No abstract

Semiconductor electronics has so far been based on the transport of charge carriers while storage of information has mainly relied upon the collective interactions of spins. A new discipline known as spintronics proposes to exploit the strong mutual influence of magnetic and electrical properties in magnetic semiconductors, which promise new types of devices and computer technologies. The mechanism for such phenomena involves the concept of magnetic polarons-microscopic clouds of magnetization composed of charge carriers and neighboring magnetic ions-which determine most of the electrical, magnetic, and optical properties of the material. In spite of the importance of this quasiparticle, its observation remains a formidable challenge. Here we report that, using the positive muon as both a donor center and a local magnetic probe, we have been able to generate and detect the magnetic polaron and determine its size and magnetic moment in the magnetic semiconductor EuS.

The magnetoresistance at temperatures below 20 K in an n-InSb/ In 0.85 Al 0.15 Sb two-dimensional electron system is studied and described in terms of antilocalization due to quantum interference under strong spin-orbit interaction. The spin-orbit interaction coefficients are extracted by fitting the magnetoresistance data to an antilocalization theory distinguishing the Rashba and Dresselhaus contributions. A good agreement between magnetoresistance data and theory suggests a Rashba coefficient ͉␣͉Ϸ0.03 eV Å and a Dresselhaus coefficient ␥ Ϸ 490 eV Å 3 . A strong contribution from the Dresselhaus term leads to pronounced anisotropy in the energy splitting induced by spin-orbit interaction in the two-dimensional electron dispersion.

No abstract

Planar Josephson junctions (JJs) made in semiconductor quantum wells with large spin-orbit coupling are capable of hosting topological superconductivity. Indium antimonide (InSb) two-dimensional electron gases (2DEGs) are particularly suited for this due to their large Landé g-factor and high carrier mobility, however superconducting hybrids in these 2DEGs remain unexplored. Here we create JJs in high quality InSb 2DEGs and provide evidence of ballistic superconductivity over micron-scale lengths. A Zeeman field produces distinct revivals of the supercurrent in the junction, associated with a 0− π transition. We show that these transitions can be controlled by device design, and tuned in-situ using gates. A comparison between experiments and the theory of ballistic π -Josephson junctions gives excellent quantitative agreement. Our results therefore establish InSb quantum wells as a promising new material platform to study the interplay between superconductivity, spin-orbit interaction and magnetism.

No abstract

Majorana zero modes are leading candidates for topological quantum computation due to non-local qubit encoding and non-abelian exchange statistics. Spatially separated Majorana modes are expected to allow phase-coherent single-electron transport through a topological superconducting island via a mechanism referred to as teleportation. Here we experimentally investigate such a system by patterning an elongated epitaxial InAs-Al island embedded in an Aharonov-Bohm interferometer. With increasing parallel magnetic field, a discrete sub-gap state in the island is lowered to zero energy yielding persistent 1e-periodic Coulomb blockade conductance peaks (e is the elementary charge). In this condition, conductance through the interferometer is observed to oscillate in a perpendicular magnetic field with a flux period of h/e (h is Planck's constant), indicating coherent transport of single electrons through the islands, a signature of electron teleportation via Majorana modes.

The spin and phase coherence times of the itinerant electrons in n-InSb thin films were experimentally determined by analyzing the low-temperature magnetoresistance in antilocalization theory. The results indicate a very weak temperature dependence below 10 K for the spin coherence time. The dependence of the spin coherence time on carrier density demonstrates that the Elliott-Yafet mechanism is predominantly responsible for electron-spin relaxation in n-type InSb at low temperatures. The phase coherence time follows an inverse temperature dependence, in accordance with the electron-electron Nyquist dephasing mechanism.