Thermopower across the stripe critical point ofLa1.6−xNd0.4SrxCuO4: Evidence for a quantum critical point in a hole-doped high-Tcsuperconductor

摘要

The thermopower S of the high-Tc superconductor La(1.6-x)Nd(0.4)Sr(x)CuO(4)was measured as a function of temperature T near its pseudogap critical point,the critical hole doping p* where the pseudogap temperature T* goes to zero.Just above p*, S/T varies as ln(1/T) over a decade of temperature. Below p*,S/T undergoes a large increase below T*. As with the temperature dependence ofthe resistivity, which is linear just above p* and undergoes a large upturnbelow T*, these are typical signatures of a quantum phase transition. Thissuggests that p* is a quantum critical point below which some order sets in,causing a reconstruction of the Fermi surface, whose fluctuations arepresumably responsible for the linear-T resistivity and logarithmicthermopower. We discuss the possibility that this order is the "stripe" orderknown to exist in this material.