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arXiv · 1901.08699

Enhancement of superconductivity by pressure-induced critical ferromagnetic fluctuations in UCoGe

Masahiro Manago·Shunsaku Kitagawa·Kenji Ishida·Kazuhiko Deguchi·Noriaki K. Sato·Tomoo Yamamura
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Abstract

A $^{59}$Co nuclear quadrupole resonance (NQR) was performed on a single-crystalline ferromagnetic (FM) superconductor UCoGe under pressure. The FM phase vanished at a critical pressure $P_c$, and the NQR spectrum just below $P_c$ showed phase separation of the FM and paramagnetic (PM) phases below Curie temperature $T_{\textrm{Curie}}$, suggesting first-order FM quantum phase transition (QPT). We found that the internal field was absent above $P_c$, but the superconductivity is almost unchanged. This result suggests the existence of the nonunitary to unitary transition of the superconductivity around $P_c$. Nuclear spin-lattice relaxation rate $1/T_1$ showed the FM critical fluctuations around $P_c$, which persist above $P_c$ and are clearly related to superconductivity in the PM phase. This FM QPT is understood to be a weak first order with critical fluctuations. $1/T_1$ sharply decreased in the superconducting (SC) state above $P_c$ with a single component, in contrast to the two-component $1/T_1$ in the FM SC state, indicating that the inhomogeneous SC state is a characteristic feature of the FM SC state in UCoGe.

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Masahiro Manago, Shunsaku Kitagawa, Kenji Ishida, Kazuhiko Deguchi, Noriaki K. Sato, Tomoo Yamamura. 2019-01-25. Enhancement of superconductivity by pressure-induced critical ferromagnetic fluctuations in UCoGe. https://doi.org/10.1103/physrevb.99.020506

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