Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session P41: Spins in Non-magnetic Semiconductors |
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Sponsoring Units: GMAG DMP FIAP DCOMP Chair: Raphael Daveau, Cornell University Room: 707 |
Wednesday, March 4, 2020 2:30PM - 2:42PM |
P41.00001: Band structure probe of near Surface InAs Quantum Wells Brenden A Magill, Giti Khodaparast, Sunil K Thapa, Christopher J Stanton, Joseph Yuan, Mehdi Hatefipour, William Mayer, Matthieu Dartiailh, Kasra Sardashti, Kaushini S Wickramasinghe, Javad Shabani, Y. H. Matsuda, Zhuo Yang, Yoshimitsu Kohama Near surface InAs quantum wells (QW) have recently attracted a great deal of interest as tools to explore mesoscopic and topological superconductivity. These shallow QWs can interact strongly with superconducting layers which can be epitaxially grown on their surfaces. In this talk, we present a combined experimental and theoretical approach to study the band structure of these QWs. The effective mass and g-factors in these QWs were determined using high field cyclotron resonance (CR). Unlike GaAs, narrow gap systems like InAs have large nonparabolicity in their band structures.The band parameters extracted from our CR experiments are consistent with those obtained from Shubnikov de Hass measurements and agree remarkably well with the theoretical calculations. Our band structure models include strong mixing of the conduction and valence bands which leads to a large non-parabolicity. The calculations accurately describe the experimental observations and allowing us to accurately map the effective mass and g-factor as a function of magnetic field, Landau level index, and the well width for different near surface InAs QWs. |
Wednesday, March 4, 2020 2:42PM - 2:54PM |
P41.00002: Weak-antilocalization Induced by Spin-orbit Interaction in Two-dimensional Tellurium Chang Niu, Zhuocheng Zhang, Gang Qiu, Yixiu Wang, Wenzhuo Wu, Peide (Peter) Ye Tellurium (Te) is an intrinsic p-type semiconductor with a narrow bandgap of 0.35eV, whose hexagonal crystal structure is formed by van der Waals interaction between each helical atom chains. Through controllable atomic layer deposition (ALD) grow dielectric doping, we can access transport properties of Te conduction band. Here we report experimental results regarding weak-antilocalization (WAL) effect in n-type two-dimensional (2D) Te films at cryogenic temperatures. The gate and temperature dependence on WAL shows D'yakonov-Perel (DP) mechanism plays the main role in spin relaxation and electron-electron (e-e) interaction is dominant for phase relaxation, which matches well with Iordanskii, Lyanda-Geller, and Pikus (ILP) theory. Also, phase coherence length of Te extracted from WAL feature reaches 573nm at T=1K and transition from weak-localization (WL) to weak-antiocalization (WAL) is observed by tuning the gate bias, indicating its potential for future tunable spintronic applications. |
Wednesday, March 4, 2020 2:54PM - 3:06PM |
P41.00003: Magneto-optical properties of n-type InAsP films in ultrahigh magnetic fields Sunil K Thapa, Christopher J Stanton, Brenden A Magill, Rathsara R Herath Mudiyanselage, Giti Khodaparast, Y. H. Matsuda, Zhuo Yang, Yoshimitsu Kohama, Sukgeun Choi, Chris J Palmstrom InAsP ternary alloys have immense prospect for optoelectronic and quantum communication devices due to their variable band gap of 0.35-1.35 eV and tunability in the g-factors. We present a theoretical/experimental study of the magneto-optical properties of n-type InAsxP1−x films (x=0.07,0.34) in ultrahigh magnetic fields in the Faraday’s geometry at T=300 K using k.p method with modified 8-band Pidgeon-Brown model. The calculated Landau-level Fan diagram for x=0.34 suggests a near-zero g-factor. Moreover, the Field-dependent Fermi levels and the absorption coefficients show a very strong corroboration with the Cyclotron Resonance (CR) measurements, both in position and the strength. In this study, we also employed ultrafast Time Resolved Differential Reflectivity (TRDR) and ultrafast time resolved Magneto-optic Kerr Effect (MOKE) to provide information on the carrier and spin relaxation dynamics. |
Wednesday, March 4, 2020 3:06PM - 3:18PM |
P41.00004: Ultralong spin coherence in MAPbI3 single crystals revealed by ultrafast optics Yue Yao, Matthew Sheffield, Heshan Hewa Walpitage, Isaac P Brown Heft, Ye Liu, Zhenyi Ni, Jinsong Huang, Yan Li Hybrid organic-inorganic perovskites (HOIPs) have demonstrated remarkable optoelectronic properties with their unprecedented rate of increase in solar cell efficiency, and their applications have been quickly extended to many areas, including light emitting diodes, lasing, and photo detection. Recent studies have also revealed their great potential in spintronics because of spin-dependent optical transitions, long spin lifetimes, and predicted large spin-orbit coupling effects for potential spin manipulation. Our previous study revealed long spin lifetimes (T2*) exceeding 1 ns at 4 K on MAPbI3 polycrystalline films despite the presence of large spin-orbit coupling. Here, in order to exclude the influence of the polycrystalline structure and obtain intrinsic spin dynamics, we investigate spin dynamics on high quality MAPbI3 single crystals by time-resolved Faraday rotation (TRFR). The spin lifetime improved by an order of magnitude when compared to polycrystalline films, which suggests the long spin lifetime is an intrinsic property of MAPbI3. Combining the TRFR measurements with circularly-polarized photoluminescence, we analyze the interplay between carrier dynamics and spin dynamics upon optical excitation of spin-polarized carriers in this HOIP. |
Wednesday, March 4, 2020 3:18PM - 3:30PM |
P41.00005: Probing the cubic crystal anisotropy and spin-orbit interaction in GaAs heterostructures using hole quantum point contacts Karina Hudson, Ashwin Srinivasan, Dmitry Miserev, Qingwen WANG, Oleh Klochan, Ian Farrer, David A Ritchie, Alex Hamilton Understanding the form of the spin-orbit interaction (SOI) in semiconductors such as GaAs is a prerequisite for engineering of topological superconducting and insulating states in these materials. Zeeman spin-splitting transport measurements in p-type 1D quantum point contacts (QPCs) are an effective probe of the SOI. Previous measurements have shown that there is a strong anisotropy in the in-plane g-factors in hole QPCs due to SOI (g||I > g⊥I), which can be explained as arising from a second k4B Zeeman term in addition to the established k2B Zeeman term1. |
Wednesday, March 4, 2020 3:30PM - 3:42PM |
P41.00006: Origin of Rashba-Dresselhaus effect in a Pb-free ferroelectric nitride perovskite. Subhadeep Bandyopadhyay, Indra Dasgupta First principles electronic structure calculations have been employed to investigate the Rashba-Dresselhaus spin splitting of the bands in a Pb-free non-toxic ferroelectric nitride perovskite. Our first principles results are supplemented with effective k.p model analysis. A systematic study of orthorhombic and rhombohedral phases of this system reveal the importance of symmetry in realizing the nature of the splitting of bands around the time reversal invariant k-points. In the orthorhombic structure it shows linear Rashba-Dresselhaus splitting where nonsymmorphic symmetries play an important role in enhancing the band splitting in the kz = π/c plane. While the rhombohedral phase shows existence of unique higher order Rashba-Dresselhaus term which mixes with the linear Rashba-Dresselhaus term to produce unusual pattern of out-of-plane spin component in the spin texture that may find application in spintronics. |
Wednesday, March 4, 2020 3:42PM - 3:54PM |
P41.00007: Efficient spin to charge conversion at strained amorphous-Si thin film interfaces Ravindra G Bhardwaj, Anand Katailiha, Paul C Lou, Sandeep Kumar Interfacial asymmetry in conjunction with strain engineering can provide an alternate pathway to achieve efficient and controllable spin to charge conversion. This hypothesis is experimentally verified using spin-Seebeck effect measurement in case of B-doped amorphous-Si thin film interface. The spin-Seebeck voltage and spin-Hall angle in amorphous-Si is found to be an order of magnitude larger than the corresponding value for Pt thin film spin detector. Further, the spin-Seebeck effect is greatly enhanced in the multilayer heterostructures and it diminishes when the strain effects in the sample are reduced. The inhomogeneous strain induces strong interfacial Rashba-Dresselhaus spin-orbit coupling in the two-dimensional electron gas at the metal-Si interface. The resulting intrinsic inverse spin-Hall effect is the underlying cause of efficient spin to charge conversion, which is of the same order as the topological surface states. This study gives a new direction of research for spin-caloritronics applications using strain engineering and amorphous materials. |
Wednesday, March 4, 2020 3:54PM - 4:06PM |
P41.00008: Dephasing in quasi-1D wires: Non-Markovian noise and correlations due to itinerant spin interactions Matthew Foster, Seth M Davis Motivated by the interest in many-body localization, we revisit the problem of dephasing due to electron-electron scattering in quasi-1D (many channel) wires. The effectively Markovian bath due to Coulomb interactions dephases at any nonzero temperature [1]. The effect of short-ranged (e.g. spin exchange) electron-electron scattering is more subtle. The latter induces a non-Markovian, diffusive noise kernel. Formally the field theory describing the dephasing in the presence of a purely diffusive bath has an upper critical spatial dimension of d = 4, and is strongly coupled in d = 1 [2]. We show that a perturbative expansion in the diffusive noise kernel is well-defined but unphysical at long times. We also consider the case of both Coulomb and spin-exchange scattering, using the former to physically regularize the latter. In this case we find "rephasing" contributions at second order that are in contrast to the Markovian limit [3]. We discuss possible experimental signatures. |
Wednesday, March 4, 2020 4:06PM - 4:18PM |
P41.00009: Radial spin texture in elemental tellurium with chiral crystal structure Masato Sakano, Motoaki Hirayama, Takanari Takahashi, Shuntaro Akebi, Mitsuhiro Nakayama, Kenta Kuroda, Kazuaki Taguchi, Tomoki Yoshikawa, Koji Miyamoto, Taichi Okuda, Kanta Ono, Hiroshi Kumigashira, Toshiya Ideue, Yoshihiro Iwasa, Mitsuishi Natsuki, Kyoko Ishizaka, Shik Shin, Takashi Miyake, Shuichi Murakami, Takao Sasagawa, Takeshi Kondo Trigonal tellurium has a chiral crystal structure which is characterized by a lack of mirror symmetry and an inversion center, resulting in the inequivalent right- and left-handed structures. To reveal the spin textures of chiral crystals, here we investigate the spin and electronic structure in p-type semiconductor elemental tellurium by using spin- and angle-resolved photoemission spectroscopy. Our data demonstrate that the highest valence band crossing the Fermi level has a spin component parallel to the momentum of electron around the Brillouin zone corners. Significantly, we have also confirmed that the spin polarization is reversed in the crystal with the opposite chirality. The results indicate that the spin textures of the right- and left-handed chiral crystals are hedgehog-like, leading to unconventional magnetoelectric effects and nonreciprocal phenomena. |
Wednesday, March 4, 2020 4:18PM - 4:30PM |
P41.00010: Prediction of momentum dependent spin splitting in antiferromagnetic compounds without spin-orbit coupling Linding Yuan, Zhi Wang, Jun-Wei Luo, Alex Zunger The Conventional way of creating spin splitting entails the involvement of spin orbit coupling (SOC). The latter entails heavy elements that lead to weak bonds and undesirable defects. Can one generate spin splitting without relying on SOC? We identify the magnetic symmetry conditions that produce AFM prototypes having spin splitting even at TRIM points without external magnetic field and even when SOC is set to zero. The resulting spin splitting in AFM arises from the coupling between electron spin and the position coordinates which is k dependent and of the same order as the Thomas term. Band structures of specific compounds are worked out within DFT showing the effects. |
Wednesday, March 4, 2020 4:30PM - 4:42PM |
P41.00011: Response of Bloch Electrons to Electric Fields William Kerr We consider the response of spinful Bloch electrons to external electric fields; the electrons’ unperturbed Hamiltonian is the one given by Dresselhaus [1], including the spin-orbit interaction. We write matrices for the system observables with respect to the Bloch basis states of the unperturbed Hamiltonian, truncate them to two bands, and use them to obtain their Heisenberg equations of motion. The equation for the velocity contains not only the anomalous velocity term obtained by Karplus and Luttinger [2] [expressed in terms of the now-familiar (position operator) Berry connection [3]], but also additional terms involving “quasi-connections” from the momentum and spin operators. We apply the equations of motion resulting from this procedure to a two-dimensional model of a ferromagnet with the Dresselhaus linear-in-wavevector spin-orbit interaction and an exchange field term. We find for this model that the anomalous velocity is dominated by the term coming from the spin operator rather than the position operator. |
Wednesday, March 4, 2020 4:42PM - 4:54PM |
P41.00012: Birefringent Spin-Lasers David Jiayu Cao, Gaofeng Xu, Velimir Labinac, Igor Zutic Introducing spin-polarized carriers in semiconductor lasers reveals an alternative path to realize room-temperature spintronic applications, beyond the usual magnetoresistive effects[1]. Through carrier recombination, the angular momentum of the spin-polarized carriers is transferred to photons, thus leading to the circularly polarized emitted light. Surprisingly, a large birefringence[2], considered detrimental in both conventional and spin-lasers, has been demonstrated to lead to ultrafast operation with an order of magnitude faster modulation frequency [3] than in the best commercial lasers. By using transparent rate equations we explain how the birefringence can provide key differences in the modulation frequency of the intensity and polarization of light emitted from a laser. We reveal that for such ultrafast operation it is important to have a short spin relaxation time in the active region of the semiconductor lasers, typically made of quantum wells. |
Wednesday, March 4, 2020 4:54PM - 5:06PM |
P41.00013: Modeling of the Mn-Carrier Exchange Interaction in Colloidal CdSe/CdMnS Nanoplatelets with a Multilayer Core and Magnetically Doped Shell James Pientka, Arman Najafi, Steven Tarasek, Savas Delikanli, Peiyao Zhang, Tenzin Norden, Sushant Shendre, Manoj Sharma, Arinjoy Bhattacharya, Nima Taghipour, Hilmi Volkan Demir, Athos Petrou, Tim Thomay A Colloidal Nanoplatelet is a two-dimensional semiconductor nanocrystal heterostructure that allows for wavefunction engineering by controlling their composition and or thickness. With the inclusion of a shell doped with magnetic ions around a non-magnetic core, there exists a carrier mediated exchange interaction between the excitonic spin density and the Mn spins. Through the exchange interaction, magnetic effects such as Zeeman splitting and the excitonic photoluminescence circular polarization can be controlled by varying the shell thickness and or Mn content [1,2]. The previous works did not take into account on how the exitonic wavefunction is affected by the addition of the magnetically doped shell. Here, we present a model that includes the carrier mediated exchange interaction and study its effect on the excitonic wavefunction. [1] S. Delikanl et al.,ACS. Nano 2015 9, 12, 12473-12479 [2] F. Muckel et al., Nano Lett. 2018, 18, 2047−2053. |
Wednesday, March 4, 2020 5:06PM - 5:18PM |
P41.00014: Correlated States and Frustration in Magnetic Quantum Dots with Multiple Occupancy Tiago Campos, James Pientka, Alex Matos Abiague, Jong E Han, Igor Zutic Magnetically doped semiconductor quantum dots (QDs) provide an enhanced control of magnetic ordering as compared to their bulk-like counterparts [1]. Unlike in the bulk structures, adding a single carrier in a magnetic QD can have important ramifications. An extra carrier can both strongly change the total carrier spin and the temperature of the onset of magnetization. Recent experiments reveal how multiple carrier occupancy is optically controlled in Mn-doped II-VI QDs [2] and motivate studies of strongly-correlated states in these systems. While Wigner molecules, as the nanoscale manifestation of correlation effects in Wigner crystals, have been extensively studied in nonmagnetic QDs, their generalizations in magnetic QDs are largely unexplored [3]. Using exact diagonalization and conditional probability density we reveal peculiar manifestations of strongly-correlated states in Mn-doped QDs. The spatial control of Mn-dopants provides a platform to examine the role of magnetic frustration and the shell-structure formation with the change in the strength of Coulomb interaction. |
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P41.00015: Theory of Excitonic Phases in an Electron-Hole Double-Layer System with Relativistic Spin-Orbit Interaction Yeyang Zhang, Ke Chen, Ryuichi Shindou We propose helicoidal and helical excitonic insulator phases in a Coulomb-coupled two-dimensional electron-hole double layer (EHDL) system with relativistic spin-orbit interaction. Previously, it was proposed that layered InAs/AlSb/GaInSb heterostructure is an ideal experimental platform for searching excitonic condense phases, while its electron layer has non-negligible Rashba interaction. We clarify that due to the Rashba term, the spin-triplet (spin-1) and spin-singlet (spin-0) excitonic fields in the EHDL system forms either helicoidal or helical structure, depending on its coupling with an in-plane Zeeman field. We provide a comprehensive understanding of electric and magnetic properties of these condensed phases as well as their low-energy collective modes. |
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