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 S40: Other Defects |
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Sponsoring Units: DMP Chair: Sieun Chae, University of Michigan Room: Room 232 |
Thursday, March 9, 2023 8:00AM - 8:12AM |
S40.00001: Spatial and time-resolved single-dopant band bending fluctuations in semiconductors measured with electrostatic force microscopy Peter H Grutter In frequency-modulated atomic force microscopy (fm-AFM) the measured frequency shift is quadratic in applied bias for metallic samples and probes. However, for semiconducting samples, band bending effects must be considered, resulting in non-parabolic bias curves. We have developed a theoretical framework to quantitatively describe a metal-insulator semiconductor (MIS) device formed out of a metallic AFM tip, vacuum gap, and semiconducting sample [1]. This framework allows us to measure dopant concentration, bandgap and band bending timescales of different types of defects on semiconductors with nm scale resolution. |
Thursday, March 9, 2023 8:12AM - 8:24AM |
S40.00002: Persistent luminescence in rare-earth doped wide band-gap materials Khang Hoang On March 12, 1993, after two years of trial and error, Murayam, Takeuchi, Aoki, and Matsuzawa of Nemoto & Co., Ltd. (Japan) successfully developed a new-generation phosphor, SrAl2O4:Eu2+,Dy3+, opening up a new era of scientific research on persistent luminescence. Three decades later, despite great progress in understanding the phenomenon and in discovering new materials, details of the underlying mechanism for the persistent luminescence observed in rare-earth (RE) doped SrAl2O4 and similar materials are still under debate, and the search for new or improved persistent phosphors is still largely trial and error. In this talk, on the 30-year anniversary of the Nemota team’s discovery, we present the first detailed understanding of native point defects and RE (co)dopants in SrAl2O4 based on results from hybrid density-functional defect calculations, assign the absorption and emission bands experimentally observed in Eu-doped SrAl2O4, including the material's characteristic green and blue emissions, to specific defect configurations and optical transitions, and identify charge carrier trapping centers responsible for the delayed luminescence. Our work will call for a re-assessment of all the mechanisms previously proposed for RE-doped SrAl2O4. |
Thursday, March 9, 2023 8:24AM - 8:36AM |
S40.00003: Nanoscale variations in the Rashba parameter of BiTeI Ruizhe Kang, Jian-Feng Ge, Yang He, Zhihuai Zhu, Daniel T Larson, Mohammed Saghir, Geetha Balakrishnan, Jennifer E Hoffman BiTeI is a polar semiconductor with a strong spin-orbit coupling (SOC), which results in a large Rashba spin splitting. Due to a potential impact on spintronics and magnetoelectrics, it is essential to understand the behavior of single impurities in this material. Using scanning tunneling microscopy (STM) and spectroscopy (STS), we imaged ring-like charging states of single-atom defects on the iodine surface of BiTeI. By density functional theory (DFT) calculation, we identified the three types of defects that induce the charge rings. We use the bias dependence of the ring radius as a local probe for surface charge density. Remarkably, we correlate the defect-quantified local charge density with the local Rashba energy of spin band splitting. Our results help understand the impact of a single defect on Rashba effect, which could play a role in making spintronic devices. |
Thursday, March 9, 2023 8:36AM - 8:48AM |
S40.00004: Quantum embedding studies of substitutional Er3+ defects in monolayer WS2 Gabriel I López-Morales, Alexander Hampel, Vinod M Menon, Cyrus E Dreyer, Johannes Flick, Carlos A Meriles Single rare-earth (RE) impurities feature electronically screened 4f states that result in hours-long coherence times and, in the case of Er3+, homogeneous linewidths as narrow as 50 Hz within the telecom band. Harnessing the intrinsic potential of Er3+ and other REs as spin-qubits requires finding suitable host materials that avoid unwanted decoherence sources, e.g., strain and hyperfine interactions, while being easily integrated with current device technology. An interesting option along these lines is tungsten disulfide (WS2), a low spin-active-nuclei van der Waals material with a 2.1-eV bandgap and sizable lattice constant. Motivated by these considerations, we employ computational methods based on quantum embedding techniques to study an Er3+ substitution (ErW) in monolayer WS2. The technique has been applied to similar systems and is based on the constrained random phase approximation (cRPA) and a localized basis via Wannierization to construct an effective Hamiltonian that explicitly treats the correlations within a subspace chosen to comprise the 4f-like defect states of the ErW center. Spin-orbit interactions are added both implicitly within the cRPA and explicitly within the effective Hamiltonian through atomic-like spin-orbit terms. The obtained results within these methods help in describing the electronic structure and 4f–4f excitations of Er3+ more quantitatively, with the potential for being extended to other defect systems based on RE dopants in similar host matrices. |
Thursday, March 9, 2023 8:48AM - 9:00AM |
S40.00005: Pseudogap Feature in the Electronic Density of States of Weakly Localized Ge2Sb2Te5 Samples Nicholas Mazzucca, Junjing Zhao, Marc Bockrath, Despina A Louca, Utpal Chatterjee Phase change materials such as Ge2Sb2Te5 (GST) are known to exhibit electronic localization phenomena [1,2]. We have studied bulk single crystals of GST and Ge2Sb2Te5(1−x) Se5x(GSST) using a comprehensive approach that incorporates angle-resolved photoemission spectroscopy (ARPES) and magnetic field-dependent electronic transport measurements. We observe that as x, i.e., the amount of Se substitution of Te, increases, a transition occurs from a bad metal to a weakly localized system for x ≥ xc~ 0.6. The positive magnetoresistance trend in samples with x ≥ xc indicates the presence of strong spin-orbit coupling, while the temperature dependence of both the resistance and the extracted phase coherence length implies strong electronic interactions. At the same time, ARPES measurements show finite electronic density of states (DOS) for all values of x, which is expected in the case of weak localization [3]. However, above xc, the DOS is partially suppressed (pseudogapped) at the chemical potential, and this suppression is significantly broader than what one would expect from e.g. [3]. Our results establish that GSST can act as a model system for a tunable disordered metal with appreciable electronic interactions, where the interplay between electronic correlations and disorder can manifest itself via an emergent pseudogap behavior in the DOS. |
Thursday, March 9, 2023 9:00AM - 9:12AM |
S40.00006: Spin Dependent Transient Spectroscopy Kenneth J Myers, Patrick M Lenahan, James P Ashton, Jason T Ryan Abstract |
Thursday, March 9, 2023 9:12AM - 9:24AM Author not Attending |
S40.00007: Magnetotransport properties at Low-temperature of Thallium doped PbTe grown by Molecular Beam Epitaxy. Ali Nichols, Elizabeth Leblanc, Thomas Myers, Nikoleta Theodoropoulou We have grown PbTe thin films, of various thicknesses, on single crystal CdTe(211)B substrates by Molecular Beam Epitaxy. PbTe is a narrow gap semiconductor that crystallizes in the rock-salt structure. PbTe is an important thermoelectric material with figure of merit (ZT) exceeding 2.0. The films are doped with Thallium (Tl) acting as an acceptor, the only impurity known to cause superconductivity in PbTe, even though it can be doped with other impurities to similar carrier concentrations levels. We investigate the low temperature magnetotransport properties of PbTe films doped Tl. We find evidence of a Kondo effect below 15K for high Tl doping with hole carrier concentrations ranging from 1014 to 1015 cm-2. |
Thursday, March 9, 2023 9:24AM - 9:36AM |
S40.00008: Effects of excess electron-hole pairs on defect migration in semiconductors Andrew O'Hara, Daniel M Fleetwood, Ronald D Schrimpf, Sokrates T Pantelides Irradiation of semiconductors by various sources, including X-rays, lasers, and ion strikes, leads to the generation of large concentrations of free electrons and holes. Wide-band-gap, compound semiconductors are often used in power electronics where large voltages are applied to devices. However, the combination of energetic-heavy-ion irradiation and large electric fields may lead to catastrophic device failure (i.e., burnout). The role of defects in such failures is generally an open question. Typically, modification of the defect diffusion barrier by an electric field follows ?Emigr = Eqd for a field of strength E applied to a defect in charge state q, with d being half a hopping length. In this work, using density-functional theory, we investigate the role of significant concentrations of free electrons and holes in modifying the migration barriers. We find that the presence of defect-induced electronic resonances in either the conduction or valence bands can have a significant impact. A number of related issues, results, and connections to experimental data will be discussed. |
Thursday, March 9, 2023 9:36AM - 9:48AM |
S40.00009: GGA-SCAN failure to describe multiple valance states of copper Hannes Raebiger, Noriyuki Egawa, Soungmin Bae The Strongly Constrained and appropriately normed meta-GGA (GGA-SCAN) is a parameter-free first principles density-functional celebrated for correctly describing spectral properties of strongly correlated systems. GGA-SCAN correctly predicts the gapping of e.g. Mott insulators and cuprite superconductors, where conventional GGA functionals fail. We test GGA-SCAN's predictive power for thermochemical formation enthalpies of cuprous oxide Cu2O, cupric oxide CuO, and YBa2Cu3O7-δ (YBCO), and find that SCAN fails to predict the relative stability of Cu+I(d10) vs. Cu+II(d9), excessively stabilizing Cu+II(d9) such that Cu2O is thermochemically unstable. Ensuingly, GGA-SCAN also predicts unphysical defect structures for YBCO at small δ. While conventional GGA functionals can be corrected for both spectral and thermochemical properties by Hubbard-U corrections, GGA-SCAN cannot. |
Thursday, March 9, 2023 9:48AM - 10:00AM |
S40.00010: High-throughput study of s- and p-element point defects in 4H-SiC Oscar E Bulancea-Lindvall, Joel Davidsson, Viktor Ivady, Rickard Armiento, Igor A. Abrikosov Wide band-gap semiconductors such as silicone carbide (SiC) is of high interest as a host for a great variety of defect systems with optical emission and spin properties suitable for quantum technologies. However, the space of possible defect systems is incredibly vast, particularly so when including dopants, and identifying additionally promising defects is challenging. High-throughput approaches to defect identification and property prediction offer a systematic solution to this issue. In particular, we employ the workflow package ADAQ1, capable of defect generation, screening and spin-optical property characterization using density functional theory. The ability of ADAQ for defect search and identification was recently demonstrated, where several previously unidentified related photoluminescence lines could be matched to defects via exhaustive search.2 In a following large-scale endeavor, we have created and screened more than 40,000 single and double defects with s- and p-element dopants in 4H-SiC, discerning those of optimal stability and prospects. In this presentation, we explore this collection of defects and highlight extrinsic defect systems of particular interest. |
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