Floquet states in (LaNiO$_3$)$_2$/(LaAlO$_3$)$_N$ heterostructures grown along the (111) direction

TL;DR

This paper explores how circularly and linearly polarized light can be used to control the electronic band structure of LaNiO3/LaAlO3 heterostructures grown along the (111) direction, revealing tunable Floquet states and band touchings.

Contribution

It introduces a detailed Floquet-Bloch theoretical framework to analyze light-induced modifications of the electronic structure in LaNiO3/LaAlO3 heterostructures, including effective Hamiltonians and optical conductivity calculations.

Findings

Light amplitude can independently tune first and second-neighbor hopping.

Quadratic and Dirac band touchings are sensitive to light polarization and intensity.

The extended oxygen p-orbital model agrees with the nickel d-orbital effective model.

Abstract

Using Floquet-Bloch theory we study the effect of circularly and linearly polarized light on the electronic structure of (LaNiO$_3$)$_2$/(LaAlO$_3$)$_N$ heterostructure grown along the (111) direction. In equilibrium, a tight-binding fit to the first principles band structure shows that nearest-neighbor hopping plays a dominant role while second-neighbor hopping breaks the particle-hole symmetry and determines the finer band features. The four bands of the LaNiO$_3$ bilayer exhibit both quadratic band touching points and Dirac points. By varying the amplitude of the incident light, one can independently tune the first and second-neighbor hopping for fixed frequency, which leads to considerable control over the Floquet band structure. We investigate this control in detail, and study how the quadratic and Dirac band touchings are influenced by the polarization and intensity of the light. We derive effective 2-band Hamiltonians (for both quadratic and Dirac band touching points) that accurately captures these results. We further study an extended model which explicitly includes oxygen $p$-orbitals and compare the results to the effective model that contains only the nickel $d$-orbitals. We conclude with a computation of the frequency dependent optical Hall conductivity using the full four band model and analyze the various inter-band contributions of the Floquet modes.