Tsunami Solitons Emerging from Superconducting Gap

Abstract: We propose a classical integrable system exhibiting the tsunami-like solitons with rocky-desert-like disordered stationary background. One of the Lax operator describing this system is interpretable as a Bogoliubov-de Gennes Hamiltonian in parity-mixed superconductor. The family of integrable equations is generated from this seed operator by Krichever's method, whose pure $s$-wave limit includes the coupled Schr\"odinger-Boussinesq hierarchy applied to plasma physics. A linearly unstable finite background with superconducting gap supports the tsunami-soliton solution, where the propagation of the step structure turns back at a certain moment, accompanied with the oscillation on the opposite side. In addition, the equation allows inhomogeneous stationary solutions with arbitrary number of bumps at arbitrary positions, which we coin \textit{the KdV rocks}. In the Zakharov-Shabat scheme, the tsunami solitons are created from the Bogoliubov quasiparticles in energy gap and the KdV rocks from normal electrons/holes. The unexpected large space of stationary solutions comes from the non-coprime Lax pair and the multi-valued Baker-Akhiezer functions on the Riemann surface, formulated in terms of higher-rank holomorphic bundles by Krichever and Novikov. Furthermore, the concept of \textit{isodispersive phases} is introduced to characterize quasiperiodic multi-tsunami backgrounds and consider its classification.