Non-magnetic impurity effects in antiferromagnetic superconductor DyNi₂B₂C

Abstract

Abstract. Borocarbide DyNi2B2C is an antiferromagnetic superconductor exhibiting an intriguing property of the superconducting transition within the stable antiferromagnetic structure. Such a salient feature provides a possible stage for the antiferromagnetismdriven exotic superconductivity. We investigate the effect of non-magnetic impurities on the superconductivity in DyNi2B2C by the substitution of Ni for Pt in order to verify the possibility of non-s-wave superconductivity in this compound. In the polycrystalline samples, the superconducting transition temperature Tc in DyNi2B2C with Tc = 5.5 K is rapidly suppressed in Dy(Ni1−xPtx)2B2C where the x = 0.03 substitution lowers the Tc down to Tc < 2 K. Such a remarkable suppression of the superconductivity strongly suggests the realization of the non-s-wave superconductivity in DyNi2B2C. IntroductionQuaternary borocarbides RNi 2 B 2 C (R = Tb, Dy, Ho, Er, Tm) have attracted much interest for more than a decade due to the interplay of magnetism and superconductivity [1]. DyNi 2 B 2 C is one of the magnetic borocarbides where superconductivity coexists with longrange antiferromagnetic (AF) ordering. The salient feature of this compound is that the superconducting transition at T c = 6.0 K occurs within the AF phase with the Néel temperature T N = 10.6 K: T c < T N [2]. The AF structure of the Dy sublattice in DyNi 2 B 2 C, as depicted in Fig. 1, has the wave vector Q 0 = (0, 0, 1) where ferromagnetically aligned ab planes stack antiparallel along the c direction [2].Since the ferromagnetic ab sheets in the AF structure in DyNi 2 B 2 C can disturb the in-plane Cooper pair formation, it is expected that the pairing mechanism, or the superconducting gap structure of DyNi 2 B 2 C is different from the non-magnetic borocarbides YNi 2 B 2 C and LuNi 2 B 2 C which are considered to be anisotropic s-wave superconductors [3,4]. Recently, possibility of a new exotic superconductivity which can be realized within AF phase has been discussed in an AF heavy-fermion superconductor UPd 2 Al 3 [5]. Similar to DyNi 2 B 2 C, UPd 2 Al 3 meets the condition T c < T N , and has the AF structure where the ferromagnetic ab sheets are stacked antiparallel along the c direction. In UPd 2 Al 3 , unconventional superconductivity with d-wave symmetry mediated by the AF fluctuation has been suggested experimentally [6]. It is worthwhile, therefore, to verify the possibility of unconventional superconductivity also in DyNi 2 B 2 C.