Zooming on the quantum critical point in Nd-LSCO

Recent studies of the high-T(c) superconductor La(1.6-x)Nd(0.4)Sr(x)CuO(4) (Nd-LSCO) have found a linear-T inplane resistivity rho(ab) and a logarithmic temperature dependence of the thermopower S/T at a hole doping p = 0.24 and a Fermi-surface reconstruction just below p = 0.24 [1,2]. These are typical signatures of a quantum critical point (QCP). Here we report data on the c-axis resistivity rho(c)(T) of Nd-LSCO measured as a function of temperature near this QCP, in a magnetic field large enough to entirely suppress superconductivity. Like rho(ab), rho(c) shows an upturn at low temperature, a signature of Fermi surface reconstruction caused by stripe order. Tracking the height of the upturn as it decreases with doping enables us to pin down the precise location of the QCP where stripe order ends, at p* = 0.235 +/- 0.005. We propose that the temperature T(p) below which the upturn begins marks the onset of the pseudogap phase, found to be roughly twice as high as the stripe-ordering temperature in this material. (C) 2009 Elsevier B.V. All rights reserved.