Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session T52: Spins in Topological and Spin-Orbit Materials IIFocus Recordings Available
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Sponsoring Units: GMAG DMP FIAP Chair: Tiancong Zhu, University of California, Berkeley Room: McCormick Place W-475A |
Thursday, March 17, 2022 11:30AM - 12:06PM |
T52.00001: Growth and Magnetism of Van der Waals Magnetic Topological Insulators Invited Speaker: Anna Isaeva Magnetic topological insulators (MTI) combine a non-trivial topology of the electron band spectrum with a long-range magnetic order. These narrow-gap semiconductors are intensely explored as a promising platform that harbors new physics and enables new technological applications. |
Thursday, March 17, 2022 12:06PM - 12:18PM |
T52.00002: Spectroscopic characterization of 2D van der Waals antiferromagnetic topological insulators MnBi2Te4(Bi2Te3)n Gyan B Khatri, Jaesuk Kwon, Gregory Fritjofson, Mingda Guo, Ran Cheng, Simranjeet Singh, Hechang Lei, Enrique Del Barco The recent discovery of 2D van der Walls (vdW) magnetic topological insulators (TIs) has opened new avenues towards spintronics research from combining unique electronic properties arising from nontrivial band structures and the magnetic degree of freedom when magnetic ordering also establishes in the same material. MnBi2Te4(Bi2Te3)n represents an excellent example of this, being identified as a vdW TI with antiferromagnetic ordering for n=0,1,2. While emphasis has been placed into studying its electronic and magnetic properties using techniques like ARPES, transport, and magnetometry, a comprehensive detailed experimental spectroscopic characterization of these materials at low frequencies is missing. In this study we perform a series of low frequency measurements at varied temperatures and magnetic fields strengths and orientations that show clear antiferromagnetic modes in compounds with n=1 and n=2. The motion of the antiferromagnetic modes with the direction of application of the magnetic field reveal the anisotropic nature of the system, characterized by an easy magnetic symmetry axis and a corrugated hard plane that change slightly with the stoichiometry variation. Our results show how the transition temperature also varies between n=1 and n=2 compounds, indicating that the exchange interaction originating the antiferromagnetic order changes with the interlayer configuration. |
Thursday, March 17, 2022 12:18PM - 12:30PM |
T52.00003: Interlayer magnetophononic coupling in MnBi2Te4 Hari Padmanabhan The emergence of magnetism in quantum materials creates a platform to realize spin-based applications in spintronics, magnetic memory, and quantum information science. A key to unlocking new functionalities in these materials is the discovery of tunable coupling between spins and other microscopic degrees of freedom. We present evidence for magnetophononic coupling in the layered magnetic topological insulator MnBi2Te4. Employing magneto-Raman spectroscopy, we observe phonon spectral weight anomalies across magnetic field-driven phase transitions, despite the absence of discernible static structural changes. This behavior is a consequence of a magnetophononic wave-mixing process that allows for the excitation of zone-boundary phonons that are otherwise ‘forbidden’ by momentum conservation. A microscopic description of this phenomenon using density functional theory highlights the critical role played by phonons modulating the interlayer exchange coupling. Moreover, signatures of magnetophononic coupling are also observed in the time domain at sub-picosecond timescales through the ultrafast excitation and detection of coherent phonons across magnetic transitions. In light of the intimate connection between magnetism and topology in MnBi2Te4, the magnetophononic coupling represents an important step towards coherent on demand manipulation of magnetic topological phases. |
Thursday, March 17, 2022 12:30PM - 12:42PM |
T52.00004: Magnons and magnetic fluctuations in atomically thin MnBi2Te4 David Lujan, Jeongheon Choe, Martin A Rodriguez-vega, Zhipeng Ye, Aritz Leonardo, Timothy N Nunley, Liang Juan Chang, Shang-Fan Lee, Jiaqiang Yan, Gregory A Fiete, Rui He, Xiaoqin (Elaine) Li Intrinsic magnetic topological insulators MnBi2Te4 host novel quantum phases. Here we investigate collective spin excitations (i.e. magnons) and spin fluctuations in atomically thin MnBi2Te4 flakes using Raman spectroscopy. In a two-septuple layer with non-trivial topology, magnon characteristics evolve as an external magnetic field tunes the ground state through three ordered phases: anti-ferromagnet, canted antiferromagnet, and ferromagnet. Raman selection rules are determined by both the crystal symmetry and magnetic order for their respective magnetic phases. The magnon energy is determined by different interaction terms. Using non-interacting spin-wave theory, we extract the spin-wave gap at zero magnetic field, an anisotropy energy, and interlayer exchange from Raman spectra. Magnetic fluctuations increase with reducing layer thickness and may prevent a long-range magnetic order in a single septuple layer. |
Thursday, March 17, 2022 12:42PM - 12:54PM |
T52.00005: Concurrent observation of robust anti-damping torque and inverse spin Hall effect in Fe75Co25/Bi2Te3 multilayers Rajeev Nepal, vinay Sharma, Weipeng Wu, Anthony Johnson, Matthias Benjamin Jungfleisch, Ramesh C Budhani In this work, we made ferromagnet (FM) -Topological insulator (TI) heterostructures by depositing metallic FM Fe75Co25 (FeCo) epitaxial films capped with TI Bi2Te3 in an ultrahigh vacuum sputtering system. Contrary to the common observation of enhancement in Gilbert damping α on spin pumping, the multilayers of FeCo/Bi2Te3 exhibit a decrease in α with increase in Bi2Te3 thickness which is likely to be the effect of high anti-damping torque [1]. The quantification of room temperature spin-to-charge conversion has been made using two complementary techniques: ferromagnetic resonance (FMR) based inverse spin Hall effect (ISHE) measurement and femto-second light-pulse induced terahertz emission. Our results indicate that both FMR and ultrafast spin-current injection are promising complementary tools to investigate ISHE and high anti-damping torque. |
Thursday, March 17, 2022 12:54PM - 1:06PM |
T52.00006: Interfacial antidamping spin-orbit torques in topological insulator/ferromagnet bilayers induced by skew scattering Alessandro Veneri, David T Perkins, Aires Ferreira, Branislav K Nikolic, Marko Petrovic Spin-orbit torque (SOT) [1] in topological-insulator/ferromagnet (TI/FM) bilayers offers a promising route toward highly efficient magnetic random access memory, as demonstrated by recent experiments [2] where FM magnetization has been switched along the direction perpendicular to the interface using current densities that are two orders of magnitude smaller than those originally used in heavy-metal/FM bilayers and traditional spin-transfer torque in magnetic tunnel junctions. However, the microscopic mechanisms behind this efficiency -- the interplay between spin-momentum locked surface states, two-dimensional electron gas typically present due to band bending and defects in the bulk, and impurities on the surface -- are still poorly understood. Here we show that a nonperturbative treatment of proximity magnetic effects, spin-orbit coupling and disorder in a minimal model of a TI/FM bilayer leads to new types of both antidamping-like and field-like SOTs of pure interfacial origin, which are overlooked by previous microscopic theories. Most notably, a robust skew scattering mechanism is found to enable a current-induced nonequilibrium spin density in all three spatial directions [3,4], instead of the in-plane longitudinal polarization usually found [5] (in clean systems) in response to an injected transverse charge current. We present analytical expressions for the spin-density–charge-current response function in the weak disorder limit and perform a detailed numerical analysis to obtain the ensuing magnetization dynamics in the FM layer [6]. We find that the standard antidamping-like and field-like SOTs are strongly renormalized by the interfacial skew scattering mechanism, thus demonstrating that the usually assumed to be necessary [1] effects stemming from three-dimensional transport are not essential. |
Thursday, March 17, 2022 1:06PM - 1:18PM |
T52.00007: Epitaxial In2Se3 as a spin sensitive barrier for electrical detection of current generated spin in the topological insulator Bi2Se3 Connie H Li, Jisoo Moon, Olaf M Van T Erve, Enrique Cobas, Darshana Wickramaratne, Michelle D Johannes, Berend T Jonker Amorphous tunnel barriers such as aluminum oxide have typically been utilized to detect spin polarizations generated by spin-momentum locking in topological insulators (TIs) such as Bi2Se3. Here we report epitaxial crystalline In2Se3 grown by molecular beam epitaxy as a spin sensitive barrier on Bi2Se3, where both share a similar structure and a common anion. Raman spectroscopy indicate that the In2Se3 is β-phase. Density function theory (DFT) calculations confirm that the linearly dispersing Bi2Se3 surface states and their spin-momentum locking is preserved at the Bi2Se3/β-In2Se3 interface. Spin potentiometric measurements on epitaxial Fe/In2Se3/Bi2Se3 heterostructures demonstrated electrical detection of the current-generated spin in the topologically protected Bi2Se3 surface states arising from spin-momentum locking, where the projection of the TI spin onto the magnetization of the ferromagnet is manifested as a voltage. Distinct low and high voltage signals are measured depending on the parallel or antiparallel alignment of TI spin and magnetization. These results demonstrate that In2Se3 is a viable spin sensitive barrier for the detection of current-generated spins in TI. This first demonstration of an epitaxial crystalline spin sensitive barrier that can be grown directly on Bi2Se3 is an important step towards fully epitaxial topological spintronic devices. |
Thursday, March 17, 2022 1:18PM - 1:30PM |
T52.00008: Giant g-factor in metamorphic InAsSb/InSb superlattices with ultra-narrow bandgap Sergey Suchalkin, Yuxuan Jiang, Zhigang Jiang, Maksim Ermolaev, Gela Kipshidze, Seongphill Moon, Mykhaylo Ozerov, Dmitry Smirnov Semiconductor materials with high g-factor are potential key component for spintronic and quantum information processing devices. Enhancement of electron g-factor is promoted by admixing of the valence band states to the conduction band ones and is typically high in narrow bandgap materials with large spin orbit coupling. In type II superlattices (SLs) where the bandgap can be reduced by increasing the SL period, g-factor enhancement is impeded by spatial separation between the conduction and valence band states. Here we present metamorphic InAsSb/InSb SLs, where the effective lattice constant can be controlled and ultra-narrow bandgaps can be realized in SLs with thin layers. In the metamorphic SLs the overlap between electron and hole states can be effectively varied, so g-factor can be widely tuned from 30 to 110. A giant g-factor of 104, which is nearly twice larger than that of InSb, was extracted from polarization-resolved far-infrared magneto absorption spectra. The Landau levels in InAsSb/InSb SLs are found nearly 100% spin-polarized at low magnetic fields. |
Thursday, March 17, 2022 1:30PM - 1:42PM |
T52.00009: Effective g-factor and phase-coherent transport in InAsSb/InSb double quantum wells Alisha Vira, Tianhao Zhao, Luojia Zhang, Phillip N First, Wei Pan, Maksim Ermolaev, Gela Kipshidze, Sergey Suchalkin, Zhigang Jiang High-quality semiconductor structures with large Landé g-factors are a cornerstone of many fundamental applications in spintronics and quantum information processing with topological qubits. Here, we propose the InAsSb/InSb double quantum wells (DQWs), grown by molecular-beam epitaxy (MBE) on a virtual substrate, as such a material system, with additional advantages of tunable bandgaps and the possibility of tuning the band topology. Specifically, using the tilted magnetic field method, we show that the in-plane electron g-factor in InAsSb/InSb DQWs is large (> 20), which we deduce from the coincidence of the spin levels of adjacent Landau levels. We further study the phase-coherent transport in InAsSb/InSb DQWs from weak anti-localization measurements and conclude that the dominant decoherence mechanism in our samples is electron-electron scattering. |
Thursday, March 17, 2022 1:42PM - 1:54PM |
T52.00010: Zero-field spin splitting in high-mobility undoped InSb1-xAsx heterostructures Sara Metti, Di Xiao, Candice Thomas, Michael J Manfra We report on the electrical properties of a series of undoped InSb1-xAsx quantum wells grown on GaAs substrates. We study three samples with Arsenic concentrations of 5, 13, and 19%. At 5% As concentration the two-dimensional electron gas (2DEG) displays a mobility peak of 24 m2 /Vs at a density of 2.5 × 1015 m-2 ; this value is comparable to previously reported values for binary InSb quantum wells of similar design. High mobility and strong spin-orbit coupling allow us to observe beating in the Shubnikov de Haas oscillations at low magnetic field, facilitating assessment of the Rashba coupling parameter. A gate tunable zero-field spin splitting was observed, increasing with higher As concentration when comparing samples at fixed 2DEG density. The maximum Rashba parameter extracted is ~ 300 meVÅ for the 19% As sample. |
Thursday, March 17, 2022 1:54PM - 2:06PM |
T52.00011: Anisotropy of spin states in PbTe nanowire quantum dots in the absence of charging energy. Maksim Gomanko, Erik P. A. M. Bakkers, Sergey M Frolov, Sander G Schellingerhout, Eline de Jong We study semiconductor PbTe nanowires with quantum dots in the absence of Coulomb blockade. These materials from group IV-VI are of interest for the realization of spin-qubits, due to high g-factor, spin-orbit interaction, and the possibility to perform isotopic purification. |
Thursday, March 17, 2022 2:06PM - 2:18PM |
T52.00012: Magnetic analysis of Heusler / III-V semiconductor interfaces using density functional theory Brett Heischmidt, Maituo Yu, Derek Dardzinski, James Etheridge, Saeed Moayedpour, Paul A Crowell, Noa Marom, Vlad S Pribiag Heusler compounds are of high interest due to their half-metallic, superconducting or topological properties. Here we use a PBE+U approach in density functional theory to investigate the interfacial properties of X2MnIn (X=Ni,Ti) magnetic Heusler compounds with lattice-matched high-spin-orbit coupling III-V semiconductors (InAs, InSb) that have attracted interest, for example, as potential platforms for Majorana modes. We first show a convincing lack of induced moment in the semiconductor, which suggests proximity-induced magnetic exchange correlations are unlikely to arise in these interfaces. We then analyze the interfaces in the context of their suitability for injecting high spin polarizations through layer-resolved polarization and band projection analyses. |
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