Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session G71: Interfacial Oxide Two-Dimensional Electron SystemsFocus Recordings Available
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Sponsoring Units: DMP Chair: Brendan Faeth, Cornell University Room: Hyatt Regency Hotel -Jackson Park C |
Tuesday, March 15, 2022 11:30AM - 12:06PM |
G71.00001: Two-dimensional superconductivity and anisotropic transport at KTaO3 (111) interfaces Invited Speaker: Anand Bhattacharya
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Tuesday, March 15, 2022 12:06PM - 12:18PM |
G71.00002: Nanoscale control of the metal-insulator transition in LAO/KTO heterostructures Muqing Yu, Changjiang Liu, Xi Yan, Dengyu Yang, Qianheng Du, Dillon D Fong, Anand Bhattacharya, Patrick R Irvin, Jeremy Levy Recent reports of superconductivity at the KTaO3 (KTO) interfaces [1] introduce new challenges and opportunities for understanding of superconductivity at oxide interfaces. Here we report nanoscale control of the metal-to-insulator transition at LAO/KTO (110) and (111) interfaces. Devices are created using two distinct methods: (1) conductive-AFM lithography [2] and (2) Ultra-low-voltage electron beam lithography [3]. At low temperatures, these devices show superconductivity, tunable by electric fields, as well as strong anisotropy along different crystallographic axes. The creation of nanoscale devices offers new paths for the investigation of underlying mechanisms of superconductivity. Our results also demonstrate that this material system may find its applications in quantum devices that incorporate strong spin-orbit interactions, nanoscale dimensions, and superconducting behavior. |
Tuesday, March 15, 2022 12:18PM - 12:30PM |
G71.00003: Nematicity driven by superconducting correlations: Application to (111) KTaO3 interface 2DEG. Arun Paramekanti, Finn Lasse Buessen, Sopheak Sorn, Ivar Martin Recent experiments have discovered nematic transport and superconductivity in the two-dimensional electron gas (2DEG) at the (111) KTaO3 oxide interface. Motivated by these observations, a k.p model for the 2DEG was proposed and shown to exhibit a Z3 nematic instability due to electron interactions. We argue that such an instability might lead to the formation of nematogens - mesoscopic domains with local nematicity but no global nematic order. When superconducting fluctuations are coupled to these nematogens, we show using Landau theory and Monte Carlo simulations that the directional delocalization of Cooper pairs favors global symmetry breaking. Using a resistor network calculation, we show that such a system shows strong transport anisotropy below a temperature which is closely tied to the superconducting fluctuations. We qualitatively discuss the impact of disorder, residual strains, and magnetic field induced frustration of nematic order. Our results qualitatively explain many of the observations on the (111) KTaO3 interface 2DEG, and may be generalized to other superconducting systems such as Cu/Nb doped topological insulator Bi2Se3. |
Tuesday, March 15, 2022 12:30PM - 12:42PM |
G71.00004: Tunable ferromagnetic 2D electron gases at the oxide interface: LaTiO3/EuTiO3 Hyungki Shin, Chong Liu, Fengmiao Li, Simon Godin, Ronny Sutarto, Bruce A Davidson, Ke Zou Two-dimensional electron gases (2DEGs) with emergent ferromagnetism attracts lots of attention because of the added spin-degree of freedom and their potential for functional applications. Here, we investigate the ferromagnetic 2DEGs formed at the heterostructure of a polar-antiferromagnetic LaTiO3 on a non-polar antiferromagnetic oxide EuTiO3. These heterostructures show robust ferromagnetism in magneto-transport measurements. We discuss the possible mechanisms of the emergent magnetic orderings. Anomalous Hall effects with hump-like behavior are also observed in particular samples, sensitive to the exact growth conditions. The magnetism in this system is highly tunable. Our results may lead to a new route to controlling emergent magnetic properties at the oxide interfaces and broadening their applications as functional magnetic devices. |
Tuesday, March 15, 2022 12:42PM - 12:54PM |
G71.00005: Angle Dependence of Hall Measurements in LaAlO3/SrTiO3 Nanostructures Aditi Nethwewala, Hyungwoo Lee, Jianan Li, Jung-Woo Lee, Chang-Beom Eom, Patrick Irvin, Jeremy Levy We investigate the Hall response of nanoscale LaAlO3/SrTiO3 Hall crosses [1] as a function of their orientation with respect to the crystallographic direction. Nonlinear Hall effect (NHE) is observed at all angular orientations. Interestingly, the field at which the slope of Hall response changes varies with the orientation of the nanocross with respect to the crystallographic direction, remaining highly reproducible at a given angle. Additionally, the shape of the nonlinear Hall response is observed to diverge from the nominally reported S-shape, at given angular orientations. This characteristic angular dependence of the Hall response shows possible coupling between the NHE and ferroelastic domains at the LaAlO3/SrTiO3 interface. |
Tuesday, March 15, 2022 12:54PM - 1:06PM |
G71.00006: Properties of LaTiO3/SrTiO3 Hall Bars Defined with a Programmable Diamond Scribe Maya Bostock, Jeremy Levy, Patrick R Irvin, Muqing Yu, Aaron S Greenberg, Ki-Tae Eom, Chang-Beom Eom Hall bars are often used to characterize the electrical and magnetic properties of 2D materials. In some instances, the surfaces are sensitive to application of photoresist, and other techniques for defining a Hall bar shape must be employed. We describe a method for programmatic scribing of microstructures that employ a sharp diamond stylus attached to a computer-controlled robotic arm. Hall bars are etched into LaTiO3/SrTiO3 (LTO/STO) heterostructures, which are subsequently characterized at cryogenic temperatures and magnetic fields. |
Tuesday, March 15, 2022 1:06PM - 1:18PM |
G71.00007: Effect of Temperature on Conductivity Decay of LaAlO3/SrTiO3 Nanostructures Aaron S Greenberg, Dengyu Yang, Philip H Shenk, Joseph A Albro, Muqing Yu, Ki-Tae Eom, Chang Beom Eom, Patrick R Irvin, Jeremy Levy
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Tuesday, March 15, 2022 1:18PM - 1:30PM |
G71.00008: Tunable giant non-linear optical susceptibility in BaSnO3 quantum wells Wente Li, Alexander A Demkov, Ali K Hamze The use of materials optical nonlinearity offers a promising path towards on-chip low power electro-optic functionalities. Decades ago, artificially engineered semiconductor quantum wells (QWs) have been proposed to enhance the optical nonlinearity. Recently, intersubband transitions have been observed in metal-oxide-based QWs, e.g. LaAlO3/SrTiO3, where the confinement can be very strong. We propose a new QW structure based on BaSnO3 (BSO), which holds both advantages of strong confinement in metal-oxide-based QWs as well as small effective mass similar to semiconductors. We use the combination of mesoscopic and microscopic simulations to study BSO-based QWs electronic structure. We then investigate and demonstrate the giant and tunable nonlinearity in BSO QWs. |
Tuesday, March 15, 2022 1:30PM - 1:42PM |
G71.00009: Design of wide bandgap Al2O3/BaSnO3quantum well Suyeong Jang, Wei Guo, Jamie Warner, Stefan Zollner, Agham Posadas, Hyoju Park, Wente Li, Alexander A Demkov Quantum wells are made up of a larger bandgap “barrier” material sandwiching the smaller bandgap “well” material. Typically made of semiconductors, they are used as lasers, photodetectors, modulators, and other devices. BaSnO3 has very high mobility (150cm^2/V-s for thin film) and a wide bandgap(~3.1eV) which makes it a great candidate for the transparent conductive films material which has applications such as electrodes for optical devices, solar cells and light emitting diodes. We report a quantum well with a large conduction band offset of 3.5eV comprising as a “barrier” material and BSO as a “well” material. The small conduction band offset (less than 1eV) of semiconductor quantum wells only allows for intersubband transitions at a mid or far infrared range. The oxide quantum well allows intersubband transitions from visible to infrared range. Using molecular beam epitaxy, we grow quantum well structures and use reflection-energy electron diffraction (RHEED), X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy to confirm the film quality and composition. We have explored quantum wells with three BSO different thickness to observe the blue shift of the absorption edge due to quantum confinement using ellipsometry. |
Tuesday, March 15, 2022 1:42PM - 1:54PM |
G71.00010: Oxide two-dimensional electron gas with high mobility at room temperature Kitae Eom, Hanjong Paik, Jinsol Seo, Neil G Campbell, Evgeny Y Tsymbal, Sang Ho Oh, Mark S Rzchowski, Darrell G Schlom, Chang-Beom Eom The prospect of 2-dimensional electron gases (2DEGs) possessing high mobility at room temperature in wide-bandgap perovskite stannates is enticing for oxide electronics, particularly to realize transparent and high-electron mobility transistors. Nonetheless only a small number of studies to date report 2DEGs in BaSnO3-based heterostructures. Here, we report 2DEG formation at the LaScO3/BaSnO3 (LSO/BSO) interface with a room-temperature mobility of 60 cm2/V·s at a carrier concentration of 1.7×1013 cm-2. This is an order of magnitude higher mobility at room temperature than achieved in SrTiO3-based 2DEGs. We achieved this by combining a thick BSO buffer layer with an ex-situ high-temperature treatment, which not only reduces the dislocation density but also produces a SnO2-terminated atomically flat surface, followed by the growth of an overlying BSO/LSO interface. Using weak-beam dark field imaging and in-line electron holography technique, we reveal a reduction of the threading dislocation density, and provide direct evidence for the spatial confinement of a 2DEG at the BSO/LSO interface. Our work opens a new pathway to explore the exciting physics of stannate-based 2DEGs at application-relevant temperatures for oxide nanoelectronics. |
Tuesday, March 15, 2022 1:54PM - 2:06PM |
G71.00011: High mobility subbands at a correlated oxide interface Mengke Ha, Zhiyuan Qin, Dawei Qiu, Qing Xiao, Changjian Ma, Danqing Liu, Guanglei Cheng The 3d orbitals at the LaAlO3/SrTiO3 (LAO/STO) interface host a manifold of correlated phenomena including electron pairing without superconductivity. These electrons are postulated to reside in multiple quantum wells close to the interface, however, the defect structure at the interface often hampers clean transport study at the strong coupling regime in the low-density limit. Here by tailoring the interface design rule, we report an observation of highly mobile subbands at the LAO/STO interface with low field mobility exceeding 30,000 cm2/Vs. Ultra-low field aperiodic quantum oscillations (0-2 T) are present, and a doubling of the oscillation frequency is observed upon back gating. Our results suggest the observed subbands may reside in quasi-1D ferroelastic domain boundaries which host exeptionally light electrons and pairs. |
Tuesday, March 15, 2022 2:06PM - 2:18PM |
G71.00012: A Laser-ARPES view on the 2D electron systems at LaAlO3/SrTiO3 and Al/SrTiO3 interfaces Flavio Y Bruno, S. McKeown Walker, Margherita Boselli, E. Martinez, Stefano Gariglio, Jean-Marc Triscone, F. Baumberger We have measured the electronic structure of the two-dimensional electron system (2DES) found at the Al/SrTiO3 (Al/STO) and LaAlO3/SrTiO3 (LAO/STO) interfaces by means of laser angle resolved photoemission spectroscopy (ARPES) taking advantage of the large photoelectron escape depth at low photon energy. We demonstrate the possibility of tuning the electronic density in Al/STO by varying the Al layer thickness and show that the electronic structure evolution is well described by self-consistent tight binding supercell calculations but differs qualitatively from a rigid band shift model. We show that both 2DES are strongly coupled to longitudinal optical phonons, in agreement with previous reports of a polaronic ground state in related STO based 2DES. Tuning the electronic density in Al/STO to match that of LAO/STO allows to discuss similarities and differences between both systems, we estimate that the intrinsic LAO/STO 2DES has a bandwidth of ≈ 50 meV and a carrier density of ≈ 6 1013 cm-2. |
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