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Abstract
Andreev reflection conductance spectra are obtained on nanoscale ballistic junctions between Au tips and single crystals of the pure and Cd-doped heavy-fermion superconductor CeCoIn 5. Background conductance asymmetry starting at the heavy-fermion coherence temperature T* (∼45 K) and increasing with decreasing temperature down to T c (2.3 K) signifies the emerging heavy-fermion liquid in CeCoIn 5. Below T c, enhancement of the sub-gap conductance arises from Andreev reflection, but the Blonder–Tinkham–Klapwijk theory dictates that the Fermi velocity mismatch should yield no Andreev reflection. The signal we do observe is several times weaker than that observed in conventional superconductors, but consistent with other heavy-fermion superconductor data reported. Data taken in the (0 0 1), (1 1 0), and (1 0 0) orientations provide consistent and reliable spectroscopic evidence for d x 2 - y 2 symmetry of the superconducting order parameter. Conductance spectra on the (1 0 0) surface of 10% Cd-doped CeCoIn 5 show intriguing behaviors following antiferromagnetic and subsequent superconducting transitions.
Highlights
The so-called 1-1-5 family of heavy-fermion compounds continue to draw much attention because of their unique physical properties
We have reported Andreev reflection [5] spectroscopy results on CeCoIn5 along three different crystallographic orientations, providing the first spectroscopic evidence for dx2Ày2 symmetry [6,7,8]
Normalized conductance spectra of CeCoIn5 along the two in-plane directions are displayed in Fig. 1, together with calculated conductance curves using the d-wave B.V. doi:10.1016/j.physb.2007.10.228Blonder–Tinkham–Klapwijk (BTK) model [12]
Summary
The so-called 1-1-5 family of heavy-fermion compounds continue to draw much attention because of their unique physical properties. Blonder–Tinkham–Klapwijk (BTK) model [11,12] by considering energy-dependent density of states and two-fluid behavior [13] in heavy fermions. Our conductance spectra on 10% Cd-doped CeCoIn5 reveal signatures for coexisting/competing phases of superconductivity and antiferromagnetism, in line with the reported phase diagram [14].
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