Abstract
We have investigated the effect of Yb substitution on the Pauli-limited, heavy-fermion superconductor, CeCoIn5. Yb acts as a non-magnetic divalent substituent for Ce throughout the entire doping range, equivalent to hole doping on the rare-earth site. We found that the upper critical field in (Ce,Yb)CoIn5 is Pauli limited, yet the reduced (H,T) phase diagram is insensitive to disorder, as expected in the purely orbitally limited case. We use the Pauli-limiting field, the superconducting condensation energy and the electronic specific-heat coefficient to determine the Wilson ratio (RW), the ratio of the specific-heat coefficient to the Pauli susceptibility in CeCoIn5. The method is applicable to any Pauli-limited superconductor in the clean limit.
Highlights
Introduction. – Heavy-fermion (HF) systems have been an ideal playground for investigating unconventional superconductivity (SC) since the discovery of SC in this class of materials [1,2]
CeCoIn5 is an ambient pressure SC with Tc = 2.3 K [6] and has the unique feature of an antiferromagnetic (AFM) quantum critical point located near the upper critical field Hc2, indicating that AFM is superseded by SC [7,8]
The change of the SC transition from second to first order for transition temperatures Tc T ∗ ∼ 0.7 Tc0 [9] combined with the discovery of a second SC phase in the large B/T region of the phase diagram lead to the suggestion that CeCoIn5 is the first realization [10,11] of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state [12,13]
Summary
PACS 74.25.Dw – Superconductivity phase diagrams PACS 74.70.Tx – Heavy-fermion superconductors PACS 74.62.Dh – Effects of crystal defects, doping and substitution. Abstract – We have investigated the effect of Yb substitution on the Pauli-limited, heavy-fermion superconductor, CeCoIn5. Much of the attention has been focused on the symmetry of the superconducting order parameter and the interplay/competition between SC and magnetism [3] Such investigations laid ground for magnetism as the origin of Cooper pairing, since SC in HF seems to occur invariably in close proximity to a T = 0 magnetic instability [4]. We report a specific-heat investigation of CeCoIn5 as a function of Yb substitution to Ce. Yb acts as a non-magnetic divalent substituent for Ce throughout the entire doping range, equivalent to hole doping on the rareearth site.
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