Linear temperature dependence of resistivity and change in the Fermi surface at the pseudogap critical point ofahigh-Tc superconductor

A fundamental question for high-emperature superconductors is the nature of the pseudogap phase, which lies between the Mott insulator at zero doping and the Fermi liquid at high doping p (refs1, 2). Here we report on the behaviour of charge carriers near the zero-temperature onset of this phase, namely at the critical doping p*, where the pseudogap temperature T* goes to zero, accessed by investigating a material in which superconductivity can be fully suppressed by a steady magnetic field. Just below p*, the normal-state resistivity and Hall coefficient of La 1.6x Nd 0.4 Sr x CuO 4 are found to rise simultaneously as the temperature drops below T*, suggesting a change in the Fermi surface with a large associated drop in conductivity. At p*, the resistivity shows a linear temperature dependence as the temperature approaches zero, a typical signature of a quantum critical point. These findings impose new constraints on the mechanisms responsible for inelastic scattering and Fermi-surface transformation in theories of the pseudogap phase.