76
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Bordács S, Checkelsky JG, Murakawa H, Hwang HY, Tokura Y. Landau level spectroscopy of Dirac electrons in a polar semiconductor with giant Rashba spin splitting. PHYSICAL REVIEW LETTERS 2013; 111:166403. [PMID: 24182286 DOI: 10.1103/physrevlett.111.166403] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2013] [Indexed: 06/02/2023]
Abstract
Optical excitations of BiTeI with large Rashba spin splitting have been studied in an external magnetic field (B) applied parallel to the polar axis. A sequence of transitions between the Landau levels (LLs), whose energies are in proportion to √B were observed, being characteristic of massless Dirac electrons. The large separation energy between the LLs makes it possible to detect the strongest cyclotron resonance even at room temperature in moderate fields. Unlike in 2D Dirac systems, the magnetic field induced rearrangement of the conductivity spectrum is directly observed.
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77
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Xie Y, Bell C, Hikita Y, Harashima S, Hwang HY. Enhancing electron mobility at the LaAlO₃ /SrTiO₃ interface by surface control. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2013; 25:4735-4738. [PMID: 23852878 DOI: 10.1002/adma.201301798] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2013] [Revised: 05/24/2013] [Indexed: 06/02/2023]
Abstract
Mobility of electrons confined at the LaAlO₃ /SrTiO₃ interface is significantly enhanced by surface control using surface charges and adsorbates, reaching a low temperature value more than 20 000 cm(2) V(-1) s(-1) . A uniform trend that mobility increases with decreasing sheet carrier density is observed.
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78
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Han JW, Lee KH, Hwang HY, Kim KB. Off-pump coronary revascularization performed concomitant with non-cardiovascular surgery. J Cardiothorac Surg 2013. [PMCID: PMC3844581 DOI: 10.1186/1749-8090-8-s1-o179] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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79
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Oh SJ, Lee KH, Hwang HY, Kim KH, Kim KB, Ahn H. Long term results of valve-sparing aortic root reconstruction. J Cardiothorac Surg 2013. [PMCID: PMC3844728 DOI: 10.1186/1749-8090-8-s1-o49] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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80
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Lee JS, Xie YW, Sato HK, Bell C, Hikita Y, Hwang HY, Kao CC. Titanium dxy ferromagnetism at the LaAlO3/SrTiO3 interface. NATURE MATERIALS 2013; 12:703-706. [PMID: 23727948 DOI: 10.1038/nmat3674] [Citation(s) in RCA: 95] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2013] [Accepted: 04/29/2013] [Indexed: 06/02/2023]
Abstract
A number of recent transport and magnetization studies have shown signs of ferromagnetism in the LaAlO3/SrTiO3 heterostructure, an unexpected property with no bulk analogue in the constituent materials. However, no experiment thus far has provided direct information on the host of the magnetism. Here we report spectroscopic investigations of the magnetism using element-specific techniques, including X-ray magnetic circular dichroism and X-ray absorption spectroscopy, along with corresponding model calculations. We find direct evidence for in-plane ferromagnetic order at the interface, with Ti(3+) character in the dxy orbital of the anisotropic t2g band. These findings establish a striking example of emergent phenomena at oxide interfaces.
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81
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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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82
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Fan K, Hwang HY, Liu M, Strikwerda AC, Sternbach A, Zhang J, Zhao X, Zhang X, Nelson KA, Averitt RD. Nonlinear terahertz metamaterials via field-enhanced carrier dynamics in GaAs. PHYSICAL REVIEW LETTERS 2013; 110:217404. [PMID: 23745933 DOI: 10.1103/physrevlett.110.217404] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2012] [Revised: 03/05/2013] [Indexed: 05/14/2023]
Abstract
We demonstrate nonlinear metamaterial split ring resonators (SRRs) on GaAs at terahertz frequencies. For SRRs on doped GaAs films, incident terahertz radiation with peak fields of ~20-160 kV/cm drives intervalley scattering. This reduces the carrier mobility and enhances the SRR LC response due to a conductivity decrease in the doped thin film. Above ~160 kV/cm, electric field enhancement within the SRR gaps leads to efficient impact ionization, increasing the carrier density and the conductivity which, in turn, suppresses the SRR resonance. We demonstrate an increase of up to 10 orders of magnitude in the carrier density in the SRR gaps on semi-insulating GaAs. Furthermore, we show that the effective permittivity can be swept from negative to positive values with an increasing terahertz field strength in the impact ionization regime, enabling new possibilities for nonlinear metamaterials.
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83
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Sakano M, Bahramy MS, Katayama A, Shimojima T, Murakawa H, Kaneko Y, Malaeb W, Shin S, Ono K, Kumigashira H, Arita R, Nagaosa N, Hwang HY, Tokura Y, Ishizaka K. Strongly spin-orbit coupled two-dimensional electron gas emerging near the surface of polar semiconductors. PHYSICAL REVIEW LETTERS 2013; 110:107204. [PMID: 23521291 DOI: 10.1103/physrevlett.110.107204] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2012] [Indexed: 06/01/2023]
Abstract
We investigate the two-dimensional highly spin-polarized electron accumulation layers commonly appearing near the surface of n-type polar semiconductors BiTeX (X=I, Br, and Cl) by angular-resolved photoemission spectroscopy. Because of the polarity and the strong spin-orbit interaction built in the bulk atomic configurations, the quantized conduction-band subbands show giant Rashba-type spin splitting. The characteristic 2D confinement effect is clearly observed also in the valence bands down to the binding energy of 4 eV. The X-dependent Rashba spin-orbit coupling is directly estimated from the observed spin-split subbands, which roughly scales with the inverse of the band-gap size in BiTeX.
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84
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Rana KG, Yajima T, Parui S, Kemper AF, Devereaux TP, Hikita Y, Hwang HY, Banerjee T. Hot electron transport in a strongly correlated transition-metal oxide. Sci Rep 2013; 3:1274. [PMID: 23429420 PMCID: PMC3572443 DOI: 10.1038/srep01274] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2013] [Accepted: 01/29/2013] [Indexed: 11/18/2022] Open
Abstract
Oxide heterointerfaces are ideal for investigating strong correlation effects to electron transport, relevant for oxide-electronics. Using hot-electrons, we probe electron transport perpendicular to the La0.7Sr0.3MnO3 (LSMO)- Nb-doped SrTiO3 (Nb:STO) interface and find the characteristic hot-electron attenuation length in LSMO to be 1.48 ± 0.10 unit cells (u.c.) at −1.9 V, increasing to 2.02 ± 0.16 u.c. at −1.3 V at room temperature. Theoretical analysis of this energy dispersion reveals the dominance of electron-electron and polaron scattering. Direct visualization of the local electron transport shows different transmission at the terraces and at the step-edges.
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85
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Kim JS, Hwang HY, Cho KR, Park EA, Lee W, Paeng JC, Lee DS, Kim HK, Sohn DW, Kim KB. Intramyocardial transfer of hepatocyte growth factor as an adjunct to CABG: phase I clinical study. Gene Ther 2012; 20:717-22. [PMID: 23151518 DOI: 10.1038/gt.2012.87] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2012] [Revised: 08/31/2012] [Accepted: 10/08/2012] [Indexed: 11/09/2022]
Abstract
The purpose of this phase I clinical trial was to evaluate the safety, tolerability and potential efficacy of VM202, naked DNA expressing two isoforms of hepatocyte growth factor, as an adjunct therapy to coronary artery bypass grafting (CABG) in patients with ischemic heart disease (IHD). Nine patients were assigned to receive increasing doses (0.5 to 2.0 mg) of VM202 injected into the right coronary artery (RCA) territory following completion of CABG for the left coronary artery territory. Patients were evaluated for safety and tolerability, and changes in myocardial functions were monitored via echocardiography, cardiac magnetic resonance imaging and myocardial single photon emission computed tomography throughout 6-month follow-up period. No serious complication related to VM202 was observed throughout the 6-month follow-up period. Global myocardial functions (wall motion score index, P=0.0084; stress perfusion, P=0.0002) improved during the follow-up period. In the RCA region, there was an increase in the stress perfusion (baseline vs 3-month, P=0.024; baseline vs 6-month, P=0.024) and also in the wall thickness of the diastolic and systolic phases. Intramyocardial injection of VM202 can be safely used in IHD patients with the tolerable dose of 2.0 mg. In addition, VM202 might appear to have improved regional myocardial perfusion and wall thickness in the injected region.
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86
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Kalisky B, Bert JA, Bell C, Xie Y, Sato HK, Hosoda M, Hikita Y, Hwang HY, Moler KA. Scanning probe manipulation of magnetism at the LaAlO3/SrTiO3 heterointerface. NANO LETTERS 2012; 12:4055-9. [PMID: 22769056 DOI: 10.1021/nl301451e] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Manipulation of magnetism is a longstanding goal of research in exotic materials. In this work, we demonstrate that the small ferromagnetic patches in LaAlO(3)/SrTiO(3) heterostructures can be dramatically changed by in situ contact of a scanning probe. Our results provide a platform for manipulation of small magnets through either a strong magneto-elastic coupling or sensitivity to surface modification. The ability to locally control magnetism is particularly interesting due to the presence of superconductivity with strong spin-orbit coupling in LaAlO(3)/SrTiO(3).
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87
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Kalisky B, Bert JA, Klopfer BB, Bell C, Sato HK, Hosoda M, Hikita Y, Hwang HY, Moler KA. Critical thickness for ferromagnetism in LaAlO3/SrTiO3 heterostructures. Nat Commun 2012; 3:922. [DOI: 10.1038/ncomms1931] [Citation(s) in RCA: 170] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2012] [Accepted: 05/28/2012] [Indexed: 11/09/2022] Open
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88
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King PDC, He RH, Eknapakul T, Buaphet P, Mo SK, Kaneko Y, Harashima S, Hikita Y, Bahramy MS, Bell C, Hussain Z, Tokura Y, Shen ZX, Hwang HY, Baumberger F, Meevasana W. Subband structure of a two-dimensional electron gas formed at the polar surface of the strong spin-orbit perovskite KTaO3. PHYSICAL REVIEW LETTERS 2012; 108:117602. [PMID: 22540511 DOI: 10.1103/physrevlett.108.117602] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2011] [Indexed: 05/31/2023]
Abstract
We demonstrate the formation of a two-dimensional electron gas (2DEG) at the (100) surface of the 5d transition-metal oxide KTaO3. From angle-resolved photoemission, we find that quantum confinement lifts the orbital degeneracy of the bulk band structure and leads to a 2DEG composed of ladders of subband states of both light and heavy carriers. Despite the strong spin-orbit coupling, our measurements provide a direct upper bound for the potential Rashba spin splitting of only Δk(parallel)}~0.02 Å(-1) at the Fermi level. The polar nature of the KTaO3(100) surface appears to help mediate the formation of the 2DEG as compared to nonpolar SrTiO3(100).
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89
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Daranciang D, Highland MJ, Wen H, Young SM, Brandt NC, Hwang HY, Vattilana M, Nicoul M, Quirin F, Goodfellow J, Qi T, Grinberg I, Fritz DM, Cammarata M, Zhu D, Lemke HT, Walko DA, Dufresne EM, Li Y, Larsson J, Reis DA, Sokolowski-Tinten K, Nelson KA, Rappe AM, Fuoss PH, Stephenson GB, Lindenberg AM. Ultrafast photovoltaic response in ferroelectric nanolayers. PHYSICAL REVIEW LETTERS 2012; 108:087601. [PMID: 22463572 DOI: 10.1103/physrevlett.108.087601] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2011] [Indexed: 05/22/2023]
Abstract
We show that light drives large-amplitude structural changes in thin films of the prototypical ferroelectric PbTiO3 via direct coupling to its intrinsic photovoltaic response. Using time-resolved x-ray scattering to visualize atomic displacements on femtosecond time scales, photoinduced changes in the unit-cell tetragonality are observed. These are driven by the motion of photogenerated free charges within the ferroelectric and can be simply explained by a model including both shift and screening currents, associated with the displacement of electrons first antiparallel to and then parallel to the ferroelectric polarization direction.
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90
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Hwang HY, Iwasa Y, Kawasaki M, Keimer B, Nagaosa N, Tokura Y. Emergent phenomena at oxide interfaces. NATURE MATERIALS 2012; 11:103-13. [PMID: 22270825 DOI: 10.1038/nmat3223] [Citation(s) in RCA: 714] [Impact Index Per Article: 59.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Recent technical advances in the atomic-scale synthesis of oxide heterostructures have provided a fertile new ground for creating novel states at their interfaces. Different symmetry constraints can be used to design structures exhibiting phenomena not found in the bulk constituents. A characteristic feature is the reconstruction of the charge, spin and orbital states at interfaces on the nanometre scale. Examples such as interface superconductivity, magneto-electric coupling, and the quantum Hall effect in oxide heterostructures are representative of the scientific and technological opportunities in this rapidly emerging field.
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91
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Wakabayashi Y, Yamasaki Y, Bell C, Hikita Y, Hwang HY, Kimura T. Growth Temperature Dependence of the LaAlO3/SrTiO3Interfacial Structure. ACTA ACUST UNITED AC 2011. [DOI: 10.1088/1742-6596/320/1/012074] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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92
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Wadati H, Geck J, Hawthorn DG, Higuchi T, Hosoda M, Bell C, Hikita Y, Hwang HY, Schussler-Langeheine C, Schierle E, Weschke E, Sawatzky GA. Electronic structure of the SrTiO3/LaAlO3interface revealed by resonant soft x-ray scattering. ACTA ACUST UNITED AC 2011. [DOI: 10.1088/1757-899x/24/1/012012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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93
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Kim M, Bell C, Kozuka Y, Kurita M, Hikita Y, Hwang HY. Fermi surface and superconductivity in low-density high-mobility δ-doped SrTiO3. PHYSICAL REVIEW LETTERS 2011; 107:106801. [PMID: 21981518 DOI: 10.1103/physrevlett.107.106801] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2011] [Indexed: 05/31/2023]
Abstract
The electronic structure of low-density n-type SrTiO3 δ-doped heterostructures is investigated by angular dependent Shubnikov-de Haas oscillations. In addition to a controllable crossover from a three- to two-dimensional Fermi surface, clear beating patterns for decreasing dopant layer thicknesses are found. These indicate the lifting of the degeneracy of the conduction band due to subband quantization in the two-dimensional limit. Analysis of the temperature-dependent oscillations shows that similar effective masses are found for all components, associated with the splitting of the light electron pocket. The dimensionality crossover in the superconducting state is found to be distinct from the normal state, resulting in a rich phase diagram as a function of dopant layer thickness.
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94
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Ishida Y, Kanto H, Kikkawa A, Taguchi Y, Ito Y, Ota Y, Okazaki K, Malaeb W, Mulazzi M, Okawa M, Watanabe S, Chen CT, Kim M, Bell C, Kozuka Y, Hwang HY, Tokura Y, Shin S. Common origin of the circular-dichroism pattern in angle-resolved photoemission spectroscopy of SrTiO3 and Cu(x)Bi2Se3. PHYSICAL REVIEW LETTERS 2011; 107:077601. [PMID: 21902429 DOI: 10.1103/physrevlett.107.077601] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2011] [Revised: 06/30/2011] [Indexed: 05/31/2023]
Abstract
Circular dichroism in the angular distribution of photoelectrons from SrTiO(3):Nb and Cu(x)Bi(2)Se(3) is investigated by 7-eV laser angle-resolved photoemission spectroscopy. In addition to the well-known node that occurs in the circular dichroism pattern when the incidence plane matches the mirror plane of the crystal, we show that another type of node occurs when the mirror plane of the crystal is vertical to the incidence plane and the electronic state is two-dimensional. The flower-shaped circular dichroism patterns in the angular distribution occurring around the Fermi level of SrTiO(3):Nb and around the Dirac point of Cu(x)Bi(2)Se(3) are explained on equal footings. We point out that the penetration depth of the topological states of Cu(x)Bi(2)Se(3) depends on momentum.
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95
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Yamamoto R, Bell C, Hikita Y, Hwang HY, Nakamura H, Kimura T, Wakabayashi Y. Structural comparison of n-type and p-type LaAlO3/SrTiO3 interfaces. PHYSICAL REVIEW LETTERS 2011; 107:036104. [PMID: 21838380 DOI: 10.1103/physrevlett.107.036104] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2011] [Indexed: 05/31/2023]
Abstract
Using a surface x-ray diffraction technique, we investigated the atomic structure of two types of interfaces between LaAlO3 and SrTiO3, that is, p-type (SrO/AlO2) and n-type (TiO2/LaO) interfaces. Our results demonstrate that the SrTiO3 in the sample with the n-type interface has a large polarized region, while that with the p-type interface has a limited polarized region. In addition, atomic intermixing was observed to extend deeper into the SrTiO3 substrate at the n-type interface compared to the p type. These differences result in distinct degrees of band bending, which likely contributes to the striking contrast in electrical conductivity between the two types of interfaces.
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96
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Xie Y, Bell C, Hikita Y, Hwang HY. Tuning the electron gas at an oxide heterointerface via free surface charges. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2011; 23:1744-1747. [PMID: 21400617 DOI: 10.1002/adma.201004673] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2010] [Indexed: 05/30/2023]
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97
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Yajima T, Hikita Y, Hwang HY. A heteroepitaxial perovskite metal-base transistor. NATURE MATERIALS 2011; 10:198-201. [PMID: 21258354 DOI: 10.1038/nmat2946] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2010] [Accepted: 12/14/2010] [Indexed: 05/30/2023]
Abstract
'More than Moore' captures a concept for overcoming limitations in silicon electronics by incorporating new functionalities in the constituent materials. Perovskite oxides are candidates because of their vast array of physical properties in a common structure. They also enable new electronic devices based on strongly-correlated electrons. The field effect transistor and its derivatives have been the principal oxide devices investigated thus far, but another option is available in a different geometry: if the current is perpendicular to the interface, the strong internal electric fields generated at back-to-back heterojunctions can be used for oxide electronics, analogous to bipolar transistors. Here we demonstrate a perovskite heteroepitaxial metal-base transistor operating at room temperature, enabled by interface dipole engineering. Analysis of many devices quantifies the evolution from hot-electron to permeable-base behaviour. This device provides a platform for incorporating the exotic ground states of perovskite oxides, as well as novel electronic phases at their interfaces.
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98
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Xie Y, Bell C, Yajima T, Hikita Y, Hwang HY. Charge Writing at the LaAlO3/SrTiO3 surface. NANO LETTERS 2010; 10:2588-2591. [PMID: 20518539 DOI: 10.1021/nl1012695] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Biased conducting-tip atomic force microscopy (AFM) has been shown to write and erase nanoscale metallic lines at the LaAlO(3)/SrTiO(3) interface. Using various AFM modes, we show the mechanism of conductivity switching is the writing of surface charge. These charges are stably deposited on a wide range of LaAlO(3) thicknesses, including bulk crystals. A strong asymmetry with writing polarity was found for 1 and 2 unit cells of LaAlO(3), providing experimental evidence for a theoretically predicted built-in potential.
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99
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Kourkoutis LF, Song JH, Hwang HY, Muller DA. Microscopic origins for stabilizing room-temperature ferromagnetism in ultrathin manganite layers. Proc Natl Acad Sci U S A 2010; 107:11682-5. [PMID: 20547875 PMCID: PMC2900658 DOI: 10.1073/pnas.1005693107] [Citation(s) in RCA: 125] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
La(0.7)Sr(0.3)MnO(3) is a conducting ferromagnet at room temperature. Combined with thin SrTiO(3) layers, the resulting heterostructures could be used as highly spin-polarized magnetic-tunnel-junction memories. However, when shrunk to dimensions below an apparent critical thickness, the structures become insulating and ferromagnetic ordering is suppressed. Interface spin and charge modulations are thought to create an interfacial dead layer, thus fundamentally limiting the use of this material in atomic-scale devices. The thickness of this dead layer, and whether it is intrinsic, is still controversial. Here we use atomic-resolution electron spectroscopy to demonstrate that the degradation of the magnetic and transport properties of La(0.7)Sr(0.3)MnO(3)/SrTiO(3) multilayers correlates with atomic intermixing at the interfaces, and the presence of extended two-dimensional cation defects in the La(0.7)Sr(0.3)MnO(3) layers (in contrast to three-dimensional precipitates in thick films). When these extrinsic defects are eliminated, metallic ferromagnetism at room temperature can be stabilized in five-unit-cell-thick manganite layers in superlattices, placing the upper limit for any intrinsic dead layer at two unit cells per interface.
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100
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Abstract
Correlated electrons in transition metal oxides can form a variety of electronic phases. The phase change between these various states gives rise to novel device functions, including sensing, signal conversion, and nonvolatile memory, and is now at the frontier of research on "emergent research device materials." Those oxide devices may have an advantage over conventional semiconductor devices for added functionality and future downsizing to the nanoscale. The elucidation of the microscopic physics behind their operation is a key step for further development.
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