Effect of spin-orbit coupling on the high harmonics from the topological Dirac semimetal Na3Bi

TL;DR

This study uses first-principles simulations and an analytical model to explore how spin-orbit coupling influences high-harmonic generation in the topological Dirac semimetal Na3Bi, revealing effects on ionization, electron dynamics, and harmonic emission.

Contribution

It provides a comprehensive analysis of spin-orbit coupling effects on high-harmonic generation in Na3Bi, combining simulations with a new analytical framework.

Findings

SOC modifies the bandstructure and ionization process.

SOC causes different responses in spin channels to laser fields.

SOC influences the timing and coupling of charge and spin currents.

Abstract

In this work, we performed extensive first-principles simulations of high-harmonic generation in the topological Diract semimetal Na3Bi using a time-dependent density functional theory framework, focusing on the effect of spin-orbit coupling (SOC) on the harmonic response. We also derived a general analytical model describing the microscopic mechanism of strong-field dynamics in presence of spin-orbit coupling, starting from a locally U(1)xSU(2) gauge-invariant Hamiltonian. Our results reveal that SOC: (i) affects the strong-field ionization by modifying the bandstructure of Na3Bi, (ii) modifies the electron velocity, making each spin channel to react differently to the pump laser field, (iii) changes the emission timing of the emitted harmonics. Moreover, we show that the SOC affects the harmonic emission by directly coupling the charge current to the spin currents, paving the way to the high-harmonic spectroscopy of spin currents in solids.