cuprate superconductors*

The pairing symmetry of high-T_c cuprate superconductors has been unsolved over 30 years. Most researchers have believed that the pairing symmetry is d_x2_-y2 (d) wave, nevertheless, several objections have been still suggested. Recently the objection was also disclosed [1]. We reanalyze the data of thermal conductivity, κ, announced as experimental evidence of d-wave symmetry, which showed the presence of a finite value at nearest T=0 K in a curve of κ/T vs T² in thermal conductivity [2]. This is the metal characteristic coming from the nodes of the d-wave electronic structure of clover [2]. The characteristic of the curve of κ/T vs T² increases a residual linear value of κ/T with going to T=0 K, which does not describe the pairing symmetry characteristic of κ. We redrew the curve of κ/T vs T² to the curve of κ vs T, deduced experimental data below 0.2 K unobservable by experiment through polynomial fitting, and discovered the behavior of the conductivity with nonlinear and no residual linear value. This is evidence denying d-wave symmetry, rather, supports s-wave symmetry. [1] arXiv:1710.07754. [2] M. Sutherland et al., Phys, Rev. B 67, 174520 (2003).