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

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

doi:10.1103/PhysRevB.99.020506

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

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

DOI 10.1103/PhysRevB.99.020506 · Physical Review B

T1

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Abstract

A Co59 nuclear quadrupole resonance (NQR) was performed on a single-crystalline ferromagnetic (FM) superconductor UCoGe under pressure. The FM phase vanished at a critical pressure Pc, and the NQR spectrum just below Pc showed phase separation of the FM and paramagnetic (PM) phases below Curie temperature TCurie, suggesting first-order FM quantum phase transition (QPT). We found that the internal field was absent above Pc, but the superconductivity is almost unchanged. This result suggests the existence of the nonunitary to unitary transition of the superconductivity around Pc. Nuclear spin-lattice relaxation rate 1/T1 showed the FM critical fluctuations around Pc, which persist above Pc 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/T1 sharply decreased in the superconducting (SC) state above Pc with a single component, in contrast to the two-component 1/T1 in the FM SC state, indicating that the inhomogeneous SC state is a characteristic feature of the FM SC state in UCoGe.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
UCoGe Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	0.46	Pressure unresolved	onset
UCoGe Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	0.46	0.67 GPa	onset
UGe2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown
URhGe Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown