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Register a new userPhase coherent transport in Kondo/superconducting hybrid structures
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We present measurements of the transport properties of hybrid structures consisting of a Kondo AuFe film and a superconducting Al film. The temperature dependence of the resistance indicates the existence of the superconducting proximity effect in the Kondo AuFe wires over the range of $sim0.5$ $mu$m. Electronic phase coherence in the Kondo AuFe wires has been confirmed by observing the Aharanov-Bohm effect in the magnetoresistance of the loop structure. The amplitude of the magnetoresistance oscillations shows a reentrant behavior with a maximum at $sim$ 870 mK, which results from an interplay between the Kondo effect and the superconducting proximity effect.
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In this minireview, we outline the recent experimental and theoretical progress in the creation, characterization and manipulation of Majorana bound states (MBSs) in semiconductor-superconductor (SC) hybrid structures. After an introductory overview of the broader field we specifically focus on four of our recent projects in this direction. We show that the emergence of Fano resonances in the differential conductance in a normal lead-Majorana nanowire-quantum dot setup can be exploited to determine if a single MBS is contacted by the normal lead and the quantum dot providing an experimental test of the non-locality of MBSs. In the second project, the tunnel-coupling to two MBSs in an $s$-wave SC-Majorana nanowire Josephson junction (JJ) leads to a finite contribution of the MBSs to the equilibrium Josephson current probing directly the local spin-singlet contribution of the Majorana pair. We then shift our focus from MBSs forming in nanowire systems to MBSs forming in topological JJs. In a single sheet of buckled silicene with proximity induced superconductivity two local electric fields can be used to tune the junction between a topologically trivial and topologically non-trivial regime. In a Corbino geometry topological Josephson junction two MBSs harbored in Josephson vortices can rotate along the JJ and, in the course of this, will be exchanged periodically in the phase difference of the JJ. The tunneling current in a metal tip coupled to the JJ is shown to exhibit signs of the anyonic braiding phase of two MBSs.
We investigate the subgap bulk transport through short and wide superconducting hybrid structures based on HgTe quantum wells (QWs). We show that the differential conductance of a normal metal-insulator-superconductor (NIS) proximity structure behaves in a qualitatively different way with respect to the topological phase of the HgTe QW. We compare the differential conductance for the NIS structure within the wave-matching method based on the Bogoliubov-de Gennes equation and the matrix method based on the normal-state scattering matrix and find that the two models agree for highly-doped N and S contacts. We also show that the effect of a possible Rashba spin-orbit interaction on the differential conductance can be significant for weakly doped N and S contacts. Our findings should be important in samples with a large aspect ratio where bulk contributions in transport are dominant.
We present an exhaustive theoretical analysis of a double-loop Josephson proximity interferometer, as the one recently realized by Strambini et al. for the control of the Andreev spectrum via an external magnetic field. This system, called $omega$-SQUIPT, consists of a T-shaped diffusive normal metal (N) attached to three superconductors (S) forming a double loop configuration. By using the quasiclassical Green function formalism, we calculate the local normalized density of states, the Josephson currents through the device and the dependence of the former on the length of the junction arms, the applied magnetic field and the S/N interface transparencies. We show that by tuning the fluxes through the double loop, the system undergoes transitions from a gapped to a gapless state. We also evaluate the Josephson currents flowing in the different arms as a function of magnetic fluxes and explore the quasi-particle transport, by considering a metallic probe tunnel-coupled to the Josephson junction and calculating its I-V characteristics. Finally, we study the performances of the $omega$-SQUIPT and its potential applications, by investigating its electrical and magnetometric properties.
The emerging field of phase-coherent caloritronics (from the Latin word calor, i.e., heat) is based on the possibility to control heat currents using the phase difference of the superconducting order parameter. The goal is to design and implement thermal devices able to master energy transfer with a degree of accuracy approaching the one reached for charge transport by contemporary electronic components. This can be obtained by exploiting the macroscopic quantum coherence intrinsic to superconducting condensates, which manifests itself through the Josephson and the proximity effect. Here, we review recent experimental results obtained in the realization of heat interferometers and thermal rectifiers, and discuss a few proposals for exotic non-linear phase-coherent caloritronic devices, such as thermal transistors, solid-state memories, phase-coherent heat splitters, microwave refrigerators, thermal engines and heat valves. Besides being very attractive from the fundamental physics point of view, these systems are expected to have a vast impact on many cryogenic microcircuits requiring energy management, and possibly lay the first stone for the foundation of electronic thermal logic.
Majarona fermions (MFs) were predicted more than seven decades ago but are yet to be identified [1]. Recently, much attention has been paid to search for MFs in condensed matter systems [2-10]. One of the seaching schemes is to create MF at the interface between an s-wave superconductor (SC) and a 3D topological insulator (TI) [11-13]. Experimentally, progresses have been achieved in the observations of a proximity-effect-induced supercurrent [14-16], a perfect Andreev reflection [17] and a conductance peak at the Fermi level [18]. However, further characterizations are still needed to clarify the nature of the SC-TI interface. In this Letter, we report on a strong proximity effect in Pb-Bi2Te3 hybrid structures, based on which Josephson junctions and superconducting quantum interference devices (SQUIDs) can be constructed. Josephson devices of this type would provide a test-bed for exploring novel phenomena such as MFs in the future.
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