Low-temperature phonon thermal conductivity of single-crystallineNd2CuO4: Effects of sample size and surface roughness

Abstract

The effect of sample size and surface roughness on the phonon thermal conductivity κp of Nd2CuO4 single crystals was studied down to 50 mK. At 0.5 K, κp is proportional to √ A, where A is the cross-sectional area of the sample. This demonstrates that κp is dominated by boundary scattering below 0.5 K or so. However, the expected T 3 dependence of κp is not observed down to 50 mK. Upon roughing the surfaces, the T 3 dependence is restored, showing that departures from T 3 are due to specular reflection of phonons off the mirror-like sample surfaces. We propose an empirical power law fit, to κp ∼ T α (where α < 3) in cuprate single crystals. Using this method, we show that recent thermal conductivity studies of Zn doping in YBa2Cu3Oy re-affirm the universal heat conductivity of d-wave quasiparticles at T → 0. To understand the pairing mechanism in a superconductor, it is essential to know the symmetry of the order parameter. In this context, measurements of lowtemperature thermal conductivity κ, which probes the low-energy quasiparticle excitations, has emerged as a powerful probe of the order parameter in superconductors. For conventional s-wave superconductors with a fully gapped excitation spectrum, the linear-temperature electronic contribution to thermal conductivity is zero at T → 0, i.e. the residual linear term κ 0 /T = 0. This can be seen in the single-gap s-wave superconductor Nb,

Doping evolution of the superconducting gap structure in the underdoped iron arsenideBa1−xKxFe2As2revealed by thermal conducti

“…46, 47 We see that for H = 0, κ 0 /T = 0 for all samples, within error bars. At the highest doping (T c = 37 − 38 K), κ 0 /T remains negligible even when a magnetic field of 15 T is applied.…”

Heat transport inRbFe2As2single crystals: Evidence for nodal superconducting gap

“…The thermal conductivity at very low temperature can be usually fitted to κ/T = a + bT α−1 , in which the two terms aT and bT α represent contributions from electrons and phonons, respectively. The power α is typically between 2 and 3, due to specular reflections of phonons at the boundary [33,34]. Since all the curves in Fig.…”

“…In Fig. 3, the in-plane thermal conductivity of RbFe 2 As 2 single crystal in zero and applied field is plotted as κ/T vs T [33,34]. The thermal conductivity at very low temperature can be usually fitted to κ/T = a + bT α−1 , in which the two terms aT and bT α represent contributions from electrons and phonons, respectively.…”

Fully gapped superconducting state in Au 2 Pb: A natural candidate for topological superconductor

“…3, we present the temperature dependence of the in-plane thermal conductivity for Au 2 Pb single crystal in zero and magnetic fields. The thermal conductivity at very low temperature usually can be fitted to κ/T = a + bT α−1 [31,32], where the two terms aT and bT α represent contributions from electrons and phonons, respectively. In order to obtain the residual linear term κ 0 /T contributed by electrons, we extrapolate κ/T to T = 0 K. Because of the specular reflections of phonons at the sample surfaces, the power α in the second term is typically between 2 and 3 [31,32].…”