Unconventional supercondnuctivity in the itinerant ferromagnet UGe; Ge-NQR study under pressure

Harada, Atsushi*; Kawasaki, Shinji*; Mukuda, Hidekazu*; Kitaoka, Yoshio*; Haga, Yoshinori   ; Yamamoto, Etsuji  ; Onuki, Yoshichika; Ito, Kohei*; Haller, E. E.*; Harima, Hisatomo*

The superconducting characteristics on the itinerant ferromagnetic superconductor UGe have been investigated via the Ge-NQR measurements under pressure () near the critical pressure where the first-order transition takes place from the low-temperature () and low- ferromagnetic phase (FM2) to high- and high- one (FM1). The measurements of nuclear spin-lattice relaxation rate have revealed a power-law like behavior as without the coherence peak, whereas at low temperatures, it deviates from the dependence to a -linear like behavior. These results that depend on the pressure are well understood in terms of non-unitary spin-triplet pairing state where the ferromagnetic up-spin band is gapped, but the down-spin band remains gapless at the Fermi level. We will argue an intimate relationship of the onset of SC with FM1 and FM2.