Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session S46: Complex Oxide Interfaces & Heterostructures -- Electronic and transport propertiesFocus
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Sponsoring Units: DMP Chair: Ryan Comes, Auburn University Room: BCEC 212 |
Thursday, March 7, 2019 11:15AM - 11:27AM |
S46.00001: Strain-engineered SrSnO3 films with high room-temperature electron mobility Tianqi Wang, Abhinav Prakash, Yongqi Dong, Tristan Truttmann, Ashley Bucsek, Richard D James, Dillon D Fong, Jong-Woo Kim, Philip Ryan, Hua Zhou, Turan Birol, Bharat Jalan Bulk SrSnO3 (SSO) exhibits four crystalline polymorphs as a function of temperature. Through comprehensive thin film growth using novel radical-based MBE approach, synchrotron x-ray scattering, electronic transport, and first-principles calculations, we report on the stabilization of different polymorphs of SSO at room temperature (RT), in thin film form. Compressive strain stabilized the high-symmetry tetragonal phase of SSO at RT, which, in bulk, exists only at temperatures between 1062 K and 1295 K. A mobility enhancement of over 300% in the doped tetragonal phase of SSO films compared with the low-temperature orthorhombic polymorph was achieved. We will discuss these results in the context of the role of strain, doping, and disorder on structure and electronic transport of doped SSO films. |
Thursday, March 7, 2019 11:27AM - 11:39AM |
S46.00002: Electrostatic gating of MBE-grown SrSnO3 films using ion-gel Laxman Raju Thoutam, Jin Yue, Abhinav Prakash, Tianqi Wang, Bharat Jalan Electrostatic gating using ion-gel is an effective way to dynamically tune electronic phase transitions in solid materials. We report the first experimental findings of reversible electrostatic control of insulator-to-metal transition in La-doped SrSnO3 films grown by the hybrid molecular beam epitaxy method. The low temperature sheet resistance (Rs) of the films were modulated over four orders of magnitude at an applied gate voltage of +4V. The careful analysis of the temperature dependent transport properties reveal a smooth crossover from strong-localization to weak-localization behavior at 2 K with increased positive gate voltages. We further discuss the nature of quantum corrections that are responsible for the upturn in Rs at low temperatures and its effect on the induced carrier density, on the metallic side of insulator-to-metal transition. The excellent overlap of the measured Rs (at zero gate bias) before and after multiple sequence of Rs vs T measurements at different applied gate biases indicate the true reversible and electrostatic control of the gating process in stannate systems. |
Thursday, March 7, 2019 11:39AM - 11:51AM |
S46.00003: Wide Range Reversible Transport Modulation and Electron Density Dependence of Mobility in Ion-Gel-Gated BaSnO3 Films Helin Wang, Jeffery J Walter, Koustav Ganguly, Abhinav Prakash, Biqiong Yu, Guichuan Yu, Han Fu, Martin Greven, Chris Leighton Rapid progress has been made with BSO films since the report of room temperature mobility >300 cm2V-1s-1 in bulk crystals. Questions remain over mobility-limiting mechanisms, however. Here we report doping-dependent electronic transport in epitaxial-BSO-based electric double layer transistors using ion gel electrolytes. Over an exceptional gate voltage window of -3 to +4 V, at 300 K, electrostatic gating mechanisms dominate, supported by reversible transport response and operando synchrotron X-ray diffraction experiments. This is in stark contrast with many complex oxides and, vitally, is attributed here to the exceptionally small diffusivity of oxygen vacancies in BSO. Wide-range voltage control of resistance is demonstrated in a series of undoped and initially chemically n-doped BSO films, including a strong to weak localization crossover. Interfacial electron density (n) and mobility (µ) are extracted from two-channel conduction modelling and the µ-n relation is probed from ~1018 cm-3 to >1020 cm-3. Universally, µ increases rapidly with n before decreasing above ~1020 cm-3, potentially due to surface scattering. The highest µ achieved is 140 cm2V-1s-1 in La-doped BSO films by increasing µ with gating by up to 55%. |
Thursday, March 7, 2019 11:51AM - 12:03PM |
S46.00004: Weak (anti)localization in NdTiO3/SrTiO3 Heterointerfaces Xinxin Cai, Yilikal Ayino, Jin Yue, Peng Xu, Bharat Jalan, Vlad S Pribiag The quasi-two-dimensional interfacial electron gas formed at complex oxide interfaces exhibits a wide range of interesting physical properties including spin-orbit coupling and magnetism. We report magneto-transport studies on NdTiO3/SrTiO3heterostructures grown by hybrid molecular beam epitaxy. The magneto-transport behavior exhibits a systematic crossover between weak antilocalization and weak localization with changing temperature. The weak-antilocalization analysis of the magnetoresistance provides information about the spin and phase relaxation mechanisms and may indicate the interplay between the interfacial magnetism and spin-orbit coupling. |
Thursday, March 7, 2019 12:03PM - 12:15PM |
S46.00005: Quantised conductance of one-dimensional strongly-correlated electrons in a ZnO heterostructure Hangtian Hou, Yusuke Kozuka, Jun-wei Liao, Luke W Smith, Dean Kos, Jonathan Griffiths, Joseph Falson, Atsushi Tsukazaki, Masashi Kawasaki, Christopher J Ford Oxide heterostructures are versatile platforms with which to research and create novel functional nanostructures. We have developed one-dimensional (1D) quantum-wire devices using quantum point contacts on MgZnO/ZnO heterostructures and observe ballistic electron transport with conductance quantised in units of 2e2/h. Using DC-bias and in-plane-field measurements, we find that the g-factor is enhanced to around 6.8, more than three times the value in bulk ZnO. We show that the effective mass m* increases as the electron density decreases, resulting from the strong electron-electron interactions. In this strongly interacting 1D system we study features matching the '0.7' conductance anomalies up to the fifth subband. We demonstrate that high-mobility oxide heterostructures such as this can provide good alternatives to conventional III-V semiconductors in spintronics and quantum computing as they do not have their unavoidable dephasing from nuclear spins. This paves a way for the development of qubits benefiting from the low defects of an undoped heterostructure together with the long spin lifetimes achievable in silicon. |
Thursday, March 7, 2019 12:15PM - 12:27PM |
S46.00006: The formation of small polaron at the conducting LaAlO3/SrTiO3 interface Weilong Kong, Jun Zhou, Ming Yang, Yuan Ping Feng The interplays among various degrees of freedom such as charge, spin, orbital and lattice generate striking physical properties in oxide heterostructures that are not observed in their parent bulk materials. In this study, via first-principles calculations, we show that the excess electrons at the conducting LaAlO3/SrTiO3 (LAO/STO) interface favor the formation of polaron states. These electrons interact strongly with the lowest dxy orbital of the interfacial Ti lattices, forming localized splitting states. Compared with SrTiO3 bulk, the formation of the polaron states is more favorable at LAO/STO interface, which is ascribed to the reduced dimensionality and lattice symmetry. These results suggest that some of the excess electrons are localized and do not contribute to the transport effectively, and also shed light on a new direction to understand various novel properties of the conducting LAO/STO interface. |
Thursday, March 7, 2019 12:27PM - 12:39PM |
S46.00007: Systematic Study of Superconductivity in Hybrid MBE-grown Sr1-xNdxTiO3 Films Jin Yue, Yilikal Ayino, Laxman Raju Thoutam, Vlad Pribiag, Bharat Jalan Ever since the discovery of superconductivity in n-doped SrTiO3 (STO) (1018 – 1021 cm-3), STO has received significant attention. More recently, it has been shown that superconductivity can be stabilized at much lower concentrations (5.5×1017 cm-3) using oxygen-vacancy doped STO raising many questions on the role of dopants and disorder on superconductivity in STO. To-date, these works have been limited to the bulk STO single crystals. In this talk, we will present the first systematic study of superconductivity in epitaxial n-doped Sr1-xNdxTiO3 films grown using hybrid molecular beam epitaxy. We will also discuss the role of dopants, point disorder, and epitaxial strain on the superconductivity and normal state transport in doped STO films. |
Thursday, March 7, 2019 12:39PM - 12:51PM |
S46.00008: Electrical control of phase transitions through ion transfer in oxide superlattices Di Yi, Yujia Wang, Hongtao Yuan, Olaf M Van T Erve, Michael Veit, Purnima Balakrishnan, Yongseong Choi, Alpha N'Diaye, Padraic Shafer, Elke Arenholz, Berend Jonker, Pu Yu, Yuri Suzuki Electrical control of phase transitions through ion transfer has been of great interest recently. Ion transfer can have a dramatic influence on a material’s electronic, magnetic and optical properties, and thereby provides a powerful tool for fundamental research and enables many practical applications. However only a few materials have been found to exhibit significant tunability and good reversibility of electrically controlled ion transfer. In this talk, we show that superlattices comprised of the 5d oxide SrIrO3 and 3d oxide La1-xSrxMnO3 exhibit a reversible phase change under ionic liquid gating. Ionic liquid gating modulates the lattice constant by seven percent and modifies the valence of both Mn and Ir cations. The gate voltage induces a reversible transition between a ferromagnetic metallic state and a nonmagnetic insulating state, along with a large modulation of optical transmittance. Secondary ion mass spectrometry indicates that these reversible transitions are mediated by the transfer of hydrogen and oxygen ions in the superlattices. Single layer films of the constituent materials do not exhibit such significant changes in properties. Our study shows that the electrically controlled ion transfer can be engineered by designing materials at the atomic scale. |
Thursday, March 7, 2019 12:51PM - 1:27PM |
S46.00009: Emergent Phenomena at Mott Insulator/ Band Insulator Interfaces Invited Speaker: Yuri Suzuki Complex oxide interfaces have been explored extensively in recent years as emergent phenomena, ranging from magnetism, metallicity, superconductivity to spin-orbit coupling, have been generated at these interfaces due to electronic, magnetic, orbital reconstruction etc. Electronic reconstruction at a Mott insulator/ band insulator interface has been predicted to exhibit a wide range of emergent electronic and magnetic behavior. A particularly interesting model system is the LaTiO3/ SrTiO3 interface where electronic reconstruction gives rise to low dimensional metallic behavior accompanied by giant Rashba spin-orbit coupling. We studied ultrathin films of LaTiO3 on SrTiO3 substrates where interface reconstruction dominates the transport behavior. We found evidence for giant Rashba spin splitting in two sets of Shubnikov-de Haas oscillations associated with an inner and outer Fermi surface, Berry phase of π, substantial anisotropic magnetoresistance and a weak anti-localization correction to the magnetoconductivity. Together these results indicate a large Rashba coupling coefficient of 2.0 x 10-11 eV-m which is an order of magnitude larger than other complex oxide interfaces. Such a large Rashba coupling suggests that such a Mott/band insulator interface may be an excellent candidate for spin current-based electronics. |
Thursday, March 7, 2019 1:27PM - 1:39PM |
S46.00010: Controlled epitaxial growth and oxygen excess doping of the Mott insulator LaTiO3 Ralph Claessen, Philipp Scheiderer, Matthias Schmitt, Judith Gabel, Michael Zapf, Martin Stübinger, Philipp Schütz, Lenart Dudy, Christoph Schlueter, Tien-Lin Lee, Michael Sing Here we demonstrate that thin films of the prototypical Mott insulator LaTiO3 grown by pulsed laser deposition under oxygen atmosphere are readily tuned by excess oxygen doping across the line of the band-filling controlled Mott transition in the electronic phase diagram [1]. The detected insulator to metal transition is characterized by a strong change in resistivity of several orders of magnitude. The use of suitable substrates and capping layers to inhibit oxygen diffusion facilitates full control of the oxygen content and renders the films stable against exposure to ambient conditions. These achievements represent a significant advancement in control and tuning of the electronic properties of LaTiO3+x thin films making it a promising channel material in future Mottronic devices. |
Thursday, March 7, 2019 1:39PM - 1:51PM |
S46.00011: Surface Studies of SrTiO3 Films Grown by Hybrid MBE Suresh Thapa, Miles Blanchet, William Bowers, Elyssa B Roeder, Shalinee Chikara, Ryan Comes Hybrid oxide molecular beam epitaxy (hMBE), where transition metal cations are delivered using a metal-organic precursor, has emerged as the state-of-the-art approach to the synthesis of electronic-grade complex oxide films. However, numerous questions remain regarding the mechanism of the growth process and the surface properties of the resulting films. To examine these properties, thin film SrTiO3 (STO) was prepared by hMBE using a titanium tetraisopropoxide precursor for Ti delivery and an elemental Sr source on STO and (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates with varying Sr:Ti flux ratios. The grown samples are transferred to an appended x-ray photoelectron spectroscopy (XPS) system to the MBE under ultra high vacuum to analyse the surface properties. Ion scattering spectroscopy measurements were also performed in the same system to correlate the XPS data with the surface termination. To compare the results with previously reported bulk measurements, samples were also examined using Rutherford backscattering and x-ray diffraction. These studies help to explain the mechanisms of hMBE growth and the resulting surface structure of films grown within the MBE growth window. |
Thursday, March 7, 2019 1:51PM - 2:03PM |
S46.00012: Charge Transfer and Built-in Electric Fields Between the Crystalline Oxide SrNbxTi1-xO3-δ and Silicon Zheng Hui Lim, Nicholas F Quackenbush, Aubrey Penn, Matthew Chrysler, mark bowden, Zihua Zhu, James Ablett, Tien-Lin Lee, James LeBeau, Joseph Woicik, Peter Sushko, Scott Chambers, Joseph Ngai Heterojunctions between semiconductors and oxides are fundamental to field-effect devices that have revolutionized information technology. However, their principal functionality remains as capacitors within the metal-insulator-semiconductor (MIS) paradigm. Here we report charge transfer and the formation of built-in electric fields across heterojunctions between single-crystalline SrNbxTi1-xO3-δ and Si(001). A non-monotonic anomaly in the sheet resistance is observed, accompanied by a crossover in sign of the Hall resistance which indicates the formation of a hole gas in the Si and the presence of strong built-in fields. Hard X-ray photoelectron spectroscopy measurements reveal pronounced asymmetric features in both the SrNbxTi1-xO3-δ and Si core-level spectra that we show arise from built-in fields. Analysis of these unprecedented asymmetries enables band-bending to be spatially mapped across the heterojunction. Control of charge transfer and built-in fields opens a pathway to realize hybrid pn-junctions, isotype junctions etc., that elevate the functionality of semiconductor-oxide heterojunctions beyond the MIS paradigm. |
Thursday, March 7, 2019 2:03PM - 2:15PM |
S46.00013: Direct Measurement of Band Edge Profiles at Epitaxial Oxide/Semiconductor Heterojunctions Scott Chambers, Petr Sushko, Nicholas F Quackenbush, Joseph Woicik, Zheng Hui Lim, Matthew Chrysler, Joseph Ngai, Tien-Lin Lee, James Ablett, mark bowden, Zihua Zhu, Aubrey Penn, James LeBeau Band edge profiles for semiconductor heterojunctions can be approximated using transport data and/or calculated from first principles, assuming an atomistic materials structure. However, direct and accurate experimental measurement has not been possible by traditional means. We have used hard x-ray photoelectron spectroscopy (HAXPES) to extract band edge profiles from core-level spectra by developing an effective algorithm that fits experimental heterostructure spectra to sums of flat-band spectra, measured for pure reference materials, in which the binding energies are exhaustively varied to sample the phase space of physically reasonable potential profiles over all layers within the HAXPES probe depth. We apply this method to heterojunctions of n-SrNbxTi1-xO3 and intrinsic Si(001), prepared by molecular beam epitaxy. Heterojunction formation results in a Si hole gas and a surface depleted dead layer in the SrNbxTi1-xO3. The band edge profiles resulting from the HAXPES fitting reveal both of these features, and match what is expected based on Hall data remarkably well. In this talk, we present highlights of this analysis. |
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