Cnoidal wave supersolidity in nonequilibrium states is dynamically unstable at finite temperature

Abstract: The possible existence of an exotic phase of matter rigid like a solid but able to sustain persistent and dissipation-less flow like a superfluid, a "supersolid", has been the subject of intense theoretical and experimental efforts since the discovery of superfluidity in Helium-4. Recently, it has been proposed that nonlinear periodic modulations known as cnoidal waves, that naturally emerge in Bose-Einstein condensates, provide a promising platform to find and study supersolidity in nonequilibrium phases of matter. Nevertheless, so far the analysis has been limited to a one-dimensional zero-temperature system. By combining the dissipative Gross-Pitaevskii equation with a finite temperature holographic model, we show that the proposed cnoidal wave supersolid phases of matter are always energetically and dynamically unstable at finite temperature. We ascribe this instability to the dynamics of the "elastic" Goldstone mode arising as a direct consequence of translational order. Finally, we study the dynamical instability of the supersolid state and connect it to the production of topological defects during the relaxation towards a final homogeneous equilibrium state with smaller superflow current, similar to the Landau instability dynamics in superfluids. Our results suggest that the supersolidity of cnoidal waves can emerge only as a transient phenomenon and not as a truly equilibrium and stable ground state.