title: Superconductivity of the Sr2Ca12Cu24O41 spin-ladder system: are the superconducting pairing and the spin-gap formation of the same origin?
abstract: Pressure-induced superconductivity in a spin-ladder cuprate Sr2Ca12Cu24O41 has not been studied on a microscopic level thus far although the superconductivity was already discovered in 1996. We have improved the high-pressure technique using a large high-quality crystal, and succeeded in studying the superconductivity using 63Cu nuclear magnetic resonance. We found that the anomalous metallic state reflecting the spin-ladder structure is realized and the superconductivity possesses an s-wave-like character in the meaning that a finite gap exists in the quasiparticle excitation: At a pressure of 3.5 GPa, we observed two excitation modes in the normal state from the relaxation rate T-11. One gives rise to an activation-type component in T-11, and the other T-linear component linking directly with the superconductivity. This gapless mode likely arises from free motion of holon-spinon bound states appearing by hole doping, and the pairing of them likely causes the superconductivity.
authors.affiliation: Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan. naokif@issp.u-tokyo.ac.jp
authors.forename: Naoki
authors.initials: N
authors.lastname: Fujiwara
authors.forename: Nobuo
authors.initials: N
authors.lastname: Môri
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Uwatoko
authors.forename: Takehiko
authors.initials: T
authors.lastname: Matsumoto
authors.forename: Naoki
authors.initials: N
authors.lastname: Motoyama
authors.forename: Shinichi
authors.initials: S
authors.lastname: Uchida