Novel anisotropy in the superconducting gap structure of   Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta} probed by quasiparticle heat transport
  Since the nature of pairing interactions is manifested in the superconducting gap symmetry, the exact gap structure, particularly any deviation from the simple d_{x^2-y^2} symmetry, would help elucidating the pairing mechanism in high-T_c cuprates. Anisotropic heat transport measurement in Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta} (Bi-2212) reveals that the quasiparticle populations are different for the two nodal directions and thus the gap structure must be uniquely anisotropic, suggesting that pairing is governed by interactions with a rather complicated anisotropy. Intriguingly, it is found that the "plateau" in the magnetic-field dependence of the thermal conductivity is observed only in the b-axis transport. 
Yoichi Ando, J. Takeya, Yasushi Abe, X. F. Sun, and A. N. Lavrov   (CRIEPI)