Coherent transmission of superconducting carriers through a ∼2 μm polar semiconductor

Abstract

Coherent transmission of Cooper pairs through a non-superconducting medium is a key challenge for hybrid electronics with superconductors, normal metals and semiconductors. While superconductor-normal metal-superconductor (SNS) junctions have been known for quite sometime, including a low carrier density region or a two-dimensional electron gas (2DEG) in the path of superconducting electrons is relatively less explored. Indeed, this is due to the limited choice of materials that would make ohmic contacts to such systems, while simultaneously supporting a superconducting phase. In this paper we show a coherent transmission of supercurrent through a degenerate semiconductor over a length ≈2μm with a critical magnetic field B c ≈8T at 1.6K and T c ≈5K at zero magnetic field. This length scale is much larger than the typical thickness of a Josephson junction. Our system is a fragment of a GaN nanowall network that has been shown to support a high mobility 2DEG (μ n >10 4 cm 2 V −1 s −1 ). The current and voltage probes were superconducting tungsten-gallium composite electrodes and the measurements could be done in four-probe geometry. We demonstrate ballistic type carrier transport with a near ideal transparency of 1 and a critical current (I c ) large enough such that the Josephson coupling parameter . Some features in magneto-transport data suggest that there is possibly a small magnetic moment forming in the semiconductor fragment. In addition the combination of a T c typical of elemental metallic superconductors, but a critical field that appears to be higher than the Clogston-Chandrasekhar limit, may be indicative of the emergence of a triplet pairing mechanism in these structures.

Self-biased current, magnetic interference response, and superconducting vortices in tilted Weyl semimetals with disorder

“…( 11). This finding may explain a recent experiment where a long-ranged supercurrent was observed through a Josephson junction made of WTe 2 Weyl semimetal 51 inline with pre-vious works 70,71,[73][74][75] . In the singlet channel we recover the results of a conventional SNS junction (up to the zero order of α z p −1 F ).…”

“…Hence, we now proceed to apply our formulated quasiclassical model to hybrid structures made of disordered Weyl semimetals and superconductors, which are practical platforms that the Eilenberger and Usadel equations are able to describe them properly. We note that the quasiclassical Eilenbeger and Usadel approaches were also generalized for spin-orbit coupled systems [70][71][72][73][74][75] , surface channels of topological insulators [63][64][65] , and black phosphorus monolayer (phosphorene) 27 in the presence of superconductivity and a Zeeman field. A specific configuration is depicted in Fig.…”

Polarization induced two dimensional confinement of carriers in wedge shaped polar semiconductors

“…The study further predicts a very high electron mobility in this channel [16]. This prediction is also consistent with the experimental observation of high conductivity [17][18][19][20] and long phase coherence length [18,21,22] of electrons in the networks of wedge-shaped c-oriented GaN nanowalls. It will be interesting to understand the mechanism of spin transport through this channel.…”

Spin transport in polarization induced two-dimensional electron gas channel in c-GaN nano-wedges

“…The study further predicts remarkably high electron mobility in this channel, which arises due to the natural separation of the electrons (in the middle) from the ionized donors (at the boundaries) 21 . These predictions are also supported by the experimental findings of high conductivity 23 – 26 and long phase coherence length 24 , 27 , 28 for electrons in networks of c -oriented GaN nano-wedges. Since the 2D confinement takes place deep inside the structure, the symmetry between the conduction and valence band is intact over the entire potential profile.…”