Spontaneous Breaking of Rotational Symmetry in Superconductors

Abstract

We show that homogeneous superconductors with broken spin/isospin symmetry lower their energy via a transition to a novel superconducting state where the Fermi surfaces are deformed to a quasiellipsoidal form at zero total momentum of Cooper pairs. In this state, the gain in the condensation energy of the pairs dominates over the loss in the kinetic energy caused by the lowest order (quadrupole) deformation of Fermi surfaces from the spherically symmetric form. The phase transition from the spherically symmetric state to the superconducting state with broken rotational symmetry is first order.

Thermodynamics of Ultracold Fermi Gases

“…Exotic phases with spin-asymmetric pairing are predicted to be stable, the most famous one being the Fulde-Ferrell-Larkin-Ovchinnikov state in which the order parameter is modulated in space [56,57]. Among other proposals, we mention a gapless (`breached pair') super uid state [58], or a state with deformed Fermi surfaces [59]. However these states are expected to occupy a very small part of the phase diagram and their observation may require a substantial experimental e ort.…”

Nonequilibrium pairing instability in ultracold Fermi gases with population imbalance

“…Unbalanced Fermi gases [25] are currently attracting a great deal of experimental and theoretical interest. One of the aims is to detect exotic paired states [24,26,27,28] that have been elusive so far in conventional solid-state systems.…”

Propagation of the ultrashort pulsed beam with ultrabroad bandwidth in the dispersive medium

“…The first alternative is the deformed Fermi sphere (DFS) superconductor [73]. In this phase, the unequal Fermi surfaces of the two paired species are deformed so that they can intersect, and then pairing can occur in the vicinity of this intersection.…”