Two-channel point-contact tunneling theory of superconductors

Abstract

We introduce a two-channel tunneling model to generalize the widely used BTK theory of point-contact conductance between a normal metal contact and superconductor. Tunneling of electrons can occur via localized surface states or directly, resulting in a Fano resonance in the differential conductance $G=dI/dV$. We present an analysis of $G$ within the two-channel model when applied to soft point-contacts between normal metallic silver particles and prototypical heavy-fermion superconductors CeCoIn${}_5$ and CeRhIn${}_5$ at high pressures. In the normal state the Fano line shape of the measured $G$ is well described by a model with two tunneling channels and a large temperature-independent background conductance. In the superconducting state a strongly suppressed Andreev reflection signal is explained by the presence of the background conductance. We report Andreev signal in CeCoIn${}_5$ consistent with standard $d_{x^2-y^2}$-wave pairing, assuming an equal mixture of tunneling into [100] and [110] crystallographic interfaces. Whereas in CeRhIn${}_5$ at 1.8 and 2.0 GPa the signal is described by a $d_{x^2-y^2}$-wave gap with reduced nodal region, i.e., increased slope of the gap opening on the Fermi surface. A possibility is that the shape of the high-pressure Andreev signal is affected by the proximity of a line of quantum critical points that extends from 1.75 to 2.3 GPa, which is not accounted for in our description of the heavy-fermion superconductor.

13 pages, 13 figures

References in corpus (15)

• "Deconfined" quantum critical points
• Quantum criticality
• Hidden Magnetism and Quantum Criticality in the Heavy Fermion Superconductor CeRhIn5
• Imaging the Fano Lattice to 'Hidden Order' Transition in URu2Si2
• Visualizing heavy fermions emerging in a quantum critical Kondo lattice
• Andreev Reflection in Heavy-Fermion Superconductors and Order Parameter Symmetry in CeCoIn_5
• Electron Cotunneling into a Kondo Lattice
• Spectroscopic Evidence for Multiple Order Parameter Components in the Heavy Fermion Superconductor CeCoIn_5
• Electronic Duality in Strongly Correlated Matter
• Quantum waveguide theory of Andreev reflection in multiband superconductors: the case of Fe-pnictides
• Probing the nodal gap in the pressure-induced heavy fermion superconductor CeRhIn5
• The Fano effect in the point contact spectroscopy of heavy electron materials
• Point-contact spectroscopy in heavy-fermion superconductors
• Andreev reflection and order parameter symmetry in heavy-fermion superconductors: the case of CeCoIn${}_5$
• Electron transmission in normal/heavy-fermion superconductor junctions

Cited by in corpus (3)

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• Hybridization-Controlled Pseudogap State in the Quantum Critical Superconductor CeCoIn5
• Long-time joint spectra and entanglement of two photoelectrons originating in interacting auto-ionization systems