arXiv subjects

Bob de Ronde

Publications and source records attributed to Bob de Ronde.

5 recordsLinked to original sources

arXiv2019

Zeeman effect induced 0-$π$ transitions in ballistic Dirac semimetal Josephson junctions

One of the consequences of Cooper pairs having a finite momentum in the interlayer of a Josephson junction, is $π$-junction behavior. The finite momentum can either be due to an exchange field in ferromagnetic Josephson junctions, or due to the Zeeman effect. Here, we report the observation of Zeeman effect induced 0-$π$ transitions in Bi$_{1-x}$Sb$_x$, 3D Dirac semimetal-based Josephson junctions. The large g-factor of the Zeeman effect from a magnetic field applied in the plane of the junction allows tuning of the Josephson junctions from 0- to $π$- regimes. This is revealed by sign changes in the modulation of the critical current by applied magnetic field of an asymmetric superconducting quantum interference device (SQUID). Additionally, we directly measure a non-sinusoidal current-phase relation in the asymmetric SQUID, consistent with models for ballistic Josephson transport.

cond-mat.mes-hall↗

arXiv2019

Non-local signatures of the chiral magnetic effect in Dirac semimetal Bi$_{0.97}$Sb$_{0.03}$

The field of topological materials science has recently been focussing on three-dimensional Dirac semimetals, which exhibit robust Dirac phases in the bulk. However, the absence of characteristic surface states in accidental Dirac semimetals (DSM) makes it difficult to experimentally verify claims about the topological nature using commonly used surface-sensitive techniques. The chiral magnetic effect (CME), which originates from the Weyl nodes, causes an $\textbf{E}\cdot\textbf{B}$-dependent chiral charge polarization, which manifests itself as negative magnetoresistance. We exploit the extended lifetime of the chirally polarized charge and study the CME through both local and non-local measurements in Hall bar structures fabricated from single crystalline flakes of the DSM Bi$_{0.97}$Sb$_{0.03}$. From the non-local measurement results we find a chiral charge relaxation time which is over one order of magnitude larger than the Drude transport lifetime, underlining the topological nature of Bi$_{0.97}$Sb$_{0.03}$.

cond-mat.mtrl-sci↗

arXiv2017

Interaction between counter-propagating quantum Hall edge channels in the 3D topological insulator BiSbTeSe$_2$

The quantum Hall effect is studied in the topological insulator BiSbTeSe$_2$. By employing top- and back-gate electric fields at high magnetic field, the Landau levels of the Dirac cones in the top and bottom topological surface states can be tuned independently. When one surface is tuned to the electron-doped side of the Dirac cone and the other surface to the hole-doped side, the quantum Hall edge channels are counter-propagating. The opposite edge mode direction, combined with the opposite helicities of top and bottom surfaces, allows for scattering between these counter-propagating edge modes. The total Hall conductance is integer valued only when the scattering is strong. For weaker interaction, a non-integer quantum Hall effect is expected and measured.

cond-mat.mes-hall↗

arXiv2017

$4π$ periodic Andreev bound states in a Dirac semimetal

Electrons in a Dirac semimetals possess linear dispersion in all three spatial dimensions, and form part of a developing platform of novel quantum materials. Bi$_{1-x}$Sb$_x$ supports a three-dimensional Dirac cone at the Sb-induced band inversion point. Nanoscale phase-sensitive junction technology is used to induce superconductivity in this Dirac semimetal. Radio frequency irradiation experiments reveal a significant contribution of 4$π$-periodic Andreev bound states to the supercurrent in Nb-Bi$_{0.97}$Sb$_{0.03}$-Nb Josephson junctions. The conditions for a substantial $4π$ contribution to the supercurrent are favourable because of the Dirac cone's topological protection against backscattering, providing very broad transmission resonances. The large g-factor of the Zeeman effect from a magnetic field applied in the plane of the junction, allows tuning of the Josephson junctions from 0 to $π$ regimes.

cond-mat.supr-con↗

arXiv2012

All-optical Switching of a Microcavity Repeated at Terahertz Rates

We have performed ultrafast pump-probe experiments on a GaAs-AlAs microcavity with a resonance near 1300 nm in the "original" telecom band. We exploit the virtually instantaneous electronic Kerr effect to repeatedly and reproducibly switch a GaAs-AlAs planar microcavity. We achieve repetition times as fast as 300 fs, thereby breaking the THz modulation barrier. The rate of the switching in our experiments is only determined by optics and not by material related relaxation. Our results offer novel opportunities for fundamental studies of cavity-QED and optical information processing in sub-picosecond time scale.

physics.optics↗