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内容記述 |
Recently, UTe2 has attracted much interest as a strong candidate for the spin-triplet superconductor due to its large upper critical field exceeding the Pauli limiting field. A lot of experimental and theoretical approaches have been attempted, however, the superconducting symmetry in UTe2 remains unclear and an important problem. To investigate the superconducting symmetry in UTe2, we constructed an “f-d-p model” that is an effective model of UTe2. This model reproduces the quasi-two-dimensional Fermi surfaces and the antiferromagnetic fluctuations peak at (0, 𝜋, 0). Solving the linearized Eliashberg equation within third-order perturbation theory (TOPT) using the f-d-p model, we have obtained the point-node-like s-wave superconducting state as the most likely pairing state. This obtained gap structure is consistent with the specific heat measurements. Nuclear magnetic resonance measurements show the absence of the Hebel-Slichter peak in the spin-lattice relaxation (1/T1). To confirm that the point-node-like s-wave pairing state is consistent with the NMR measurements, we calculated 1/T1 in the f-d-p model. In numerical calculations, we use the gap function of the point-node-like and isotropic s-wave pairing state and compare the scale of the Hebel-Slichter peak in both cases. As a result, we show that although the Hebel-Slichter peak becomes smaller due to the anisotropy of the gap structure, the Hebel-Slichter peak is too large to ignore. Moreover, we show the result of 1/T1 using the random phase approximation (RPA). In the calculation based on RPA, we consider not only the point-node-like s-wave pairing state but also various spin-triplet states, for instance, Au, B1u, B2u, or B3u states. |
