Browsing by Subject "Hall effect"

Now showing 1 - 5 of 5

All Electrical Control and Temperature Dependence of the Spin and Valley Hall Effect in Monolayer WSe2 Transistors
(2022-02-23) Li, Xintong; Liu, Zhida; Liu, Yihan; Karki, Suyogya; Li, Xiaoqin; Akinwande, Deji; Incorvia, Jean Anne C.
Heavy metal-based two-dimensional van der Waals materials have a large, coupled spin and valley Hall effect (SVHE) that has potential use in spintronics and valleytronics. Optical measurements of the SVHE have largely been performed below 30 K and understanding of the SVHE-induced spin/valley polarizations that can be electrically generated is limited. Here, we study the SVHE in monolayer p-type tungsten diselenide (WSe2). Kerr rotation (KR) measurements show the spatial distribution of the SVHE at different temperatures, its persistence up to 160 K, and that it can be electrically modulated via gate and drain bias. A spin/valley drift and diffusion model together with reflection spectra data is used to interpret the KR data and predict a lower-bound spin/valley lifetime of 4.1 ns below 90 K and 0.26 ns at 160 K. The excess spin and valley per unit length along the edge is calculated to be 109 per micron at 45 K, which corresponds to a spin/valley polarization on the edge of 6%. These results are important steps towards practical use of the SVHE.
Berry phase related effects in ferromagnetic metal materials
(2011-05) Yang, Shengyuan; Niu, Qian; MacDonald, Allan H.; Erskine, James L.; Li, Xiaoqin; Register, Leonard F.
The concept of Berry phase, since its proposition in 1984, has found numerous applications and appears in almost every branch of physics today. In this work, we study several physical effects in ferromagnetic metal materials which are manifestations of the Berry phase. We first show that when a domain wall in a ferromagnetic nanowire is undergoing precessional motion, it pumps an electromotive force which follows a universal Josephson-type relation. We discover that the integral of the electromotive force over one pumping cycle is a quantized topological invariant equal to integer multiples of h/e, which does not depend on the domain wall geometry nor its detailed dynamic evolution. In particular, when a domain wall in a nanowire is driven by a constant magnetic field, we predict that the generated electromotive force is proportional to the applied field with a simple coefficient consisting of only fundamental constants. Our theoretical prediction has been successfully confirmed by experiments. Similar effect known as spin pumping occurs in magnetic multilayer heterostructures, where a precessing free magnetic layer pumps a spin current into its adjacent normal metal layers. Based on this effect, we propose two magnetic nanodevices that can be useful in future spintronics applications: the magnetic Josephson junction and the magneto-dynamic battery. The magnetic Josephson junction has a drastic increase in resistance when the applied current exceeds a critical value determined by the magnetic anisotropy. The magneto-dynamic battery acts as a conventional charge battery in a circuit with well-defined electromotive force and internal resistance. We investigate the condition under which the power output and efficiency of the battery can be optimized. Finally we study the side jump contribution in the anomalous Hall effect of a uniformly magnetized ferromagnetic metal. The side jump contribution, although arises from disorder scattering, was believed to be independent of both the scattering strength and the disorder density. Nevertheless, we find that it has a sensitive dependence on the spin structure of the disorder potential. We therefore propose a classification scheme of disorder scattering according to their spin structures. When two or more classes of disorders are present, the value of side jump is no longer fixed but depends on the relative disorder strength between classes. Due to this competition, the side jump contribution could flow from one class dominated limit to another class dominated limit when certain system control parameter changes. Our result indicates that the magnon scattering plays a role distinct from the normal impurity scattering and the phonon scattering in the anomalous Hall effect, because they belong to different scattering classes.
Quantifying spin Hall topological Hall effect in ultrathin Tm 3 Fe 5 O 12 / Pt bilayers
(2022-07-22) Nunley, T. Nathan; Guo, Side; Chang, Liang-Juan; Lujan, David; Choe. Jeongheon; Lee, Shang-Fan; Yang, Fengyuan; Li, Xiaoqin
Recent reports have shown that thulium iron garnet (TmIG) based bilayers are promising material platforms for realizing small, room-temperature skyrmions. For potential applications, it is imperative to accurately evaluate electrical readout signals of skyrmions. In this context, the topological Hall effect has been considered as a characteristic signature of skyrmion formation. Unlike previous studies that have modeled the anomalous Hall effect in ultrathin TmIG/Pt bilayers, we isolate its contribution to the electrical readout signal by directly measuring the magnetic hysteresis loops using a sensitive Sagnac magneto-optical Kerr effect technique. Our combined optical and electrical measurements reveal that the spin Hall topological Hall resistivity is considerably larger than previously estimated values. Our finding further indicates that skyrmions can exist at room-temperature and near-zero applied magnetic fields.
Quantifying spin Hall topological Hall effect in ultrathin Tm 3 Fe 5 O 12 / Pt bilayers
(2022-07-22) Nunley, T. Nathan; Guo, Side; Chang, LIang-Juan; Choe, Jeongheon; Lee, Shang-Fan; Yang, Fengyuan; Li, Xiaoqin
Recent reports have shown that thulium iron garnet (TmIG) based bilayers are promising material platforms for realizing small, room-temperature skyrmions. For potential applications, it is impera- tive to accurately evaluate electrical read-out signals of skyrmions. In this context, the topological Hall eﬀect has been considered as a characteristic signature of skyrmion formation. Unlike previous studies that have modeled the anomalous Hall eﬀect in ultrathin TmIG/Pt bilayers, we isolate its contribution to the electrical read-out signal by directly measuring the magnetic hysteresis loops using a sensitive Sagnac magneto-optical Kerr eﬀect technique. Our combined optical and electrical measurements reveal that the spin-Hall topological Hall resistivity is considerably larger than previ- ously estimated values. Our ﬁnding further indicates that skyrmions can exist at room-temperature and near-zero applied magnetic ﬁelds.
Thermal Hall effect in insulating quantum materials
(Elsevier, 2022-09-13) Guo, Shucheng; Xu, Youming; Cheng, Ran; Zhou, Jianshi; Chen, Xi
The emerging ﬁeld of quantum materials involves an exciting new class of materials in which charge, spin, orbital, and lattice degrees of freedom are inter- twined, exhibiting a plethora of exotic physical properties. Quantum materials include, but are not limited to, superconductors, topological quantum matter, and systems with frustrated spins, which enable a wide range of potential applications in biomedicine, energy transport and conversion, quantum sensing, and quantum information processing.