From Kondo Lattices to Kondo Superlattices

Abstract

Realizing new classes of ground states in strongly correlated electron systems continues to be at the forefront of condensed matter physics. Heavy-fermion materials, whose electronic structure is essentially three-dimensional, are one of the most suitable systems for obtaining novel electronic states because they demonstrate many fascinating properties. Recently, a state-of-the-art MBE technique has been developed to reduce the dimensionality of the heavy electrons by fabricating heavy fermion superlattices, which can produce new electronic states present in two-dimensional (2D) heavy fermion system. In superlattices of antiferromagnetic heavy fermion CeIn3 and conventional metal LaIn3, the magnetic order is suppressed by reducing the thickness of the CeIn3 layers. The 2D confinement of heavy fermion also leads to the enhancement of the effective mass and the deviation from the Fermi liquid properties, which are associated with the dimensional tuning of quantum criticality. In superconducting superlattices of heavy fermion superconductor CeCoIn5 and nonmagnetic metal YbCoIn5, superconductivity is realized even at one-unit-cell-thick layer of CeCoIn5. The thickness reduction of the CeCoIn5 layers drastically changes the temperature and angular dependencies of the upper critical field. This result would be attributed to a suppression of the Pauli pair-breaking effect through the local inversion symmetry breaking (ISB) at the interfaces of CeCoIn5 block layers. The importance of the ISB in this system has also been supported by site-selective nuclear magnetic resonance spectroscopy. In addition, recent experiment of CeCoIn5/YbCoIn5 superlattices have shown that the degree of the ISB are controllable, which offers the prospect of achieving even more fascinating superconducting states. These Kondo superlattices, thus, pave the way for exploring unusual metallic and superconducting states.