Phase crystals
Journal article, 2020

Superconductivity owes its properties to the phase of the electron pair condensate that breaks the U(1) symmetry. In the most traditional ground state, the phase is uniform and rigid. The normal state can be unstable towards special inhomogeneous superconducting states: the Abrikosov vortex state and the Fulde-Ferrell-Larkin-Ovchinnikov state. Here we show that the phase-uniform superconducting state can go into a fundamentally different and more ordered nonuniform ground state, which we refer to as a phase crystal. This state breaks translational invariance through formation of a spatially periodic modulation of the phase, manifested by unusual superflow patterns and circulating currents, that also break time-reversal symmetry. We list the general conditions needed for realization of phase crystals. Using microscopic theory, we then derive an analytic expression for the superfluid density tensor for the case of a nonuniform environment in a semi-infinite superconductor. We demonstrate how the surface quasiparticle states enter the superfluid density and identify phase crystallization as the main player in several previous numerical observations in unconventional superconductors, and predict the existence of a similar phenomenon in superconductor-ferromagnetic structures. This analytic approach provides a unifying aspect for the exploration of boundary-induced quasiparticles and collective excitations in superconductors. More generally, we trace the origin of phase crystallization to nonlocal properties of the gradient energy, which implies the existence of similar pattern-forming instabilities in many other contexts.

Author

Patric Holmvall

Chalmers, Microtechnology and Nanoscience (MC2), Applied Quantum Physics

Mikael Fogelström

Chalmers, Microtechnology and Nanoscience (MC2)

Tomas Löfwander

Chalmers, Microtechnology and Nanoscience (MC2), Applied Quantum Physics

Anton Vorontsov

Montana State University

Physical Review Research

2643-1564 (eISSN)

Vol. 2 1 013104

Areas of Advance

Nanoscience and Nanotechnology (SO 2010-2017, EI 2018-)

Materials Science

Subject Categories

Physical Sciences

Atom and Molecular Physics and Optics

Other Physics Topics

Condensed Matter Physics

Roots

Basic sciences

Infrastructure

C3SE (Chalmers Centre for Computational Science and Engineering)

DOI

10.1103/PhysRevResearch.2.013104

More information

Latest update

1/28/2021