講演者： Huiqui Yuan 氏（Natinal High Magnetic Field Lab. Los Alamos）
日時：１２月　５日（水）　午後３時００分から
場所： 青山学院大学　理工学部（相模原キャンパス）Ｌ棟６階　Ｌ６０３室

題目： 「Superconductivity in materials without inversion symmetry」

要旨：
　The recent discovery of superconductivity in heavy fermion system CePt3Si has 
stimulated tremendous efforts to reveal the novel superconducting pairing state
 in materials lacking inversion symmetry. In this talk, I will present the results 
of magnetic penetration depth for the cubic systems Li2(Pd1-xPtx)3B and Y2C3.
 These materials lack inversion symmetry and show no evidence of magnetism or 
heavy fermion behavior, therefore providing us a great opportunity to study 
broken parity superconductivity.
 The low temperature penetration depth  (T) shows an exponential behavior in 
Li2Pd3B, but follows a linear temperature dependence in Li2Pt3B. These results 
are best understood as arising from the admixing of spin-singlet and spin-triplet 
order parameters [H. Q. Yuan, et al., Phys. Rev. Lett. 97, 017006 (2006)], which 
is only allowed when inversion symmetry is broken. The triplet contribution is weak 
in Li2Pd3B, a BCS-like superconductor with an anisotropic gap. 
With increased spin-orbit coupling, the spin-triplet component dominates in Li2Pt3B, 
producing line nodes in the energy gap. Upon substituting Pd with Pt, we found that 
the triplet component eventually develops with increasing the Pt-content x. The 
existence of (T) ~ T over a wide Pd/Pt doping region indicates that the triplet state 
is rather robust against impurity scattering in non-centrosymmetric superconductors.
 In Y2C3, the low temperature penetration depth shows a weak linear temperature 
dependence, suggesting the existence of nodes in the superconducting energy gap.
 Again we attribute it to the admixture of spin singlet and spin-triplet states, 
as a result of broken inversion symmetry.

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共催：　青山学院大学　理工学会