Kota Ishihara, Assistant Professor, Kenichiro Hashimoto, Associate Professor, Takasada Shibauchi, Professor, the Department of Advanced Materials Science, the Graduate School of Frontier Sciences (GSFS); and Yuta Mizukami, Associate Professor, the Tohoku University (Assistant Professor, the GSFS, at the time of the project) led the research project.

Abstract

Chiral spin-triplet superconductivity is a topologically nontrivial pairing state with broken time-reversal symmetry, which can host Majorana quasiparticles. The heavy-fermion superconductor UTe₂ exhibits peculiar properties of spin-triplet pairing, and the possible chiral state has been actively discussed. However, the symmetry and nodal structure of its order parameter in the bulk, which determine the Majorana surface states, remains controversial. Here we focus on the number and positions of superconducting gap nodes in the ground state of UTe₂. Our magnetic penetration depth measurements for three field orientations in three crystals all show the power-law temperature dependence with exponents close to 2, which excludes single-component spin-triplet states. The anisotropy of low-energy quasiparticle excitations indicates multiple point nodes near the k_y- and k_z-axes in momentum space. These results can be consistently explained by a chiral B_3u + iA_u non-unitary state, providing fundamentals of the topological properties in UTe₂.　　　　

Article

〈Publication〉    Nature Communications (May 23, 2023)
〈Title〉    Chiral superconductivity in UTe₂ probed by anisotropic low-energy excitations
〈Authors〉    Kota Ishihara*, Masaki Roppongi, Masayuki Kobayashi, Kumpei Imamura, Yuta Mizukami, Hironori Sakai, Petr Opletal, Yoshifumi Tokiwa, Yoshinori Haga, Kenichiro Hashimoto, and Takasada Shibauchi*
〈DOI〉    10.1038/s41467-023-38688-y
〈URL〉    https://www.nature.com/articles/s41467-023-38688-y