Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session S36: Semiconductor Spintronics: Optics and DevicesFocus Live
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Sponsoring Units: GMAG DMP FIAP DCOMP Chair: Alexandre Bourassa, University of Chicago |
Thursday, March 18, 2021 11:30AM - 11:42AM Live |
S36.00001: Probing ultrahigh magneto-optical properties and time-resolved spin dynamics in InAsP ternary alloys Sunil Thapa, Christopher J Stanton, Brenden A Magill, Rathsara Herath Mudiyanselage, Giti Khodaparast, Yasuhiro Matsuda, Zhuo Yang, Yoshimitsu Kohama, Sukgeun Choi, Chris J Palmstrom InAsP ternary alloys are not only important for potential spintronics applications owing to their tunability of their g-factors but also for high speed electronic and optoelectronic devices due to their variable band gap of 0.35-1.35 eV. We present a room temperature cyclotron resonance (CR) study of n-type InAsxP1−x (x=0.07,0.34) films in ultrahigh magnetic fields in the Faraday’s geometry. Our results are compared to theoretical calculations based on the k.p method with a modified 8-band Pidgeon-Brown model with good agreement. A near-zero g-factor is suggested by the theoretical Landau-level fan diagram for x=0.34, and the absorption coefficients show excellent agreement with the CR measurements. As an important extension, we investigate light-induced spin dynamics in the non-magnetic InAs0.34P0.66 employing ultrafast degenerate time resolved Magneto-optic Kerr Effect (MOKE) using the Voigt geometry. At the pump/probe energy of 960 nm at 300 K, our polarization-resolved B=0 data show helicity-dependent spin relaxation times. Moreover for the right-circularly polarized pump, we have probed a B-dependent relaxation time and precession frequency. |
Thursday, March 18, 2021 11:42AM - 12:18PM Live |
S36.00002: Ultrafast Spin-Lasers Invited Speaker: Nils Gerhardt In times of ultrahigh definition video streaming, cloud computing and Internet of Things, the Internet structure is the key enabler of the global digitization. To meet future communication bandwidth requirements, especially in hyperscale datacenters, new concepts for optical short-range communication systems with high modulation bandwidth and low energy consumption are urgently needed. A very promising approach is to use spin and polarization modulation and their superior dynamics in spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs) instead of conventional intensity modulated laser devices. Here, the coupling via angular momentum exchange between the spin states of the charge carriers and the photons plays a decisive role [1]. The dynamics of the coupled spin system are typically decoupled from the intensity dynamics of the laser and can be modulated at frequencies > 200 GHz [1]. The modulation response of spin lasers can be described analogously to a driven damped harmonic oscillator with a resonance frequency that can be directly controlled and increased by birefringence in the resonator. Furthermore, the ultrafast modulation response in spin-VCSELs can be obtained for low bias currents and is not severely affected by high temperatures [2]. This opens up new possibilities for high-speed transmission systems with very low power consumption. |
Thursday, March 18, 2021 12:18PM - 12:30PM Live |
S36.00003: 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[4]. 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. |
Thursday, March 18, 2021 12:30PM - 12:42PM Live |
S36.00004: Spin lasers as coupled harmonic oscillators Velimir Labinac, Gaofeng Xu, David Jiayu Cao, Igor Zutic A large birefringence in semiconductor spin lasers offers an ultrafast operation in which the polarization of the emitted light can be modulated an order of magnitude faster than the intensity of the emitted light in the best conventional lasers [1,2]. We reveal that the complex dynamical operation in a spin laser can be accurately described by the model of coupled harmonic oscillators. Our description relies on the recently developed nonlinear equations for the intensity of the polarization-resolved emitted light [3]. By linearizing these equations and using a small signal analysis we find that the modulation of the intensity or polarization of the emitted light can be effectively represented by the two weakly-coupled harmonic oscillators of different resonant frequencies. We discuss how this intuitive description of spin lasers allows us to study their unexplored operation regimes and optimize their performance. |
Thursday, March 18, 2021 12:42PM - 12:54PM Live |
S36.00005: Rate-equations description of spin lasers Krish Patel, Gaofeng Xu, Igor Zutic Lasers in which spin-polarized carriers are injected provide paths to different practical room-temperature spintronic devices, not limited to magnetoresistive effects [1]. The rate equations that describe the dynamics of spin lasers have relied on a linear gain mode, in spite of the nonlinear dependence of gain on the carrier density [2]. We apply a nonlinear gain model based on accurate electronic structure calculations to develop a more general description of spin lasers and reveal the effects of such a nonlinear gain model on the dynamics of spin lasers. |
Thursday, March 18, 2021 12:54PM - 1:06PM Live |
S36.00006: Electronic transport in quantum InSb nanowire spin-valve devices Zedong Yang, Brett Heischmidt, Sasa Gazibegovic, Ghada Badawy, Diana Car, Paul A Crowell, Erik P. A. M. Bakkers, Vlad Pribiag Semiconductor nanowires (NWs) with strong spin-orbital interaction, such as InSb NWs, are a leading platform in realizing future Majorana zero modes based quantum computing devices. However, the need for applying external magnetic fields can suppress the superconductivity and place geometric restrictions on the device. Hybrid magnet-nanowire devices can help to circumvent this issue. To study the integration of ferromagnetic materials, we fabricated InSb NW spin-valve devices and investigated spin transport. Spin-polarized transport leads to hysteretic magnetoconductance, which can be tuned through electrostatic gating. We find that the transport is phase-coherent and, for contact spacings of a few hundred nanometers, also quasi-ballistic1. In the few modes regime, we observe a strong modulation of conductance with gating, accompanied by a distinct magnetoconductance hysteresis, suggesting that the device acts as a spin filter. Our results present a path for realizing Majorana modes without the need to apply external magnetic fields and could be relevant for developing quantum spintronic devices based on semiconductor nanowires. |
Thursday, March 18, 2021 1:06PM - 1:18PM Live |
S36.00007: Electric field control of photoluminescence polarization in Ge/SiGe quantum wells Simone Rossi, Enrico Talamas Simola, Giovanni Isella, Fabio Pezzoli Spin manipulation is a crucial aspect for fundamental investigations and the future application of spin-based optoelectronics [1]. Within this field, group IV semiconductors have shown appealing properties such as long spin lifetime, isotopic purification and compatibility with Si manufacturing processing. For practical purposes, electrically-induced spin manipulation through the Rashba effect would be highly desirable [2]. However, such a possibility has received little attention in heterostructures made of group-IV materials. In this work we present a polarization-resolved photoluminescence study in a cylindrical p-i-n diode where the intrinsic region of the device consists of Ge QWs in Si0.15Ge0.85 barriers. Different excitation power densities are investigated in a bias range from -5 to +4V. At 4K we observed a non-monotonic behaviour of the degree of circular polarization when varying the optical pump density and a non-trivial response with the bias, suggesting the presence of competing dynamical effects. Our work presents a starting point for a deeper understanding of spin-dependent properties in group IV heterostructures and their fine control by electrical means. |
Thursday, March 18, 2021 1:18PM - 1:30PM Live |
S36.00008: Magneto-optical investigation of spin and carrier kinetics in Ge1-xSnx/Ge heterostructures Elisa Vitiello, Simone Rossi, Christopher A. Broderick, Giorgio Gravina, Andrea Balocchi, Xavier Marie, Eoin P. O’Reilly, Maksym Myronov, Fabio Pezzoli Germanium-tin alloys have sparked interest thanks to their ability to tailor electronic properties by strain and band-gap engineering and their compatibility with silicon technology. Exciting improvements in lasing performances and photodetection efficiencies in the strategic mid-infrared wavelength range have been recently enabled by out-of-equilibrium growth techniques1. |
Thursday, March 18, 2021 1:30PM - 1:42PM Live |
S36.00009: Optical injection of spin current in direct bandgap group IV semiconductors Gabriel Fettu, John Edward Sipe, Oussama Moutanabbir Ge1-x Snx is an emerging direct bandgap semiconductor that can be monolithically grown on silicon wafers, thus enabling a variety of monolithic photonic and optoelectronic devices. Here we exploit recent progress in group IV bandgap engineering to investigate the optical processes of spin current injection in a silicon-compatible platform. Understanding these processes is a critical step towards coherent optical photon-to-spin conversion, which is a long-sought-after strategy for surmounting current fundamental limits in optical schemes that hinder the long-distance distribution of entanglement. To this end, charge carrier, spin, current, and spin current injection in relaxed and strained Ge1-x Snx alloy are calculated. A full Brillouin zone, 30 band kp model is used to extract the band structure necessary for the evaluation of these injection rates. In the independent particle approximation, carrier injection and optical orientation for one- and two-photon absorption are determined, and for the two-photon absorption, properties such as the anisotropy and linear-circular dichroism are presented. Interference terms related to the coherent control of carrier, spin populations, and charge, spin currents are evaluated for a bichromatic field of frequencies ω and 2ω. |
Thursday, March 18, 2021 1:42PM - 1:54PM Live |
S36.00010: Magneto-Optical and Magneto-Transport Studies of Near Surface InAs Quantum Wells Brenden A Magill, Giti Khodaparast, Sunil Thapa, Christopher J Stanton, Joseph Yuan, Mehdi Hatefipour, William a Mayer, Matthieu Dartiailh, Kasra Sardashti, Kaushini S Wickramasinghe, Javad Shabani, Yasuhiro Matsuda, Zhuo Yang, Yoshimitsu Kohama Near surface InAs quantum wells (QWs) have recently attracted interest as tools to explore mesoscopic and topological superconductivity. These shallow narrow gap QWs can interact strongly with superconducting layers. In this talk, we present a combined magneto-optical, magneto-transport, 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). 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. |
Thursday, March 18, 2021 1:54PM - 2:06PM Live |
S36.00011: Dynamic Nuclear Polarization and Nuclear-Induced Frequency Focusing in Gallium Arsenide under periodic optical electron spin pumping Michael Dominguez, Joseph Iafrate, Vanessa A Sih Periodic optically pumped electron spins in gallium arsenide polarize the nuclear spin system by a process called dynamic nuclear polarization. These polarized nuclei will create an effective magnetic field that acts on the electron spin system and affects the electron system such that the Larmor precession frequency will synchronize to discrete values; this effect is known as nuclear-induced frequency focusing. These discrete frequencies correspond to integer or half-integer multiples of the optical pulse repetition frequency. The observation of nuclear-induced frequency focusing and its dependence on pump wavelength is corroborated by numerical calculations using a model incorporating optical orientation and the optical Stark effect (Phys. Rev. B 101, 205203 (2020)). This model can be used to predict the time-dependent frequency focusing behavior of the nuclear spin system. |
Thursday, March 18, 2021 2:06PM - 2:18PM Live |
S36.00012: Observation of carrier concentration dependent spintronic terahertz emission from n-GaN/NiFe heterostructures Eric Vetter, Melike Biliroglu, Dovletgeldi Seyitliyev, Pramod Reddy, Ronny Kirste, Zlatko Sitar, Ramon Collazo, Kenan Gundogdu, Dali Sun The development of terahertz (THz) spintronics has created a paradigm shift in the generation of THz radiation through the combination of ultrafast magnetism and spin-based electronics. However, research in this area has primarily focused on all-metallic devices comprising a ferromagnetic thin film adjacent to a non-magnetic heavy metal. Here, we report the experimental observation of spintronic THz emission from an n-doped wide bandgap semiconductor, n-GaN. We found that the amplitude of THz emission strongly depends on the carrier concentration of the semiconductor layer, which could be attributed to the tunable Rashba state occurring at the n-GaN/ferromagnet interface. Our work offers exciting prospects for pursuing wide bandgap semiconductor-based spintronic THz devices and demonstrating their intriguing spin Hall physics at the ultrafast timescale. |
Thursday, March 18, 2021 2:18PM - 2:30PM Live |
S36.00013: SiGe Spintronic Devices with High-k Dielectric Gates Jennifer DeMell, Gregory Stephen, Chomani K. Gaspe, Christopher J K Richardson, Adam L Friedman SiGe is an attractive material for future advanced electronic devices desired for beyond Moore’s law high performance computing. For spintronic devices in particular, SiGe offers extremely high mobilities that can lead to long spin diffusion lengths and a spin-orbit coupling that can be used to control spin relaxation in spin valves—a prerequisite for any spinFET device. Moreover, SiGe is amenable to scaling and is compatible with most commercial device fabrication facilities in foundries. Here, we grow compressively strained Ge quantum wells with relaxed Si0.2Ge0.8 barriers using molecular beam epitaxy. We fabricate devices to determine the basic properties of the films using both charge and spin state variables and perform a systematic study to create a method of growing high-quality high-k dielectrics (hafnia and alumina) by atomic layer deposition to allow gating of these devices. We present magnetotransport results for both the charge- and spin-based devices from 3 K - 300 K at fields up to 2.5 T and compare these results for multiple samples. |
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