Angular Position of Nodes in the Superconducting Gap of YBCO

Abstract

The thermal conductivity of a YBa 2 Cu 3 O 6.9 detwinned single crystal has been studied as a function of the relative orientation of the crystal axes and a magnetic field rotating in the Cu-O planes. Measurements were carried out at several different temperatures below T c (0.5 K < T< 25 K) and at a fixed field of 30 kOe. A four-fold symmetry characteristic of a superconducting gap with nodes at odd multiples of 45 degrees in k-space was resolved. Experiments were performed to exclude a possible macroscopic origin for such a four-fold symmetry such as sample shape or anisotropic pinning. Our results impose an upper limit of 10% on the weight of the s-wave component of the essentially d-wave superconducting order parameter of YBCO. 74.25.Fy, 74.72.Bk, 72.15.Eb Typeset using REVT E X 1

Identification of the bulk pairing symmetry in high-temperature superconductors: Evidence for an extendedswave with eight line nodes

“…[38]). Moreover, thermal conductivity of YBCO as a function of angle of an inplane magnetic field relative to the crystal axes has been studied both theoretically and experimentally [39,40]. A theoretical calculation for the angular dependence of the magnetothermal conductivity [39] shows that an extended s-wave gap produces a more symmetric angular variation than a d-wave gap.…”

Superconducting Gap Structure ofκ−(BEDT−TTF)2Cu(NCS)2Izawa1, Yamaguchi2, Sasaki3 et al. 2001Phys. Rev. Lett.217101403View full textAdd to dashboardCite

“…Third and most importantly, it is indeed a directional probe, sensitive to the relative orientation among the thermal flow, the magnetic field, and nodal directions of the order parameter, as we will discuss in detail later. In fact, a clear fourfold modulation of the in-plane thermal conductivity κ with an in-plane magnetic field which reflects the angular position of nodes of d x 2 −y 2 symmetry was observed in YBa 2 Cu 3 O 7−δ [12,13] and 2D heavy fermion superconductor CeCoIn 5 [18], while such a modulation was absent in Nb and the B-phase of UPt 3 with an isotropic gap in the basal plane [13,19]. These fact demonstrate that the thermal conductivity tensor can be a relevant probe of the superconducting gap structure.…”

“…In particular, it was demonstrated both experimentally and theoretically that the thermal conductivity is a powerful tool for probing the anisotropic gap structure [12][13][14][15][16][17][18]. Thermal conductivity has some advantages, compared to other experiments.…”

Evidence for Nodal Quasiparticles in the Nonmagnetic SuperconductorYNi2B2Cvia Field-Angle-Dependent Heat Capacity

“…Unlike gapless superconductivity, which can occur in conventional superconductors, the Fermi momenta of these quasiparticles are restricted to nodal regions of the Fermi surface, giving a strong directional dependence to various physical properties. While pioneering work by Salamon and coworkers [1,2] and by subsequent experimenters [3,4] demonstrated the directionality of thermally excited nqp's via the thermal conductivity, direct detection has proven elusive.…”