Anisotropic Effect of Cd and Hg Doping on the Pauli Limited SuperconductorCeCoIn5

Abstract

We investigated the effect of Cd and Hg doping on the first order superconducting (SC) transition and the high field-low temperature SC state of CeCoIn 5 by measuring the specific heat of CeCo(In 1−x Cd x ) 5 with x=0.0011, 0.0022 and 0.0033 and CeCo(In 1−x Hg x ) 5 with x=0.00016, 0.00032, and 0.00048 at temperatures down to 0.1 K and fields up to 14 T. Cd substitution rapidly suppresses the cross-over temperature T 0 , where the superconducting transition changes from second to first order, to T =0 K with x=0.0022 for H [100], while it remains roughly constant up to x=0.0033 for H [001]. The associated anomaly of the proposed FFLO state in Hg-doped samples is washed out by x=0.00048, while remaining at the same temperature, indicating high sensitivity of that state to impurities. We interpret these results as supporting the non-magnetic, possibly FFLO, origin of the high field -low temperature state in CeCoIn 5 .

Influence of s± symmetry on unconventional superconductivity in pnictides above the Pauli limit – two-band model study

“…It is a clean system [14], with a layered structure suggesting a quasi-2D nature of electrons [15] and the Maki parameter is estimated to be α 5 [16]. Moreover, theoretical works suggest that this phase can exist in the presence of impurities [17][18][19][20][21] and incommensurate spin density waves [22,23], which is consistent with the experimental results [24][25][26][27][28]. Because Fe-based superconductors (FeSC) also have some of these features (they are also layered [29][30][31][32][33][34] clean [35,36] materials with relatively high Maki parameter α ∼ 1−2 [36][37][38][39][40]) we can expect the existence of the FFLO phase [41][42][43].…”

Superconductivity and Non-Fermi-Liquid Behavior in the Heavy-Fermion Compound CeCo1−xNixIn5

“…Nevertheless, M eq (B) seems to change continuously at H c2 , indicating that the first-order transition of the SC breaking by the magnetic field changes into the secondorder one with increasing x. This variation is also found in the other doped alloys, 18,29) and hence, the disorder induced by doping is considered to commonly affect the nature of the transition at H c2 .…”

“…[7][8][9] In magnetic fields, the spin degrees of freedom are significantly coupled with the stability of the SC order; a strong Pauli paramagnetic effect gives rise to a first-order transition at the SC upper critical field H c2 below 0.7 K, 7,[10][11][12] and the SC phase coexistent with AFM spin modulation evolves just below H c2 at very low temperatures. [13][14][15][16][17][18] Furthermore, the existence of the AFM-QCP at ∼ H c2 is strongly suggested from the observations of the NFL behavior in the paramagnetic phase above H c2 , including the − ln T divergence in specific heat divided by temperature, the T -linear dependence in magnetization, and electrical resistivity. 10,19,20) In fact, the long-range AFM orders are generated by substituting the ions for the elements in CeCoIn 5 , such as Nd for Ce, 21,22) Rh for Co, [23][24][25][26] and Cd, Hg, and Zn for In.…”

Behavior of the Quantum Critical Point and the Fermi-Liquid Domain in the Heavy Fermion Superconductor CeCoIn5 Studied by Resistivity

“…[4][5][6] Furthermore, an antiferromagnetic phase has been observed under high magnetic fields in the basal plane, but only inside the superconducting mixed state. [7][8][9][10] CeCoIn 5 is also easily turned antiferromagnetic upon Rh doping, 11) as well as Cd 12) and Hg 13) doping. And back in 2003, it was already discovered by two groups 14,15) that for fields parallel to the c-axis, the range of existence of the Fermi liquid regime seemed to shrink on approaching H c2 (0) from the high field region, pointing to a possible QCP in the immediate vicinity of that field.…”