57 research outputs found
Interaction-mediated surface state instability in disordered three-dimensional topological superconductors with spin SU(2) symmetry
We show that arbitrarily weak interparticle interactions destabilize the
surface states of 3D topological superconductors with spin SU(2) invariance
(symmetry class CI), in the presence of non-magnetic disorder. The conduit for
the instability is disorder-induced wavefunction multifractality. We argue that
time-reversal symmetry breaks spontaneously at the surface, so that
topologically-protected states do not exist for this class. The
interaction-stabilized surface phase is expected to exhibit ferromagnetic
order, or to reside in an insulating plateau of the spin quantum Hall effect.Comment: v2: 5+3 pages, 1 figure; expanded introduction, added background on
topological superconductors and multifractality, technical details relegated
to sup info (published version
Relaxation and persistent oscillations of the order parameter in the non-stationary BCS theory
We determine the limiting dynamics of a fermionic condensate following a
sudden perturbation for various initial conditions. We demonstrate that
possible initial states of the condensate fall into two classes. In the first
case, the order parameter asymptotes to a constant value. The approach to a
constant is oscillatory with an inverse square root decay. This happens, e.g.,
when the strength of pairing is abruptly changed while the system is in the
paired ground state and more generally for any nonequilibrium state that is in
the same class as the ground state. In the second case, the order parameter
exhibits persistent oscillations with several frequencies. This is realized for
nonequilibrium states that belong to the same class as excited stationary
states. Our classification of initial states extends the concept of excitation
spectrum to nonequilibrium regime and allows one to predict the evolution
without solving equations of motion.Comment: 8 pages, 4 figure
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