CeCoIn<sub>5</sub> ("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.
CeCoIn<sub>5</sub> is a member of a rich family of heavy-fermion compounds. CeIn<sub>3</sub> is heavy-fermion metal with cubic crystal structure that orders antiferromagnetically below 10K. With applying external pressure, antiferromagnetism in CeIn<sub>3</sub> is continuously suppressed, and a superconducting dome emerges in the phase diagram near the antiferromagnetic quantum critical point. CeCoIn<sub>5</sub> has a tetragonal crystal structure, and the unit cell of CeCoIn<sub>5</sub> can be considered as 'CeIn<sub>3</sub> with an additional CoIn<sub>2</sub> layer per unit cell'. Closely related to CeCoIn<sub>5</sub> is the heavy-fermion material CeRhIn<sub>5</sub>, which has the same crystal structure and which orders antiferromagnetically below 4K, but does not become superconducting at ambient pressure. At high pressure CeRhIn<sub>5</sub> becomes superconducting with a maximum T<sub>c</sub> slightly above 2 K at a pressure around 2 GPa, and at the same pressure the Fermi surface of CeRhIn<sub>5</sub> changes suggesting so-called local quantum criticality. Also the compound PuCoGa<sub>5</sub>, which is a superconductor with T<sub>c</sub> 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 CeCoIn<sub>5</sub> has been very successful soon after the discovery of the material, and large single crystals of CeCoIn<sub>5</sub>, 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.)
The upper critical magnetic field H<sub>c2</sub> of the superconducting state of CeCoIn<sub>5</sub> is anisotropic, in accordance with the crystal structure and other physical properties. For magnetic fields applied along the [100] direction, H<sub>c2</sub> amounts to approximately 11.6 T, and H<sub>c2</sub> for fields along the [001] directions 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 CeCoIn<sub>5</sub>, and indications were found that certain regimes in the phase diagram of this material should be interpreted in terms of the FuldeâÂÂFerrellâÂÂLarkinâÂÂOvchinnikov (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.