Anomalous enhancement of the Nernst effect at the crossover between a Fermi liquid and a strange metal

A strange-metal state appears in many strongly correlated materials, so understanding its nature is a crucial problem in condensed matter physics. This knowledge could provide important insight into high-temperature superconductivity and quantum criticality, but standard Fermi-liquid theory fails in strange metals. Establishing an alternative theory has been a long-standing challenge and fundamental aspects of strange metals-including the nature of their charge carriers-remain elusive. Here we report the observation of a large Nernst response in the strange-metal state in a two-dimensional superconductor 2M-WS2. Specifically, when the system enters the strange-metal state from the Fermi-liquid state, the Nernst coefficient increases to be comparable to the vortex Nernst signal in superconducting cuprates, and it is highly sensitive to carrier mobility. The temperature and magnetic field dependence of the Nernst peak rule out the relevance of both Landau quasiparticles and superconductivity. Instead, the Nernst peak at the crossover indicates a change in carrier entropy when entering the strange-metal state. The presence of such an anomalous Nernst response is further confirmed in other iconic strange metals, suggesting its universality and places experimental constraints on the mechanism of strange metals. The transport behaviour of strange metals is distinct from weakly interacting Fermi liquids. Now, a large thermoelectric response has been shown at the transition between those two states.