Department of Physics, Fudan University, Shanghai 200433, China
| | - Shiyou Chen
- Key Laboratory of Polar Materials and Devices (MOE), East China Normal University, Shanghai 200241, China
| | - Hongjun Xiang
- State Key Laboratory of Surface Physics, Key Laboratory for Computational Physical Sciences (MOE), Collaborative Innovation Center of Advanced Microstructure, Department of Physics, Fudan University, Shanghai 200433, China
| | - Xin-Gao Gong
- State Key Laboratory of Surface Physics, Key Laboratory for Computational Physical Sciences (MOE), Collaborative Innovation Center of Advanced Microstructure, Department of Physics, Fudan University, Shanghai 200433, China
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152
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Mechanical writing of n-type conductive layers on the SrTiO3 surface in nanoscale. Sci Rep 2015; 5:10841. [PMID: 26042679 PMCID: PMC4455303 DOI: 10.1038/srep10841] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2015] [Accepted: 05/01/2015] [Indexed: 11/22/2022] Open
Abstract
The fabrication and control of the conductive surface and interface on insulating SrTiO3 bulk provide a pathway for oxide electronics. The controllable manipulation of local doping concentration in semiconductors is an important step for nano-electronics. Here we show that conductive patterns can be written on bare SrTiO3 surface by controllable doping in nanoscale using the mechanical interactions of atomic force microscopy tip without applying external electric field. The conductivity of the layer is n-type, oxygen sensitive, and can be effectively tuned by the gate voltage. Hence, our findings have potential applications in oxide nano-circuits and oxygen sensors.
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153
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Du Y, Peng HY, Mao H, Jin KX, Wang H, Li F, Gao XY, Chen W, Wu T. Evolution of the SrTiO3-MoO3 Interface Electronic Structure: An in Situ Photoelectron Spectroscopy Study. ACS APPLIED MATERIALS & INTERFACES 2015; 7:11309-11314. [PMID: 25964994 DOI: 10.1021/acsami.5b01698] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Modifying the surface energetics, particularly the work function of advanced materials, is of critical importance for a wide range of surface- and interface-based devices. In this work, using in situ photoelectron spectroscopy, we investigated the evolution of electronic structure at the SrTiO3 surface during the growth of ultra-thin MoO3 layers. Because of the large work function difference between SrTiO3 and MoO3, the energy band alignment on the SrTiO3 surface is significantly modified. The charge transfer and dipole formation at the SrTiO3-MoO3 interface leads to a large modulation of work function and to apparent doping in SrTiO3. The measured evolutions of electronic structure and upward band bending suggest that the growth of ultra-thin MoO3 layers is a powerful tool with which to modulate the surface energetics of SrTiO3, and this surface engineering approach could be generalized to other functional oxides.
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Affiliation(s)
- Yuanmin Du
- †Materials Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
| | - Hai Yang Peng
- ‡, Advanced LSI Technology Laboratory, Corporate Research and Development Center, Toshiba Corporation, Kawasaki 212-8582, Japan
| | - Hongying Mao
- ⊥Department of Physics, Hangzhou Normal University, Hangzhou 310036, PR China
| | - Ke Xin Jin
- #Department of Applied Physics, Northwestern Polytechnical University, Xi'an 710072, PR China
| | - Hong Wang
- †Materials Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
| | - Feng Li
- †Materials Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
| | - Xing Yu Gao
- ∇Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, PR China
| | | | - Tom Wu
- †Materials Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
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154
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Li C, Cao Y, Bai Y, Li A, Zhang S, Wu D. Electromechanical Response from LaAlO3/SrTiO3 Heterostructures. ACS APPLIED MATERIALS & INTERFACES 2015; 7:10146-10151. [PMID: 25919989 DOI: 10.1021/am509113j] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
LaAlO3 ultrathin films, 10 unit cells in thickness, have been deposited epitaxially on TiO2-terminated (001) SrTiO3 substrates with various O2 pressures. Electromechanical response from the LaAlO3/SrTiO3 heterostructures is studied using combined piezoresponse force microscopy, electrostatic force microscopy, and scanning Kelvin probe microscopy. Oxygen vacancies are found to be responsible for the observed piezoelectric response but only for samples deposited with an oxygen pressure lower than 10(-5) mbar. However, ambient humidity is demonstrated to have a significant effect on the electromechanical response. The observations are discussed in terms of modulations on the intrinsic electrostriction in LAO/STO by an electric field induced by nonuniform distribution of either oxygen vacancies in the bulk or ionic adsorbates on the surface of LAO.
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Affiliation(s)
- Chen Li
- National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Yuyuan Cao
- National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Yuhang Bai
- National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Aidong Li
- National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Shantao Zhang
- National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Di Wu
- National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
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155
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Cheng G, Tomczyk M, Lu S, Veazey JP, Huang M, Irvin P, Ryu S, Lee H, Eom CB, Hellberg CS, Levy J. Electron pairing without superconductivity. Nature 2015; 521:196-9. [DOI: 10.1038/nature14398] [Citation(s) in RCA: 120] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2014] [Accepted: 03/04/2015] [Indexed: 11/09/2022]
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156
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Kumar P, Dogra A, Bhadauria PPS, Gupta A, Maurya KK, Budhani RC. Enhanced spin-orbit coupling and charge carrier density suppression in LaAl1-xCrxO3/SrTiO3 hetero-interfaces. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:125007. [PMID: 25743442 DOI: 10.1088/0953-8984/27/12/125007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We report a gradual suppression of the two-dimensional electron gas (2DEG) at the LaAlO(3)/SrTiO(3) interface on substitution of chromium at the Al sites. The sheet carrier density at the interface (n□) drops monotonically from ∼2.2 × 10(14) cm(-2) to ∼2.5 × 10(13) cm(-2) on replacing ≈60% of the Al sites by Cr and the sheet resistance (R□) exceeds the quantum limit for localization (h/2e(2)) in the concentrating range 40-60% of Cr. The samples with Cr ⩽40% show a distinct minimum (T(m)) in metallic R□(T) whose position shifts to higher temperatures on increasing the substitution. Distinct signatures of Rashba spin-orbit interaction (SOI) induced magnetoresistance (MR) are seen in R□ measured in out of plane field (H⊥) geometry at T ⩽ 8 K. Analysis of these data in the framework of Maekawa-Fukuyama theory allows extraction of the SOI critical field (H(SO)) and time scale (τ(SO)) whose evolution with Cr concentration is similar as with the increasing negative gate voltage in LAO/STO interface. The MR in the temperature range 8 K ⩽ T ⩽ T(m) is quadratic in the field with a +ve sign for H⊥ and -ve sign for H∥. The behaviour of H∥ MR is consistent with Kondo theory which in the present case is renormalized by the strong Rashba SOI at T < 8 K.
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Affiliation(s)
- Pramod Kumar
- CSIR-National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi-110012, India
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157
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Rotella H, Copie O, Pautrat A, Boullay P, David A, Pelloquin D, Labbé C, Frilay C, Prellier W. Two components for one resistivity in LaVO3/SrTiO3 heterostructure. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:095603. [PMID: 25688927 DOI: 10.1088/0953-8984/27/9/095603] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
A series of 100 nm LaVO3 thin films have been synthesized on (0 0 1)-oriented SrTiO3 substrates using the pulsed laser deposition technique, and the effects of growth temperature are analyzed. Transport properties reveal a large electronic mobility and a non-linear Hall effect at low temperature. In addition, a cross-over from a semiconducting state at high-temperature to a metallic state at low-temperature is observed, with a clear enhancement of the metallic character as the growth temperature increases. Optical absorption measurements combined with the two-bands analysis of the Hall effect show that the metallicity is induced by the diffusion of oxygen vacancies in the SrTiO3 substrate. These results allow us to understand that the film/substrate heterostructure behaves as an original semiconducting-metallic parallel resistor, and electronic transport properties are consistently explained.
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Affiliation(s)
- H Rotella
- Laboratoire CRISMAT, CNRS UMR 6508, ENSICAEN et Université de Caen, 6 Bd Maréchal Juin, 14050 Caen Cedex 4, France. NUSNNI-NanoCore, National University of Singapore, 117411 Singapore
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158
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Chen Y, Trier F, Kasama T, Christensen DV, Bovet N, Balogh ZI, Li H, Thydén KTS, Zhang W, Yazdi S, Norby P, Pryds N, Linderoth S. Creation of high mobility two-dimensional electron gases via strain induced polarization at an otherwise nonpolar complex oxide interface. NANO LETTERS 2015; 15:1849-1854. [PMID: 25692804 DOI: 10.1021/nl504622w] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The discovery of two-dimensional electron gases (2DEGs) in SrTiO3-based heterostructures provides new opportunities for nanoelectronics. Herein, we create a new type of oxide 2DEG by the epitaxial-strain-induced polarization at an otherwise nonpolar perovskite-type interface of CaZrO3/SrTiO3. Remarkably, this heterointerface is atomically sharp and exhibits a high electron mobility exceeding 60,000 cm(2) V(-1) s(-1) at low temperatures. The 2DEG carrier density exhibits a critical dependence on the film thickness, in good agreement with the polarization induced 2DEG scheme.
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Affiliation(s)
- Yunzhong Chen
- Department of Energy Conversion and Storage, Technical University of Denmark , Risø Campus, 4000 Roskilde, Denmark
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159
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Photoresponse dynamics in amorphous-LaAlO3/SrTiO3 interfaces. Sci Rep 2015; 5:8393. [PMID: 25670163 PMCID: PMC4323649 DOI: 10.1038/srep08393] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2014] [Accepted: 01/02/2015] [Indexed: 11/08/2022] Open
Abstract
The time-resolved photoconductance of amorphous and crystalline LaAlO3/SrTiO3 interfaces, both hosting an interfacial 2-dimensional electron gas, is investigated under irradiation by variable-wavelengths, visible or ultraviolet photons. Unlike bare SrTiO3 single crystals, showing relatively small photoconductance effects, both kinds of interfaces exhibit an intense and highly persistent photoconductance with extraordinarily long characteristic times. The temporal behaviour of the extra photoinduced conductance persisting after light irradiation shows a complex dependence on interface type (whether amorphous or crystalline), sample history and irradiation wavelength. The experimental results indicate that different mechanisms of photoexcitation are responsible for the photoconductance of crystalline and amorphous LaAlO3/SrTiO3 interfaces under visible light. We propose that the response of crystalline samples is mainly due to the promotion of electrons from the valence bands of both SrTiO3 and LaAlO3. This second channel is less relevant in amorphous LaAlO3/SrTiO3, where the higher density of point defects plays instead a major role.
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160
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Scheurer MS, Schmalian J. Topological superconductivity and unconventional pairing in oxide interfaces. Nat Commun 2015; 6:6005. [DOI: 10.1038/ncomms7005] [Citation(s) in RCA: 87] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Accepted: 11/14/2014] [Indexed: 11/09/2022] Open
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161
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Herranz G, Singh G, Bergeal N, Jouan A, Lesueur J, Gázquez J, Varela M, Scigaj M, Dix N, Sánchez F, Fontcuberta J. Engineering two-dimensional superconductivity and Rashba spin-orbit coupling in LaAlO₃/SrTiO₃ quantum wells by selective orbital occupancy. Nat Commun 2015; 6:6028. [PMID: 25583368 PMCID: PMC4308716 DOI: 10.1038/ncomms7028] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2014] [Accepted: 12/03/2014] [Indexed: 11/09/2022] Open
Abstract
The discovery of two-dimensional electron gases (2DEGs) at oxide interfaces-involving electrons in narrow d-bands-has broken new ground, enabling the access to correlated states that are unreachable in conventional semiconductors based on s- and p- electrons. There is a growing consensus that emerging properties at these novel quantum wells-such as 2D superconductivity and magnetism-are intimately connected to specific orbital symmetries in the 2DEG sub-band structure. Here we show that crystal orientation allows selective orbital occupancy, disclosing unprecedented ways to tailor the 2DEG properties. By carrying out electrostatic gating experiments in LaAlO3/SrTiO3 wells of different crystal orientations, we show that the spatial extension and anisotropy of the 2D superconductivity and the Rashba spin-orbit field can be largely modulated by controlling the 2DEG sub-band filling. Such an orientational tuning expands the possibilities for electronic engineering of 2DEGs at LaAlO3/SrTiO3 interfaces.
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Affiliation(s)
- Gervasi Herranz
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, 08193 Bellaterra, Catalonia, Spain
| | - Gyanendra Singh
- LPEM-UMR8213/CNRS-ESPCI ParisTech-UPMC, PSL University, 10 rue Vauquelin, 75005 Paris, France
| | - Nicolas Bergeal
- LPEM-UMR8213/CNRS-ESPCI ParisTech-UPMC, PSL University, 10 rue Vauquelin, 75005 Paris, France
| | - Alexis Jouan
- LPEM-UMR8213/CNRS-ESPCI ParisTech-UPMC, PSL University, 10 rue Vauquelin, 75005 Paris, France
| | - Jérôme Lesueur
- LPEM-UMR8213/CNRS-ESPCI ParisTech-UPMC, PSL University, 10 rue Vauquelin, 75005 Paris, France
| | - Jaume Gázquez
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, 08193 Bellaterra, Catalonia, Spain
| | - María Varela
- 1] Materials Science &Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA [2] GFMC, Department de Fisica Aplicada III &Instituto Pluridisciplinar, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - Mateusz Scigaj
- 1] Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, 08193 Bellaterra, Catalonia, Spain [2] Departament de Física, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Catalonia, Spain
| | - Nico Dix
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, 08193 Bellaterra, Catalonia, Spain
| | - Florencio Sánchez
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, 08193 Bellaterra, Catalonia, Spain
| | - Josep Fontcuberta
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, 08193 Bellaterra, Catalonia, Spain
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162
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Marshall MSJ, Becerra-Toledo AE, Marks LD, Castell MR. Defects on Strontium Titanate. DEFECTS AT OXIDE SURFACES 2015. [DOI: 10.1007/978-3-319-14367-5_11] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
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163
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Zhang Y, Wang J, Sahoo MPK, Shimada T, Kitamura T. Mechanical control of magnetism in oxygen deficient perovskite SrTiO3. Phys Chem Chem Phys 2015; 17:27136-44. [PMID: 26415718 DOI: 10.1039/c5cp04310g] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Magnetism changes with pressure for deficient SrTiO3. A negative pressure enhances the magnetic moment while a positive pressure eliminates it.
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Affiliation(s)
- Yajun Zhang
- Department of Engineering Mechanics
- School of Aeronautics and Astronautics
- Zhejiang University
- Hangzhou 310027
- China
| | - Jie Wang
- Department of Engineering Mechanics
- School of Aeronautics and Astronautics
- Zhejiang University
- Hangzhou 310027
- China
| | - MPK Sahoo
- Department of Engineering Mechanics
- School of Aeronautics and Astronautics
- Zhejiang University
- Hangzhou 310027
- China
| | - Takahiro Shimada
- Department of Mechanical Engineering and Science
- Kyoto University
- Kyoto 615-8540
- Japan
| | - Takayuki Kitamura
- Department of Mechanical Engineering and Science
- Kyoto University
- Kyoto 615-8540
- Japan
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164
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Hamada I, Shimizu R, Ohsawa T, Iwaya K, Hashizume T, Tsukada M, Akagi K, Hitosugi T. Imaging the evolution of d states at a strontium titanate surface. J Am Chem Soc 2014; 136:17201-6. [PMID: 25429689 DOI: 10.1021/ja509231w] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Oxide electronics is a promising alternative to the conventional silicon-based semiconductor technology, owing to the rich functionalities of oxide thin films and heterostructures. In contrast to the silicon surface, however, the electronic structure of the SrTiO3 surface, the most important substrate for oxide thin films growth, is not yet completely understood. Here we report on the electronic states of a reconstructed (001) surface of SrTiO3 determined in real space, with scanning tunneling microscopy/spectroscopy and density functional theory calculations. We found a remarkable energy dependence of the spectroscopic image: Theoretical analysis reveals that symmetry breaking at the surface lifts the degeneracy in the t2g state (dxy, dyz, and dzx) of Ti 3d orbitals, whose anisotropic spatial distribution leads to a sharp transition in the spectroscopic image as a function of energy. The knowledge obtained here could be used to gain further insights into emergent phenomena at the surfaces and interfaces with SrTiO3.
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Affiliation(s)
- Ikutaro Hamada
- Advanced Institute for Materials Research (AIMR), Tohoku University , Sendai 980-8577, Japan
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165
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A dye-sensitized visible light photocatalyst-Bi24O31Cl10. Sci Rep 2014; 4:7384. [PMID: 25488704 PMCID: PMC4260216 DOI: 10.1038/srep07384] [Citation(s) in RCA: 75] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2014] [Accepted: 11/19/2014] [Indexed: 11/25/2022] Open
Abstract
The p-block semiconductors are regarded as a new family of visible-light photocatalysts because of their dispersive and anisotropic band structures as well as high chemical stability. The bismuth oxide halides belong to this family and have band structures and dispersion relations that can be engineered by modulating the stoichiometry of the halogen elements. Herein, we have developed a new visible-light photocatalyst Bi24O31Cl10 by band engineering, which shows high dye-sensitized photocatalytic activity. Density functional theory calculations reveal that the p-block elements determine the nature of the dispersive electronic structures and narrow band gap in Bi24O31Cl10. Bi24O31Cl10 exhibits excellent visible-light photocatalytic activity towards the degradation of Rhodamine B, which is promoted by dye sensitization due to compatible energy levels and high electronic mobility. In addition, Bi24O31Cl10 is also a suitable photoanode material for dye-sensitized solar cells and shows power conversion efficiency of 1.5%.
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166
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Goniakowski J, Noguera C. Conditions for electronic reconstruction at stoichiometric polar/polar interfaces. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:485010. [PMID: 25374280 DOI: 10.1088/0953-8984/26/48/485010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Relying on first principles simulations of ZnO(0 0 0 1)/MgO(1 1 1), MgO(1 1 1)/CaO(1 1 1) and AlN(0 0 0 1)/GaN(0 0 0 1) interfaces and examples taken from the literature, we discuss under which conditions stoichiometric polar/polar interfaces may display an electronic reconstruction. We point out the role of the three contributions to the interfacial polarization discontinuity--structure, valence and electronic terms--of interfacial strains, and of finite size effects. Depending upon their relative values, the interfaces may be polar (compensated by an electron reconstruction), non-polar, or polar uncompensated at low thickness. We stress that, in superlattices or heterostructures made of thin layers, the prediction of the interface polarity character from the bulk properties of the two materials may be questionable.
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Affiliation(s)
- Jacek Goniakowski
- CNRS, UMR 7588, Institut des Nanosciences de Paris, F-75005 Paris, France. Sorbonne Universités, UPMC Université Paris 06, UMR 7588, INSP, F-75005 Paris, France
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167
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Santander-Syro AF, Fortuna F, Bareille C, Rödel TC, Landolt G, Plumb NC, Dil JH, Radović M. Giant spin splitting of the two-dimensional electron gas at the surface of SrTiO3. NATURE MATERIALS 2014; 13:1085-1090. [PMID: 25306421 DOI: 10.1038/nmat4107] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2014] [Accepted: 09/05/2014] [Indexed: 06/04/2023]
Abstract
Two-dimensional electron gases (2DEGs) forming at the interfaces of transition metal oxides exhibit a range of properties, including tunable insulator-superconductor-metal transitions, large magnetoresistance, coexisting ferromagnetism and superconductivity, and a spin splitting of a few meV (refs 10, 11). Strontium titanate (SrTiO3), the cornerstone of such oxide-based electronics, is a transparent, non-magnetic, wide-bandgap insulator in the bulk, and has recently been found to host a surface 2DEG (refs 12-15). The most strongly confined carriers within this 2DEG comprise two subbands, separated by an energy gap of 90 meV and forming concentric circular Fermi surfaces. Using spin- and angle-resolved photoemission spectroscopy (SARPES), we show that the electron spins in these subbands have opposite chiralities. Although the Rashba effect might be expected to give rise to such spin textures, the giant splitting of almost 100 meV at the Fermi level is far larger than anticipated. Moreover, in contrast to a simple Rashba system, the spin-polarized subbands are non-degenerate at the Brillouin zone centre. This degeneracy can be lifted by time-reversal symmetry breaking, implying the possible existence of magnetic order. These results show that confined electronic states at oxide surfaces can be endowed with novel, non-trivial properties that are both theoretically challenging to anticipate and promising for technological applications.
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Affiliation(s)
- A F Santander-Syro
- CSNSM, Université Paris-Sud and CNRS/IN2P3, Bâtiments 104 et 108, 91405 Orsay cedex, France
| | - F Fortuna
- CSNSM, Université Paris-Sud and CNRS/IN2P3, Bâtiments 104 et 108, 91405 Orsay cedex, France
| | - C Bareille
- CSNSM, Université Paris-Sud and CNRS/IN2P3, Bâtiments 104 et 108, 91405 Orsay cedex, France
| | - T C Rödel
- 1] CSNSM, Université Paris-Sud and CNRS/IN2P3, Bâtiments 104 et 108, 91405 Orsay cedex, France [2] Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin-BP48, 91192 Gif-sur-Yvette, France
| | - G Landolt
- 1] Physik-Institut, Universität Zürich, Winterthurerstrasse 190 8057 Zürich, Switzerland [2] Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - N C Plumb
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - J H Dil
- 1] Physik-Institut, Universität Zürich, Winterthurerstrasse 190 8057 Zürich, Switzerland [2] Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland [3] Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
| | - M Radović
- 1] Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland [2] Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland [3] SwissFEL, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
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168
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Nemes NM, Calderón MJ, Beltrán JI, Bruno FY, García-Barriocanal J, Sefrioui Z, León C, García-Hernández M, Muñoz MC, Brey L, Santamaría J. Signatures of a two-dimensional ferromagnetic electron gas at the La0.7Sr0.3MnO3/SrTiO3 interface arising from orbital reconstruction. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2014; 26:7516-7520. [PMID: 25327446 DOI: 10.1002/adma.201402829] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2014] [Revised: 08/29/2014] [Indexed: 06/04/2023]
Abstract
The magnetoresistance of La0.7Sr0.3MnO3/SrTiO3 superlattices with magnetic field rotating out-of-plane shows unexpected peaks for in-plane fields. Resistivity calculations with spin-orbit coupling reveal that orbital reconstruction at the manganite interface leads to a 2D ferromagnetic electron gas coupled antiparallel to the manganite "bulk". These orbital and magnetic reconstructions are supported by X-ray linear dichroism and ab initio calculations.
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Affiliation(s)
- Norbert Marcel Nemes
- GFMC, Departamento de Física Aplicada III, Universidad Complutense de Madrid, Campus Moncloa, E-28040, Madrid, Spain; Laboratorio de Heteroestructuras con aplicación en Spintronica, Unidad Asociada Consejo Superior de Investigaciones Científicas/Universidad Complutense Madrid, Sor Juana Inés de la Cruz, 3, E-28049, Madrid, Spain
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169
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Deacon-Smith DEE, Scanlon DO, Catlow CRA, Sokol AA, Woodley SM. Interlayer cation exchange stabilizes polar perovskite surfaces. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2014; 26:7252-6. [PMID: 25196987 PMCID: PMC4241033 DOI: 10.1002/adma.201401858] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2014] [Revised: 07/10/2014] [Indexed: 05/15/2023]
Abstract
Global optimization is used to study the structure of the polar KTaO3 (001) surface. It is found that cation exchange near the surface leads to the most stable structure. This mechanism is likely to be general to metal oxides containing cations of differing charge.
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Affiliation(s)
- Daniel E E Deacon-Smith
- University College London, Kathleen Lonsdale Materials Chemistry, 20 Gordon Street, London, WC1H 0AJ, UK
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170
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Walker SM, de la Torre A, Bruno FY, Tamai A, Kim TK, Hoesch M, Shi M, Bahramy MS, King PDC, Baumberger F. Control of a two-dimensional electron gas on SrTiO₃(111) by atomic oxygen. PHYSICAL REVIEW LETTERS 2014; 113:177601. [PMID: 25379937 DOI: 10.1103/physrevlett.113.177601] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Indexed: 06/04/2023]
Abstract
We report on the formation of a two-dimensional electron gas (2DEG) at the bare surface of (111) oriented SrTiO3. Angle resolved photoemission experiments reveal highly itinerant carriers with a sixfold symmetric Fermi surface and strongly anisotropic effective masses. The electronic structure of the 2DEG is in good agreement with self-consistent tight-binding supercell calculations that incorporate a confinement potential due to surface band bending. We further demonstrate that alternate exposure of the surface to ultraviolet light and atomic oxygen allows tuning of the carrier density and the complete suppression of the 2DEG.
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Affiliation(s)
- S McKeown Walker
- Département de Physique de la Matière Condensée, Universitée de Genève, 24 Quai Ernest-Ansermet, 1211 Genève 4, Switzerland
| | - A de la Torre
- Département de Physique de la Matière Condensée, Universitée de Genève, 24 Quai Ernest-Ansermet, 1211 Genève 4, Switzerland
| | - F Y Bruno
- Département de Physique de la Matière Condensée, Universitée de Genève, 24 Quai Ernest-Ansermet, 1211 Genève 4, Switzerland
| | - A Tamai
- Département de Physique de la Matière Condensée, Universitée de Genève, 24 Quai Ernest-Ansermet, 1211 Genève 4, Switzerland
| | - T K Kim
- Diamond Light Source, Harwell Campus, Didcot OX11 0DE, United Kingdom
| | - M Hoesch
- Diamond Light Source, Harwell Campus, Didcot OX11 0DE, United Kingdom
| | - M Shi
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - M S Bahramy
- Quantum-Phase Electronics Center, Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan and RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
| | - P D C King
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, Fife KY16 9SS, United Kingdom
| | - F Baumberger
- Département de Physique de la Matière Condensée, Universitée de Genève, 24 Quai Ernest-Ansermet, 1211 Genève 4, Switzerland and Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland and SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, Fife KY16 9SS, United Kingdom
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171
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Pesquera D, Scigaj M, Gargiani P, Barla A, Herrero-Martín J, Pellegrin E, Valvidares SM, Gázquez J, Varela M, Dix N, Fontcuberta J, Sánchez F, Herranz G. Two-dimensional electron gases at LaAlO3/SrTiO3 interfaces: orbital symmetry and hierarchy engineered by crystal orientation. PHYSICAL REVIEW LETTERS 2014; 113:156802. [PMID: 25375731 DOI: 10.1103/physrevlett.113.156802] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2014] [Indexed: 06/04/2023]
Abstract
Recent findings show the emergence of two-dimensional electron gases (2DEGs) at LaAlO(3)/SrTiO(3) interfaces along different orientations; yet details on band reconstructions have remained so far unknown. Via x-ray linear dichroism spectroscopy, we demonstrate that crystal symmetry imposes distinctive 2DEG orbital hierarchies on (001)-and (110)-oriented quantum wells, allowing selective occupancy of states of different symmetry. Such orientational tuning expands the possibilities for electronic engineering of 2DEGs and opens up enticing opportunities to understand the link between orbital symmetry and complex correlated states at LaAlO(3)/SrTiO(3) quantum wells.
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Affiliation(s)
- D Pesquera
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, Bellaterra E-08193, Catalonia, Spain
| | - M Scigaj
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, Bellaterra E-08193, Catalonia, Spain and Departamento de Física, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Catalonia, Spain
| | - P Gargiani
- ALBA Synchrotron Light Source, Carretera BP 1413 km 3.3, E-08290 Cerdanyola del Vallès, Barcelona, Spain
| | - A Barla
- Istituto di Struttura della Materia, ISM CNR, Area Science Park Basovizza (Ts), Trieste I-34149, Italy
| | - J Herrero-Martín
- ALBA Synchrotron Light Source, Carretera BP 1413 km 3.3, E-08290 Cerdanyola del Vallès, Barcelona, Spain
| | - E Pellegrin
- ALBA Synchrotron Light Source, Carretera BP 1413 km 3.3, E-08290 Cerdanyola del Vallès, Barcelona, Spain
| | - S M Valvidares
- ALBA Synchrotron Light Source, Carretera BP 1413 km 3.3, E-08290 Cerdanyola del Vallès, Barcelona, Spain
| | - J Gázquez
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, Bellaterra E-08193, Catalonia, Spain
| | - M Varela
- Departamento Física Aplicada III, Universidad Complutense de Madrid, Madrid, 28040 Spain and Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - N Dix
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, Bellaterra E-08193, Catalonia, Spain
| | - J Fontcuberta
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, Bellaterra E-08193, Catalonia, Spain
| | - F Sánchez
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, Bellaterra E-08193, Catalonia, Spain
| | - G Herranz
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, Bellaterra E-08193, Catalonia, Spain
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172
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Lin C, Demkov AA. Consequences of oxygen-vacancy correlations at the SrTiO3 interface. PHYSICAL REVIEW LETTERS 2014; 113:157602. [PMID: 25375742 DOI: 10.1103/physrevlett.113.157602] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2014] [Indexed: 06/04/2023]
Abstract
The Kondo effect and ferromagnetism are the two many-body phenomena that emerge at the SrTiO(3) interfaces with polar materials, but do not occur in bulk SrTiO(3). By regarding the oxygen vacancy (OV) in SrTiO(3) as a magnetic impurity, we show that these two interface-specific phenomena can be attributed to the vacancies residing in the top TiO(2) plane of SrTiO(3). We identify three crucial ingredients: the local orbital mixing caused by an OV, reduced symmetry at the interface, and a strong in-plane stray electric field of the polar material. All three factors combine to result in the coupling between the impurity and conduction band at the interface, and can lead to both emergent phenomena. An OV-based Anderson impurity model is derived and solved using the numerical renormalization group method. The Kondo and Curie temperatures are estimated. Several experiments are discussed based on this interpretation.
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Affiliation(s)
- Chungwei Lin
- Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA
| | - Alexander A Demkov
- Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA
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173
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Mawrie A, Biswas T, Ghosh TK. Magnetotransport properties of 2D fermionic systems with k-cubic Rashba spin-orbit interaction. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:405301. [PMID: 25211532 DOI: 10.1088/0953-8984/26/40/405301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The spin-orbit interaction in heavy hole gas formed at p-doped semiconductor heterojunctions and electron gas at SrTiO3 surfaces is cubic in momentum. Here we report magnetotransport properties of k-cubic Rashba spin-orbit coupled 2D fermionic systems. We study longitudinal and Hall components of the resistivity tensor analytically as well as numerically. The longitudinal resistivity shows a beating pattern due to different Shubnikov-de Haas (SdH) oscillation frequencies f ± for spin-up and spin-down fermions. We propose empirical forms of f ± as exact expressions are not available, which are being used to find locations of the beating nodes. The beating nodes and the number of oscillations between any two successive nodes obtained from exact numerical results are in excellent agreement with those calculated from the proposed empirical formula. In the Hall resistivity, an additional Hall plateau appears between the two conventional ones as the spin-orbit coupling constant increases. The width of this additional plateau increases with spin-orbit coupling constant.
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Affiliation(s)
- Alestin Mawrie
- Department of Physics, Indian Institute of Technology-Kanpur, Kanpur-208 016, India
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174
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Wang Z, Hao X, Gerhold S, Mares P, Wagner M, Bliem R, Schulte K, Schmid M, Franchini C, Diebold U. Stabilizing Single Ni Adatoms on a Two-Dimensional Porous Titania Overlayer at the SrTiO 3(110) Surface. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2014; 118:19904-19909. [PMID: 25177410 PMCID: PMC4148460 DOI: 10.1021/jp506234r] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2014] [Revised: 07/29/2014] [Indexed: 05/24/2023]
Abstract
Nickel vapor-deposited on the SrTiO3(110) surface was studied using scanning tunneling microscopy, photoemission spectroscopy (PES), and density functional theory calculations. This surface forms a (4 × 1) reconstruction, composed of a 2-D titania structure with periodic six- and ten-membered nanopores. Anchored at these nanopores, Ni single adatoms are stabilized at room temperature. PES measurements show that the Ni adatoms create an in-gap state located at 1.9 eV below the conduction band minimum and induce an upward band bending. Both experimental and theoretical results suggest that Ni adatoms are positively charged. Our study produces well-dispersed single-adatom arrays on a well-characterized oxide support, providing a model system to investigate single-adatom catalytic and magnetic properties.
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Affiliation(s)
- Zhiming Wang
- Institute
of Applied Physics, Vienna University of
Technology, Wiedner Hauptstraße
8-10, 1040 Vienna, Austria
| | - Xianfeng Hao
- Institute
of Applied Physics, Vienna University of
Technology, Wiedner Hauptstraße
8-10, 1040 Vienna, Austria
| | - Stefan Gerhold
- Institute
of Applied Physics, Vienna University of
Technology, Wiedner Hauptstraße
8-10, 1040 Vienna, Austria
| | - Petr Mares
- Institute
of Applied Physics, Vienna University of
Technology, Wiedner Hauptstraße
8-10, 1040 Vienna, Austria
- CEITEC BUT, Technicka 10, 61669 Brno, Czech Republic
| | - Margareta Wagner
- Institute
of Applied Physics, Vienna University of
Technology, Wiedner Hauptstraße
8-10, 1040 Vienna, Austria
| | - Roland Bliem
- Institute
of Applied Physics, Vienna University of
Technology, Wiedner Hauptstraße
8-10, 1040 Vienna, Austria
| | - Karina Schulte
- MAX IV Laboratory, Lund University, Ole
Römers väg 1, 223 63 Lund, Sweden
| | - Michael Schmid
- Institute
of Applied Physics, Vienna University of
Technology, Wiedner Hauptstraße
8-10, 1040 Vienna, Austria
| | - Cesare Franchini
- Faculty of Physics
and Center for Computational Materials Science, University of Vienna, Sensengasse 8/12, 1090 Vienna, Austria
| | - Ulrike Diebold
- Institute
of Applied Physics, Vienna University of
Technology, Wiedner Hauptstraße
8-10, 1040 Vienna, Austria
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175
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Plumb NC, Salluzzo M, Razzoli E, Månsson M, Falub M, Krempasky J, Matt CE, Chang J, Schulte M, Braun J, Ebert H, Minár J, Delley B, Zhou KJ, Schmitt T, Shi M, Mesot J, Patthey L, Radović M. Mixed dimensionality of confined conducting electrons in the surface region of SrTiO3. PHYSICAL REVIEW LETTERS 2014; 113:086801. [PMID: 25192117 DOI: 10.1103/physrevlett.113.086801] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2014] [Indexed: 06/03/2023]
Abstract
Using angle-resolved photoemission spectroscopy, we show that the recently discovered surface state on SrTiO(3) consists of nondegenerate t(2g) states with different dimensional characters. While the d(xy) bands have quasi-2D dispersions with weak k(z) dependence, the lifted d(xz)/d(yz) bands show 3D dispersions that differ significantly from bulk expectations and signal that electrons associated with those orbitals permeate the near-surface region. Like their more 2D counterparts, the size and character of the d(xz)/d(yz) Fermi surface components are essentially the same for different sample preparations. Irradiating SrTiO(3) in ultrahigh vacuum is one method observed so far to induce the "universal" surface metallic state. We reveal that during this process, changes in the oxygen valence band spectral weight that coincide with the emergence of surface conductivity are disproportionate to any change in the total intensity of the O 1s core level spectrum. This signifies that the formation of the metallic surface goes beyond a straightforward chemical doping scenario and occurs in conjunction with profound changes in the initial states and/or spatial distribution of near-E(F) electrons in the surface region.
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Affiliation(s)
- N C Plumb
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - M Salluzzo
- CNR-SPIN, Complesso Universitario Monte S. Angelo, Via Cinthia I-80126, Napoli, Italy
| | - E Razzoli
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - M Månsson
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland and Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland and Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland
| | - M Falub
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - J Krempasky
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - C E Matt
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland and Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland
| | - J Chang
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland and Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - M Schulte
- Department Chemie, Ludwig-Maximilians-Universität München, 81377 München, Germany
| | - J Braun
- Department Chemie, Ludwig-Maximilians-Universität München, 81377 München, Germany
| | - H Ebert
- Department Chemie, Ludwig-Maximilians-Universität München, 81377 München, Germany
| | - J Minár
- Department Chemie, Ludwig-Maximilians-Universität München, 81377 München, Germany and New Technologies-Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen, Czech Republic
| | - B Delley
- Condensed Matter Theory Group, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - K-J Zhou
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - T Schmitt
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - M Shi
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - J Mesot
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland and Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland and Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland
| | - L Patthey
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland and SwissFEL, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
| | - M Radović
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland and Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland and SwissFEL, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
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176
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Cooper VR, Seo SSA, Lee S, Kim JS, Choi WS, Okamoto S, Lee HN. Transparent conducting oxides: a δ-doped superlattice approach. Sci Rep 2014; 4:6021. [PMID: 25109668 PMCID: PMC4127498 DOI: 10.1038/srep06021] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2014] [Accepted: 07/25/2014] [Indexed: 11/30/2022] Open
Abstract
Metallic states appearing at interfaces between dissimilar insulating oxides exhibit intriguing phenomena such as superconductivity and magnetism. Despite tremendous progress in understanding their origins, very little is known about how to control the conduction pathways and the distribution of charge carriers. Using optical spectroscopic measurements and density-functional theory (DFT) simulations, we examine the effect of SrTiO3 (STO) spacer layer thickness on the optical transparency and carrier distribution in La δ-doped STO superlattices. We experimentally observe that these metallic superlattices remain highly transparent to visible light; a direct consequence of the appropriately large gap between the O 2p and Ti 3d states. In superlattices with relatively thin STO layers, we predict that three-dimensional conduction would occur due to appreciable overlap of quantum mechanical wavefunctions between neighboring δ-doped layers. These results highlight the potential for using oxide heterostructures in optoelectronic devices by providing a unique route for creating novel transparent conducting oxides.
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Affiliation(s)
- Valentino R Cooper
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Sung S Ambrose Seo
- 1] Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA [2] Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506, USA
| | - Suyoun Lee
- 1] Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA [2] Electronic Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791, Korea
| | - Jun Sung Kim
- Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - Woo Seok Choi
- 1] Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA [2] Department of Physics, Sungkyunkwan University, Suwon, Gyeonggi-do 440-746, Korea
| | - Satoshi Okamoto
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Ho Nyung Lee
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
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177
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Franchini C. Hybrid functionals applied to perovskites. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:253202. [PMID: 24871431 DOI: 10.1088/0953-8984/26/25/253202] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
After being used for years in the chemistry community to describe molecular properties, hybrid functionals have been increasingly and successfully employed for a wide range of solid state problems which are not accurately accessible by standard density functional theory. In particular, the upsurge of interest in transition metal perovskite-based compounds, motivated by their technological relevance and functional ductility, has incentivized the use of hybrid functionals for realistic applications, as hybrid functionals appear to be capable of capturing the complex correlated physics of this class of oxide material, characterized by a subtle coupling between several competing interactions (lattice, orbital, spin). Here we present a map of recent applications of hybrid functionals to perovskites, aiming to cover an ample spectra of cases, including the 'classical' 3d compounds (manganites, titanates, nickelates, ferrites, etc.), less conventional examples from the the 4d (technetiates) and 5d (iridates) series, and the (non-transition metal) sp perovskite BaBiO3. We focus our attention on the technical aspects of the hybrid functional formalism, such as the role of the mixing and (for range-separated hybrids) screening parameters, and on an extended array of physical phenomena: pressure- and doping-induced insulator-to-metal and structural phase transitions, multiferroism, surface and interface effects, charge ordering and localization effects, and spin-orbit coupling.
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Affiliation(s)
- Cesare Franchini
- University of Vienna, Faculty of Physics and Center for Computational Materials Science, Sensengasse 8/12, A-1090 Vienna, Austria
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178
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Long-range electronic reconstruction to a dxz,yz-dominated Fermi surface below the LaAlO₃/SrTiO₃ interface. Sci Rep 2014; 4:5338. [PMID: 24939804 PMCID: PMC4061544 DOI: 10.1038/srep05338] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2014] [Accepted: 05/27/2014] [Indexed: 11/08/2022] Open
Abstract
Low dimensionality, broken symmetry and easily-modulated carrier concentrations provoke novel electronic phase emergence at oxide interfaces. However, the spatial extent of such reconstructions - i.e. the interfacial "depth" - remains unclear. Examining LaAlO₃/SrTiO₃ heterostructures at previously unexplored carrier densities n(2D) ≥ 6.9 × 10(14) cm(-2), we observe a Shubnikov-de Haas effect for small in-plane fields, characteristic of an anisotropic 3D Fermi surface with preferential dxz,yz orbital occupancy extending over at least 100 nm perpendicular to the interface. Quantum oscillations from the 3D Fermi surface of bulk doped SrTiO₃ emerge simultaneously at higher n(2D). We distinguish three areas in doped perovskite heterostructures: narrow (<20 nm) 2D interfaces housing superconductivity and/or other emergent phases, electronically isotropic regions far (>120 nm) from the interface and new intermediate zones where interfacial proximity renormalises the electronic structure relative to the bulk.
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179
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Visikovskiy A, Mitsuhara K, Hazama M, Kohyama M, Kido Y. The atomic and electronic structures of NiO(001)∕Au(001) interfaces. J Chem Phys 2014; 139:144705. [PMID: 24116639 DOI: 10.1063/1.4820823] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The atomic and electronic structures of NiO(001)∕Au(001) interfaces were analyzed by high-resolution medium energy ion scattering (MEIS) and photoelectron spectroscopy using synchrotron-radiation-light. The MEIS analysis clearly showed that O atoms were located above Au atoms at the interface and the inter-planar distance of NiO(001)∕Au(001) was derived to be 2.30 ± 0.05 Å, which was consistent with the calculations based on the density functional theory (DFT). We measured the valence band spectra and found metallic features for the NiO thickness up to 3 monolayer (ML). Relevant to the metallic features, electron energy loss analysis revealed that the bandgap for NiO(001)∕Au(001) reduced with decreasing the NiO thickness from 10 down to 5 ML. We also observed Au 4f lines consisting of surface, bulk, and interface components and found a significant electronic charge transfer from Au(001) to NiO(001). The present DFT calculations demonstrated the presence of an image charge beneath Ni atoms at the interface just like alkali-halide∕metal interface, which may be a key issue to explain the core level shift and band structure.
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Affiliation(s)
- A Visikovskiy
- Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka 819-0395, Japan
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180
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Rice WD, Ambwani P, Bombeck M, Thompson JD, Haugstad G, Leighton C, Crooker SA. Persistent optically induced magnetism in oxygen-deficient strontium titanate. NATURE MATERIALS 2014; 13:481-487. [PMID: 24658116 DOI: 10.1038/nmat3914] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2013] [Accepted: 02/12/2014] [Indexed: 06/03/2023]
Abstract
Strontium titanate (SrTiO3) is a foundational material in the emerging field of complex oxide electronics. Although its bulk electronic and optical properties are rich and have been studied for decades, SrTiO3 has recently become a renewed focus of materials research catalysed in part by the discovery of superconductivity and magnetism at interfaces between SrTiO3 and other non-magnetic oxides. Here we illustrate a new aspect to the phenomenology of magnetism in SrTiO3 by reporting the observation of an optically induced and persistent magnetization in slightly oxygen-deficient bulk SrTiO3-δ crystals using magnetic circular dichroism (MCD) spectroscopy and SQUID magnetometry. This zero-field magnetization appears below ~18 K, persists for hours below 10 K, and is tunable by means of the polarization and wavelength of sub-bandgap (400-500 nm) light. These effects occur only in crystals containing oxygen vacancies, revealing a detailed interplay between magnetism, lattice defects, and light in an archetypal complex oxide material.
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Affiliation(s)
- W D Rice
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - P Ambwani
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - M Bombeck
- Experimentelle Physik 2, Technische Universität Dortmund, D-44227 Dortmund, Germany
| | - J D Thompson
- Materials Physics and Applications, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - G Haugstad
- Characterization Facility, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - C Leighton
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - S A Crooker
- National High Magnetic Field Laboratory, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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181
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Bristowe NC, Ghosez P, Littlewood PB, Artacho E. The origin of two-dimensional electron gases at oxide interfaces: insights from theory. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:143201. [PMID: 24637267 DOI: 10.1088/0953-8984/26/14/143201] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The response of oxide thin films to polar discontinuities at interfaces and surfaces has generated enormous activity due to the variety of interesting effects that it gives rise to. A case in point is the discovery of the electron gas at the interface between LaAlO3 and SrTiO3, which has since been shown to be quasi-two-dimensional, switchable, magnetic and/or superconducting. Despite these findings, the origin of the two-dimensional electron gas is highly debated and several possible mechanisms remain. Here we review the main proposed mechanisms and attempt to model expected effects in a quantitative way with the ambition of better constraining what effects can/cannot explain the observed phenomenology. We do it in the framework of a phenomenological model constructed to provide an understanding of the electronic and/or redox screening of the chemical charge in oxide heterostructures. We also discuss the effect of intermixing, both conserving and not conserving the total stoichiometry.
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Affiliation(s)
- N C Bristowe
- Theoretical Materials Physics, University of Liège, B-4000 Sart-Tilman, Belgium. Theory of Condensed Matter, Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK
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182
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Chen YZ, Bovet N, Kasama T, Gao WW, Yazdi S, Ma C, Pryds N, Linderoth S. Room temperature formation of high-mobility two-dimensional electron gases at crystalline complex oxide interfaces. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2014; 26:1462-1467. [PMID: 24338762 DOI: 10.1002/adma.201304634] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2013] [Indexed: 06/03/2023]
Abstract
Well-controlled sub-unit-cell layer-bylayer epitaxial growth of spinel alumina is achieved at room temperature on a TiO2 -terminated SrTiO3 single-crystalline substrate. By tailoring the interface redox reaction, 2D electron gases with mobilities exceeding 3000 cm 2 V(-1) s(-1) are achieved at this novel oxide interface.
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Affiliation(s)
- Y Z Chen
- Department of Energy Conversion and Storage, Technical University of Denmark, Risø Campus, 4000, Roskilde, Denmark
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183
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Abstract
Two-dimensional electron gases (2DEGs) at oxide heterostructures are attracting considerable attention, as these might one day substitute conventional semiconductors at least for some functionalities. Here we present a minimal setup for such a 2DEG--the SrTiO3(110)-(4 × 1) surface, natively terminated with one monolayer of tetrahedrally coordinated titania. Oxygen vacancies induced by synchrotron radiation migrate underneath this overlayer; this leads to a confining potential and electron doping such that a 2DEG develops. Our angle-resolved photoemission spectroscopy and theoretical results show that confinement along (110) is strikingly different from the (001) crystal orientation. In particular, the quantized subbands show a surprising "semiheavy" band, in contrast with the analog in the bulk, and a high electronic anisotropy. This anisotropy and even the effective mass of the (110) 2DEG is tunable by doping, offering a high flexibility to engineer the properties of this system.
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184
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Gerhold S, Wang Z, Schmid M, Diebold U. Stoichiometry-driven switching between surface reconstructions on SrTiO 3(001). SURFACE SCIENCE 2014; 621:L1-L4. [PMID: 24748691 PMCID: PMC3990415 DOI: 10.1016/j.susc.2013.10.015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/30/2013] [Accepted: 10/14/2013] [Indexed: 06/03/2023]
Abstract
Controlling the surface structure on the atomic scale is a major difficulty for most transition metal oxides; this is especially true for the ternary perovskites. The influence of surface stoichiometry on the atomic structure of the SrTiO3(001) surface was examined with scanning tunneling microscopy, low-energy electron diffraction, low-energy He+ ion scattering (LEIS), and X-ray photoelectron spectroscopy (XPS). Vapor deposition of 0.8 monolayer (ML) strontium and 0.3 ML titanium, with subsequent annealing to 850 °C in 4 × 10- 6 mbar O2, reversibly switches the surface between c(4 × 2) and (2 × 2) reconstructions, respectively. The combination of LEIS and XPS shows a different stoichiometry that is confined to the top layer. Geometric models for these reconstructions need to take into account these different surface compositions.
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Affiliation(s)
- Stefan Gerhold
- Institute of Applied Physics, Vienna University of Technology, Austria
| | - Zhiming Wang
- Institute of Applied Physics, Vienna University of Technology, Austria
| | - Michael Schmid
- Institute of Applied Physics, Vienna University of Technology, Austria
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185
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Takeyasu K, Fukada K, Ogura S, Matsumoto M, Fukutani K. Two charged states of hydrogen on the SrTiO3(001) surface. J Chem Phys 2014; 140:084703. [DOI: 10.1063/1.4866645] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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186
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King PDC, McKeown Walker S, Tamai A, de la Torre A, Eknapakul T, Buaphet P, Mo SK, Meevasana W, Bahramy MS, Baumberger F. Quasiparticle dynamics and spin–orbital texture of the SrTiO3 two-dimensional electron gas. Nat Commun 2014; 5:3414. [DOI: 10.1038/ncomms4414] [Citation(s) in RCA: 126] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Accepted: 02/07/2014] [Indexed: 11/10/2022] Open
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187
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Shang J, Hao W, Lv X, Wang T, Wang X, Du Y, Dou S, Xie T, Wang D, Wang J. Bismuth Oxybromide with Reasonable Photocatalytic Reduction Activity under Visible Light. ACS Catal 2014. [DOI: 10.1021/cs401025u] [Citation(s) in RCA: 269] [Impact Index Per Article: 26.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Affiliation(s)
- Jun Shang
- Center
of Materials Physics and Chemistry, and Department of Physics, Beihang University, Beijing 100191, P. R. China
| | - Weichang Hao
- Center
of Materials Physics and Chemistry, and Department of Physics, Beihang University, Beijing 100191, P. R. China
- Institute
for Superconducting and Electronic Materials, University of Wollongong, Wollongong
NSW 2522, Australia
| | - Xiaojun Lv
- Key
Laboratory of Photochemical Conversion and Optoelectronic Materials,
and HKU-CAS Joint Laboratory on New Materials, Technical Institute
of Physics and Chemistry, Chinese Academy of Sciences (CAS), Beijing 100190, P. R. China
| | - Tianmin Wang
- Center
of Materials Physics and Chemistry, and Department of Physics, Beihang University, Beijing 100191, P. R. China
| | - Xiaolin Wang
- Institute
for Superconducting and Electronic Materials, University of Wollongong, Wollongong
NSW 2522, Australia
| | - Yi Du
- Institute
for Superconducting and Electronic Materials, University of Wollongong, Wollongong
NSW 2522, Australia
| | - Shixue Dou
- Institute
for Superconducting and Electronic Materials, University of Wollongong, Wollongong
NSW 2522, Australia
| | - Tengfeng Xie
- College
of Chemistry, Jilin University, Changchun 130012, P. R. China
| | - Dejun Wang
- College
of Chemistry, Jilin University, Changchun 130012, P. R. China
| | - Jiaou Wang
- Beijing
Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, P. R. China
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188
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Bareille C, Fortuna F, Rödel TC, Bertran F, Gabay M, Cubelos OH, Taleb-Ibrahimi A, Le Fèvre P, Bibes M, Barthélémy A, Maroutian T, Lecoeur P, Rozenberg MJ, Santander-Syro AF. Two-dimensional electron gas with six-fold symmetry at the (111) surface of KTaO3. Sci Rep 2014; 4:3586. [PMID: 24394996 PMCID: PMC3882744 DOI: 10.1038/srep03586] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2013] [Accepted: 12/03/2013] [Indexed: 11/09/2022] Open
Abstract
Two-dimensional electron gases (2DEGs) at transition-metal oxide (TMO) interfaces, and boundary states in topological insulators, are being intensively investigated. The former system harbors superconductivity, large magneto-resistance, and ferromagnetism. In the latter, honeycomb-lattice geometry plus bulk spin-orbit interactions lead to topologically protected spin-polarized bands. 2DEGs in TMOs with a honeycomb-like structure could yield new states of matter, but they had not been experimentally realized, yet. We successfully created a 2DEG at the (111) surface of KTaO3, a strong insulator with large spin-orbit coupling. Its confined states form a network of weakly-dispersing electronic gutters with 6-fold symmetry, a topology novel to all known oxide-based 2DEGs. If those pertain to just one Ta-(111) bilayer, model calculations predict that it can be a topological metal. Our findings demonstrate that completely new electronic states, with symmetries not realized in the bulk, can be tailored in oxide surfaces, promising for TMO-based devices.
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Affiliation(s)
- C. Bareille
- CSNSM, Université Paris-Sud and CNRS/IN2P3, Bâtiments 104 et 108, 91405 Orsay cedex, France
| | - F. Fortuna
- CSNSM, Université Paris-Sud and CNRS/IN2P3, Bâtiments 104 et 108, 91405 Orsay cedex, France
| | - T. C. Rödel
- CSNSM, Université Paris-Sud and CNRS/IN2P3, Bâtiments 104 et 108, 91405 Orsay cedex, France
- Universität Würzburg, Experimentelle Physik VII, Am Hubland, 97074 Würzburg, Germany
| | - F. Bertran
- Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin-BP48, 91192 Gif-sur-Yvette, France
| | - M. Gabay
- Laboratoire de Physique des Solides, Université Paris-Sud and CNRS, Bâtiment 510, 91405 Orsay, France
| | - O. Hijano Cubelos
- Laboratoire de Physique des Solides, Université Paris-Sud and CNRS, Bâtiment 510, 91405 Orsay, France
| | - A. Taleb-Ibrahimi
- Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin-BP48, 91192 Gif-sur-Yvette, France
| | - P. Le Fèvre
- Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin-BP48, 91192 Gif-sur-Yvette, France
| | - M. Bibes
- Unité Mixte de Physique CNRS/Thales, Campus de l'Ecole Polytechnique, 1 Av. A. Fresnel, 91767 Palaiseau, France and Université Paris-Sud, 91405 Orsay, France
| | - A. Barthélémy
- Unité Mixte de Physique CNRS/Thales, Campus de l'Ecole Polytechnique, 1 Av. A. Fresnel, 91767 Palaiseau, France and Université Paris-Sud, 91405 Orsay, France
| | - T. Maroutian
- Institut d'Electronique Fondamentale, Université Paris-Sud and CNRS, Bâtiment 220, 91405 Orsay, France
| | - P. Lecoeur
- Institut d'Electronique Fondamentale, Université Paris-Sud and CNRS, Bâtiment 220, 91405 Orsay, France
| | - M. J. Rozenberg
- Laboratoire de Physique des Solides, Université Paris-Sud and CNRS, Bâtiment 510, 91405 Orsay, France
| | - A. F. Santander-Syro
- CSNSM, Université Paris-Sud and CNRS/IN2P3, Bâtiments 104 et 108, 91405 Orsay cedex, France
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189
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Stevanović V, Lany S, Ginley DS, Tumas W, Zunger A. Assessing capability of semiconductors to split water using ionization potentials and electron affinities only. Phys Chem Chem Phys 2014; 16:3706-14. [DOI: 10.1039/c3cp54589j] [Citation(s) in RCA: 197] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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190
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Annadi A, Zhang Q, Renshaw Wang X, Tuzla N, Gopinadhan K, Lü WM, Roy Barman A, Liu ZQ, Srivastava A, Saha S, Zhao YL, Zeng SW, Dhar S, Olsson E, Gu B, Yunoki S, Maekawa S, Hilgenkamp H, Venkatesan T, Ariando. Anisotropic two-dimensional electron gas at the LaAlO₃/SrTiO₃ (110) interface. Nat Commun 2013; 4:1838. [PMID: 23673623 PMCID: PMC3674248 DOI: 10.1038/ncomms2804] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2012] [Accepted: 03/25/2013] [Indexed: 11/15/2022] Open
Abstract
The observation of a high-mobility two-dimensional electron gas between two insulating complex oxides, especially LaAlO3/SrTiO3, has enhanced the potential of oxides for electronics. The occurrence of this conductivity is believed to be driven by polarization discontinuity, leading to an electronic reconstruction. In this scenario, the crystal orientation has an important role and no conductivity would be expected, for example, for the interface between LaAlO3 and (110)-oriented SrTiO3, which should not have a polarization discontinuity. Here we report the observation of unexpected conductivity at the LaAlO3/SrTiO3 interface prepared on (110)-oriented SrTiO3, with a LaAlO3-layer thickness-dependent metal-insulator transition. Density functional theory calculation reveals that electronic reconstruction, and thus conductivity, is still possible at this (110) interface by considering the energetically favourable (110) interface structure, that is, buckled TiO2/LaO, in which the polarization discontinuity is still present. The conductivity was further found to be strongly anisotropic along the different crystallographic directions with potential for anisotropic superconductivity and magnetism, leading to possible new physics and applications. Although LaAlO3 and SrTiO3 are both insulators, when they are brought together at a (100) interface, a highly conducting two-dimensional electron gas forms between them. Annandi et al. show that this also happens at a (110) interface, counter to expectations that it should not.
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Affiliation(s)
- A Annadi
- NUSNNI-Nanocore, National University of Singapore, Singapore 117411, Singapore
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191
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Lin C, Demkov AA. Electron correlation in oxygen vacancy in SrTiO3. PHYSICAL REVIEW LETTERS 2013; 111:217601. [PMID: 24313525 DOI: 10.1103/physrevlett.111.217601] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Indexed: 06/02/2023]
Abstract
Oxygen vacancies are an important type of defect in transition metal oxides. In SrTiO3 they are believed to be the main donors in an otherwise intrinsic crystal. At the same time, a relatively deep gap state associated with the vacancy is widely reported. To explain this inconsistency we investigate the effect of electron correlation in an oxygen vacancy (OV) in SrTiO3. When taking correlation into account, we find that the OV-induced localized level can at most trap one electron, while the second electron occupies the conduction band. Our results offer a natural explanation of how the OV in SrTiO3 can produce a deep in-gap level (about 1 eV below the conduction band bottom) in photoemission, and at the same time be an electron donor. Our analysis implies that an OV in SrTiO3 should be fundamentally regarded as a magnetic impurity, whose deep level is always partially occupied due to the strong Coulomb repulsion. An OV-based Anderson impurity model is derived, and its implications are discussed.
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Affiliation(s)
- Chungwei Lin
- Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA
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192
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Chang YJ, Moreschini L, Bostwick A, Gaines GA, Kim YS, Walter AL, Freelon B, Tebano A, Horn K, Rotenberg E. Layer-by-layer evolution of a two-dimensional electron gas near an oxide interface. PHYSICAL REVIEW LETTERS 2013; 111:126401. [PMID: 24093281 DOI: 10.1103/physrevlett.111.126401] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2013] [Indexed: 06/02/2023]
Abstract
We report the momentum-resolved measurement of a two-dimensional electron gas at the LaTiO(3)/SrTiO(3) interface by angle-resolved photoemission spectroscopy (ARPES). Thanks to an advanced sample preparation technique, the orbital character of the conduction electrons and the electronic correlations can be accessed quantitatively as each unit cell layer is added. We find that all of these quantities change dramatically with distance from the interface. These findings open the way to analogous studies on other heterostructures, which are traditionally a forbidden field for ARPES.
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Affiliation(s)
- Young Jun Chang
- Advanced Light Source (ALS), E. O. Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA and Department of Physical Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany and Department of Physics, University of Seoul, Seoul 130-743, Korea
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193
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Rault JE, Dionot J, Mathieu C, Feyer V, Schneider CM, Geneste G, Barrett N. Polarization sensitive surface band structure of doped BaTiO3(001). PHYSICAL REVIEW LETTERS 2013; 111:127602. [PMID: 24093301 DOI: 10.1103/physrevlett.111.127602] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2013] [Revised: 07/30/2013] [Indexed: 06/02/2023]
Abstract
We present a spatial and wave-vector resolved study of the electronic structure of micron sized ferroelectric domains at the surface of a BaTiO(3)(001) single crystal. The n-type doping of the BaTiO(3) is controlled by in situ vacuum and oxygen annealing, providing experimental evidence of a surface paraelectric-ferroelectric transition below a critical doping level. Real space imaging of photoemission threshold, core level and valence band spectra show contrast due to domain polarization. Reciprocal space imaging of the electronic structure using linearly polarized light provides unambiguous evidence for the presence of both in- and out-of-plane polarization with two- and fourfold symmetry, respectively. The results agree well with first principles calculations.
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Affiliation(s)
- J E Rault
- CEA, DSM/IRAMIS/SPCSI, F-91191 Gif-sur-Yvette Cedex, France
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194
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Wang Z, Li F, Meng S, Zhang J, Plummer EW, Diebold U, Guo J. Strain-induced defect superstructure on the SrTiO3(110) surface. PHYSICAL REVIEW LETTERS 2013; 111:056101. [PMID: 23952421 DOI: 10.1103/physrevlett.111.056101] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2013] [Indexed: 05/24/2023]
Abstract
We report on a combined scanning tunneling microscopy and density functional theory calculation study of the SrTiO(3) (110)-(4 × 1) surface. It is found that antiphase domains are formed along the [11[over ¯]0]-oriented stripes on the surface. The domain boundaries are decorated by defect pairs consisting of Ti(2)O(3) vacancies and Sr adatoms, which relieve the residual stress. The formation energy of and interactions between vacancies result in a defect superstructure. It is suggested that the density and distributions of defects can be tuned by strain engineering, providing a flexible platform for the designed growth of complex oxide materials.
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Affiliation(s)
- Zhiming Wang
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China
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195
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Yamada Y, Sato HK, Hikita Y, Hwang HY, Kanemitsu Y. Measurement of the femtosecond optical absorption of LaAlO3/SrTiO3 heterostructures: evidence for an extremely slow electron relaxation at the interface. PHYSICAL REVIEW LETTERS 2013; 111:047403. [PMID: 23931405 DOI: 10.1103/physrevlett.111.047403] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2013] [Indexed: 06/02/2023]
Abstract
The photocarrier relaxation dynamics of an n-type LaAlO3/SrTiO3 heterointerface is investigated using femtosecond transient absorption (TA) spectroscopy at low temperatures. In both LaAlO3/SrTiO3 heterostructures and electron-doped SrTiO3 bulk crystals, the TA spectrum shows a Drude-like free carrier absorption immediately after excitation. In addition, a broad absorption band gradually appears within 40 ps, which corresponds to the energy relaxation of photoexcited free electrons into self-trapped polaron states. We reveal that the polaron formation time is enhanced considerably at the LaAlO3/SrTiO3 heterointerface as compared to bulk crystals. Further, we discuss the interface effects on the electron relaxation dynamics in conjunction with the splitting of the t2g subbands due to the interface potential.
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Affiliation(s)
- Yasuhiro Yamada
- Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
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196
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Matsuda T, Yoshida Y, Mitsuhara K, Kido Y. The structure of SrTiO3(001)-2 × 1 surface analyzed by high-resolution medium energy ion scattering coupled with ab initio calculations. J Chem Phys 2013; 138:244705. [PMID: 23822262 DOI: 10.1063/1.4811485] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
High-resolution medium energy ion scattering (MEIS) spectrometry coupled with photoelectron spectroscopy revealed unambiguously that the initial SrTiO3(001) surface chemically etched in a buffered NH4F-HF solution was perfectly terminated with a single-layer (SL) of TiO2(001) and annealing the surface at 600-800 [ordinal indicator, masculine]C in ultrahigh vacuum (UHV) led to a (2 × 1)-reconstructed surface terminated with a double-layer (DL) of TiO2(001). After annealing in UHV, rock-salt SrO(001) clusters with two atomic layer height grew epitaxially on the DL-TiO2(001)-2 × 1 surface with a coverage of 20%-30%. High-resolution MEIS in connection with ab initio calculations demonstrated the structure of the DL-TiO2(001)-2 × 1 surface close to that proposed by Erdman et al. [Nature (London) 419, 55 (2002)] rather than that predicted by Herger et al. [Phys. Rev. Lett. 98, 076102 (2007)]. Based on the MEIS analysis combined with the ab initio calculations, we propose the most probable (2 × 1) surface structure.
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Affiliation(s)
- Taishi Matsuda
- Department of Physics, Ritsumeikan University, Kusatsu, Shiga-ken 525-8577, Japan
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197
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Berner G, Sing M, Fujiwara H, Yasui A, Saitoh Y, Yamasaki A, Nishitani Y, Sekiyama A, Pavlenko N, Kopp T, Richter C, Mannhart J, Suga S, Claessen R. Direct k-space mapping of the electronic structure in an oxide-oxide interface. PHYSICAL REVIEW LETTERS 2013; 110:247601. [PMID: 25165961 DOI: 10.1103/physrevlett.110.247601] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2013] [Indexed: 06/03/2023]
Abstract
The interface between LaAlO(3) and SrTiO(3) hosts a two-dimensional electron system of itinerant carriers, although both oxides are band insulators. Interface ferromagnetism coexisting with superconductivity has been found and attributed to local moments. Experimentally, it has been established that Ti 3d electrons are confined to the interface. Using soft x-ray angle-resolved resonant photoelectron spectroscopy we have directly mapped the interface states in k space. Our data demonstrate a charge dichotomy. A mobile fraction contributes to Fermi surface sheets, whereas a localized portion at higher binding energies is tentatively attributed to electrons trapped by O vacancies in the SrTiO(3). While photovoltage effects in the polar LaAlO(3) layers cannot be excluded, the apparent absence of surface-related Fermi surface sheets could also be fully reconciled in a recently proposed electronic reconstruction picture where the built-in potential in the LaAlO(3) is compensated by surface O vacancies serving also as a charge reservoir.
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Affiliation(s)
- G Berner
- Physikalisches Institut and Röntgen Center for Complex Materials Systems (RCCM), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - M Sing
- Physikalisches Institut and Röntgen Center for Complex Materials Systems (RCCM), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
| | - H Fujiwara
- Division of Materials Physics, Graduate School of Engineering Science, Osaka University, Osaka 560-8531, Japan
| | - A Yasui
- Condensed Matter Science Division, Japan Atomic Energy Agency, SPring-8, Hyogo 679-5148, Japan
| | - Y Saitoh
- Condensed Matter Science Division, Japan Atomic Energy Agency, SPring-8, Hyogo 679-5148, Japan
| | - A Yamasaki
- Faculty of Science and Engineering, Konan University, Kobe 658-8501, Japan
| | - Y Nishitani
- Faculty of Science and Engineering, Konan University, Kobe 658-8501, Japan
| | - A Sekiyama
- Division of Materials Physics, Graduate School of Engineering Science, Osaka University, Osaka 560-8531, Japan
| | - N Pavlenko
- Center for Electronic Correlations and Magnetism, Experimental Physics VI, Universität Augsburg, D-86135 Augsburg, Germany and Center for Electronic Correlations and Magnetism, Theoretical Physics III, Universität Augsburg, D-86135 Augsburg, Germany and Max Planck Institute for Solid State Research, Heisenbergstraße 1, D-70569 Stuttgart, Germany
| | - T Kopp
- Center for Electronic Correlations and Magnetism, Experimental Physics VI, Universität Augsburg, D-86135 Augsburg, Germany
| | - C Richter
- Center for Electronic Correlations and Magnetism, Experimental Physics VI, Universität Augsburg, D-86135 Augsburg, Germany and Max Planck Institute for Solid State Research, Heisenbergstraße 1, D-70569 Stuttgart, Germany
| | - J Mannhart
- Max Planck Institute for Solid State Research, Heisenbergstraße 1, D-70569 Stuttgart, Germany
| | - S Suga
- Institute of Scientific & Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan
| | - R Claessen
- Physikalisches Institut and Röntgen Center for Complex Materials Systems (RCCM), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
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198
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Gate-tunable polarized phase of two-dimensional electrons at the LaAlO3/SrTiO3 interface. Proc Natl Acad Sci U S A 2013; 110:9633-8. [PMID: 23708121 DOI: 10.1073/pnas.1221453110] [Citation(s) in RCA: 93] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Controlling the coupling between localized spins and itinerant electrons can lead to exotic magnetic states. A novel system featuring local magnetic moments and extended 2D electrons is the interface between LaAlO3 and SrTiO3. The magnetism of the interface, however, was observed to be insensitive to the presence of these electrons and is believed to arise solely from extrinsic sources like oxygen vacancies and strain. Here we show the existence of unconventional electronic phases in the LaAlO3/SrTiO3 system pointing to an underlying tunable coupling between itinerant electrons and localized moments. Using anisotropic magnetoresistance and anomalous Hall effect measurements in a unique in-plane configuration, we identify two distinct phases in the space of carrier density and magnetic field. At high densities and fields, the electronic system is strongly polarized and shows a response, which is highly anisotropic along the crystalline directions. Surprisingly, below a density-dependent critical field, the polarization and anisotropy vanish whereas the resistivity sharply rises. The unprecedented vanishing of the easy axes below a critical field is in sharp contrast with other coupled magnetic systems and indicates strong coupling with the moments that depends on the symmetry of the itinerant electrons. The observed interplay between the two phases indicates the nature of magnetism at the LaAlO3/SrTiO3 interface as both having an intrinsic origin and being tunable.
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199
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Vildosola V, Güller F, Llois AM. Mechanism to generate a two-dimensional electron gas at the surface of the charge-ordered semiconductor BaBiO3. PHYSICAL REVIEW LETTERS 2013; 110:206805. [PMID: 25167440 DOI: 10.1103/physrevlett.110.206805] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2012] [Indexed: 06/03/2023]
Abstract
In this Letter, we find by means of first-principles calculations a new physical mechanism to generate a two-dimensional electron gas, namely, the breaking of charge ordering at the surface of a charge-ordered semiconductor due to the incomplete oxygen environment of the surface ions. The emergence of the 2D gas is independent of the presence of oxygen vacancies or polar discontinuities; this is a self-doping effect. This mechanism might apply to many charge-ordered systems, in particular, we study the case of BaBiO(3)(001). Our calculations show that the outer layer of the Bi-terminated simulated surface turns more cubiclike and metallic while the inner layers remain in the insulating monoclinic state that the system present in the bulk form. On the other hand, the metallization does not occur for the Ba termination, a fact that makes this system appealing for nanostructuring. Finally, in view of the bulk properties of this material under doping, this particular finding sets another possible route for future exploration: the potential scenario of 2D superconductivity at the BaBiO(3) surface.
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Affiliation(s)
- Verónica Vildosola
- Departamento de Materia Condensada, Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, CONICET, (1650) San Martín, Argentina
| | - Francisco Güller
- Departamento de Materia Condensada, Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, CONICET, (1650) San Martín, Argentina and Departamento de Física, Universidad de Buenos Aires, Ciudad Universitaria Pabellón I, (1428) Buenos Aires, Argentina
| | - Ana María Llois
- Departamento de Materia Condensada, Gerencia de Investigación y Aplicaciones, Comisión Nacional de Energía Atómica, CONICET, (1650) San Martín, Argentina and Departamento de Física, Universidad de Buenos Aires, Ciudad Universitaria Pabellón I, (1428) Buenos Aires, Argentina
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200
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Moser S, Moreschini L, Jaćimović J, Barišić OS, Berger H, Magrez A, Chang YJ, Kim KS, Bostwick A, Rotenberg E, Forró L, Grioni M. Tunable polaronic conduction in anatase TiO2. PHYSICAL REVIEW LETTERS 2013; 110:196403. [PMID: 23705725 DOI: 10.1103/physrevlett.110.196403] [Citation(s) in RCA: 94] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2013] [Indexed: 06/02/2023]
Abstract
Oxygen vacancies created in anatase TiO(2) by UV photons (80-130 eV) provide an effective electron-doping mechanism and induce a hitherto unobserved dispersive metallic state. Angle resolved photoemission reveals that the quasiparticles are large polarons. These results indicate that anatase can be tuned from an insulator to a polaron gas to a weakly correlated metal as a function of doping and clarify the nature of conductivity in this material.
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Affiliation(s)
- S Moser
- Advanced Light Source (ALS), Berkeley, California 94720, USA
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