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Kundu AK, Liu Y, Petrovic C, Valla T. Valence band electronic structure of the van der Waals ferromagnetic insulators: VI[Formula: see text] and CrI[Formula: see text]. Sci Rep 2020; 10:15602. [PMID: 32973193 PMCID: PMC7515918 DOI: 10.1038/s41598-020-72487-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2020] [Accepted: 08/28/2020] [Indexed: 12/03/2022] Open
Abstract
Ferromagnetic van der Waals (vdW) insulators are of great scientific interest for their promising applications in spintronics. It has been indicated that in the two materials within this class, CrI[Formula: see text] and VI[Formula: see text], the magnetic ground state, the band gap, and the Fermi level could be manipulated by varying the layer thickness, strain or doping. To understand how these factors impact the properties, a detailed understanding of the electronic structure would be required. However, the experimental studies of the electronic structure of these materials are still very sparse. Here, we present the detailed electronic structure of CrI[Formula: see text] and VI[Formula: see text] measured by angle-resolved photoemission spectroscopy (ARPES). Our results show a band-gap of the order of 1 eV, sharply contrasting some theoretical predictions such as Dirac half-metallicity and metallic phases, indicating that the intra-atomic interaction parameter (U) and spin-orbit coupling (SOC) were not properly accounted for in the calculations. We also find significant differences in the electronic properties of these two materials, in spite of similarities in their crystal structure. In CrI[Formula: see text], the valence band maximum is dominated by the I 5p, whereas in VI[Formula: see text] it is dominated by the V 3d derived states. Our results represent valuable input for further improvements in the theoretical modeling of these systems.
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Affiliation(s)
- Asish K. Kundu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973 USA
| | - Yu Liu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973 USA
- Present Address: Los Alamos National Laboratory, MS K764, Los Alamos, NM 87545 USA
| | - C. Petrovic
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973 USA
| | - T. Valla
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973 USA
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2
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Valla T, Drozdov IK, Gu GD. Disappearance of superconductivity due to vanishing coupling in the overdoped Bi[Formula: see text]Sr[Formula: see text]CaCu[Formula: see text]O[Formula: see text]. Nat Commun 2020; 11:569. [PMID: 31996671 PMCID: PMC6989516 DOI: 10.1038/s41467-020-14282-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2019] [Accepted: 12/24/2019] [Indexed: 11/09/2022] Open
Abstract
In cuprate superconductors, superconductivity is accompanied by a plethora of orders and phenomena that complicate our understanding of superconductivity in these materials. Prominent in the underdoped regime, these orders weaken or vanish with overdoping. Here, we approach the superconducting phase from the more conventional overdoped side. We present angle-resolved photoemission spectroscopy studies of Bi[Formula: see text]Sr[Formula: see text]CaCu[Formula: see text]O[Formula: see text], cleaved and annealed in ozone to increase the doping all the way to the non-superconducting phase. We show that the mass renormalization in the antinodal region of the Fermi surface that possibly reflects the pairing, weakens with doping and completely disappears precisely where superconductivity disappears. This is the evidence that in the overdoped regime, superconductivity is determined primarily by the coupling strength. A doping dependence and an abrupt disappearance above the transition temperature eliminate phononic mechanism of the observed renormalization and identify the onset of spin-fluctuations as its likely origin.
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Affiliation(s)
- T. Valla
- Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, NY 11973 USA
| | - I. K. Drozdov
- Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, NY 11973 USA
| | - G. D. Gu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, NY 11973 USA
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3
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Drozdov IK, Pletikosić I, Kim CK, Fujita K, Gu GD, Davis JCS, Johnson PD, Božović I, Valla T. Phase diagram of Bi 2Sr 2CaCu 2O 8+δ revisited. Nat Commun 2018; 9:5210. [PMID: 30523265 PMCID: PMC6283832 DOI: 10.1038/s41467-018-07686-w] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Accepted: 11/12/2018] [Indexed: 11/09/2022] Open
Abstract
In cuprate superconductors, the doping of carriers into the parent Mott insulator induces superconductivity and various other phases whose characteristic temperatures are typically plotted versus the doping level p. In most materials, p cannot be determined from the chemical composition, but it is derived from the superconducting transition temperature, Tc, using the assumption that the Tc dependence on doping is universal. Here, we present angle-resolved photoemission studies of Bi2Sr2CaCu2O8+δ, cleaved and annealed in vacuum or in ozone to reduce or increase the doping from the initial value corresponding to Tc = 91 K. We show that p can be determined from the underlying Fermi surfaces and that in-situ annealing allows mapping of a wide doping regime, covering the superconducting dome and the non-superconducting phase on the overdoped side. Our results show a surprisingly smooth dependence of the inferred Fermi surface with doping. In the highly overdoped regime, the superconducting gap approaches the value of 2Δ0 = (4 ± 1)kBTc.
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Affiliation(s)
- I K Drozdov
- Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, NY, 11973, USA
| | - I Pletikosić
- Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, NY, 11973, USA
- Department of Physics, Princeton University, Princeton, NJ, 08544, USA
| | - C-K Kim
- Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, NY, 11973, USA
| | - K Fujita
- Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, NY, 11973, USA
| | - G D Gu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, NY, 11973, USA
| | - J C Séamus Davis
- Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, NY, 11973, USA
- Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, NY, 14853, USA
| | - P D Johnson
- Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, NY, 11973, USA
| | - I Božović
- Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, NY, 11973, USA
| | - T Valla
- Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, NY, 11973, USA.
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4
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Pletikosić I, von Rohr F, Pervan P, Das PK, Vobornik I, Cava RJ, Valla T. Band Structure of the IV-VI Black Phosphorus Analog and Thermoelectric SnSe. Phys Rev Lett 2018; 120:156403. [PMID: 29756873 DOI: 10.1103/physrevlett.120.156403] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2017] [Revised: 09/29/2017] [Indexed: 06/08/2023]
Abstract
The success of black phosphorus in fast electronic and photonic devices is hindered by its rapid degradation in the presence of oxygen. Orthorhombic tin selenide is a representative of group IV-VI binary compounds that are robust and isoelectronic and share the same structure with black phosphorus. We measure the band structure of SnSe and find highly anisotropic valence bands that form several valleys having fast dispersion within the layers and negligible dispersion across. This is exactly the band structure desired for efficient thermoelectric generation where SnSe has shown great promise.
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Affiliation(s)
- I Pletikosić
- Department of Physics, Princeton University, Princeton, NJ 08544, USA
- Condensed Matter and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - F von Rohr
- Department of Chemistry, Princeton University, Princeton, NJ 08544, USA
| | - P Pervan
- Institut za fiziku, HR-10000 Zagreb, Croatia
| | - P K Das
- Istituto Officina dei Materiali (IOM-CNR), Laboratorio TASC, I-34149 Trieste, Italy
- International Centre for Theoretical Physics, I-34151 Trieste, Italy
| | - I Vobornik
- Istituto Officina dei Materiali (IOM-CNR), Laboratorio TASC, I-34149 Trieste, Italy
| | - R J Cava
- Department of Chemistry, Princeton University, Princeton, NJ 08544, USA
| | - T Valla
- Condensed Matter and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA
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5
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Kushwaha SK, Pletikosić I, Liang T, Gyenis A, Lapidus SH, Tian Y, Zhao H, Burch KS, Lin J, Wang W, Ji H, Fedorov AV, Yazdani A, Ong NP, Valla T, Cava RJ. Sn-doped Bi1.1Sb0.9Te2S bulk crystal topological insulator with excellent properties. Nat Commun 2016; 7:11456. [PMID: 27118032 PMCID: PMC4853473 DOI: 10.1038/ncomms11456] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2015] [Accepted: 03/30/2016] [Indexed: 12/03/2022] Open
Abstract
A long-standing issue in topological insulator research has been to find a bulk single crystal material that provides a high-quality platform for characterizing topological surface states without interference from bulk electronic states. This material would ideally be a bulk insulator, have a surface state Dirac point energy well isolated from the bulk valence and conduction bands, display quantum oscillations from the surface state electrons and be growable as large, high-quality bulk single crystals. Here we show that this material obstacle is overcome by bulk crystals of lightly Sn-doped Bi1.1Sb0.9Te2S grown by the vertical Bridgman method. We characterize Sn-BSTS via angle-resolved photoemission spectroscopy, scanning tunnelling microscopy, transport studies, X-ray diffraction and Raman scattering. We present this material as a high-quality topological insulator that can be reliably grown as bulk single crystals and thus studied by many researchers interested in topological surface states. An ideal topological insulator possesses an insulating bulk and a unique conducting surface however such behaviour is typically inhibited by bulk conduction due to defects. Here, the authors show that Sn-doped Bi1.1Sb0.9Te2S grown by the vertical Bridgman technique might overcome this hurdle.
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Affiliation(s)
- S K Kushwaha
- Frick Chemistry Laboratory, Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA
| | - I Pletikosić
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.,Brookhaven National Laboratory, Condensed Matter Physics and Materials Science Department, Upton, New York 11973, USA
| | - T Liang
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - A Gyenis
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - S H Lapidus
- X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - Yao Tian
- Department of Physics, University of Toronto, Toronto, Ontario, Canada M5S 1A7
| | - He Zhao
- Department of Physics, Boston College, Boston, Massachusetts 02467-3804, USA
| | - K S Burch
- Department of Physics, Boston College, Boston, Massachusetts 02467-3804, USA
| | - Jingjing Lin
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - Wudi Wang
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - Huiwen Ji
- Frick Chemistry Laboratory, Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA
| | - A V Fedorov
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Ali Yazdani
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - N P Ong
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - T Valla
- Brookhaven National Laboratory, Condensed Matter Physics and Materials Science Department, Upton, New York 11973, USA
| | - R J Cava
- Frick Chemistry Laboratory, Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA
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6
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Kogar A, Vig S, Thaler A, Wong MH, Xiao Y, Reig-I-Plessis D, Cho GY, Valla T, Pan Z, Schneeloch J, Zhong R, Gu GD, Hughes TL, MacDougall GJ, Chiang TC, Abbamonte P. Surface Collective Modes in the Topological Insulators Bi_{2}Se_{3} and Bi_{0.5}Sb_{1.5}Te_{3-x}Se_{x}. Phys Rev Lett 2015; 115:257402. [PMID: 26722943 DOI: 10.1103/physrevlett.115.257402] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2015] [Indexed: 06/05/2023]
Abstract
We used low-energy, momentum-resolved inelastic electron scattering to study surface collective modes of the three-dimensional topological insulators Bi_{2}Se_{3} and Bi_{0.5}Sb_{1.5}Te_{3-x}Se_{x}. Our goal was to identify the "spin plasmon" predicted by Raghu and co-workers [Phys. Rev. Lett. 104, 116401 (2010)]. Instead, we found that the primary collective mode is a surface plasmon arising from the bulk, free carriers in these materials. This excitation dominates the spectral weight in the bosonic function of the surface χ^{"}(q,ω) at THz energy scales, and is the most likely origin of a quasiparticle dispersion kink observed in previous photoemission experiments. Our study suggests that the spin plasmon may mix with this other surface mode, calling for a more nuanced understanding of optical experiments in which the spin plasmon is reported to play a role.
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Affiliation(s)
- A Kogar
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - S Vig
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - A Thaler
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - M H Wong
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - Y Xiao
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - D Reig-I-Plessis
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - G Y Cho
- Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea
| | - T Valla
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Z Pan
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - J Schneeloch
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - R Zhong
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - G D Gu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - T L Hughes
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - G J MacDougall
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - T-C Chiang
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
| | - P Abbamonte
- Department of Physics and Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA
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7
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Johnson PD, Yang HB, Rameau JD, Gu GD, Pan ZH, Valla T, Weinert M, Fedorov AV. Spin-orbit interactions and the nematicity observed in the fe-based superconductors. Phys Rev Lett 2015; 114:167001. [PMID: 25955070 DOI: 10.1103/physrevlett.114.167001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2014] [Indexed: 06/04/2023]
Abstract
High-resolution angle-resolved photoelectron spectroscopy is used to examine the electronic band structure of FeTe_{0.5}Se_{0.5} near the Brillouin zone center. A consistent separation of the α_{1} and α_{2} bands is observed with little k_{z} dependence of the α_{1} band. First-principles calculations for bulk and thin films demonstrate that the antiferromagnetic coupling between the Fe atoms and hybridization-induced spin-orbit effects lifts the degeneracy of the Fe d_{xz} and d_{yz} orbitals at the zone center leading to orbital ordering. These experimental and computational results provide a natural microscopic basis for the nematicity observed in the Fe-based superconductors.
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Affiliation(s)
- P D Johnson
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - H-B Yang
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - J D Rameau
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - G D Gu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Z-H Pan
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - T Valla
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - M Weinert
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53201, USA
| | - A V Fedorov
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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8
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Arguello CJ, Rosenthal EP, Andrade EF, Jin W, Yeh PC, Zaki N, Jia S, Cava RJ, Fernandes RM, Millis AJ, Valla T, Osgood RM, Pasupathy AN. Quasiparticle interference, quasiparticle interactions, and the origin of the charge density wave in 2H-NbSe2. Phys Rev Lett 2015; 114:037001. [PMID: 25659014 DOI: 10.1103/physrevlett.114.037001] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2014] [Indexed: 06/04/2023]
Abstract
We show that a small number of intentionally introduced defects can be used as a spectroscopic tool to amplify quasiparticle interference in 2H-NbSe2 that we measure by scanning tunneling spectroscopic imaging. We show, from the momentum and energy dependence of the quasiparticle interference, that Fermi surface nesting is inconsequential to charge density wave formation in 2H-NbSe2. We demonstrate that, by combining quasiparticle interference data with additional knowledge of the quasiparticle band structure from angle resolved photoemission measurements, one can extract the wave vector and energy dependence of the important electronic scattering processes thereby obtaining direct information both about the fermiology and the interactions. In 2H-NbSe2, we use this combination to confirm that the important near-Fermi-surface electronic physics is dominated by the coupling of the quasiparticles to soft mode phonons at a wave vector different from the charge density wave ordering wave vector.
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Affiliation(s)
- C J Arguello
- Department of Physics, Columbia University, New York, New York 10027, USA
| | - E P Rosenthal
- Department of Physics, Columbia University, New York, New York 10027, USA
| | - E F Andrade
- Department of Physics, Columbia University, New York, New York 10027, USA
| | - W Jin
- Department of Applied Physics and Applied Math, Columbia University, New York, New York 10027, USA
| | - P C Yeh
- Department of Applied Physics and Applied Math, Columbia University, New York, New York 10027, USA
| | - N Zaki
- Department of Electrical Engineering, Columbia University, New York, New York 10027, USA
| | - S Jia
- Department of Chemistry, Princeton University, Princeton, New Jersey 08540, USA
| | - R J Cava
- Department of Chemistry, Princeton University, Princeton, New Jersey 08540, USA
| | - R M Fernandes
- School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
| | - A J Millis
- Department of Physics, Columbia University, New York, New York 10027, USA
| | - T Valla
- Brookhaven National Laboratory, Upton, New York 11973, USA
| | - R M Osgood
- Department of Electrical Engineering, Columbia University, New York, New York 10027, USA and Department of Chemistry, Princeton University, Princeton, New Jersey 08540, USA
| | - A N Pasupathy
- Department of Physics, Columbia University, New York, New York 10027, USA
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9
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Pletikosić I, Ali MN, Fedorov AV, Cava RJ, Valla T. Electronic structure basis for the extraordinary magnetoresistance in WTe2. Phys Rev Lett 2014; 113:216601. [PMID: 25479512 DOI: 10.1103/physrevlett.113.216601] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2014] [Indexed: 05/13/2023]
Abstract
The electronic structure basis of the extremely large magnetoresistance in layered nonmagnetic tungsten ditelluride has been investigated by angle-resolved photoelectron spectroscopy. Hole and electron pockets of approximately the same size were found at low temperatures, suggesting that carrier compensation should be considered the primary source of the effect. The material exhibits a highly anisotropic Fermi surface from which the pronounced anisotropy of the magnetoresistance follows. A change in the Fermi surface with temperature was found and a high-density-of-states band that may take over conduction at higher temperatures and cause the observed turn-on behavior of the magnetoresistance in WTe2 was identified.
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Affiliation(s)
- I Pletikosić
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA and Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Mazhar N Ali
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA
| | - A V Fedorov
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - R J Cava
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA
| | - T Valla
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
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10
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Yilmaz T, Pletikosić I, Weber AP, Sadowski JT, Gu GD, Caruso AN, Sinkovic B, Valla T. Absence of a proximity effect for a thin-films of a Bi2Se3 topological insulator grown on top of a Bi2Sr2CaCu2O(8+δ) cuprate superconductor. Phys Rev Lett 2014; 113:067003. [PMID: 25148345 DOI: 10.1103/physrevlett.113.067003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2014] [Indexed: 06/03/2023]
Abstract
Proximity-induced superconductivity in a 3D topological insulator represents a new avenue for observing zero-energy Majorana fermions inside vortex cores. Relatively small gaps and low transition temperatures of conventional s-wave superconductors put hard constraints on these experiments. Significantly larger gaps and higher transition temperatures in cuprate superconductors might be an attractive alternative to considerably relax these constraints, but it is not clear whether the proximity effect would be effective in heterostructures involving cuprates and topological insulators. Here, we present angle-resolved photoemission studies of thin Bi(2)Se(3) films grown in situ on optimally doped Bi(2)Sr(2)CaCu(2)O(8+δ) substrates that show the absence of proximity-induced gaps on the surfaces of Bi(2)Se(3) films as thin as a 1.5 quintuple layer. These results suggest that the superconducting proximity effect between a cuprate superconductor and a topological insulator is strongly suppressed, likely due to a very short coherence length along the c axis, incompatible crystal and pairing symmetries at the interface, small size of the topological surface state's Fermi surface, and adverse effects of a strong spin-orbit coupling in the topological material.
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Affiliation(s)
- T Yilmaz
- Department of Physics, University of Connecticut, Storrs, Connecticut 06269, USA
| | - I Pletikosić
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA and Department of Physics, Princeton University, Princeton, New Jersey 08544, USA
| | - A P Weber
- National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - J T Sadowski
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - G D Gu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - A N Caruso
- Department of Physics, University of Missouri-Kansas City, Kansas City, Missouri 64110, USA
| | - B Sinkovic
- Department of Physics, University of Connecticut, Storrs, Connecticut 06269, USA
| | - T Valla
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
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11
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Petrović M, Šrut Rakić I, Runte S, Busse C, Sadowski JT, Lazić P, Pletikosić I, Pan ZH, Milun M, Pervan P, Atodiresei N, Brako R, Šokčević D, Valla T, Michely T, Kralj M. The mechanism of caesium intercalation of graphene. Nat Commun 2014; 4:2772. [PMID: 24212475 DOI: 10.1038/ncomms3772] [Citation(s) in RCA: 170] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Accepted: 10/15/2013] [Indexed: 12/23/2022] Open
Abstract
Properties of many layered materials, including copper- and iron-based superconductors, topological insulators, graphite and epitaxial graphene, can be manipulated by the inclusion of different atomic and molecular species between the layers via a process known as intercalation. For example, intercalation in graphite can lead to superconductivity and is crucial in the working cycle of modern batteries and supercapacitors. Intercalation involves complex diffusion processes along and across the layers; however, the microscopic mechanisms and dynamics of these processes are not well understood. Here we report on a novel mechanism for intercalation and entrapment of alkali atoms under epitaxial graphene. We find that the intercalation is adjusted by the van der Waals interaction, with the dynamics governed by defects anchored to graphene wrinkles. Our findings are relevant for the future design and application of graphene-based nano-structures. Similar mechanisms can also have a role for intercalation of layered materials.
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Affiliation(s)
- M Petrović
- Institut za fiziku, Bijenička 46, 10000 Zagreb, Croatia
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12
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Pletikosić I, Gu GD, Valla T. Inducing a Lifshitz transition by extrinsic doping of surface bands in the topological crystalline insulator Pb1-xSnxSe. Phys Rev Lett 2014; 112:146403. [PMID: 24765995 DOI: 10.1103/physrevlett.112.146403] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2014] [Indexed: 06/03/2023]
Abstract
The narrow gap semiconductor Pb1-xSnxSe was investigated for topologically protected surface states in its rocksalt structural phase for x=0.45, 0.23, 0.15, and 0. Angle-resolved photoelectron spectroscopy of intrinsically p-doped samples showed a clear indication of two Dirac cones, eccentric about the time-reversal invariant point X¯ of the surface Brillouin zone for all but the x=0 sample. Adsorption of alkalies gradually filled the surface bands with electrons, driving the x>0 topological crystalline insulator systems through Lifshitz transitions, and from a holelike to electronlike Fermi surface. The electron-doped bands in x>0 samples exhibited the full configuration of the Dirac cones, also confirming electron-hole symmetry of the surface bands.
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Affiliation(s)
- I Pletikosić
- Department of Physics, Princeton University, Princeton, New Jersey 08544, USA and Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - G D Gu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - T Valla
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
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Abstract
Abstract
Previous work has shown that numerical simulation does not provide a correct description of compression experiments if the rheology of the polymer in the solid state is deduced from tensile tests. Therefore, a new method is proposed for the determination of the coefficients of G'sell's constitutive equation, in order to simulate the forging process. It also gives access to a parameter characterizing the friction conditions between the polymer and the tool. It is based on isothermal compression of polymer cylinders with an appropriate geometry and on its complete interpretation by means of computer simulation using the finite element code FORGE2. This original procedure is applied to polyoxymethylene.
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Affiliation(s)
- J. M. Haudin
- Centre de Mise en Forme des Matériaux, Ecole des Mines de Paris, Sophia-Antipolis, France
| | - B. Monasse
- Centre de Mise en Forme des Matériaux, Ecole des Mines de Paris, Sophia-Antipolis, France
| | - T. Valla
- Centre de Mise en Forme des Matériaux, Ecole des Mines de Paris, Sophia-Antipolis, France
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Pan ZH, Fedorov AV, Gardner D, Lee YS, Chu S, Valla T. Measurement of an exceptionally weak electron-phonon coupling on the surface of the topological insulator Bi2Se3 using angle-resolved photoemission spectroscopy. Phys Rev Lett 2012; 108:187001. [PMID: 22681106 DOI: 10.1103/physrevlett.108.187001] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2011] [Indexed: 06/01/2023]
Abstract
Gapless surface states on topological insulators are protected from elastic scattering on nonmagnetic impurities which makes them promising candidates for low-power electronic applications. However, for widespread applications, these states should have to remain coherent at ambient temperatures. Here, we studied temperature dependence of the electronic structure and the scattering rates on the surface of a model topological insulator, Bi2Se3, by high-resolution angle-resolved photoemission spectroscopy. We found an extremely weak broadening of the topological surface state with temperature and no anomalies in the state's dispersion, indicating exceptionally weak electron-phonon coupling. Our results demonstrate that the topological surface state is protected not only from elastic scattering on impurities, but also from scattering on low-energy phonons, suggesting that topological insulators could serve as a basis for room-temperature electronic devices.
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Affiliation(s)
- Z-H Pan
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
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Valla T, Pan ZH, Gardner D, Lee YS, Chu S. Photoemission spectroscopy of magnetic and nonmagnetic impurities on the surface of the Bi2Se3 topological insulator. Phys Rev Lett 2012; 108:117601. [PMID: 22540510 DOI: 10.1103/physrevlett.108.117601] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2011] [Indexed: 05/31/2023]
Abstract
Dirac-like surface states on surfaces of topological insulators have a chiral spin structure that suppresses backscattering and protects the coherence of these states in the presence of nonmagnetic scatterers. In contrast, magnetic scatterers should open the backscattering channel via the spin-flip processes and degrade the state's coherence. We present angle-resolved photoemission spectroscopy studies of the electronic structure and the scattering rates upon the adsorption of various magnetic and nonmagnetic impurities on the surface of Bi2Se3, a model topological insulator. We reveal a remarkable insensitivity of the topological surface state to both nonmagnetic and magnetic impurities in the low impurity concentration regime. Scattering channels open up with the emergence of hexagonal warping in the high-doping regime, irrespective of the impurity's magnetic moment.
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Affiliation(s)
- T Valla
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
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Reininger R, Hulbert SL, Johnson PD, Sadowski JT, Starr DE, Chubar O, Valla T, Vescovo E. The electron spectro-microscopy beamline at National Synchrotron Light Source II: a wide photon energy range, micro-focusing beamline for photoelectron spectro-microscopies. Rev Sci Instrum 2012; 83:023102. [PMID: 22380074 DOI: 10.1063/1.3681440] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
A comprehensive optical design for a high-resolution, high-flux, wide-energy range, micro-focused beamline working in the vacuum ultraviolet and soft x-ray photon energy range is proposed. The beamline is to provide monochromatic radiation to three photoelectron microscopes: a full-field x-ray photoelectron emission microscope and two scanning instruments, one dedicated to angle resolved photoemission spectroscopy (μ-ARPES) and one for ambient pressure x-ray photoelectron spectroscopy and scanning photoelectron microscopy (AP-XPS/SPEM). Microfocusing is achieved with state of the art elliptical cylinders, obtaining a spot size of 1 μm for ARPES and 0.5 μm for AP-XPS/SPEM. A detailed ray tracing analysis quantitatively evaluates the overall beamline performances.
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Affiliation(s)
- R Reininger
- Photon Sciences Directorate, Brookhaven National Laboratory, Upton, New York 11973, USA
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Pan ZH, Vescovo E, Fedorov AV, Gardner D, Lee YS, Chu S, Gu GD, Valla T. Electronic structure of the topological insulator Bi2Se3 using angle-resolved photoemission spectroscopy: evidence for a nearly full surface spin polarization. Phys Rev Lett 2011; 106:257004. [PMID: 21770666 DOI: 10.1103/physrevlett.106.257004] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2011] [Indexed: 05/31/2023]
Abstract
We performed high-resolution spin- and angle-resolved photoemission spectroscopy studies of the electronic structure and the spin texture on the surface of Bi2Se3, a model TI. By tuning the photon energy, we found that the topological surface state is well separated from the bulk states in the vicinity of kz = Z plane of the bulk Brillouin zone. The spin-resolved measurements in that region indicate a very high degree of spin polarization of the surface state, ~0.75, much higher than previously reported. Our results demonstrate that the topological surface state on Bi2Se3 is highly spin polarized and that the dominant factors limiting the polarization are mainly extrinsic.
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Affiliation(s)
- Z-H Pan
- Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, New York 11973, USA
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Pan ZH, Camacho J, Upton MH, Fedorov AV, Howard CA, Ellerby M, Valla T. Electronic structure of superconducting KC8 and nonsuperconducting LiC6 graphite intercalation compounds: evidence for a graphene-sheet-driven superconducting state. Phys Rev Lett 2011; 106:187002. [PMID: 21635120 DOI: 10.1103/physrevlett.106.187002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2010] [Revised: 09/17/2010] [Indexed: 05/30/2023]
Abstract
We have performed photoemission studies of the electronic structure in LiC(6) and KC(8), a nonsuperconducting and a superconducting graphite intercalation compound, respectively. We have found that the charge transfer from the intercalant layers to graphene layers is larger in KC(8) than in LiC(6), opposite of what might be expected from their chemical composition. We have also measured the strength of the electron-phonon interaction on the graphene-derived Fermi surface to carbon derived phonons in both materials and found that it follows a universal trend where the coupling strength and superconductivity monotonically increase with the filling of graphene π(*) states. This correlation suggests that both graphene-derived electrons and graphene-derived phonons are crucial for superconductivity in graphite intercalation compounds.
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Affiliation(s)
- Z-H Pan
- Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, New York 11973, USA
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Zhang L, Zhang Y, Khodas M, Valla T, Zaliznyak IA. Metal to insulator transition on the N=0 Landau level in graphene. Phys Rev Lett 2010; 105:046804. [PMID: 20867875 DOI: 10.1103/physrevlett.105.046804] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2010] [Indexed: 05/29/2023]
Abstract
The magnetotransport in single layer graphene has been experimentally investigated in magnetic fields up to 18 T as a function of temperature. A pronounced T dependence is observed for T≲50 K, which is either metallic, or insulating, depending on the filling factor ν. The metal-insulator transition (MIT) occurs at |ν{c}|∼0.65 and in the regime of the dissipative transport, where the longitudinal resistance Rxx>1/2R{K}. The critical resistivity (Rxx per square) is ρ{xx}(ν{c})≈1/2R{K} and is correlated with the appearance of zero plateau in Hall conductivity σ{xy}(ν) and peaks in σ{xx}(ν). This leads us to construct a universal low-T (n, B) phase diagram of this quantum phase transition.
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Affiliation(s)
- Liyuan Zhang
- CMPMSD, Brookhaven National Laboratory, Upton, New York 11973, USA
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Valla T, Mlle PD, Michel-Brun J, Isoard P, Coudert J, Fontanges R. Etude de la répartition annuelle, quantitative et qualitative, des micromycètes atmosphériques de la région lyonnaise. Mycoses 2009. [DOI: 10.1111/j.1439-0507.1969.tb03483.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Valla T, Camacho J, Pan ZH, Fedorov AV, Walters AC, Howard CA, Ellerby M. Anisotropic electron-phonon coupling and dynamical nesting on the graphene sheets in superconducting CaC6 using angle-resolved photoemission spectroscopy. Phys Rev Lett 2009; 102:107007. [PMID: 19392151 DOI: 10.1103/physrevlett.102.107007] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2008] [Indexed: 05/27/2023]
Abstract
We present the first angle-resolved photoemission studies of electronic structure in CaC6, a superconducting graphite intercalation compound with T_{c}=11.6 K. We find that, contrary to theoretical models, the electron-phonon coupling on the graphene-derived Fermi sheets with high-frequency graphene-derived phonons is surprisingly strong and anisotropic. The shape of the Fermi surface is found to favor a dynamical intervalley nesting via exchange of high-frequency phonons. Our results suggest that graphene sheets play a crucial role in superconductivity in graphite intercalation compounds.
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Affiliation(s)
- T Valla
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
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22
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Liu C, Samolyuk GD, Lee Y, Ni N, Kondo T, Santander-Syro AF, Bud'ko SL, McChesney JL, Rotenberg E, Valla T, Fedorov AV, Canfield PC, Harmon BN, Kaminski A. K-doping dependence of the Fermi surface of the iron-arsenic Ba1-xKxFe2As2 superconductor using angle-resolved photoemission spectroscopy. Phys Rev Lett 2008; 101:177005. [PMID: 18999778 DOI: 10.1103/physrevlett.101.177005] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2008] [Indexed: 05/27/2023]
Abstract
We use angle-resolved photoemission spectroscopy to investigate the electronic properties of the newly discovered iron-arsenic superconductor Ba_(1-x)K_(x)Fe_(2)As_(2) and nonsuperconducting BaFe_(2)As_(2). Our study indicates that the Fermi surface of the undoped, parent compound BaFe_(2)As_(2) consists of hole pocket(s) at Gamma (0,0) and larger electron pocket(s) at X (1,0), in general agreement with full-potential linearized plane wave calculations. Upon doping with potassium, the hole pocket expands and the electron pocket becomes smaller with its bottom approaching the chemical potential. Such an evolution of the Fermi surface is consistent with hole doping within a rigid-band shift model. Our results also indicate that the full-potential linearized plane wave calculation is a reasonable approach for modeling the electronic properties of both undoped and K-doped iron arsenites.
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Affiliation(s)
- Chang Liu
- Ames Laboratory and Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA
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Valla T, Kidd TE, Yin WG, Gu GD, Johnson PD, Pan ZH, Fedorov AV. High-energy kink observed in the electron dispersion of high-temperature cuprate superconductors. Phys Rev Lett 2007; 98:167003. [PMID: 17501453 DOI: 10.1103/physrevlett.98.167003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2006] [Indexed: 05/15/2023]
Abstract
Photoemission studies show the presence of a high-energy anomaly in the observed band dispersion for two families of cuprate superconductors, Bi2Sr2CaCu2O8+delta and La 2-x BaxCuO4. The anomaly, which occurs at a binding energy of approximately 340 meV, is found to be anisotropic and relatively weakly doping dependent. Scattering from short range or nearest neighbor spin excitations is found to supply an adequate description of the observed phenomena.
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Affiliation(s)
- T Valla
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
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Abstract
We present studies of the electronic structure of La(2-x)BaxCuO4, a system where the superconductivity is strongly suppressed as static spin and charge orders or "stripes" develop near the doping level of x = (1/8). Using angle-resolved photoemission and scanning tunneling microscopy, we detect an energy gap at the Fermi surface with magnitude consistent with d-wave symmetry and with linear density of states, vanishing only at four nodal points, even when superconductivity disappears at x = (1/8). Thus, the nonsuperconducting, striped state at x = (1/8) is consistent with a phase-incoherent d-wave superconductor whose Cooper pairs form spin-charge-ordered structures instead of becoming superconducting.
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Affiliation(s)
- T Valla
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA.
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Homes CC, Dordevic SV, Gu GD, Li Q, Valla T, Tranquada JM. Charge order, metallic behavior, and superconductivity in La2-xBaxCuO4 with x=1/8. Phys Rev Lett 2006; 96:257002. [PMID: 16907335 DOI: 10.1103/physrevlett.96.257002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2005] [Indexed: 05/11/2023]
Abstract
The ab-plane optical properties of a cleaved single crystal of La2-xBaxCuO4 for x=1/8 (Tc approximately =2.4 K) have been measured over a wide frequency and temperature range. The low-frequency conductivity is Drude-like and shows a metallic response with decreasing temperature. However, below approximately =60 K, corresponding to the onset of charge-stripe order, there is a rapid loss of spectral weight below about 40 meV. The behavior is quite different from that typically associated with the pseudogap in the normal state of the cuprates. Instead, the gapping of the normal-state single-particle excitations looks surprisingly similar to that observed in superconducting La2-xSrxCuO4, including the presence of a residual Drude peak with reduced weight.
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Affiliation(s)
- C C Homes
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
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Kidd TE, Valla T, Fedorov AV, Johnson PD, Cava RJ, Haas MK. Orbital dependence of the fermi liquid state in Sr2RuO4. Phys Rev Lett 2005; 94:107003. [PMID: 15783507 DOI: 10.1103/physrevlett.94.107003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2004] [Indexed: 05/24/2023]
Abstract
We have used angle-resolved photoemission spectroscopy to determine the bulk electronic structure of Sr(2)RuO(4) above and below the Fermi liquid crossover near 25 K. Our measurements indicate that the properties of the system are highly orbital dependent. The quasi-2D gamma band displays Fermi liquid behavior while the remaining low energy bands show exotic properties consistent with quasi-1D behavior. In the Fermi liquid state below 25 K, the gamma band dominates the electronic properties, while at higher temperatures the quasi-1D beta and alpha bands become more important.
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Affiliation(s)
- T E Kidd
- Physics Department, Brookhaven National Laboratory, Upton, New York 11973, USA
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Wang SC, Yang HB, Sekharan AKP, Ding H, Engelbrecht JR, Dai X, Wang Z, Kaminski A, Valla T, Kidd T, Fedorov AV, Johnson PD. Quasiparticle line shape of Sr2RuO4 and its relation to anisotropic transport. Phys Rev Lett 2004; 92:137002. [PMID: 15089639 DOI: 10.1103/physrevlett.92.137002] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2003] [Indexed: 05/24/2023]
Abstract
The bulk-representative low-energy spectrum of Sr2RuO4 can be directly measured by angle-resolved photoemission. We find that the quasiparticle spectral line shape of Sr2RuO4 is sensitive to both temperature and momentum. Along the (0,0)-(pi,0) direction, both gamma and beta bands develop a sharp quasiparticle peak near k(F) at low temperatures, but as the temperature increases the spectra quickly lose coherent weight and become broad backgrounds above approximately 130 K, which is the metal-nonmetal crossover temperature, T(M), in the c-axis resistivity. However, spectra along the (0,0)-(pi,pi) direction evolve smoothly across T(M). A simple transport model can describe both in-plane and c-axis resistivity in terms of the quasiparticle line shape. Comparisons are also made to the cuprates, with implications for two dimensionality, magnetic fluctuations, and superconductivity.
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Affiliation(s)
- S-C Wang
- Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467, USA
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Valla T, Fedorov AV, Johnson PD, Glans PA, McGuinness C, Smith KE, Andrei EY, Berger H. Quasiparticle spectra, charge-density waves, superconductivity, and electron-phonon coupling in 2H-NbSe2. Phys Rev Lett 2004; 92:086401. [PMID: 14995798 DOI: 10.1103/physrevlett.92.086401] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2003] [Indexed: 05/24/2023]
Abstract
High-resolution photoemission has been used to study the electronic structure of the charge-density wave (CDW) and superconducting dichalcogenide, 2H-NbSe2. From the extracted self-energies, important components of the quasiparticle interactions have been identified. In contrast to previously studied TaSe2, the CDW transition does not affect the electronic properties significantly. The electron-phonon coupling is identified as a dominant contribution to the quasiparticle self-energy and is shown to be very anisotropic (k dependent) and much stronger than in TaSe2.
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Affiliation(s)
- T Valla
- Department of Physics, Brookhaven National Laboratory, Upton, New York, 11973-5000, USA.
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Valla T, Johnson PD, Yusof Z, Wells B, Li Q, Loureiro SM, Cava RJ, Mikami M, Mori Y, Yoshimura M, Sasaki T. Coherence incoherence and dimensional crossover in layered strongly correlated metals. Nature 2002; 417:627-30. [PMID: 12050659 DOI: 10.1038/nature00774] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The properties of an interacting electron system depend on the electron correlations and the effective dimensionality. For example, Coulomb repulsion between electrons may inhibit, or completely block, conduction by intersite electron hopping, thereby determining whether a material is a metal or an insulator. Furthermore, correlation effects increase as the number of effective dimensions decreases; in three-dimensional systems, the low-energy electronic states behave as quasiparticles, whereas in one-dimensional systems, even weak interactions break the quasiparticles into collective excitations. Dimensionality is particularly important for exotic low-dimensional materials where one- or two-dimensional building blocks are loosely connected into a three-dimensional whole. Here we examine two such layered metallic systems with angle-resolved photoemission spectroscopy and electronic transport measurements, and we find a crossover in the number of effective dimensions from two to three with decreasing temperature. This is apparent from the observation that, in the direction perpendicular to the layers, the materials have an insulating character at high temperatures but become metal-like at low temperatures, whereas transport within the layers remains metallic over the whole temperature range. We propose that this change in effective dimensionality correlates with the presence of coherent quasiparticles within the layers.
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Affiliation(s)
- T Valla
- Physics Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
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Yusof ZM, Wells BO, Valla T, Fedorov AV, Johnson PD, Li Q, Kendziora C, Jian S, Hinks DG. Quasiparticle liquid in the highly overdoped Bi(2)Sr(2)CaCu(2)O(8+delta). Phys Rev Lett 2002; 88:167006. [PMID: 11955253 DOI: 10.1103/physrevlett.88.167006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2001] [Indexed: 05/23/2023]
Abstract
Results from the study of a highly overdoped (OD) Bi(2)Sr(2)CaCu(2)O(8+delta) with a T(c) = 51 K using angle-resolved photoemission spectroscopy are presented. We observe a sharp peak in the spectra near ( pi,0) that persists well above T(c), a nodal self-energy which approaches that seen for the Mo(110) surface state, and a more k-independent line shape at the Fermi surface than the lower-doped cuprates. This allows for a realistic comparison of the lifetime values to the experimental resistivity measurements. These observations point to the validity of the quasiparticle picture for the OD even in the normal state.
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Affiliation(s)
- Z M Yusof
- Department of Physics, University of Connecticut, 2152 Hillside Road U-46, Storrs, Connecticut 06269-3046, USA
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Johnson PD, Valla T, Fedorov AV, Yusof Z, Wells BO, Li Q, Moodenbaugh AR, Gu GD, Koshizuka N, Kendziora C, Jian S, Hinks DG. Doping and temperature dependence of the mass enhancement observed in the cuprate Bi(2)Sr(2)CaCu(2)O(8+delta). Phys Rev Lett 2001; 87:177007. [PMID: 11690300 DOI: 10.1103/physrevlett.87.177007] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2001] [Indexed: 05/23/2023]
Abstract
High-resolution photoemission is used to study the electronic structure of the cuprate superconductor, Bi(2)Sr(2)CaCu(2)O(8+delta), as a function of hole doping and temperature. A kink observed in the band dispersion in the nodal line in the superconducting state is associated with coupling to a resonant mode observed in neutron scattering. From the measured real part of the self-energy it is possible to extract a coupling constant which is largest in the underdoped regime, then decreasing continuously into the overdoped regime.
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Affiliation(s)
- P D Johnson
- Department of Physics, Brookhaven National Laboratory, Upton, New York 11973-5000, USA
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Valla T, Fedorov AV, Johnson PD, Xue J, Smith KE, DiSalvo FJ. Charge-density-wave-induced modifications to the quasiparticle self-energy in 2H- TaSe2. Phys Rev Lett 2000; 85:4759-4762. [PMID: 11082645 DOI: 10.1103/physrevlett.85.4759] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2000] [Indexed: 05/23/2023]
Abstract
The self-energy of the photohole in 2H-TaSe2 is measured by angle-resolved photoemission spectroscopy as a function of binding energy and temperature. In the charge-density wave (CDW) state, a structure in the self-energy is detected at approximately 65 meV that cannot be explained by electron-phonon scattering. A reduction in the scattering rates below this energy indicates the collapse of a major scattering channel with the formation of the CDW state accompanying the appearance of a bosonic "mode" in the excitation spectrum of the system.
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Affiliation(s)
- T Valla
- Department of Physics, Brookhaven National Laboratory, Upton, New York 11973-5000, USA
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Valla T, Fedorov AV, Johnson PD, Li Q, Gu GD, Koshizuka N. Temperature dependent scattering rates at the fermi surface of optimally doped Bi(2)Sr(2)CaCu(2)O(8+delta). Phys Rev Lett 2000; 85:828-831. [PMID: 10991409 DOI: 10.1103/physrevlett.85.828] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2000] [Indexed: 05/23/2023]
Abstract
For optimally doped Bi(2)Sr(2)CaCu(2)O(8+delta), scattering rates in the normal state are found to have a linear temperature dependence over most of the Fermi surface. In the immediate vicinity of the (pi, 0) point, the scattering rates are nearly constant in the normal state, consistent with models in which scattering at this point determines the c-axis transport. In the superconducting state, the scattering rates away from the nodal direction appear to level off and become temperature independent.
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Affiliation(s)
- T Valla
- Department of Physics, Brookhaven National Laboratory, Upton, New York 11973-5000, USA
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Valla T, Fedorov AV, Johnson PD, Wells BO, Hulbert SL, Li Q, Gu GD, Koshizuka N. Evidence for quantum critical behavior in the optimally doped cuprate Bi(2)Sr(2)CaCu(2)O(8+delta). Science 1999; 285:2110-3. [PMID: 10497125 DOI: 10.1126/science.285.5436.2110] [Citation(s) in RCA: 112] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The photoemission line shapes of the optimally doped cuprate Bi(2)Sr(2)CaCu(2)O(8+delta) were studied in the direction of a node in the superconducting order parameter by means of very high resolution photoemission spectroscopy. The peak width or inverse lifetime of the excitation displays a linear temperature dependence, independent of binding energy, for small energies, and a linear energy dependence, independent of temperature, for large binding energies. This behavior is unaffected by the superconducting transition, which is an indication that the nodal states play no role in the superconductivity. Temperature-dependent scaling suggests that the system displays quantum critical behavior.
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Affiliation(s)
- T Valla
- Department of Physics, National Synchrotron Light Source, Division of Materials Sciences, Brookhaven National Laboratory, Upton, NY 11973-5000, USA. Department of Physics, University of Connecticut, Storrs, CT 06269, USA. School of Physics, The
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Valla T, Pervan P, Milun M, Hayden AB, Woodruff DP. Electronic structure of silver and copper ultrathin films on V(100): Quantum-well states. Phys Rev B Condens Matter 1996; 54:11786-11795. [PMID: 9984970 DOI: 10.1103/physrevb.54.11786] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Šeruga M, Metikoš-Huković M, Valla T, Milun M, Hoffschultz H, Wandelt K. Electrochemical and X-ray photoelectron spectroscopy studies of passive film on tin in citrate buffer solution. J Electroanal Chem (Lausanne) 1996. [DOI: 10.1016/0022-0728(95)04502-3] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Valla T, Didillon P, Michel-Brun J, Isoard P, Coudert J, Fontanges R. [Quantitative and qualitative study of the annual occurrence of micromycetes in the atmosphere in the region of Lyon]. Mykosen 1969; 12:447-58. [PMID: 5394118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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