66 research outputs found
Giant Anisotropic Magnetoresistance in a Quantum Anomalous Hall Insulator
When a three-dimensional (3D) ferromagnetic topological insulator thin film
is magnetized out-of-plane, conduction ideally occurs through dissipationless,
one-dimensional (1D) chiral states that are characterized by a quantized,
zero-field Hall conductance. The recent realization of this phenomenon - the
quantum anomalous Hall effect - provides a conceptually new platform for
studies of edge-state transport, distinct from the more extensively studied
integer and fractional quantum Hall effects that arise from Landau level
formation. An important question arises in this context: how do these 1D edge
states evolve as the magnetization is changed from out-of-plane to in-plane? We
examine this question by studying the field-tilt driven crossover from
predominantly edge state transport to diffusive transport in Cr-doped
(Bi,Sb)2Te3 thin films, as the system transitions from a quantum anomalous Hall
insulator to a gapless, ferromagnetic topological insulator. The crossover
manifests itself in a giant, electrically tunable anisotropic magnetoresistance
that we explain using the Landauer-Buttiker formalism. Our methodology provides
a powerful means of quantifying edge state contributions to transport in
temperature and chemical potential regimes far from perfect quantization
Coherent Heteroepitaxy of Bi2Se3 on GaAs (111)B
We report the heteroepitaxy of single crystal thin films of Bi2Se3 on the
(111)B surface of GaAs by molecular beam epitaxy. We find that Bi2Se3 grows
highly c-axis oriented, with an atomically sharp interface with the GaAs
substrate. By optimizing the growth of a very thin GaAs buffer layer before
growing the Bi2Se3, we demonstrate the growth of thin films with atomically
flat terraces over hundreds of nanometers. Initial time-resolved Kerr rotation
measurements herald opportunities for probing coherent spin dynamics at the
interface between a candidate topological insulator and a large class of
GaAs-based heterostructures.Comment: To appear in Applied Physics Letter
Room temperature spin-orbit torque switching induced by a topological insulator
Recent studies on the magneto-transport properties of topological insulators
(TI) have attracted great attention due to the rich spin-orbit physics and
promising applications in spintronic devices. Particularly the strongly
spin-moment coupled electronic states have been extensively pursued to realize
efficient spin-orbit torque (SOT) switching. However, so far current-induced
magnetic switching with TI has only been observed at cryogenic temperatures. It
remains a controversial issue whether the topologically protected electronic
states in TI could benefit spintronic applications at room temperature. In this
work, we report full SOT switching in a TI/ferromagnet bilayer heterostructure
with perpendicular magnetic anisotropy at room temperature. The low switching
current density provides a definitive proof on the high SOT efficiency from TI.
The effective spin Hall angle of TI is determined to be several times larger
than commonly used heavy metals. Our results demonstrate the robustness of TI
as an SOT switching material and provide a direct avenue towards applicable
TI-based spintronic devices
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