Hybridization of sub-gap states in one-dimensional superconductor/semiconductor Coulomb islands

We present measurements of one-dimensional superconductor-semiconductor Coulomb islands, fabricated by gate confinement of a two-dimensional InAs heterostructure with an epitaxial Al layer. When tuned via electrostatic side gates to regimes without sub-gap states, Coulomb blockade reveals Cooper-pair mediated transport. When sub-gap states are present, Coulomb peak positions and heights oscillate in a correlated way with magnetic field and gate voltage, as predicted theoretically, with (anti) crossings in (parallel) transverse magnetic field indicating Rashba-type spin-orbit coupling. Overall results are consistent with a picture of overlapping Majorana zero modes in finite wires

Supercurrent transport through 1ee-periodic full-shell Coulomb islands

We experimentally investigate supercurrent through Coulomb islands, where island and leads are fabricated from semiconducting nanowires with fully surrounding superconducting shells. Applying flux along the wire yields a series of destructive Little-Parks lobes with reentrant supercurrent. We find Coulomb blockade with 2$e$ peak spacing in the zeroth lobe and 1$e$ average spacing, with regions of significant even-odd modulation, in the first lobe. Evolution of Coulomb-peak amplitude through the first lobe is consistent with a theoretical model of supercurrent carried predominantly by zero-energy states in the leads and the island.Comment: 11 pages, 5+5 figure

Tunable, Concurrent Multiband, Single Chain Radio Architecture for Low Energy 5G-RANs

This invited paper considers a key next step in the design of radio architectures aimed at supporting low energy consumption in 5G heterogeneous radio access networks. State-of-the-art mobile radios usually require one RF transceiver per standard, each working separately at any given time. Software defined radios, while spanning a wide range of standards and frequency bands, also work separately at any specific time. In 5G radio access networks, where continuous, multiband connectivity is envisaged, this conventional radio architecture results in high network power consumption. In this paper, we propose the novel concept of a concurrent multiband frequency-agile radio (CM-FARAD) architecture, which simultaneously supports multiple standards and frequency bands using a single, tunable transceiver. We discuss the subsystem radio design approaches for enabling the CM-FARAD architecture, including antennas, power amplifiers, low noise amplifiers and analogue to digital converters. A working prototype of a dual-band CM-FARAD test-bed is also presented together with measured salient performance characteristics

Coherent transport through a Majorana island in an Aharonov-Bohm interferometer

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, could also be observed, suggesting additional non-Majorana mechanisms for 1e transport through these moderately short wires

Evidence for Dirac nodes from quantum oscillations in SrFe2As2

We present a detailed study of quantum oscillations in the antiferromagnetically ordered pnictide compound SrFe2As2 as the angle between the applied magnetic field and crystalline axes is varied. Our measurements were performed on high-quality single crystals in a superconducting magnet, and in pulsed magnetic fields up to 60 T, allowing us to observe orbits from several small Fermi-surface pockets. We extract the cyclotron effective mass m☆ and frequency F for these orbits and track their values as the field is rotated away from the c axis. While a constant ratio of m☆/F is expected for a parabolic band, we observe deviations from this behavior. We conclude that this observation points to orbits derived from a band with Dirac dispersion near the Fermi level

Construction of a Microscopic Model for Yb and Tm Compounds on the Basis of a \mib{j}-\mib{j} Coupling Scheme

We provide a prescription to construct a microscopic model for heavy lanthanide systems such as Yb and Tm compounds by exploiting a $j$-$j$ coupling scheme. Here we consider a situation with a large spin-orbit coupling, in which $j$=5/2 sextet is fully occupied, while $j$=7/2 octet is partially occupied, where $j$ denotes total angular momentum. We evaluate crystalline electric field potentials and Coulomb interactions among the states of the $j$=7/2 octet to construct a local Hamiltonian in the $j$-$j$ coupling scheme. Then, it is found that the local $f$-electron states composed of the $j$=7/2 octet agree quite well with those of seven $f$ orbitals even for a realistic value of the spin-orbit coupling. As an example of the application of the present model, we discuss low-temperature multipole states of Yb- and Tm-based filled skutterudites by analyzing multipole susceptibility of the Anderson model in the $j$-$j$ coupling scheme with the use of a numerical renormalization group technique. From the comparison with the numerical results of the seven-orbital Anderson model, it is concluded that the multipole state is also well reproduced by the $j$-$j$ coupling model, even when we include the hybridization between conduction and $f$ electrons for the realistic value of the spin-orbit coupling. Finally, we briefly discuss future applications of the present prescription for theoretical research on heavy lanthanide compounds.Comment: 12 pages, 8 figures