R. W. Hill

Heat Transport in a Strongly Overdoped Cuprate: Fermi Liquid and a Pure d-Wave BCS Superconductor

The transport of heat and charge in the overdoped cuprate superconductor Tl(2)Ba2CuO(6+delta) was measured down to low temperature. In the normal state, obtained by applying a magnetic field greater than the upper critical field, the Wiedemann-Franz law is verified to hold perfectly. In the superconducting state, a large residual linear term is observed in the thermal conductivity, in quantitative agreement with BCS theory for a d-wave superconductor. This is compelling evidence that the electrons in overdoped cuprates form a Fermi liquid, with no indication of spin-charge separation.

Breakdown of Fermi-liquid theory in a copper-oxide superconductor

The behaviour of electrons in solids is well described by Landaus Fermi-liquid theory, which predicts that although electrons in a metal interact, they can still be treated as well defined fermions, which are called ‘quasiparticles’. At low temperatures, the ability of quasiparticles to transport heat is given strictly by their ability to transport charge, as described by a universal relation known as the Wiedemann–Franz law, which hitherto no material has been known to violate. High-temperature superconductors have long been thought to fall outside the realm of Fermi-liquid theory, as suggested by several anomalous properties, but this has yet to be shown conclusively. Here we report an experimental test of the Wiedemann–Franz law in the normal state of a copper-oxide superconductor, (Pr,Ce)2CuO4, which reveals that the elementary excitations that carry heat in this material are not fermions. This is compelling evidence for the breakdown of Fermi-liquid theory in high-temperature superconductors.

Thermal conductivity across the phase diagram of cuprates: Low-energy quasiparticles and doping dependence of the superconducting gap

Heat transport in the cuprate superconductors

Low-energy quasiparticles in cuprate superconductors: A quantitative analysis

{\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{y}

Highly Anisotropic Gap Function in Borocarbide Superconductor LuNi2B2C

and

Quasiparticle Transport in the Vortex State of YBa 2 Cu 3 O 6.9

{\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}

Delocalized fermions in underdoped cuprate superconductors.

was measured at low temperatures as a function of doping. A residual linear term

Low-energy quasiparticles probed by heat transport in the iron-based superconductor LaFePO

{\ensuremath{\kappa}}_{0}/T

A robust and well shielded thermal conductivity device for low temperature measurements

is observed throughout the superconducting region and it decreases steadily as the Mott insulator is approached from the overdoped regime. The low-energy quasiparticle gap extracted from

Quantum oscillatory magnetostriction of the heavy fermion material CeB6

{\ensuremath{\kappa}}_{0}/T