Normal and anomalous solitons in the theory of dynamical Cooper pairing

TL;DR

This paper derives multi-soliton solutions for the time-dependent Bogoliubov-de Gennes equations, revealing two types of solitons that describe the dynamics of fermionic condensates and their relation to stationary states.

Contribution

It introduces a novel class of multi-soliton solutions in fermionic condensate dynamics, linking soliton parameters to stationary states and unstable modes.

Findings

Normal solitons asymptote to zero-parameter states

Anomalous solitons tend to states with nonzero order parameter

Multi-soliton solutions often describe physical dynamics

Abstract

We obtain multi-soliton solutions of the time-dependent Bogoliubov-de Gennes equations or, equivalently, Gorkov equations that describe the dynamics of a fermionic condensate in the dissipationless regime. There are two kinds of solitons - normal and anomalous. At large times, normal multi-solitons asymptote to unstable stationary states of the BCS Hamiltonian with zero order parameter (normal states), while the anomalous ones tend to eigenstates characterized by a nonzero anomalous average. Under certain circumstances, multi-soliton solutions break up into sums of single solitons. In the linear analysis near the stationary states, solitons correspond to unstable modes. Generally, they are nonlinear extensions of these modes, so that a stationary state with $k$ unstable modes gives rise to a $k$-soliton solution. We relate parameters of the multi-solitons to those of the asymptotic stationary state, which determines the conditions necessary for exciting solitons. We further argue that the dynamics in many physical situations is multi-soliton.