Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session F32: Topological Surfaces and Interfaces towards Applications |
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Sponsoring Units: DCMP Chair: Tim Kidd, University of Northern Iowa Room: Room 224 |
Tuesday, March 7, 2023 8:00AM - 8:12AM |
F32.00001: Theory of magnetotransport in Bismuth (111) thin films Siddhesh Ambhire, Anand Bhattacharya, Eugene D Ark The surface states of Bismuth thin films have attracted much attention due to the large Rashba splitting and emergence of topological phase in the ultrathin limit. To gain a deeper understanding of the roles of surface/edge states in spin and charge transport in Bi thin films, we theoretically investigate the magnetotransport based on a sp3 tight-binding model for atomic bilayers stacked along the (111) direction, whereby the Rasbha spin-orbit coupling is captured by introducing a potential gradient in the surface bilayer. As compared to the simple Rashba two-band model, the tight-binding model is more realistic, allowing us to capture a hexagonally-warped electron pocket around the Gamma point – with spin-momentum-locking – as well as six spin-polarized hole pockets surrounding it. Applying an in-plane magnetic field can effectively shift – and distort -- these electron and hole pockets, which conspires with the suppression of back scatterings to give rise to unique magnetotransport effects (such as large anisotropic magnetoresistance and negative magnetoresistance). Comparison between theoretical and experimental results will be presented. |
Tuesday, March 7, 2023 8:12AM - 8:24AM |
F32.00002: Identification of an adsorption-controlled growth window for new Ge-based oxide films by MBE: Sr3GeO and Sr2MnGe2O7 David Bugallo Ferron, Yong-Jie Hu, Steven J May The advancement of the electronic industry is powered by new materials and new physics. In this work, we report the results of combining density functional theory (DFT) and CALculation of PHAse Diagrams (CALPHAD) to obtain temperature-pressure conditions of thermodynamic stability for Sr2MnGe2O7, a quaternary oxide with the melilite structure, and Sr3GeO, an antiperovskite, to aid in the synthesis of thin films by molecular beam epitaxy (MBE). The former material has recently been proposed to be a Weyl semimetal,1 and has been previously synthesized in powder form,2 while the latter is a narrow bandgap semiconductor.3 However, neither material has been stabilized as an epitaxial thin film. |
Tuesday, March 7, 2023 8:24AM - 8:36AM |
F32.00003: High-temperature Quantum Anomalous Hall effect in a macroscopic scale Cr-doped (Bi, Sb)2Te3. Hee Taek Yi, Xiong Yao, Deepti Jain, Seongshik Oh
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Tuesday, March 7, 2023 8:36AM - 8:48AM |
F32.00004: Electrical Transport of Zn-doped Dirac Semimetal Cd3As2 Films Ian Leahy, Jocienne N Nelson, Kirstin M Alberi, Anthony Rice Topological semimetals (TSMs) are emerging as materials with potential use in low powered electronics and spintronic devices but detailed studies focusing on reliable epitaxial growth, disorder, and the control of electronic states in TSM films are needed. In this work we focus on the use of alloying with Zn to modify the electronic structure and electrical transport of (Cd1-xZnx)3As2 with x = 0 - 0.23. Zn doping of Cd3As2 has been used to lower the carrier concentration and move the Fermi energy closer to the Dirac point but significant Zn doping causes a transition from a TSM to a semiconductor [1]. By tuning the growth conditions to suppress native defects [2] we are able to produce films with carrier concentrations a full order of magnitude smaller (~1017 cm-3) than other literature reports (>1018 cm-3). Lowering the starting carrier concentration enables us to tune the Fermi energy with smaller amounts of Zn doping. We will present a careful analysis of the electrical transport properties to explore the low Zn doping regime where the n-type carrier densities reach their lowest values before the electronic structure is significantly altered. |
Tuesday, March 7, 2023 8:48AM - 9:00AM |
F32.00005: Cloning the Dirac cones of bilayer graphene to the zone center by selenium adsorption Meng-Kai Lin, Tai-Chang Chiang, Jun Zhao, Joseph A Hlevyack Controlled manipulation of Dirac fermions in nontrivial systems is central to the engineering of high-performance devices with unusual but versatile transport properties. Surprisingly, through angle-resolved photoemission, we demonstrate that such band tuning can even occur through van der Waals molecular adsorption of selenium (Se) vapor onto bilayer-graphene-terminated SiC surfaces maintained at sufficiently low temperatures. Although elemental Se—a component material in many topological insulators—itself should be topological in certain structural forms, pure Se structures with nontrivial order are energetically unfavorable, and elemental topological systems themselves are quite rare. Here instead, an adsorbed Se layer on bilayer graphene, which is an ordered array of large Se8 molecules based upon our first-principles analysis, acts as a natural conduit for generating an emergent clone of graphene’s Dirac cones at the zone center. Overall, our systematic experimental and first-principles study not only reveals an underlying cloning mechanism based upon band folding but also offers a new, simple methodology for creating and/or manipulating Dirac fermions via gentle surface modification. |
Tuesday, March 7, 2023 9:00AM - 9:12AM |
F32.00006: All-perovskite ferroelectric field effect transistor based on BaSnO3 Hahoon Lee, Bongju Kim, Kookrin Char Spontaneous polarization in ferroelectricity can be applied to low-power, non-volatile memory devices as well as to neuromorphic devices. Pb(Zr,Ti)O3 (PZT) is a perovskite ferroelectric with high polarization and low coercive field value (~0.1 MV/cm). All-epitaxially grown perovskite structure PZT ferroelectric capacitors with 4% La-doped BaSnO3 (BLSO) and SrRuO3 (SRO) electrodes were fabricated with the pulsed laser deposition (PLD) methods. Effect of electrode materials on ferroelectric was studied with polarization-electric field (P-E) hysteresis measurements. Furthermore, PZT ferroelectric field effect transistors (FeFETs) with BLSO channel layer were fabricated. Counter-clockwise hystereses in transfer curves were observed, which demonstrates ferroelectric behavior on carrier modulation of n-type channel layer. |
Tuesday, March 7, 2023 9:12AM - 9:24AM |
F32.00007: Size-dependent conductivity based on modified energy-momentum dependent relaxation time YoungJun Lee, Jin Soo Lee, Young-Kyun Kwon, Seungjun Lee, SEOUNGHUN KANG As modern CMOS devices are downscaling, it is important to keep the interconnect resistivity low. Copper has been traditionally used as an interconnect material thanks to its high bulk conductivity. But its increasing rate of resistivity with size reduction becomes drastically high. It, thus, requires new interconnect materials that may replace copper. |
Tuesday, March 7, 2023 9:24AM - 9:36AM |
F32.00008: Limitation of Matthiessen's rule in estimating the in-plane thermal conductivity of thin Cu films Md Rafiqul Islam, John A Tomko, Md Shafkat Hoque, Eric R Hoglund, Sean W King, Christopher Jezewski, Colin D Landon, Daniel H Hirt, Kiumars Aryana, Colin Carver, Patrick Hopkins The scale of interconnects employed in the semiconductor industry is decreasing towards length scales comparable with the electron mean free path. As nanostructures becomes smaller, the thermal conductivity of interconnects decreases due to more frequent electron-electron, electron-phonon, or electron-system boundaries scattering. Matthiessen’s rule is used to assess these scattering contributions to the thermal conductivity of interconnects. In this work, we address the limitation of Matthiessen’s rule in estimating the thermal conductivities of copper (Cu) films at nanometer length scales. We perform thermoreflectance-based thermal conductance and ultrafast pump-probe experiments on annealed and unannealed Cu films ranging from 25 to 10000 nm thick, grown by physical vapor deposition (PVD) and electroplating methods. We directly measure the in-plane thermal conductivity of the Cu thin films via the time-domain thermoreflectance and steady-state thermoreflectance techniques. We find the in-plane thermal conductivity of thick films is relatively constant and begins to decrease when the thickness is less than the mean free path of Cu, which corresopnsds to a 35 nm Cu film. We measured the electronic-phonon coupling factors of Cu films by probing their reflectivity in the infrared. The electron-phonon coupling factor is relatively constant for all thicknesses even if the thickness is below the mean free path of Cu, indicating that electron-phonon scattering is not reducing the thermal conductivity of thin Cu films. This phenomenon is contradictory to Matthiessen’s rule, which accounts for all types of scattering in estimating thermal conductivity. |
Tuesday, March 7, 2023 9:36AM - 9:48AM |
F32.00009: Fully deep-UV transparent thin film transistors based on SrSnO3 Jihoon Seo, Juhan Kim, Jae H Kim, Jae H Kim, Kookrin Char Ultra-wide band gap semiconductors are gaining attention for their promising properties for UV optoelectronics and UV transparent electronics. Among them, La-doped SrSnO3 exhibits excellent properties both for deep-UV transparent oxide semiconductor (DUV TOS) and deep-UV transparent conducting oxide (DUV TCO). Here, we report the demonstration of thin film transistors (TFTs) with full deep-UV transparency based on SrSnO3. The sequentially strain-relaxed La-doped SrSnO3 films are grown on MgO (100) substrates with BaHfO3 and SrHfO3 buffer layer by pulsed laser deposition. TFT with a metal-insulator-semiconductor structure is fabricated using La-doped SrSnO3 as the channel layer and LaScO3 as the gate oxide. A highly La-doped SrSnO3 is used as the gate, the source, and the drain electrodes to obtain good contact and deep-UV transparency. The resultant device shows a field effect mobility value of ~8 cm2·V-1s-1 and the ION/IOFF ratio higher than 107. The optical transmittance of the entire device (including the substrate) is found to be higher than 75% at 300 nm in wavelength. |
Tuesday, March 7, 2023 9:48AM - 10:00AM |
F32.00010: Decoupling charge, lattice, and spin order with A-Site Cation Variance in Perovskite Nickelates Alessandro R Mazza, Zac Ward Strain, doping, and heterostructuring are useful avenues toward exploration of phase space in oxides. These methods are well studied in the perovskite nickelates, which have close ties between structural, electronic, and magnetic orders. However, these traditional methods can be limited in their approach. Recently, theoretical predictions have suggested size variance of the A-site sublattice in strongly correlated 3d transition metal oxides may provide an extra layer of tunability to phase response. These predictions propose the presence of potential unexplored regions in the nickelate phase diagram, which may diverge from expected trends when there is little variance in the average tolerance factor. In an experimental realization of extreme A-site cation disorder, we synthesize (Y0.2La0.2Nd0.2Sm0.2Gd0.2)NiO3, whose parent ternary oxides each have a large range of functional and structural phase transition temperatures. Transport and resonant elastic x-ray spectroscopy results demonstrate that the metal to insulator transition, monoclinic phase transition, and magnetic ordering temperatures are strongly influenced by A-site cation variance. These results suggest cation variance, such as that accessible in high entropy oxides, can be a critical order parameter in the design of correlated oxides, and that this parameter can provide continuous tunability to charge and magnetic orderings. |
Tuesday, March 7, 2023 10:00AM - 10:12AM |
F32.00011: Investigating Interface Phenomena Across Length Scales: From DFT to Empirical Molecular Dynamics Nicholas A Pike, Ruth Pachter Understanding the interface between solid materials is a complex problem that, while often investigated experimentally, is complicated theoretically by the size limitation in performing molecular dynamics (MD) simulations from first-principles, and thus empirical potentials are sought. However, generating reliable potentials to describe interfaces where the complex bonding and charge environments are considered is challenging. In this work, we derive a charge-optimized many-body (COMB) potential to describe the bonding, charge, and electrostatics of the interface between ZnSe and Al2O3, aiming to investigate the behavior at high temperatures. Our COMB potential is parameterized using density functional theory (DFT) calculations of the electronic, structural, and elastic properties of materials that may potentially be part of the interface system. Using our COMB potential in MD simulations, we can explain the effects of different ZnSe - Al2O3 interface geometries, the roughness of the interface (i.e., crystallographic steps or vacancies), and the effects of diffused interstitial species. |
Tuesday, March 7, 2023 10:12AM - 10:24AM |
F32.00012: "Assessing buffer layer effects on the local density of states in high temperature-ALD grown GaN thin films via LT-STM" Saraswati Shrestha, Aaron J Austin, Phadindra Wagle, Ujjal Lamichhane, Elena M Echeverria, Derek Meyers, David N McIlroy, Andrew Yost This study explores the influence of a AlN/Al2O3 buffer layer on GaN thin films grown via a high temperature atomic layer deposition method using B:Si (111) substrates. The surface composition and chemical bonding environment of the thin films, assessed with X-ray photoelectron spectroscopy, indicate a Ga rich surface and some metal oxide formation. The GaN films have a preferred (110) crystal oriented growth as confirmed by X-ray diffraction. Additionally, the local electronic properties of the thin films were studied via low temperature scanning tunneling microscopy (LT-STM) confirming an n-type behavior due to the GaN thin films, as is expected for Ga rich surfaces. The comparison of local density of states (LDOS) profiles of the GaN/B:Si(111) (without buffer layer), at room temperature and at low temperature ( |
Tuesday, March 7, 2023 10:24AM - 10:36AM |
F32.00013: Observation of two-dimensional small polarons at the LaAlO3/SrTiO3 interface Chi Sin Tang Two-dimensional (2D) perovskite oxide interfaces are condensed-matter systems where intriguing emergent properties can be observed. The onset of polaronic properties at such interfaces is a scientific discipline where both theoretical and experimental investigations can uncover interesting insights pertaining to many-body charge dynamics. Here, we report the direct observation of small-polarons at the LaAlO3/SrTiO3 (LAO/STO) conducting interface using high-resolution spectroscopic ellipsometry. The experimental observations are complemented by first-principles investigations further reveals a strong coupling between the interfacial electrons and the Ti-lattice that results in the formation of localized 2D small polarons. These findings resolve the longstanding issue where the experimentally derived interfacial carrier density is significantly lower than theoretically predicted values. |
Tuesday, March 7, 2023 10:36AM - 10:48AM |
F32.00014: An Electrical Conductance Study of the Spin State Switching Behavior of [Co(SQ)(Cat)(3-tpp)2] Spin Crossover Molecular Thin Films Joseph Soruco Spin crossover molecules are a class of organic materials possessing spin states that can be switched on a molecular level. Their unique properties make them intriguing candidates for future molecular based electronic devices. This is important due to the limits imposed by Moore’s law for current electronics which necessitates the development of new technology. The spin states of spin crossover molecules can be switched by a number of external stimuli, including thermal switching at a transition temperature, light induced spin state switching (usually at low temperature) and switching induced by electric or magnetic fields. While the typical method of inducing spin state switching in [Co(SQ)(Cat)(3-tpp)2] molecules is by thermal switching at its transition temperature of about 100°C. Our experiments show this type of molecule tends to lock in a given spin state. To facilitate spin state switching, we used temperature combined with an applied voltage and irradiation by light of specific wavelengths. |
Tuesday, March 7, 2023 10:48AM - 11:00AM |
F32.00015: The Effect of 2D Ti3C2 MXene on Spin State Switching of Spin Crossover Molecular Thin Films Saeed Yazdani, Jared Phillips, Brian Wyatt, Esha Mishra, Jonathan Yang, Jian Zhang, Babak Anasori, Peter A Dowben, Ruihua Cheng Spin crossover (SCO) molecules are transition metal coordination complexes that exhibit a bistability between a low spin and a high spin state, and they can be switched between these two states via an external stimulus, such as light, temperature, pressure and electric field. Their unique properties make them intriguing candidates for next-generation molecular-based electronic devices. In the case of very thin SCO molecular films, the functionality of the deposited molecules can be significantly affected by the substrate-molecule interaction. While some non-metallic substrates appear to be promising for use in SCO molecular-based devices, metallic substrates including gold and copper tend to suppress changes in the spin state of the deposited SCO molecules near the interface. In this work, we study how the behavior of SCO molecules, specifically [Fe(H2B(pz)2)2(bipy)], are affected when they are in the vicinity of a thin layer of MXene class of 2D materials Ti3C2. In particular, Ti3C2 MXene exhibits metallic electrical conductivity. Various techniques were utilized to analyze the quality of fabricated Ti3C2 thin films and electronic transport measurements show that the conductance of the [Fe(H2B(pz)2)2(bipy)] SCO molecules is enhanced. |
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