GaMnAs-based hybrid multiferroic memory device

A rapidly developing field of spintronics is based on the premise that substituting charge with spin as a carrier of information can lead to new devices with lower power consumption, non-volatility and high operational speed. Despite efficient magnetization detection, magnetization manipulation is primarily performed by current-generated local magnetic fields and is very inefficient. Here we report a novel non-volatile hybrid multiferroic memory cell with electrostatic control of magnetization based on strain-coupled GaMnAs ferromagnetic semiconductor and a piezoelectric material. We use the crystalline anisotropy of GaMnAs to store information in the orientation of the magnetization along one of the two easy axes, which is monitored via transverse anisotropic magnetoresistance. The magnetization orientation is switched by applying voltage to the piezoelectric material and tuning magnetic anisotropy of GaMnAs via the resulting stress field.Comment: 4 pages, 5 figure

Introduction to topological superconductivity and Majorana fermions

This short review article provides a pedagogical introduction to the rapidly growing research field of Majorana fermions in topological superconductors. We first discuss in some details the simplest "toy model" in which Majoranas appear, namely a one-dimensional tight-binding representation of a p-wave superconductor, introduced more than ten years ago by Kitaev. We then give a general introduction to the remarkable properties of Majorana fermions in condensed matter systems, such as their intrinsically non-local nature and exotic exchange statistics, and explain why these quasiparticles are suspected to be especially well suited for low-decoherence quantum information processing. We also discuss the experimentally promising (and perhaps already successfully realized) possibility of creating topological superconductors using semiconductors with strong spin-orbit coupling, proximity-coupled to standard s-wave superconductors and exposed to a magnetic field. The goal is to provide an introduction to the subject for experimentalists or theorists who are new to the field, focusing on the aspects which are most important for understanding the basic physics. The text should be accessible for readers with a basic understanding of quantum mechanics and second quantization, and does not require knowledge of quantum field theory or topological states of matter.Comment: 21 pages, 5 figure

Weak localization in Ga1-xMnxAs: Evidence of impurity band transport

We report the observation of negative magnetoresistance in the ferromagnetic semiconductor Ga1-xMnxAs, x=0.05-0.08, at low temperatures (T \u3c 3 K) and low magnetic fields (0 \u3c B \u3c 20 mT). We attribute this effect to weak localization. Observation of weak localization strongly suggests impurity band transport in these materials, since for valence band transport one expects either weak antilocalization due to strong spin-orbit interactions or total suppression of interference by intrinsic magnetization. In addition to the weak localization, we observe Altshuler-Aronov electron-electron interaction effects in this material

Topological response of the anomalous Hall effect in MnBi2Te4 due to magnetic canting

Three-dimensional (3D) compensated MnBi2Te4 is antiferromagnetic, but undergoes a spin-flop transition at intermediate fields, resulting in a canted phase before saturation. In this work, we experimentally show that the anomalous Hall effect (AHE) in MnBi2Te4 originates from a topological response that is sensitive to the perpendicular magnetic moment and to its canting angle. Synthesis by molecular beam epitaxy allows us to obtain a large-area quasi-3D 24-layer MnBi2Te4 with near-perfect compensation that hosts the phase diagram observed in bulk which we utilize to probe the AHE. This AHE is seen to exhibit an antiferromagnetic response at low magnetic fields, and a clear evolution at intermediate fields through surface and bulk spin-flop transitions into saturation. Throughout this evolution, the AHE is super-linear versus magnetization rather than the expected linear relationship. We reveal that this discrepancy is related to the canting angle, consistent with the symmetry of the crystal. Our findings bring to light a topological anomalous Hall response that can be found in non-collinear ferromagnetic, and antiferromagnetic phases.This article is published as Bac, S-K., K. Koller, F. Lux, J. Wang, L. Riney, K. Borisiak, W. Powers et al. "Topological response of the anomalous Hall effect in MnBi2Te4 due to magnetic canting." npj quantum materials 7, no. 1 (2022): 46. DOI: 10.1038/s41535-022-00455-5. Copyright 2022 The Author(s). Attribution 4.0 International (CC BY 4.0). Posted with permission. DOE Contract Number(s): AC02-06CH11357; NSF-DMR-1905277; AC02-07CH11358

Topological response of the anomalous Hall effect through the spin-flop transition of MnBi2Te4

MnBi2Te4 is an intrinsic magnetic topological insulator where a naturally occurring band inversion and spontaneous magnetization cooperate to yield strong, often quantized, anomalous Hall effects. Quasi-three-dimensional compensated MnBi2Te4 is antiferromagnetic, but undergoes a spin-flop transition at intermediate fields, resulting in an unusual metastable canted phase before saturation. In this work, synthesis by molecular beam epitaxy allows us to obtain a large-area 24-layer antiferromagnetic MnBi2Te4 with near-perfect compensation that hosts the phase diagram of bulk MnBi2Te4 and a strong anomalous Hall effect (AHE). This AHE exhibits an antiferromagnetic response at low magnetic fields, and a clear evolution at intermediate fields through surface and bulk spin-flop transitions and into saturation. We also show that the anomalous Hall conductivity is super-linear versus magnetization, evidencing a non-collinear magnetic texture as magnetization evolves towards saturation. The strong impact of this non-collinear magnetic structure on the AHE measured here can be promising for the realization of electronic states predicted to occur in this magnetic regime of MnBi2Te4