Field-angle-resolved anisotropy in superconducting CeCoIn5using realistic Fermi surfaces

Abstract

We compute the field-angle-resolved specific heat and thermal conductivity using realistic model band structure for the heavy-fermion superconductor CeCoIn5 to identify the gap structure and location of nodes. We use a two-band tight-binding parametrization of the band dispersion as input for the self-consistent calculations in the quasiclassical formulation of the superconductivity. Systematic analysis shows that modest in-plane anisotropy in the density of states and Fermi velocity in tetragonal crystals significantly affects the fourfold oscillations in thermal quantities, when the magnetic field is rotated in the basal plane. The Fermi surface anisotropy substantially shifts the location of the lines in the H-T plane, where the oscillations change sign compared to quasicylindrical model calculations. In particular, at high fields, the anisotropy and sign reversal are found even for isotropic gaps. Our findings imply that a simultaneous analysis of the specific heat and thermal conductivity, with an emphasis on the low energy sector, is needed to restrict potential pairing scenarios in multiband superconductors. We discuss the impact of our results on recent measurements of the Ce-115 family, namely CeT In5 with T =Co,Rh,Ir.

Unconventional superconductivity

“…The difference between An et al's C/T work's conclusions about the correct nodal direction (in the [110] direction) and previous somewhat higher temperature C/T (,H) work (Aoki et al [224]) which incorrectly assigned dxy pairing with nodes in the [100] direction is the inversion of the nodal/antinodal directions with lowering temperature in the superconducting state as theoretically explained by Vorontsov and Vekhter [77]. See also Das et al [225].…”

Differential conductance and defect states in the heavy-fermion superconductorCeCoIn5

“…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 explanation for the properties of the superconducting state in CeCoIn 5 have been hampered by insufficient insight into the material's complex electronic bandstructure 16 . This situation, however, has recently changed due to a series of groundbreaking scanning tunneling spectroscopy (STS) experiments [33][34][35] which have yielded unprecedented insight into the electronic structure of the superconducting state, providing strong evidence for its unconventional d x 2 −y 2 -wave symmetry.…”

“…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...…”

Connection between in-plane upper critical fieldHc2and gap symmetry in layeredd-wave superconductors

“…However, there is a longstanding experimental discrepancy in the angular dependence of in-plane H c2 : some experiments found that the maxima of H c2 are along the [110] direction 35 , whereas other experiments observed the maxima of H c2 along the [100] direction 9,36,37 . This discrepancy is regarded as an open puzzle in this field 9,38 , and prevents us from reaching a final consensus on the precise gap symmetry of CeCoIn 5 .…”