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.
Topological
superconductors have attracted tremendous excitement
as they are predicted to host Majorana zero modes that can be utilized
for topological quantum computing. Candidate topological superconductor
Sn1–x
In
x
Te thin films (0 < x < 0.3) grown by molecular
beam epitaxy and strained in the (111) plane are shown to host quantum
interference effects in the conductivity coexisting with superconducting
fluctuations above the critical temperature T
c. An analysis of the normal state magnetoresistance reveals
these effects. A crossover from weak antilocalization to localization
is consistently observed in superconducting samples, indicating that
superconductivity originates dominantly from charge carriers occupying
trivial states that may be strongly spin–orbit split. A large
enhancement of the conductivity is observed above T
c, indicating the presence of superconducting fluctuations.
Our results motivate a re-examination of the debated pairing symmetry
of this material when subjected to quantum confinement and lattice
strain.
We report the measurements and analysis of weak antilocalization (WAL) in Pb1-xSnxSe topological quantum wells in a new regime where the elastic scattering length is larger than the magnetic length. We achieve this regime through the development of high-quality epitaxy and doping of topological crystalline insulator (TCI) quantum wells. We obtain elastic scattering lengths that exceeds 100nm and become comparable to the magnetic length. In this transport regime, the Hikami-Larkin-Nagaoka model is no longer valid. We employ the model of Wittmann and Schmid to extract the coherence time from the magnetoresistance. We find that despite our improved transport characteristics, the coherence time may be limited by scattering channels that are not strongly carrier dependent, such as electron-phonon or defect scattering.
Ferromagnetic semiconductor Ga1–x
Mn
x
As1–y
P
y
thin films go through a metal–insulator transition at low temperature where electrical conduction becomes driven by hopping of charge carriers. In this regime, we report a colossal negative magnetoresistance (CNMR) coexisting with a saturated magnetic moment, unlike in the traditional magnetic semiconductor Ga1–
x
Mn
x
As. By analyzing the temperature dependence of the resistivity at fixed magnetic field, we demonstrate that the CNMR can be consistently described by the field dependence of the localization length, which relates to a field dependent mobility edge. This dependence is likely due to the random environment of Mn atoms in Ga1–x
Mn
x
As1–y
P
y
which causes a random spatial distribution of the mobility that is suppressed by an increasing magnetic field.
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