Broken-parity-induced crossover of thermal conduction in the Fermi-Pasta-Ulam-Tsingou lattice

Parity represents the spatial inversion symmetry of a physical phenomenon under mirror reflection. Commonly, the parity of interatomic interaction is broken in crystalline solids due to asymmetric repulsion between atoms. Symmetry breaking often involves a phase transition; however, it is still unclear if there are any comparable behaviors in crystalline solids as the result of asymmetric interatomic interaction. In this paper, we show that a crossover behavior of thermal conduction occurs in a Fermi-Pasta-Ulam-Tsingou α-β superlattice, consisting of periodic cells of arithmetically increased cubic nonlinearity, due to strengthened interaction asymmetry. Before a critical point of interaction asymmetry, thermal conductance is a cell-length-independent constant, and it becomes cell length dependent after crossing the critical point. The reflection symmetry and configuration entropy of the atomic displacement are calculated as functions of interaction asymmetry, where a discontinuity appears at the critical point in their second derivatives and thus this crossover behavior is third-order-like. We also find that the sound speed and scaling exponents of energy carriers exhibit a similar crossover owing to the strengthened interaction asymmetry. Our numerical result reveals a peculiar microscopic mechanism for adjusting thermal conduction behavior in phononic superlattice systems.