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arXiv · 0705.2944

Evidence for ferromagnetic spin-pairing superconductivity in UGe$_2$: A $^{73}$Ge-NQR study under pressure

A. Harada·S. Kawasaki·H. Mukuda·Y. Kitaoka·Y. Haga·E. Yamamoto·Y. Onuki·K. M. Itoh·E. E. Haller·H. Harima
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Abstract

We report that a novel type of superconducting order parameter has been realized in the ferromagnetic states in UGe$_2$ via $^{73}$Ge nuclear-quadrupole-resonance (NQR) experiments performed under pressure ($P$). Measurements of the nuclear spin-lattice relaxation rate $(1/T_1)$ have revealed an unconventional nature of superconductivity such that the up-spin band is gapped with line nodes, but the down-spin band remains gapless at the Fermi level. This result is consistent with that of a ferromagnetic spin-pairing model in which Cooper pairs are formed among ferromagnetically polarized electrons. The present experiment has shed new light on a possible origin of ferromagnetic superconductivity, which is mediated by ferromagnetic spin-density fluctuations relevant to the first-order transition inside the ferromagnetic states.

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A. Harada, S. Kawasaki, H. Mukuda, Y. Kitaoka, Y. Haga, E. Yamamoto, Y. Onuki, K. M. Itoh, E. E. Haller, H. Harima. 2007-05-21. Evidence for ferromagnetic spin-pairing superconductivity in UGe$_2$: A $^{73}$Ge-NQR study under pressure. https://doi.org/10.1103/physrevb.75.140502

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