arXiv subjects

M. F. Ritter

Publications and source records attributed to M. F. Ritter.

5 recordsLinked to original sources

arXiv2022

Measurements of Phase Dynamics in Planar Josephson Junctions and SQUIDs

We experimentally investigate the stochastic phase dynamics of planar Josephson junctions (JJs) and superconducting quantum interference devices (SQUIDs) defined in epitaxial InAs/Al heterostructures, and characterized by a large ratio of Josephson energy to charging energy. We observe a crossover from a regime of macroscopic quantum tunneling to one of phase diffusion as a function of temperature, where the transition temperature $T^{*}$ is gate-tunable. The switching probability distributions are shown to be consistent with a small shunt capacitance and moderate damping, resulting in a switching current which is a small fraction of the critical current. Phase locking between two JJs leads to a difference in switching current between that of a JJ measured in isolation and that of the same JJ measured in an asymmetric SQUID loop. In the case of the loop, $T^*$ is also tuned by a magnetic flux.

cond-mat.mes-hall↗

arXiv2022

Large even-odd spacing and $g$-factor anisotropy in PbTe quantum dots

PbTe is a semiconductor with promising properties for topological quantum computing applications. Here we characterize quantum dots in PbTe nanowires selectively grown on InP. Charge stability diagrams at zero magnetic field reveal large even-odd spacing between Coulomb blockade peaks, charging energies below 140$~\mathrm{μeV}$ and Kondo peaks in odd Coulomb diamonds. We attribute the large even-odd spacing to the large dielectric constant and small effective electron mass of PbTe. By studying the Zeeman-induced level and Kondo splitting in finite magnetic fields, we extract the electron $g$-factor as a function of magnetic field direction. We find the $g$-factor tensor to be highly anisotropic, with principal $g$-factors ranging from 0.9 to 22.4, and to depend on the electronic configuration of the devices. These results indicate strong Rashba spin-orbit interaction in our PbTe quantum dots.

cond-mat.mes-hall↗

arXiv2021

Semiconductor Epitaxy in Superconducting Templates

Integration of high quality semiconductor-superconductor devices into scalable and CMOS compatible architectures remains an outstanding challenge, currently hindering their practical implementation. Here, we demonstrate growth of InAs nanowires monolithically integrated on Si inside lateral cavities containing superconducting TiN elements. This technique allows growth of hybrid devices characterized by sharp semiconductor-superconductor interfaces and with alignment along arbitrary crystallographic directions. Electrical characterization at low temperature reveals proximity induced superconductivity in InAs via a transparent interface.

cond-mat.mes-hall↗

arXiv2021

On the Role of Out-of-Equilibrium Phonons in Gated Superconducting Switches

Recent experiments suggest the possibility to tune superconductivity in metallic nanowires by application of modest gate voltages. It is largely debated whether the effect is due to an electric field at the superconductor surface or small currents of high-energy electrons. We shed light on this matter by studying the suppression of superconductivity in sample geometries where the roles of electric field and electron-current flow can be clearly separated. Our results show that suppression of superconductivity does not depend on the presence or absence of an electric field at the surface of the nanowire, but requires a current of high-energy electrons. The suppression is most efficient when electrons are injected into the nanowire, but similar results are obtained also when electrons are passed between two remote electrodes at a distance $d$ to the nanowire (with $d$ in excess of $1~\mathrm{μm}$). In the latter case, high-energy electrons decay into phonons which propagate through the substrate and affect superconductivity in the nanowire by generating quasiparticles. We show that this process involves a non-thermal phonon distribution, with marked differences from the loss of superconductivity due to Joule heating near the nanowire or an increase in the bath temperature.

cond-mat.supr-con↗

arXiv2020

A superconducting switch actuated by injection of high energy electrons

Fast cryogenic switches with ultra-low power dissipation are highly sought-after for control electronics of quantum computers, space applications and next generation logic circuits. However, existing high-frequency switches are often bulky, lossy or require large source-drain and gate currents for operation, making them unsuitable for many applications and difficult to interface to semiconducting devices. Here we present an electrically controlled superconducting switch based on a metallic nanowire. Transition from superconducting to resistive state is realized by tunneling of high-energy electrons from a gate contact through an insulating barrier. Operating gate currents are several orders of magnitude smaller than the nanowire critical source-drain current, effectively resulting in a voltage-controlled device. This superconducting switch is fast, self-resets from normal to superconducting state, and can operate in large magnetic fields, making it an ideal component for low-power cryogenic applications and quantum computing architectures.

cond-mat.supr-con↗