| CeCoIn5 | |
|---|---|
| Name | CeCoIn5 |
| Caption | Crystal structure schematic of CeCoIn5 (tetragonal HoCoGa5-type) |
| Discovery date | 2001 |
| Formula | CeCoIn5 |
| Structure | Tetragonal (HoCoGa5-type) |
| Critical temperature | 2.3 K |
| Superconductivity type | Unconventional, likely d-wave (spin-singlet) |
| Elements | Ce, Co, In |
| Related | CeRhIn5, CeIrIn5, Heavy fermion |
CeCoIn5
CeCoIn5 is a heavy-fermion intermetallic compound and an unconventional superconductor discovered in the family of Ce-based 115 materials. It is a paradigmatic system for studying strong electronic correlations, quantum criticality, and unconventional pairing in condensed matter physics, and has been extensively investigated with spectroscopic, thermodynamic, and transport probes relevant to Quantum Physics.
CeCoIn5 crystallizes in a layered tetragonal HoCoGa5-type structure composed of alternating CeIn3 and CoIn2 layers stacked along the c-axis. The unit cell promotes quasi-two-dimensional electronic anisotropy that strongly influences its Fermi surface topology and superconducting properties. The crystallography was characterized in early reports by single-crystal X-ray diffraction performed at low temperatures and is often compared with sister compounds CeRhIn5 and CeIrIn5, which form the so-called "115" family important to studies of correlated electrons. High-quality single crystals are commonly grown by the flux growth technique using indium flux at laboratories such as the Los Alamos National Laboratory and University of California, San Diego groups that established many experimental benchmarks.
CeCoIn5 exhibits heavy-fermion behavior arising from the hybridization between localized 4f electrons of cerium (Ce) and itinerant conduction electrons derived from cobalt (Co) and indium (In). The Kondo lattice effect and Ruderman–Kittel–Kasuya–Yosida (RKKY) interactions compete, producing a large electronic specific heat coefficient (gamma) indicative of effective masses hundreds of times the free-electron mass. Angle-resolved photoemission spectroscopy (ARPES) and de Haas–van Alphen (dHvA) quantum oscillation experiments map a complex multi-sheet Fermi surface with pronounced two-dimensional character. The energy scales of Kondo coherence and crystal-electric-field (CEF) splitting set the low-temperature renormalized band structure that determines the superconducting instability.
Superconductivity in CeCoIn5 emerges below Tc ≈ 2.3 K and is widely accepted to be unconventional. Thermodynamic measurements (specific heat, thermal conductivity) and phase-sensitive probes point to line nodes in the superconducting gap consistent with sign-changing d-wave pairing, analogous to high-temperature cuprates but in a heavy-fermion context. Nuclear magnetic resonance (NMR) Knight-shift and spin-lattice relaxation rate studies support a predominantly spin-singlet state with strong Pauli-limiting effects; the upper critical field displays first-order transitions and an apparent Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) candidate phase under high magnetic fields and low temperatures. The pairing mechanism is generally attributed to magnetically mediated interactions from antiferromagnetic spin fluctuations, drawing theoretical connections to spin fluctuation theory and models developed by groups at institutions such as Max Planck Institute for Chemical Physics of Solids and Los Alamos National Laboratory.
CeCoIn5 sits near an antiferromagnetic quantum critical point when tuned by pressure, chemical substitution (e.g., partial replacement by Rh or Ir), or magnetic field. Its temperature–field–pressure phase diagram exhibits superconductivity adjacent to non-Fermi-liquid behavior characterized by anomalous resistivity and diverging effective mass. Neutron scattering and muon spin rotation (muSR) detect strong low-energy magnetic fluctuations and incipient antiferromagnetic correlations at particular ordering wave vectors also seen in related heavy-fermion systems. The proximity of superconductivity to quantum criticality makes CeCoIn5 a model system for studying how critical spin fluctuations mediate pairing and how competing orders (magnetism, FFLO, superconductivity) coexist or exclude one another.
Key experimental techniques applied to CeCoIn5 include specific heat and thermal conductivity measurements, NMR and nuclear quadrupole resonance (NQR), inelastic neutron scattering, scanning tunneling microscopy (STM) and spectroscopy (STS), ARPES, and quantum oscillation studies (dHvA). Notable observations include large Sommerfeld coefficients, nodal gap signatures in thermal transport, field-induced phase anomalies interpreted as FFLO-like or magnetically ordered phases, and quasiparticle interference patterns resolved by STM that reveal momentum-dependent gap structure. Experiments have been carried out at specialized facilities such as the National High Magnetic Field Laboratory and neutron sources like the Institut Laue–Langevin.
Theoretical descriptions combine Kondo-lattice models, periodic Anderson model approaches, and spin-fluctuation-mediated pairing calculations. Renormalized band-structure methods (DFT+DMFT) incorporate strong correlations to reproduce heavy quasiparticle bands and the Fermi surface topology measured experimentally. Microscopic mechanisms emphasize antiferromagnetic exchange as the pairing glue, with calculations by many groups using Eliashberg-type formalisms and diagrammatic approaches to analyze gap symmetry and field-induced phases. Competing theoretical proposals address the role of multiband effects, the influence of crystal-electric-field states of Ce 4f orbitals, and the microscopic origin of the FFLO-like phase, linking to broader theories of quantum critical superconductivity explored at universities such as Stanford University and Princeton University.
Category:Heavy-fermion superconductors Category:Intermetallic compounds