paper

Point-contact spectroscopy of the antiferromagnetic superconductor HoNi2B2C in the normal and superconducting state

arXiv:0705.3405 · doi:10.1103/PhysRevB.76.014520

Abstract

Point-contact (PC) spectroscopy measurements on antiferromagnetic (AF) (T_N=5.2K) HoNi2B2C single crystals in the normal and two different superconducting (SC) states (T_c=8.5K and $T_{c}^{*} = 5.6 K) a r er e p or t e d . T h e P C s t u d y o f t h ee l ec t r o n - b oso n (p h o n o n) in t er a c t i o n (E B (P) I) s p ec t r a l f u n c t i o n r e v e a l s p r o n o u n ce d p h o n o nma x imaa t 16, 22 an d 34 m e V . F or t h e f i r s tt im e t h e hi g h e n er g y ma x imaa t ab o u t 50 m e V an d 100 m e V a r er eso l v e d . A dd i t i o na l l y, ana d mi x t u r eo f a cr y s t a l l in e - e l ec t r i c - f i e l d (C E F) e x c i t a t i o n s w i t hama x im u mn e a r 10 m e V an d a ‘ ma g n e t i c ‘ p e ak n e a r 3 m e V a r eo b ser v e d . T h eco n t r ib u t i o n o f t h e 10 - m e V p e ak in P C E P I co n s t an t I^»_{P} C i se v a l u a t e d a s 20 - 30$ T_c^*=5.6K<T_c, with 2Î/kT_c^*=3.9. The strong coupling Eliashberg analysis of the low-temperature SC phase with T_c^*=5.6K =T_N, coexisting with the commensurate AF structure, suggests a sizable value of the EPI constant Î»_s=0.93. We also provide strong support for the recently proposed by us ''Fermi surface (FS) separation'' scenario for the coexistence of magnetism and superconductivity in magnetic borocarbides, namely, that the superconductivity in the commensurate AF phase survives at a special (nearly isotropic) FS sheet without an admixture of Ho 5d states. Above T_c^* the SC features in the PC characteristics are strongly suppressed pointing to a specific weakened SC state between T_c* and T_c.

11 pages, 8 figs, to be published in PRB, Vol.75, Iss.21