Reconstruction of Surface Electron Spectrum and Cyclotron Motion in the Charge Density Wave Phase of Weyl Semimetals.

Charge density wave (CDW) instability drastically affects the surface electron spectrum of a Weyl semimetal. We show that in the CDW phase, the Fermi arcs reconnect into either closed Fermi loops or Frieze patterns traversing the reconstructed surface mini Brillouin zone. For the closed reconnection topology, application of an out of plane magnetic field leads to a cyclotron motion of the surface electrons.

Unconventional Discontinuous Transitions in Isospin Systems.

We show that two-dimensional fermions with dispersion k^{2} or k^{4} undergo a first-order Stoner transition to a fully spin-polarized state despite the fact that the spin susceptibility diverges at the critical point. We extend our analysis to systems with dispersion k^{2α} and spin and valley isospin and show that there is a cascade of instabilities into fractional-metal states with some electron bands fully depleted; narrow intermediate ranges of partially depleted bands exist for α<1 or α>2. The susceptibility becomes large near each transition.

Robust Spectral π Pairing in the Random-Field Floquet Quantum Ising Model.

Motivated by an experiment on a superconducting quantum processor [X. Mi et al., Science 378, 785 (2022).

Coexistence of Nonequilibrium Density and Equilibrium Energy Distribution of Quasiparticles in a Superconducting Qubit.

The density of quasiparticles typically observed in superconducting qubits exceeds the value expected in equilibrium by many orders of magnitude. Can this out-of-equilibrium quasiparticle density still possess an energy distribution in equilibrium with the phonon bath? Here, we answer this question affirmatively by measuring the thermal activation of charge-parity switching in a transmon qubit with a difference in superconducting gap on the two sides of the Josephson junction. We then demonstrate how the gap asymmetry of the device can be exploited to manipulate its parity.

One-dimensional proximity superconductivity in the quantum Hall regime.

Extensive efforts have been undertaken to combine superconductivity and the quantum Hall effect so that Cooper-pair transport between superconducting electrodes in Josephson junctions is mediated by one-dimensional edge states. This interest has been motivated by prospects of finding new physics, including topologically protected quasiparticles, but also extends into metrology and device applications. So far it has proven challenging to achieve detectable supercurrents through quantum Hall conductors.