CeCoIn5

CeCoIn₅ ("Cerium-Cobalt-Indium 5") is a heavy-fermion superconductor with a layered crystal structure, with somewhat two-dimensional electronic transport properties. The critical temperature of 2.3 K is the highest among all of the Ce-based heavy-fermion superconductors.

Material system

CeCoIn₅ is a member of a rich family of heavy-fermion compounds. CeIn₃ is heavy-fermion metal with cubic crystal structure that orders antiferromagnetically below 10K. With applying external pressure, antiferromagnetism in CeIn₃ is continuously suppressed, and a superconducting dome emerges in the phase diagram near the antiferromagnetic quantum critical point. CeCoIn₅ has a tetragonal crystal structure, and the unit cell of CeCoIn₅ can be considered as 'CeIn₃ with an additional CoIn₂ layer per unit cell'.
Closely related to CeCoIn₅ is the heavy-fermion material CeRhIn₅, which has the same crystal structure and which orders antiferromagnetically below 4K, but does not become superconducting at ambient pressure. At high pressure CeRhIn₅ becomes superconducting with a maximum T_c slightly above 2 K at a pressure around 2 GPa, and at the same pressure the Fermi surface of CeRhIn₅ changes suggesting so-called local quantum criticality.
Also the compound PuCoGa₅, which is a superconductor with T_c approximately 18.5 K and which can be considered an intermediate between heavy-fermion and cuprate superconductors, has the same crystal structure.

Growth of single-crystalline CeCoIn₅ has been very successful soon after the discovery of the material, and large single crystals of CeCoIn₅, such as required for inelastic neutron scattering, have been prepared. (In contrast to some other heavy-fermion compounds where single-crystal growth is more challenging.)

Superconducting properties

The upper critical magnetic field H_c2 of the superconducting state of CeCoIn₅ is anisotropic, in accordance with the crystal structure and other physical properties. For magnetic fields applied along the 00direction, H_c2 amounts to approximately 11.6 T, and H_c2 for fields along the 01directions to 4.95 T.

The superconducting order parameter has d-wave symmetry, as established by several experiments, such as scanning tunneling microscopy (STM) and spectroscopy (STS).

Detailed studies close to the critical field have been performed on CeCoIn₅, and indications were found that certain regimes in the phase diagram of this material should be interpreted in terms of the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase.
Subsequently, the neutron-diffraction experiments showed that this regime features a more complex phase that also exhibits incommensurate antiferromagnetic order, a so-called 'Q phase'.

Evidence for a delocalization quantum phase transition without symmetry breaking is presented.

References

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Superconductors
Correlated electrons
Cerium compounds
Cobalt compounds
Indium compounds
Intermetallics