From Kondo lattices to Kondo superlattices

Abstract

Realization of new classes of ground states in strongly correlated electron systems continues to be a major issue in 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 of their intriguing properties associated with many-body effects. Recently, a state-of-theart molecular beam epitaxy technique was developed to reduce the dimensionality of heavy electron systems by fabricating artificial superlattices that include heavy fermion compounds; this approach can produce a new type of electronic state in two-dimensional (2D) heavy fermion systems. In artificial superlattices of the antiferromagnetic heavy fermion compound CeIn3 and the conventional metal LaIn3, the magnetic order is suppressed by a reduction in the thickness of the CeIn3 layers. In addition, the 2D confinement of heavy fermions leads to enhancement of the effective electron mass and deviation from the standard Fermi liquid electronic properties, which are both associated with the dimensional tuning of quantum criticality. In the superconducting superlattices of the heavy fermion superconductor CeCoIn5 and nonmagnetic metal YbCoIn5, signatures of superconductivity are observed even at the thickness of one unit-cell layer of CeCoIn5. The most remarkable feature of this 2D heavy fermion superconductor is that the thickness reduction of the CeCoIn5 layers changes the temperature and angular dependencies of the upper critical field significantly. This result is attributed to a substantial suppression of the Pauli pair-breaking effect through the local inversion symmetry breaking at the interfaces of CeCoIn5 block layers. The importance of the inversion symmetry breaking in this system has also been supported by site-selective nuclear magnetic resonance spectroscopy, which can resolve spectroscopic information from each layer separately, even within the same CeCoIn5 block layer. In addition, recent experiments involving CeCoIn5/YbCoIn5 superlattices have shown that the degree of the inversion symmetry breaking and, in turn, the Rashba splitting are controllable, offering the prospect of achieving even more fascinating superconducting states. Thus, these Kondo superlattices pave the way for the exploration of unconventional metallic and superconducting states. CONTENTS

Orbitally limited pair-density-wave phase of multilayer superconductors

“…For the sake of clarity of the main text, we include the expressions for the magnetic field H derived from the free energy density for reference here. From equations (2), (10), (11), and (12) we obtain the expression for the applied magnetic field as a function of the variational parameters f ∞ and ξ c at a given magnetic inductionB, which also allows us to obtain an expression for the lower critical field H c1 . The magnetic field reads:…”

Magnetism in f -electron superlattices

“…[1][2][3][4][5][6] Thus, it has become feasible to change the electronic structure and tune the properties of f electron materials. This is particularly important when one thinks of the interesting phenomena which can be observed in these materials, such as magnetism, unconventional superconductivity and quantum criticality.…”

Fate of Majorana Modes in CeCoIn5/YbCoIn5 Superlattices: A Test Bed for the Reduction of Topological Classification

“…The first term denotes the normal part of the Hamiltonian for each layer, while the second term denotes the hopping between the neighboring layers. The Hamiltonian locally breaks the reflection symmetry (i.e., the layer m is mapped to the layer 5 − m.), which leads to the spin-orbit interaction of Rashba type [38][39][40] . The last term represents the pairing potential of superconductors.…”