title: Kramers non-magnetic superconductivity in LnNiAsO superconductors.
abstract: We investigated a series of nickel-based oxyarsenides LnNiAsO (Ln=La, Ce, Pr, Nd, Sm) compounds. CeNiAsO undergoes two successive anti-ferromagnetic transitions at TN1=9.3 K and TN2=7.3 K; SmNiAsO becomes an anti-ferromagnet below TN≃3.5 K; NdNiAsO keeps paramagnetic down to 2 K but orders anti-ferromagnetically below TN≃1.3 K. Superconductivity was observed only in Kramers non-magnetic LaNiAsO and PrNiAsO with Tc=2.7 K and 0.93 K, respectively. The superconductivity of PrNiAsO is further studied by upper critical field and specific heat measurements, which reveal that PrNiAsO is a weakly coupled Kramers non-magnetic superconductor. Our work confirms that the nickel-based oxyarsenide superconductors are substantially different in mechanism to iron-based ones, and are likely to be described by the conventional superconductivity theory.
authors.affiliation: Department of Physics and Hangzhou Key Laboratory of Quantum Matters, Hangzhou Normal University, Hangzhou 310036, People's Republic of China.
authors.forename: Yuke
authors.initials: Y
authors.lastname: Li
authors.forename: Yongkang
authors.initials: Y
authors.lastname: Luo
authors.forename: Lin
authors.initials: L
authors.lastname: Li
authors.forename: Bin
authors.initials: B
authors.lastname: Chen
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Xu
authors.forename: Jianhui
authors.initials: J
authors.lastname: Dai
authors.forename: Xiaojun
authors.initials: X
authors.lastname: Yang
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: Guanghan
authors.initials: G
authors.lastname: Cao
authors.forename: Zhu-an
authors.initials: ZA
authors.lastname: Xu