Interlayer magnetotransport in the overdoped cuprate Tl₂Ba ₂CuO_6+x: Quantum critical point and its downslide in an applied magnetic field

Abstract

Fundamental explanations of high-temperature (high- Tc) superconductivity must account for the profound differences in the properties of the "normal" (nonsuperconducting) state at the two extremes of charge doping: heavy and light. On the light doping side, its properties clearly violate the standard Fermi-liquid theory of metals. The key to the nature of superconducting pairing lies in understanding the transition to a conventional behavior on the overdoped side. We report a convergence of the pseudogap energy scale and the boundary that separates unconventional from a conventional metal in the zero-temperature limit, both boundaries framing a V-shaped area of "strange metal" state in the temperature-doping phase space. By accessing the low-temperature regions of the phase diagram via a high-field interlayer magnetotransport in heavily doped Tl2Ba 2CuO6+x, we show that the pseudogap boundary has the hallmarks of a quantum phase transition with a zero entropy jump. The critical doping (linkage) point consistently downshifts with magnetic field in unison with the suppression of Tc, suggesting that quantum critical fluctuations that destabilize the pseudogap are connected to the superconductivity with high- Tc. © 2010 The American Physical Society.