Floquet engineering multi-channel Kondo physics

Abstract

Floquet engineering is a powerful technique using periodic potentials, typically laser light, to drive materials into regimes inaccessible in equilibrium. Here, we show that Kondo models can be driven to multi-channel degenerate points, even when the starting model is single-channel. These emergent channels are differentiated by symmetry, and their strength and number can be controlled by changing the light polarization, frequency and amplitude. Unpolarized light, constructed by polarization averaging, is particularly useful to induce three and four channel degeneracies. Multichannel Kondo models host a wide variety of exotic phenomena, including non-Abelian anyons in impurity models and composite pair superconductivity in lattice models. We demonstrate our findings on both a simple square lattice toy model and a more realistic spin-orbit coupled model for J = 5/2 Ce ions in a tetragonal environment, as relevant for the Ce 115 materials, and show that the transition temperature for composite pair superconductivity can be dynamically enhanced.

Control of Yu-Shiba-Rusinov States through a Bosonic Mode

“…This raises the question of how YSR states can be manipulated in a controlled manner [11,12]. A versatile pathway to control properties of solids is periodic driving (Floquet engineering), which can be used to manipulate both quantum impurities [13][14][15][16] as well as bulk properties [17,18], such as band structures [19][20][21], magnetic interactions [22][23][24] and superconductivity [25][26][27][28][29]. However, strong driving with time-dependent classical electromagnetic fields inevitably leads to heating via (multi-)photon absorption.…”

“…By embedding the impurity which gives rise to YSR states into a cavity, the electromagnetic field can either couple directly to the electron tunnelling between the impurity and the host, or through infrared active vibrations which in turn interact with the electronic states at the impurity. For a magnetic impurity in the Anderson model coupled to two normal metal leads, both Floquet engineering by a classical electric field [15,16] and coupling to a center of mass vibrational mode [40] have been predicted to give rise to two-channel Kondo physics. One can therefore expect that strong coupling to a photon or phonon can also open additional channels for the emergence of YSR states.…”