TY - JOUR
T1 - Abrupt enhancement of noncentrosymmetry and appearance of a spin-triplet superconducting state in Li2(Pd1-xPtx) 3B beyond x=0.8
AU - Harada, S.
AU - Zhou, J. J.
AU - Yao, Y. G.
AU - Inada, Y.
AU - Zheng, Guo Qing
PY - 2012/12/3
Y1 - 2012/12/3
N2 - We report synthesis, 195Pt, 11B, and 7Li NMR measurements, and first-principles band calculations for noncentrosymmetric superconductors Li2(Pd1-xPtx)3B (x=0, 0.2, 0.5, 0.8, 0.84, 0.9, and 1). For 0≤x≤0.8, the spin-lattice relaxation rate 1/T 1 shows a clear coherence peak just below Tc, decreasing exponentially at low temperature, and the Knight shift 195K decreases below Tc. For x=0.9 and 1.0, in contrast, 1/T1 shows no coherence peak but a T3 variation and 195K remains unchanged across T c. These results indicate that the superconducting state changes drastically from a spin-singlet dominant to a spin-triplet dominant state at x=0.8. We find that the distortion of B(Pt,Pd)6 increases abruptly above x=0.8, which leads to an abrupt enhancement of the asymmetric spin-orbit coupling as confirmed by band calculation. Such structure distortion that enhances the extent of inversion-symmetry breaking is primarily responsible for the pairing symmetry evolution. The insight obtained here provides a guideline for searching for noncentrosymmetric superconductors with a large spin-triplet component.
AB - We report synthesis, 195Pt, 11B, and 7Li NMR measurements, and first-principles band calculations for noncentrosymmetric superconductors Li2(Pd1-xPtx)3B (x=0, 0.2, 0.5, 0.8, 0.84, 0.9, and 1). For 0≤x≤0.8, the spin-lattice relaxation rate 1/T 1 shows a clear coherence peak just below Tc, decreasing exponentially at low temperature, and the Knight shift 195K decreases below Tc. For x=0.9 and 1.0, in contrast, 1/T1 shows no coherence peak but a T3 variation and 195K remains unchanged across T c. These results indicate that the superconducting state changes drastically from a spin-singlet dominant to a spin-triplet dominant state at x=0.8. We find that the distortion of B(Pt,Pd)6 increases abruptly above x=0.8, which leads to an abrupt enhancement of the asymmetric spin-orbit coupling as confirmed by band calculation. Such structure distortion that enhances the extent of inversion-symmetry breaking is primarily responsible for the pairing symmetry evolution. The insight obtained here provides a guideline for searching for noncentrosymmetric superconductors with a large spin-triplet component.
UR - http://www.scopus.com/inward/record.url?scp=84871100019&partnerID=8YFLogxK
U2 - 10.1103/PhysRevB.86.220502
DO - 10.1103/PhysRevB.86.220502
M3 - Article
AN - SCOPUS:84871100019
SN - 1098-0121
VL - 86
JO - Physical Review B - Condensed Matter and Materials Physics
JF - Physical Review B - Condensed Matter and Materials Physics
IS - 22
M1 - 220502
ER -