Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session V42: Spin Transport in Low-Dimensional SystemsFocus
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Sponsoring Units: GMAG DMP DCOMP FIAP Chair: George Kioseoglou, University of Crete Room: 389 |
Thursday, March 16, 2017 2:30PM - 2:42PM |
V42.00001: Spin transport in tri-layer MoS$_{\mathrm{2}}$ Ashutosh Tiwari, Kun Tian Strong spin-orbital coupling and the inversion asymmetry of transition-metal dichalcogenides (TMD) lead to unique spin transport characteristics under externally applied magnetic field. The presence of spin-orbital fields of opposite directions for electrons in K and K' valleys in combination with inter-valley scattering results in a nontrivial spin dynamics. This feature can be probe by measuring nonlocal resistance via electrical Hanle experiments. Optical Hanle measurements revealed 1ns spin life-time in monolayer MoS$_{\mathrm{2}}$; however, no reports have addressed electrical Hanle measurements which could provide more useful information related to valley degree of freedom for charge carriers. Here, for the first time, we report the all-electrical injection and non-local detection of spin polarized carriers in tri-layer MoS$_{\mathrm{2\thinspace }}$films. We calculated the Hanle curves theoretically when the separation between spin injector and detector is much larger than spin diffusion length. The experimentally observed curve matches the theoretically-predicted Hanle shape under the regime of slow inter-valley scattering. The estimated spin life-time was found to be around 110 ps at 30 K. [Preview Abstract] |
Thursday, March 16, 2017 2:42PM - 2:54PM |
V42.00002: Integer quantum Hall effects of Q-valley electrons in transition metal disulfides Armin Khamoshi, Zefei Wu, Ning Wang, Fan Zhang In few-layer transition metal disulfides (TMDs), the conduction bands along the GK directions shift downward energetically in the presence of interlayer interactions, forming six Q valleys related by threefold rotational symmetry and time reversal symmetry. In even layers the extra inversion symmetry requires all states to be spin degenerate, whereas in odd layers the intrinsic inversion asymmetry dictates the states to be non-degenerate at each valley. Universally, the 12-fold (6-fold) degenerate Landau levels in even (odd) layers undergo spin (valley) Zeeman splitting at relatively high magnetic fields, yielding 6-fold (3-fold) degenerate Landau levels. Our theoretical analyses are in complete harmony with our experimental observations of the Shubnikov-de Hass oscillations in high-mobility low-density TMD devices. [Reference: Nature Communications 7, 12955 (2016).] [Preview Abstract] |
Thursday, March 16, 2017 2:54PM - 3:06PM |
V42.00003: Correlation-driven topological phase transition from in-plane magnetized quantum anomalous Hall to Mott insulating phase in monolayer transition metal trichlorides Xian-Lei Sheng, Branislav K. Nikolic Based on density functional theory (DFT) calculations, we predict that a monolayer of OsCl$_3$ (a layered material whose interlayer coupling is weaker than in graphite) possesses a quantum anomalous Hall (QAH) insulating phase generated by the combination of honeycomb lattice of osmium atoms, their strong spin-orbit coupling (SOC) and ferromagnetic ground state with in-plane easy-axis. The band gap opened by SOC is $E_g \simeq 67$ meV (or $\simeq 191$ meV if the easy-axis can be tilted out of the plane by an external electric field), and the estimated Curie temperature of such anisotropic planar rotator ferromagnet is $T_\mathrm{C} \lesssim 350$ K. The Chern number $\mathcal{C}=$-1 signifies the presence of a single chiral edge state in nanoribbons of finite width, where we further show that edge states are spatially narrower for zigzag than armchair edges and investigate edge-state transport in the presence of vacancies at Os sites. Since $5d$ electrons of Os exhibit {\em both} strong SOC and moderate correlation effects, we employ DFT+U calculations to show how increasing on-site Coulomb repulsion $U$ closes the gap of QAH insulator phase at $U_c$, and then reopens the gap of topologically trivial Mott insulator phase. [Preview Abstract] |
Thursday, March 16, 2017 3:06PM - 3:18PM |
V42.00004: Kondo effect in strained layered materials Kevin Ingersent, Nancy Sandler, Sergio Ulloa The many-body Kondo screening of an impurity's magnetic moment by electrons in a host material is exquisitely sensitive to the local density of states sampled by the impurity. Such sensitivity is greatly augmented in materials with strong spin-orbit interaction, where an exponential enhancement of the characteristic Kondo temperature is possible, even in the presence of weak Zeeman fields\footnote{A. Wong et al., PRB {\bf 93}, 075148 (2016).}. In graphene and transition metal dichalcogenides (TMDs), strain fields produced by folds and bubbles can also strongly modify the density of states near these features and change which host degrees of freedom are affected by an impurity level. To elucidate these effects, we use renormalization-group methods to solve an Anderson model for a magnetic impurity in a strained layered material, allowing comparison between the Kondo physics in graphene and TMDs, which have very different spin-orbit interactions. The strain fields, reflecting also the underlying lattice symmetry of the host material, are found to modulate the competition between screening channels of different angular momenta and to alter the spin correlation functions associated with the Kondo state. [Preview Abstract] |
Thursday, March 16, 2017 3:18PM - 3:30PM |
V42.00005: Voltage-Controllable Colossal Magnetocrystalline Anisotropy in Single Layer Dichalcogenides Xuelei Sui, Tao Hu, Jianfeng Wang, Bing-Lin Gu, Wenhui Duan, Mao-sheng Miao Materials with large magnetocrystalline anisotropy and strong electric field effects are in great need for new types of memory devices that are based on electric field control of spin orientations. Instead of using modified transition metal films, we propose that some monolayer transition metal dichalcogenides are ideal candidate materials for this purpose. Using density functional calculations, we illustrate that they exhibit not only exceedingly large magnetocrystalline anisotropy (MCA) but also colossal voltage modulation under external field. Especially, spins in some materials like CrSe$_{2}$ and FeSe$_{2}$, which is strongly preferred to in-plane orientation, can be totally switched to out-of-plane direction. The effect is attributed to the large band character alteration of transition metal $d$-states around the Fermi level by electric field. We further demonstrate that strain can also greatly change MCA, and can help to improve the modulation efficiency while combining with electric field. [Preview Abstract] |
Thursday, March 16, 2017 3:30PM - 3:42PM |
V42.00006: Abstract Withdrawn
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Thursday, March 16, 2017 3:42PM - 3:54PM |
V42.00007: Topological exciton condensation and superstructures in semimetallic monolayer transition metal dichalcogenides Wenyu Shan, Di Xiao Two-dimensional materials, such as monolayer transition metal dichalcogenides, provide excellent platform to study the interplay of topology, spin-orbit coupling and interaction effect. Recently it is proposed that 1T' WTe$_2$ and MoTe$_2$ may be topological semimetals under a Peierls-like distortion. In this work, we study the semimetal-insulator transition in such type of materials driven by excitonic instability. We find a regime of topological exciton condensation in the presence of spin-orbit coupling and strong anisotropy. New superstructure is generated, which allows possible experimental detection. This work is supported by DOE Basic Energy Sciences Grant No. DE- SC0012509 [Preview Abstract] |
Thursday, March 16, 2017 3:54PM - 4:06PM |
V42.00008: Spin tunneling in two-dimensional transition-metal dichalcogenide layers Zheng Yang, Bo Hsu, Subhajit Ghosh, Getu Gebre The spin tunneling effect are studied using magnetic tunneling junctions (MTJs) with two-dimensional (2D) transition-metal dichalcogenide MX$_{\mathrm{2}}$ (M$=$Mo, W; X$=$S, Se) monolayers as the tunnel layers. The single-crystalline 2D MX$_{\mathrm{2}}$ monolayers were grown using chemical vapor deposition. As-grown 2D MX$_{\mathrm{2}}$ were transferred and fabricated into MTJ devices using lithography process. Ferromagnetic metals Co and permalloy were employed as top and bottom layers in the MTJ devices. In this presentation, the spin valve effect at low- and room-temperatures is reported; the temperature dependence and bias dependence of spin tunneling effect are reported; the layer dependence of the spin tunneling effect is reported; the annealing effect on the MTJ device is reported; antiferromagnetic-layer (such as PtMn) coupling effect in the MTJ devices is reported. Finally, the performance of MTJ devices based on MoS$_{\mathrm{2}}$, WS$_{\mathrm{2}}$, MoSe$_{\mathrm{2}}$, and WSe$_{\mathrm{2}}$ are compared. [Preview Abstract] |
Thursday, March 16, 2017 4:06PM - 4:18PM |
V42.00009: All-Electrical Spin Field Effect Transistor in van der Waals Heterostructures at Room Temperature André Dankert, Saroj Dash Spintronics aims to exploit the spin degree of freedom in solid state devices for data storage and information processing. Its fundamental concepts (creation, manipulation and detection of spin polarization) have been demonstrated in semiconductors and spin transistor structures using electrical and optical methods. However, an unsolved challenge is the realization of all-electrical methods to control the spin polarization in a transistor manner at ambient temperatures. Here we combine graphene and molybdenum disulfide (MoS$_{2})$ in a van der Waals heterostructure to realize a spin field-effect transistor (spin-FET) at room temperature. These two-dimensional crystals offer a unique platform due to their contrasting properties, such as weak spin-orbit coupling (SOC) in graphene and strong SOC in MoS$_{2}$. The gate-tuning of the Schottky barrier at the MoS$_{2}$/graphene interface and MoS$_{2}$ channel yields spins to interact with high SOC material and allows us to control the spin polarization and lifetime. This all-electrical spin-FET at room temperature is a substantial step in the field of spintronics and opens a new platform for testing a plethora of exotic physical phenomena, which can be key building blocks in future device architectures. [Preview Abstract] |
Thursday, March 16, 2017 4:18PM - 4:30PM |
V42.00010: Electronic spin transport in gate-tunable black phosphorus spin valves Jiawei Liu, Ahmet Avsar, Jun You Tan, Barbaros Oezyilmaz High charge mobility, the electric field effect and small spin-orbit coupling make semiconducting black phosphorus (BP) a promising material for spintronics device applications requiring long spin distance spin communication with all rectification and amplification actions. Towards this, we study the all electrical spin injection, transport and detection under non-local spin valve geometry in fully encapsulated ultra-thin BP devices. We observe spin relaxation times as high as 4 ns, with spin relaxation lengths exceeding 6 $\mu$m. These values are an order of magnitude higher than what have been measured in typical graphene spin valve devices [1-3]. Moreover, the spin transport depends strongly on charge carrier concentration and can be manipulated in a spin transistor-like manner by controlling electric field. This behaviour persists even at room temperature. Finally, we will show that similar to its electrical and optical properties [4], spin transport property is also strongly anisotropic. [1]. N. Tombros et al. Nature 448, 571–4 (2007). [2]. A. Avsar et al. Nano Lett., 11(6), 2363-8 (2011) [3]. A. Avsar et al., NPG Asia Materials, 8, e274 (2016). [4]. F. Xia et al., Nature Commun., 5, 4458 (2014). [Preview Abstract] |
Thursday, March 16, 2017 4:30PM - 4:42PM |
V42.00011: Spatially anisotropic Kondo effect formed from individual Co atoms on silicene/ZrB$_{2}$ Tobias Gill, Ben Warner, Henning Pr\"{u}ser, Nicolae Atodiresei, Vasile Caciuc, Antoine Fleurence, Stefan Bl\"{u}gel, Yukiko Yamada-Takamura, Cyrus Hirjibehedin Highly correlated electron interactions play a crucial role in determining the physics of high-T$_{c}$ superconductors, heavy fermions systems, and frustrated magnetism. The Kondo effect, where the spin of a magnetic impurity is screened by a cloud of electrons via many-body exchange scattering, is often used as a model to investigate the fundamentals of more complex correlated effects. Scanning Tunneling Microscopy (STM) can probe Kondo scattering at the atomic scale in real space and has been used to show that the correlated properties of the Kondo effect formed from single magnetic atoms is highly sensitive its electronic environment. Here we present a spatially anisotropic Kondo effect formed from individual Co atoms on the surface of the two-dimensional (2D) material silicene grown on ZrB$_{2}$. It is found that unlike in the case of magnetic atoms on metal surfaces the Kondo resonance is asymmetrically distributed across the Co atom in two lobes that align with the symmetry of the silicene surface. These investigations highlight how the use of electronically unusual 2D materials can be used to probe new aspects of highly correlated physics, a result that will help to better understand the complex processes involved. [Preview Abstract] |
Thursday, March 16, 2017 4:42PM - 4:54PM |
V42.00012: Independent control of spin and valley by electric field or temperature in designed silicene-based devices Xuechao Zhai We show that spin and valley can be completely and independently controlled by electric field or temperature in our designed silicene devices. First, we find that a bipolar spin-valley diode effect can be driven and controlled by applying longitudinal biases through a silicene ferromagnetic-field/interlayer-electric (Ez) field junction.This effect indicates that only one-spin (the other spin) electrons from one valley (the other valley) contribute to the conductance under positive (negative) biases, arising from the specific band-matching tunneling mechanism. By reversing the Ez direction, the conductive valley can be switched to the other while the spin orientation is reserved. Second, we propose a silicene caloritronic field effect transistor constructed of two ferromagnetic electrodes and a central Ez-field region, and find that a valley Seebeck effect is driven by a temperature difference, with currents from two different valleys flowing in opposite directions. By tuning the Ez field, a unique transition from valley Seebeck effect to spin Seebeck effect is observed. These findings provide a platform for encoding information simultaneously by the valley and spin quantum numbers of electrons in future logic circuits. [Preview Abstract] |
Thursday, March 16, 2017 4:54PM - 5:06PM |
V42.00013: Inducing Strong Magnetism in Silicene Nanoflakes through Hydrogenation Sadegh Mehdi Aghaei, Ingrid Torres, Irene Calizo The properties of 2D materials considerably change in low dimensional forms due to quantum confinement effect. The zero dimensional silicene nanoflake (SiNF) has great potential to increase performance with miniaturization. In this study, density functional theory calculations were used to examine the electronic and magnetic properties of SiNFs. It was discovered that hexagonal SiNFs exhibit non-magnetic semiconducting behavior, while triangular SiNFs are magnetic semiconductors. One approach to effectively tune the properties of SiNFs is hydrogenation due to its fine reversibility and controllability. The half-hydrogenated SiNFs were observed to offer a giant spin moment which is directly proportional to the square of the flakes size (n). The total magnetic moment for hexagonal and triangular half-hydrogenated SiNFs are found to be 3n$^{\mathrm{2}}$ and (n$^{\mathrm{2}}+$5n)/2, respectively. These nanoflakes could potentially be used for spintronic circuit devices since it has been demonstrated that strong induced spin magnetizations aligned parallel and show a substantial collective behavior by large range ferromagnetic exchange coupling. SiNFs based spin switches are offered to reveal the tuning transport properties by controlling the hydrogen coverage. [Preview Abstract] |
Thursday, March 16, 2017 5:06PM - 5:18PM |
V42.00014: Superconducting Proximity Effect in InSb Flake Jie Shen, Hao Zhang, Folkert de Vries, Önder Gül, Martijn Sol, Roy Op het Veld, Stijn Balk, Saša Gazibegović, Erik Bakkers, Leo Kouwenhoven InSb is an ideal platform to realize and braid Majorana zero modes(MZM) owing to its strong spin-orbit coupling, large Land\'{e} g-factor and high mobility. So far Majorana experiments in InSb have been limited to one-dimensional nanowire devices with Nb-based superconductors. However, braiding MZM in nanowire poses a great challenge due to the required complicated wire networks. To overcome this challenge, recent proposals have focused on the two-dimensional system, where the networks can be easily defined with a large degree of freedom using local gates. Among all proposed materials, 2D InSb flake system is one of the most promising candidates. Here, we study the superconducting proximity effect in 2D InSb flake. Our Josephson junctions based on InSb flakes contacted with NbTiN superconducting leads show a large switching current up to 500nA. Magnetic interference measurements reveal the standard Fraunhofer pattern, indicating there are no trivial edge states -- states which complicate studies of topological superconductivity in other materials systems. Moreover, quantum Hall plateaus are observed, indicating the high quality of the flake system. [Preview Abstract] |
Thursday, March 16, 2017 5:18PM - 5:30PM |
V42.00015: Cluster Methods for Dissipative Phase Transitions Oscar Viyuela Garcia, Jiasen Jin, Alberto Biella, Leonardo Mazza, Jonathan Keeling, Rosario Fazzio, Davide Rossini We show that short-range correlations have a dramatic impact on the steady-state phase diagram of quantum driven-dissipative systems. This effect, never observed in equilibrium, follows from the fact that ordering in the steady state is of dynamical origin, and is established only at very long times, whereas in thermodynamic equilibrium it arises from the properties of the (free) energy. To this end, by combining the cluster methods extensively used in equilibrium phase transitions to quantum trajectories and tensor-network techniques, we extend them to non-equilibrium phase transitions in dissipative many-body systems. We analyse in detail a model of spin-1=2 on a lattice interacting through an XYZ Hamiltonian, each of them coupled to an independent environment that induces incoherent spin flips. In the steady-state phase diagram derived from our cluster approach, the location of the phase boundaries and even its topology radically change, introducing reentrance of the paramagnetic phase as compared to the single-site mean field where correlations are neglected. Furthermore, a stability analysis of the cluster mean field indicates a susceptibility towards a possible incommensurate ordering, not present if short-range correlations are ignored. Phys. Rev. X 6, 031011 (2016) [Preview Abstract] |
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