CeCoIn₅ ("Cerium-Cobalt-Indium 5") is a heavy-fermion superconductor with a layered

crystal structure In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric patterns ...

, 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 A quantum critical point is a point in the phase diagram of a material where a continuous phase transition takes place at absolute zero. A quantum critical point is typically achieved by a continuous suppression of a nonzero temperature phase ...

. 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 superconductor Cuprate superconductors are a family of high-temperature superconducting materials made of layers of copper oxides (CuO2) alternating with layers of other metal oxides, which act as charge reservoirs. At ambient pressure, cuprate superconductor ...

s, 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 Neutron scattering, the irregular dispersal of free neutrons by matter, can refer to either the naturally occurring physical process itself or to the man-made experimental techniques that use the natural process for investigating materials. Th ...

, 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 A scanning tunneling microscope (STM) is a type of microscope used for imaging surfaces at the atomic level. Its development in 1981 earned its inventors, Gerd Binnig and Heinrich Rohrer, then at IBM Zürich, the Nobel Prize in Physics in 1986. ...

(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

{{reflist Superconductors Correlated electrons Cerium compounds Cobalt compounds Indium compounds Intermetallics