Nodal to Nodeless Superconducting Energy-Gap Structure Change Concomitant with Fermi-Surface Reconstruction in the Heavy-Fermion CompoundCeCoIn5

Pressure studies of the quantum critical alloyCe0.93Yb0.07CoIn5

“…Recall that according to the recent thermopower measurements and subsequent theoretical studies 28,29 of the parent compound CeCoIn 5 , the Fermi pockets near the M -points remain ungapped giving rise to the nonzero thermal conductivity in the superconducting state. If we now consider the results of the recent penetration depth measurements that show the disappearance of the nodes in the superconducting order parameter for x nom ≈ 0.2, 17 we conclude that with Yb doping: (a) both Fermi surfaces must be gapped below T c due to the proximity pairing effect, and (b) the absence of the nodes in the superconducting order parameter for x nom ≥ 0.2 suggest that the order parameter may have exotic symmetry, either d+ is or d+ id. 30 The d-component must be present since the order parameter of the parent compound CeCoIn 5 has d x 2 −y 2 symmetry, 31,32 while the conventional s-wave superconductivity can be ruled out due to monotonous concentration dependence of T c .…”

“…16 More recently, penetration depth measurements 17 have shown the disappearance of the nodes in the superconducting order parameter for x nom ≥ 0.2. The emergent physical picture which describes the physics of these alloys is based on the notion of coexisting electronic networks coupled to conduction electrons: one is the network of cerium ions in a local moment regime, while the other consists of ytterbium ions in a strongly intermediate-valence regime.…”

Resolution of the discrepancy between the variation of the physical properties of Ce1-xYbxCoIn5single crystals and thin films with Yb composition

“…Wavelength dispersive x--ray spectroscopy (WDS) measurements were performed using a JEOL JXA--8200 electron microprobe on all samples used in the London penetration depth study [Kim14] [Booth11,Dudy13]. This result provides direct evidence that Yb substitution induces hole doping, similar to Cd substitution [Pham06].…”

“…[Shu11,White12,Hu13,Dudy13,Singh14,Kim14,Song14], the wavelength dispersive x--ray spectroscopy (WDS) measurements were performed at Iowa State University, Ames National Laboratory, on samples studied in the penetration depth experiments and on several other samples with different Yb concentrations [Kim14], while the transmission x--ray absorption edge spectroscopy (TXAS) measurements were performed at the Stanford Synchrotron Radiation Laboratory on samples specifically prepared for the TXAS measurements. The EDS, WDS, and TXAS measurements are discussed in more detail below.…”

Differential conductance and defect states in the heavy-fermion superconductorCeCoIn5

“…CeCoIn 5 1 has long been considered the "hydrogen atom" of heavy fermion superconductivity [2][3][4][5][6][7][8] , and much experimental [9][10][11][12][13][14][15][16][17][18][19] and theoretical effort [20][21][22][23][24][25][26][27] has focused on illuminating its unconventional properties [28][29][30][31][32] , and the microscopic mechanism underlying the emergence of superconductivity. While a variety of experimental probes have reported evidence for the existence of nodes [9][10][11][12] , a sign change of the superconducting (SC) order parameter along the Fermi surface 13,14 , and spinsinglet pairing 11,12 , theoretical efforts [20][21][22][23][24][25][26] to provide a quantitative or even qualitative exp...…”