第4回 物理工学科教室談話会（講師：Prof. S. Ramakrishnan）
|講 師：||Prof. S. Ramakrishnan（Tata Institute of Fundamental Research, Mumbai, India）|
|題 目：||Noncentrosymmetric superconductivity in a clean crystal of type-II superconductor Bi-Pd|
The term ”noncentrosymmetric” characterizes the symmetry of a crystal lattice without inversion center.
In such materials the standard classification in even-parity spin-singlet and odd-parity spin triplet superconducting phases is obsolete,
because the electrons are exposed to anti-symmetric spin-orbit coupling, e.g.
Rashba-type of coupling which arises due to electric field gradient in the crystal which has no inversion symmetry.
An inherent feature is then the mixing of spin-singlet and spin-triplet Cooper pairing channels which are otherwise distinguished by parity.
This mixing of pairing states is expected to cause a two-component order parameter.
We have established1 the bulk superconductivity of a high-quality single crystal of monoclinic BiPd (a-BiPd, space group P21) below 3.8 K by studying its electrical resistivity,
magnetic susceptibility, and heat capacity.
This is the cleanest noncentrosymmetric superconductor that display anisotropy due to spin-orbit scattering and also exhibits unusual superconducting properties
due to s and p wave mixing as evidenced by the observation of Andreev bound state and multiple energy gaps via point contact measurements2.
Moreover, Fermi surface studies suggest multiband superconductivity in this compound3.
Muon spin rotation measurements indicate4 strong field dependence of the Ginzburg-Landau coefficient of this superconductor.
1.. Bhanu Joshi, A. Thamizhavel, and S. Ramakrishnan, Phys. Rev. B 84, 064518 (2011).
2.. Mintu Mondal, Bhanu Joshi, Sanjeev Kumar, Anand Kamlapure, Somesh Chandra Ganguli, Arumugam Thamizhavel, Sudhansu S. Mandal, Srinivasan Ramakrishnan, and Pratap Raychaudhuri, Phys. Rev. B 86, 094520 (2012).
3.. To be published.
4.. To be published.