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 D56: Spin Dependent Transport I |
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Sponsoring Units: GMAG Chair: Madalynn Marshall,, Oak Ridge National Lab Room: Room 304 |
Monday, March 6, 2023 3:00PM - 3:12PM |
D56.00001: Optimizing the cooperativity between magnetic and acoustic planar waves Kyongmo An The ability to adjust the cooperativity between distinct waveforms is an important feature of quantum information devices. The coupling between spin and phonon is of particular interest, which allows for long-range communication at GHz frequency [1,2]. Using local light scattering, we demonstrate that one can maximize this attribute in thin films by adjusting the orientation and strength of an external magnetic field. Their overlap can be enhanced by about a factor of 2 by coupling the Kittel mode to circularly polarized acoustic waves (out-of-plane geometry) instead of linearly polarized ones (in-plane geometry). Additionally their overlap is maximized by matching the Kittel frequency with the half-wave plate condition for the acoustic wave. Considering the frequency-dependent damping of the magnetic and acoustic systems, we find an optimum working frequency for the two quasi-particle interconversion. |
Monday, March 6, 2023 3:12PM - 3:24PM |
D56.00002: Local Symmetry Breaking Drives Picosecond Spin Domain Formation in Polycrystalline Semiconducting Films Arjun Ashoka, Satyawan Nagane, Nives Strkalj, Bart Roose, Jooyoung Sung, Judith L MacManus-Driscoll, Samuel D Stranks, Sascha Feldmann, Akshay Rao Photoinduced spin-charge interconversion in semiconductors with spin-orbit coupling could provide a route to optically addressable spintronics without the use of external magnetic fields. A central question is whether the resulting spin-associated charge currents are robust to structural disorder, which is inherent to polycrystalline semiconductors that are desirable for device applications. Using ultrafast circular polarization-resolved pump-probe microscopy with 15-fs time resolution on polycrystalline halide perovskite thin films, we observe the photoinduced ultrafast formation of spin-polarized positive and, unexpectedly, negative spin domains on the micron scale. By photoinducing a local spin polarized electronic population and imaging its transport on femtosecond timescales, we confirm that there are lateral local charge currents present. Further, the polarization of these photoinduced spin domains and lateral transport direction is switched upon switching the polarization of the pump helicity, confirming that the local spin currents are a result of local spin textures and spin-momentum locking. Micron scale variations in the intensity of optical second-harmonic generation and vertical piezoresponse suggest that the spatially varying spin textures that drive the spin domain formation arise through the presence of strong local inversion symmetry breaking via inter-grain structural disorder. We explore this hypothesis with a simple Monte Carlo model for spin transport and scattering in a spin texture disordered landscape and are able to capture the measured phenomenology. Taken together, we propose that this local symmetry breaking on the micron scale leads to spatially varying Rashba-like spin textures that drive spin-momentum locked currents, leading to local spin domain formation on picosecond timescales. Our results establish ultrafast spin domain formation in polycrystalline semiconductors as a new platform for optically addressable nanoscale spin-device physics. |
Monday, March 6, 2023 3:24PM - 3:36PM |
D56.00003: Third Harmonic Characterization of Antiferromagnetic Heterostructures Yang Cheng, Egecan Cogulu, Rachel Resnick, Justin J Michel, Nahuel N Statuto, Andrew D Kent, Fengyuan Yang Electrical switching of antiferromagnets is an exciting recent development in spintronics, which promises active antiferromagnetic devices with high speed and low energy cost. In this emerging field, there is an active debate about the mechanisms of the current-driven switching of antiferromagnets. Harmonic characterization is a powerful tool to quantify current-induced spin-orbit torques and spin Seebeck effect in heavy-metal/ferromagnet systems. However, the harmonic measurement of spin-orbit torque has never been verified in antiferromagnetic heterostructures. Here, we report for the first time harmonic measurements in Pt/a-Fe2O3 bilayers, which are explained by our modeling of higher-order harmonic voltages. As compared with ferromagnetic heterostructures where all current-induced effects appear in the second harmonic signals, the damping-like torque and thermally-induced magnetoelastic effect contributions in Pt/a-Fe2O3 emerge in the third harmonic voltage. Our results provide a new path to probe the current-induced magnetization dynamics in antiferromagnets, promoting the application of antiferromagnetic spintronic devices. |
Monday, March 6, 2023 3:36PM - 3:48PM |
D56.00004: The theory of nonlinear magnon spin current induced by the electric field Kosuke Fujiwara, Sota Kitamura, Takahiro Morimoto The magnon spin current is attracting much attention from the viewpoint of the spintronics. Unlike electrons, usually magnons do not couple with the electric field. Therefore, most of previous studies considered the magnon spin current induced by the thermal gradient or magnetic field. However, spin systems with a broken inversion symmetry supports magnetic excitations accompanying electric polarization, known as electro-magnons. Here, we consider the nonlinear magnon spin current induced by the electric field in broken inversion symmetry systems. Focusing on the dc spin current responses, we derive the formula for "the magnon spin shift current" induced by the linearly polarized light and "the spin injection current" induced by the circularly polarized light, in an analogous way to electronic nonlinear current responses. The magnon spin shift current does not depend on the relaxation time of the magnon, while the injection current is proportional to the relaxation time which we expect exhibits large responses for a long magnon lifetime. Furthermore, we clarify the relation between the magnon spin shift current and the topology of the magnon band. In addition, we demonstrate the magnon spin shift current and injection current numerically based on a few toy models and realistic models for multiferroics. |
Monday, March 6, 2023 3:48PM - 4:00PM |
D56.00005: Spin and Charge Drift Diffusion in Presence of Controllable Magnetic Field Gradients Nicholas J Harmon, Emma Z Kurth, Lana Flanigan, Dana Coleman While magnetic field gradients are well known to cause spin separation via the Stern Gerlach effect, the utilization of these gradients to induce spin currents in solid state systems has led to only a handful of investigations [1,2,3]. In this work, the spin polarization and charge dynamics are modeled by developing a set of spin drift-diffusion equations for a generic inhomogeneous field. Under certain geometries, Lorentz forces and Larmor precession can be avoided which is gives rise to analytic solutions. We focus primarily on the simple constant gradient magnetic field; under conditions of spin injection in a semiconductor, a charge current is induced by the gradient. The effects of spin relaxation and electric field are also considered. The theory of spin diffusion length under conditions of drift and diffusion is modified to treat influence of magnetic field gradients. |
Monday, March 6, 2023 4:00PM - 4:12PM |
D56.00006: Electronic Transport Properties of a Graphene-Supported Spin Crossover Fe[H2B(Pz)2]2(bipy) Complex Through Gold Electrodes: An Ab Initio Study Duy Le, Eric D Switzer, Peter A Dowben, Talat S Rahman Spin-crossover (SCO) molecules coupled to electrodes show promise as possible spintronic devices because the conductance changes with spin state. Prior ab initio transport studies find, however, that different configurations of the electrode can lead to different predictions, most likely due to the coupling of the electrodes with the molecular complex.[1] To address this, we investigate the impact on ab initio non-equilibrium Green’s function transport calculations by isolating an Fe(II) complex Fe[H2B(Pz)2]2(bipy) placed between two Au(111) electrodes by inserting graphene supports between the lead and the SCO molecule. We find that the interplay between the graphene and the SCO molecule orbitals provides transport channels within a small bias window, effectively removing the direct coupling of the electrode to the SCO molecule. These channels show different transmission profiles above and below the Fermi energy depending on whether the molecule is in the high spin (S=2) state or the low spin (S=0) state. We calculate a relatively large rise in the current for the high spin state at small bias (V = 0.1 eV), which is not seen in the low spin state, leading to a high current on/off ratio. |
Monday, March 6, 2023 4:12PM - 4:24PM |
D56.00007: Longitudinal spin Seebeck effect in paramagnetic insulator VO2 thin film Renjie Luo, Liyang Chen, Tanner Legvold, Douglas Natelson, Henry Navarro, IVAN K SCHULLER The spin Seebeck effect (SSE) involves the generation of spin current in the presence of a temperature gradient across a magnetically active material. Although much work has been done in ferrimagnetic and antiferromagnetic materials, SSE in paramagnets is considerably less studied, and the mechanism of paramagnetic SSE is still unclear. Here we present a systematic study of the longitudinal SSE (LSSE) in paramagnetic insulating thin film VO2 at low temperatures. The LSSE grows with increasing field and saturates at high field. With the increasing temperature, the magnitude of LSSE voltage at fixed heater power decreases, and varies as T-2 relationship between 15 K and 50 K. The LSSE shows the expected angular dependence with the in-plane field orientation and is linear in the heating power. The sign of the LSSE response is not consistent with mobile triplet excitations as the carriers of spin. We will place these results in the context of theoretical discussions of paramagnetic SSE response. |
Monday, March 6, 2023 4:24PM - 4:36PM |
D56.00008: Influences of Structure on Intrinsic Spin Hall Conductivity of W-N alloys Quynh Anh Thi T Nguyen, D. Duc Cuong, Minkyu Park, Sonny H. Rhim In recent works, W alloys have drawn attention in spintronics due to their high spin Hall angle up to ≈0.6 [1-3]. Here, the spin Hall conductivities (σxy) of W-N alloys are investigated using first-principles calculations. Most probable W is α-W in bcc structure, whereas β-W in A15 structure is metastable, but exhibits σxy -817 S/cm, larger than α-W. Among various compositions of W-N alloys [4,5], only W2N and WN are explored for their σxy due to their phase stability. WN, having three possible structures, has σxy = -194 S/cm by thermodynamic average. Notably, W2N in NaCl structure with 50% N vacancy, exhibits the largest σxy = -966 S/cm among W-N alloys, enhanced by 18 % over β-W. This large σxy is elucidated by the large Berry curvature around 2/3ΓX. The lifted degeneracy at 2/3ΓX is analyzed with group theory, where the Fermi level crosses the gap; thereby, only negative Berry curvature survives giving large σxy. |
Monday, March 6, 2023 4:36PM - 4:48PM |
D56.00009: A group-theoretic approach to chirality-induced spin selectivity in molecular junctions Juan José Palacios, Manuel Antonio A García Blázquez, Wynand Dednam, Linda Zotti, Enrico Lombardi Spin-orbit coupling gives rise to a range of spin-charge interconversion phenomena in non-magnetic systems where certain spatial symmetries are absent. Chirality-induced spin selectivity (CISS), a term that generically refers to a spin-dependent electron transfer in non-magnetic chiral systems, is one such case, appearing in a variety of seemingly unrelated situations ranging from inorganic materials to molecular devices. In particular, the origin of CISS in molecular junctions is a matter of an intense current debate. Here we contend that CISS can be generally and fully understood on the basis of a complete symmetry analysis of the molecular junction, and not only of the molecule. Our approach, which draws on the use of point-group symmetries within the scattering formalism for transport, shows that electrode symmetries are as important as those of the molecule when it comes to the appearance of CISS. It turns out that standalone metallic nanocontacts can exhibit spin-polarization when relative rotations which reduce the symmetry are introduced. As a corollary, molecular junctions with achiral molecules can also exhibit spin polarization along the direction of transport, provided that the whole junction is chiral in some way. This formalism also allows to predict the qualitative changes on the spin-polarization upon substitution of a chiral molecule in the junction with its enantiomeric partner. Quantum transport calculations based on DFT corroborate all of our predictions and provide further quantitative insight. |
Monday, March 6, 2023 4:48PM - 5:00PM |
D56.00010: Electrical readout of coherent spin dynamics in an antiferromagnet Shirash Regmi, Rodolfo Rodriguez, Arezoo Etesamirad, Igor Barsukov Demonstration of spin pumping [1] in antiferromagnets (AFMs) was an important milestone in AFM spintronics. As the next step, it is imperative to achieve electrical readout of ultrafast spin dynamics that would be scalable to nano-size devices, thus paving the road to AFM-based spin-torque applications [2,3]. Here we systematically study the magnetoresistive spin-to-charge conversion of coherent spin dynamics at the interface of AFM and heavy-metal (HM). Using e-beam lithography and ion-milling, we prepare Hall-bars from 5 nm Pt films on the surface of Cr2O3 bulk crystals with magnetic easy-axis, [0001], parallel and perpendicular to the AFM/HM interface. By applying magnetic field along the easy-axis, we strongly lower the AFM magnon frequencies. Using monochromatic excitation in the range of 0-40 GHz, we coherently excite the left-hand magnon mode below the spin-flop (SF) field which transitions into the Goldstone-like mode above the SF. Both modes are detected simultaneously by magnetoresistance of Pt and by induction. We demonstrate detection by longitudinal and transverse magnetoresistance and evaluate it as a function of microwave power, DC current, temperature, and crystallographic orientation of the AFM/HM interface. Our results show how electrical readout of AFM spin dynamics paves the road toward AFM spin-torque devices. |
Monday, March 6, 2023 5:00PM - 5:12PM |
D56.00011: Characterising the hole g-factor in lightly strained Ge/SiGe quantum wells with applications for hole spin qubits Matthew Rendell Holes in strained germanium have emerged as a potential system for building spin qubits, with recent demonstrations of a four qubit processor [1,2]. In this work we show that the strain can be used to alter the g-factor of the hole system in germanium. We first show that a lightly strained germanium quantum well can confine a two-dimensional (2D) hole gas with high mobility, low percolation density and low effective mass [3]. We measure the g-factor anisotropy of the 2D system and find a larger g-factor anisotropy than more strained germanium quantum wells. This result suggests that strain in germanium can be used to tune the magnitude of the spin-orbit coupling of holes. This may allow for faster spin-qubit driving or finding "sweet spots" in qubit operation [4]. |
Monday, March 6, 2023 5:12PM - 5:24PM |
D56.00012: Probing Doped Two-Dimensional Mott Insulators with Graphene Jingtian Shi We discuss the properties of the class of two-dimensional materials formed by stacking graphene and two-dimensional Mott insulators like CrI3 and RuCl3. The coupling between layers is normally weak in these systems, allowing the electrical transport of the graphene layers to be used as a weak probe of the Mott insulators. Because of large differences in chemical potential between layers, both graphene and Mott insulator layers are normally doped. We will discuss how capacitance measurements in dual-gated stacks allow to probe thermodynamic properties of the Mott insulator layers and their dependence on magnetic state, whether ferromagnetic, antiferromagnetic, or spin liquid. We will also address the nature of the coupling between the two materials and its dependence on lattice constant differences, which are normally large, relative orientation, and the magnetic configuration of the insulator using a Hartree-Fock mean-field theory description of the doped Mott insulators. |
Monday, March 6, 2023 5:24PM - 5:36PM |
D56.00013: Intricate spin textures as a source of conventional and unconventional Rashba-Edelstein effects in non-magnetic solids Jagoda L Slawinska, Karma Tenzin, Arunesh Roy, Homayoun Jafari, Frank T Cerasoli, Anooja Jayaraj, Marco Buongiorno Nardelli Studies of structure-property relationships in spintronics are essential for the design of materials that can fill specific roles in devices. For example, materials with low symmetry allow unconventional configurations of charge-to-spin conversion which can be used to generate efficient spin-orbit torques. Here, we explore the relationship between crystal symmetry and geometry of the Rashba- Edelstein effect (REE) that causes spin accumulation in response to an applied electric current. Based on a symmetry analysis performed for 230 crystallographic space groups, we identify classes of materials that can host conventional or collinear REE. Although transverse spin accumulation is commonly associated with the so-called ’Rashba materials’, we show that the presence of specific spin texture does not easily translate to the configuration of REE. More specifically, bulk crystals may simultaneously host different types of spin-orbit fields, depending on the crystallographic point group and the symmetry of the specific k-vector, which, averaged over the Brillouin zone, determine the direction and magnitude of the induced spin accumulation. To explore the connection between crystal symmetry, spin texture, and the magnitude of REE, we discuss first-principles calculations that we performed for representative materials with different symmetries. We believe that our results will be helpful for further computational and experimental studies, as well as the design of spintronics devices. |
Monday, March 6, 2023 5:36PM - 5:48PM |
D56.00014: Thermal Transport in Weakly Coupled Spin-1/2 Heisenberg-Ladders Anja S Wenger, Ewelina M Hankiewicz We investigate the weakly coupled spin-1/2 Heisenberg ladder in the low energy limit. As magnetic excitations significantly contribute to the thermal transport, we expose the ladder to a magnetic field and analyze the thermal conductivity and the specific heat capacity depending on the magnetization. |
Monday, March 6, 2023 5:48PM - 6:00PM |
D56.00015: Large unconventional anomalous Hall effect in a chiral antiferromagnetic semiconductor Changjiang Yi, Subhajit Roychowdhury, Kartik Samanta, Horst Borrmann, Maia Garcia Vergniory, Chandra Shekhar, Claudia Felser Combination of structural chirality and magnetism always plays a critical role of nontrivial electronic transport properties, nurturing unconventional contribution to the anomalous Hall effect (UAHE), in which the non-colinear or non-coplanar magnetic structure promised by chiral lattice or finite spin-chirality rising from geometric frustration takes the responsibility. Here we report a remarkable phenomenon of UAHE in an antiferromagnetic (AFM) semiconductor EuIr2P2, which possesses a potential helical AFM ground state promised by natural chiral crystalline structure. EuIr2P2 displays an anisotropic negative magnetoresistance as well as a surprising UAHE below and above Néel temperature (TN1 = 5.2 K), exhibiting large values of unconventional anomalous Hall resistivity reach to 3 mΩ cm at 2 K and 1 mΩ cm at 10 K. These behaviors can be qualitatively understood via a skew scattering mechanism originated from the promised helical magnetic structure below TN1 and finite spin-chirality rising from AFM spin fluctuation above TN1. Our results illuminate the path for comprehending the strong interaction between expected novel spin texture produced by chiral lattice and hopping carriers in AFM semiconductors. |
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