Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session P70: Metals: Magnetism, Semi-metals and Topology |
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Sponsoring Units: DCMP DMP Room: 208 |
Wednesday, March 4, 2020 2:30PM - 2:42PM |
P70.00001: Computing Transport Coefficients of Many-Body Hamiltonians by Equilibrium Averages Assa Auerbach, Ilia Khait, Noga Bashan DC transport coefficients of most strongly interacting Hamiltonians demand insurmountable computational challenges, e.g. large system sizes, long real-time evolution, and poorly controlled analytic continuation of quantum Monte Carlo data. In contrast, continued fractions expansions and the use of our new formulas for Hall-type resistivities, require only computations of equilbrium averages. These are amenable to well controlled methods, e.g. imaginary-time quantum Monte Carlo, high temperature series, and variational wavefunctions. We review continued fractions dynamical conductivity and Hall and Thermal Hall coeffiicents calculations for the Bose and Fermi Hubbard models, and the disordered Heisenberg chain. |
Wednesday, March 4, 2020 2:42PM - 2:54PM |
P70.00002: Investigation of the universal scattering rate in PdCrO_{2} by high energy electron irradiation Elina Zhakina, Philippa McGuinness, Veronika Sunko, Marcin Konczykowski, Seunghyun Khim, Markus Koenig, Andrew Mackenzie PdCrO_{2} is an extremely pure magnetic delafossite metal. It combines both possibilities for the motion of electrons in a solid: a nearly free electron metal and a Mott insulating state. |
Wednesday, March 4, 2020 2:54PM - 3:06PM |
P70.00003: Quantum Paracrystalline Shear Resonances in Metals Jun Yong Khoo, Po-Yao Chang, Falko Pientka, Inti Sodemann Unlike classical fluids, a quantum fermi liquid can support a long-lived and propagating shear sound wave, reminiscent of the transverse sound in crystals, despite lacking any form of long-range crystalline order. This mode is expected to be present in moderately interacting metals where the quasiparticle mass is renormalised to be more than twice the bare mass, but, it is hard to excite and detect because it does not involve charge density fluctuations, in contrast to the conventional plasma mode. We propose two strategies to excite and probe this unconventional mode. One is the appearance of sharp dips in the AC conductance of narrow channels when the frequency matches the energy dispersion of the shear sound. Another is the coupling of the mode to charge fluctuations under weak magnetic fields, that could allow to excite it using near field techniques such as those employed to excite plasma modes in two-dimensional metals. |
Wednesday, March 4, 2020 3:06PM - 3:18PM |
P70.00004: Polarizability and magnetoplasmons for the α-T_{3} model Godfrey Gumbs, Dipendra Dahal, Antonios Balassis, Andrii Iurov, Danhong Huang Godfrey Gumbs, Dipendra Dahal, Antonios Balassis, Andrii Iurov, and Danhong Huang |
Wednesday, March 4, 2020 3:18PM - 3:30PM |
P70.00005: The origin of sub-room temperature ferromagnetism in VSe_{2} monolayer: reduced dimension and electron correlation Taekjung Kim, Siheon Ryee, Sangkook Choi, Myung Joon Han Recently 1T-VSe_{2 }has been reported as one of the first room-temperature two-dimensional ferromagnets. However, this conclusion remains elusive both theoretically and experimentally. In this presentation we apply LDA+DMFT (local density approximation plus dynamical mean-field theory) approach to study the magnetic properties of bulk and monolayer VSe_{2}. Our results indicate that bulk 1T-VSe_{2} is a paramagnetic material as well-known but the monolayer is ferromagnetically ordered. The calculated Curie temperature is ~250K. From the detailed analysis on the electronic structure and the local spin susceptibility, we attribute the formation of local moment and the monolayer ferromagnetism to the concerted effect of quasiparticle pre-localization caused by reduced dimensionality and the electronic correlation. Further analysis shows that this ferromagnetism is vulnerable to the formation of interlayer interaction or extra charge doping, which provides the useful insight to understand the controversial experiments. |
Wednesday, March 4, 2020 3:30PM - 3:42PM |
P70.00006: Modulation of magnetism across the van der Waals interfaces Hideki Matsuoka, Mohammad Saeed Bahramy, Yue Wang, Satoshi Yoshida, Kyoko Ishizaka, Yoshihiro Iwasa, Masaki Nakano A van der Waals (vdW) heterostructure provides an indispensable material platform in modern condensed-matter researches. There, weak interlayer bonding nature ensures formation of an atomically-abrupt heterointerface beyond fundamental constraint imposed by lattice matching condition, while strong electronic coupling enables creation of an emergent electronic ground state that is missing in individual materials. Here we fabricated vdW heterostructures by molecular-beam epitaxy, where a new type of 2D magnet, vanadium selenide epitaxial thin film^{1}, was incorporated. In the presentation, we will show transport properties of those magnetic heterostructures, and discuss the interface proximity effect on 2D magnetism. [1] M. Nakano et al, Intrinsic 2D ferromagnetism in V_{5}Se_{8} epitaxial thin films. arXiv:1910.01959. |
Wednesday, March 4, 2020 3:42PM - 3:54PM |
P70.00007: High-Temperature Ferromagnetic Resonance in FePt Thin Films Chuanpu Liu, Kumar Srinivasan, Antony Ajan, Ethan McCollum, Mingzhong Wu Understanding of damping processes in ferromagnetic thin films at temperatures (T) near the Curie temperature (T_{c}) has significant implications for heat-assisted magnetic recording and magnetic sensors operating at elevated temperatures. Recent ferromagnetic resonance (FMR) studies [PR Applied 10, 054046 (2018)] using out-of-plane fields showed that there are two major relaxation processes in granular L1_{0}-odered FePt thin films at 10-45 K below T_{c}: two-magnon scattering and spin-flip magnon-electron scattering; with a decrease in T, the FMR linewidth increases due to the enhancement of the two-magnon scattering. This presentation reports high-T FMR studies on continuous FePt thin films with cubic structures, rather than L1_{0} structures. The films are 6-nm thick and have T_{c}≈680 K; the FMR measurements were performed over 300-620 K in out-of-plane fields. As opposed to the L1_{0} FePt films, the cubic FePt films show an FMR linewidth that decreases with a decrease in T. This T dependence suggests that the spin-flip magnon-electron scattering is dominant over the two-magnon scattering; the two-magnon scattering is weak because it is expected to be absent in continuous films under out-of-plane fields. |
Wednesday, March 4, 2020 3:54PM - 4:06PM |
P70.00008: Structure and Magnetism of New Metastable Fe_{8}Co_{8}N_{2} Compound Balamurugan Balasubramanian, Rabindra Pahari, Shah Valloppilly, Xingzhong Li, Ralph Skomski, Xiaoshan Xu, Cai-Zhuang Wang, Kai-Ming Ho, David Sellmyer Recently, the discovery of new magnetic materials with high magnetocrystalline anisotropy K_{1}, large saturation magnetic polarization J_{s}, and high Curie Temperature T_{c} has been accelerated by efficient computational and non-equilibrium fabrication methods [1-4]. Guided by theoretical predictions [4], we have produced a new Fe_{8}Co_{8}N_{2} compound in the form of nanoparticles using a cluster-deposition method and characterized it by XRD, XPS, STEM, EDS and magnetometry measurements. The nanoparticles have a stoichiometry of about Fe_{8}Co_{8}N_{2 }and exhibit a uniform elemental distribution of Fe, Co and N. A Rietveld refinement of XRD data shows that the new compound crystallizes in a tetragonal structure [space group I4/m (87), a = 6.188 Å and c = 5.669 Å]. Fe_{8}Co_{8}N_{2} exhibits appreciable magnetic properties, K_{1} = 16 Mergs/cm^{3}, J_{s} = 17.6 kG, and T_{c} = 650 K, which are promising for a wide range of applications including information and energy processing. |
Wednesday, March 4, 2020 4:06PM - 4:18PM |
P70.00009: Topology on a new facet of bismuth Hsin Lin, Chuang-Han Hsu, XIAOTING ZHOU, Tay-Rong Chang, Qiong Ma, Nuh Gedik, Arun Bansil, Suyang Xu, Liang Fu Bismuth-based materials have been instrumental in the development of topological physics, even though bulk bismuth itself has been long thought to be topologically trivial. A recent study has, however, shown that bismuth is in fact a higher-order topological insulator featuring one-dimensional (1D) topological hinge states protected by three-fold rotational and inversion symmetries. In this talk, we uncover another hidden facet of the band topology of bismuth by showing that bismuth is also a first-order topological crystalline insulator protected by a two-fold rotational symmetry. As a result, its $(1\bar{1}0)$ surface exhibits a pair of gapless Dirac surface states. Remarkably, these surface Dirac cones are unpinned in the sense that they are not restricted to locate at specific $k$ points in the $(1\bar{1}0)$ surface Brillouin zone. These unpinned 2D Dirac surface states could be probed directly via various spectroscopic techniques. Our analysis also reveals the presence of a distinct, previously uncharacterized set of 1D topological hinge states protected by the two-fold rotational symmetry. Our study thus provides a comprehensive understanding of the topological band structure of bismuth. |
Wednesday, March 4, 2020 4:18PM - 4:30PM |
P70.00010: The relation between ferromagnetism and structure in half-metallic transition metal oxides Mohammad Saghayezhian, Zhen Wang, Hangwen Guo, Rongying Jin, Yimei Zhu, Jiandi Zhang, E Ward Plummer Interface-driven magnetic properties such as exchange bias and inverted hysteresis are highly sought after in modern functional materials, where at least two magnetically active layers are required. Ability to achieve these functionalities in a single layer thin film (monolithic) reduces the dimensionality while enriching the magnetism. Here we uncover a previously unseen part of the phase diagram of a monolithic epitaxial thin film of La_{0.67}Sr_{0.33}MnO_{3} on SrTiO_{3} which exhibits inverted hysteresis, spontaneous magnetic reversal and exchange bias due to a structural gradient in oxygen octahedral network. We have mapped the phase diagram of this material and discovered that at a specific oxygen pressure and above a critical thickness, a complex magnetic behavior appears. Atomic-scale characterization shows that this peculiar magnetism is closely linked to continuous structural gradient that creates three distinct regions within the film, each with a different magnetism onset. Extracting oxygen octahedral geometry by electron microscopy, we found that the Curie temperature is directly correlated with the bond angle. This study illustrates the importance of octahedral geometry in the magnetic properties of the materials. |
Wednesday, March 4, 2020 4:30PM - 4:42PM |
P70.00011: Anomalous suppression of higher-order nonlinearities in 3D Dirac semimetals Jeremy Lim, Yee Sin Ang, Lay Kee Ang, Liang Jie Wong Three dimensional Dirac semimetals are often thought to share the same essential physics as 2D Dirac materials. Here, we present a counter-intuitive feature of 3D Dirac semimetals that sets them apart from their 2D counterparts: the absence of field-induced intraband nonlinearities beyond the third order at zero temperature at or near a critical field strength. Our closed-form intraband current expressions show that this effect is robust against changes in incident field polarization and phase, and remains significant at finite temperatures. Our theory is in excellent agreement with nonperturbative numerical simulations of the field-induced electron dynamics. Additionally, we identify regimes where 3D Dirac semimetals effectively function as bulk versions of 2D Dirac semimetals with the potential for superior performance in terms of high-harmonic generation. Our work fills a vital gap in understanding the nonlinear response of bulk Dirac electrons, and paves the way for the development of chip-integrable, nanophotonic devices and optoelectronics based on Dirac materials. |
Wednesday, March 4, 2020 4:42PM - 4:54PM |
P70.00012: Topological Semimetal in a Chiral Crystal with Large Chern Numbers, Multifold Band Crossings, and Long Fermi-arcs Maia G Vergniory Topological semimetals (TSs) in structurally chiral crystals (which possess a handedness due to |
Wednesday, March 4, 2020 4:54PM - 5:06PM |
P70.00013: Polar and Phase Domain Walls in Weyl Semimetallic MoTe_{2}: New Paradigm for Topological Interfacial States Fei-Ting Huang, Seong Joon Lim, Sobhit Singh, Jinwoong Kim, Lunyong Zhang, Jaewook Kim, M.-W Chu, Karin M Rabe, David Vanderbilt, Sang-Wook Cheong Much of the dramatic growth in research on topological materials has focused on topologically protected surface states. While the domain walls of topological materials such as Weyl semimetals with broken inversion or time-reversal symmetry can provide a new paradigm for exploring topological interfacial states, such investigations have received little attention to date. Utilizing in-situ cryogenic transmission electron microscopy combined with first-principles calculations, we discover intriguing domain-wall structures in MoTe_{2}, both between polar variants of the low-temperature(T) Weyl phase, and between this and the high-T higher-order topological phase. We demonstrate how polar domain walls can be manipulated with electron beams, and show that phase domain walls tend to form superlattice-like structures along the c axis. Scanning tunneling microscopy indicates a possible signature of a conducting hinge state at phase domain walls. Our results open new avenues for investigating topological interfacial states and unveiling multifunctional aspects of domain walls in topological materials. |
Wednesday, March 4, 2020 5:06PM - 5:18PM |
P70.00014: Giant extrinsic anomalous Hall effect in the Kagome, Dirac Antimonide KV_{3}Sb_{5} Yaojia Wang The electronic anomalous Hall effect (AHE), where charge carriers acquire a velocity component orthogonal to an applied electric field, is one of the most fundamental and widely studied phenomena in physics. There are several different AHE mechanisms known falling into intrinsic and extrinsic regimes. The skew scattering mechanism (extrinsic) applies to high conductivity materials and has traditionally focused on ferromagnetic metals. Here we report the observation of a giant extrinsic AHE in KV_{3}Sb_{5}, an exfoliable Dirac semimetal with a spin 1/2 Kagome layer of Vanadium atoms. Our exfoliated flake devices reach low resistivity ~1.6 μΩ cm at low temperature and even though KV_{3}Sb_{5} shows no magnetic ordering down to 0.25 K, the anomalous Hall conductivity (AHC) reaches ~10000 Ω^{-1}cm^{-1} with a skew constant of 0.013, nearly an order of magnitude larger than Fe. Surprisingly, the AHE scales with the square of the longitudinal conductivity, defying expectations from skew scattering theory. This observation invites a wider variety of materials to be investigated for giant anomalous AHE including metallic magnetically frustrated materials and cluster magnets as well as posing new fundamental questions about high conductivity AHE mechanisms. |
Wednesday, March 4, 2020 5:18PM - 5:30PM |
P70.00015: Quantum squeezing and coherence of magnons detected by spin transport Wolfgang Belzig, Akashdeep Kamra We predict the emergence of novel magnetic quasiparticles, mediated by magnetic dipolar interactions, even for a uniform ground states. These quasiparticles exhibit a spin ranging from zero to above 1 [1]. Of particular interest is our finding that the eigenmodes in an easy-axis antiferromagnet are spin-zero quasiparticles instead of the widely believed spin-1 magnons [2]. These unusual properties originate from a competition between quantum mechanical squeezing (increasing the spin) and hybridization (decreasing the spin).We show that spin-current noise measurement can reveal this fundamental quantum phenomenon [1] in full analogy to the effective charge known from shot noise measurements. Antiferromagnetic magnons are shown to exhibit giant antanglement, which might be used as quantum battery [3]. Finally, we show that by adding two normal metal spin current detectors, the magnon coherence can be tested by measuring the cross correlations [4]in analogy to the well-kown second-order coherence. |
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