Superconductivity in charge Kondo systems

Topological quantum materials hold great promise for future technological applications. Their unique electronic properties, such as protected surface states and exotic quasiparticles, offer opportunities for designing novel electronic devices, spintronics, and quantum information processing. The origin of the interplay between various electronic orders in topological quantum materials, such as superconductivity and magnetism, remains unclear, particularly whether these electr...

In this study, a possible non-quasiparticle glue for superconductivity of both conventional and unconventional superconductors is explored in a pure electron picture. It is shown clearly that the moving electrons due to the electromagnetic interaction can self-organize into some quasi-one-dimensional real-space charge stripes, which can further form some thermodynamically stable vortex lattices with trigonal or tetragonal symmetry. The relationships among the charge stripes, ...

We find new mechanism of superconductivity beyond the spin-fluctuation theory, the standard model for unconventional superconductivity in the weak coupling approach, where Kondo fluctuations result in multi-gap superconductivity around an antiferromagnetic quantum critical point of the slave-fermion theory. Fingerprints of the hybridization mechanism are two kinds of resonance modes in not only spin but also charge fluctuations, originating from $d-wave$ pairing of conduction...

A recent analysis of optical conductivity data which has provided strong evidence for coupling of the charge carriers to the 41 meV spin resonance, seen in the superconducting state of optimally doped Y123, is extended to other systems. We find that the corresponding spin resonance is considerably broader in Tl2201 and Y124 than it is in Bi2212. On the other hand, in overdoped Tl2201 with T_c = 23 K no resonance forms. A more specific interpretation of the optical data in ter...

It is argued that a new mechanism and many-body theory of superconductivity are required for doped correlated insulators. Here we review the essential features of and the experimental support for such a theory, in which the physics is driven by the kinetic energy.

We propose a possible charge fluctuation effect expected in layered superconducting materials. In the multireference density functional theory, relevant fluctuation channels for the Josephson coupling between superconducting layers include the interlayer pair hopping derived from the Coulomb repulsion. When interlayer single-electron tunneling processes are irrelevant in the Kohn-Sham electronic band structure calculation, the two-body effective interactions stabilize a super...

A review of the low temperature properties of Kondo lattice systems is presented within the mean-field approximation, focusing on the different characteristic energy scales. The Kondo temperature, T_K, and the Fermi liquid coherence energy, T_0, are analyzed as functions of the electronic filling, the shape of the non-interacting density of states, and the concentration of magnetic moments. These two scales can vanish, corresponding to a breakdown of the Kondo effect when an ...

The interplay of magnetic energies in a Kondo lattice is the underlying physics of a heavy fermion system. Creating an artificial Kondo lattice system by localizing the moments in an ordered metallic array provides a prototype system to tune and study the energetic interplay while avoiding the complications introduced by random alloying of the material. In this article, we create a Kondo lattice system by fabricating a hexagonally ordered nanostructured array using niobium as...

The Kondo effect, an eminent manifestation of many-body physics in condensed matter, is traditionally explained as exchange scattering of conduction electrons on a spinful impurity in a metal. The resulting screening of the impurity's local moment by the electron Fermi sea is characterized by a Kondo temperature $T_K$, below which the system enters a non-perturbative strongly-coupled regime. In recent years, this effect has found its realizations beyond the bulk-metal paradig...

In these lecture notes of the Autumn School on Correlated Electrons 2017 I discuss the relationships among the Kondo physics and the Mott transition.