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Floquet engineering triplet superconductivity in superconductors with spin-orbit coupling or altermagnetism

Takehito Yokoyama

TL;DR

This work investigates how high-frequency light can optically generate and control triplet superconductivity in systems with spin-orbit coupling or altermagnetism by applying the Floquet-Magnus expansion to a Bogoliubov–de Gennes framework. The authors show that dynamical gap oscillations generate triplet components at first order in the drive (Ω^{-1}) in spin-singlet superconductors with Rashba SOC and in unitary triplet superconductors with altermagnetism, while static gaps produce triplet channels only at second order (Ω^{-2}); explicit forms for the induced d-vectors and their magnitudes are derived, with illustrative parameter estimates. In spin-singlet Rashba systems, a triplet d-vector {\bf d}_b({\bf k}) and mixing Δ_a({\bf k}) arise, scaling as 1/Ω with J_2(Bessel) factors, while in altermagnetic triplets, nonunitary components appear via {\bf d}_a and related terms; second-order corrections for static gaps yield triplet components proportional to Re(ξ_2^* g_2)/Ω^2 or through exchange-field–driven terms that can produce nonunitarity. The results suggest a route to optically generate and tune triplet superconductivity and potentially realize Floquet-topological superconducting states, with experimental probes such as time-resolved ARPES or STM discussed as possible observations.

Abstract

We study superconductivitiy under light irradiation based on the Floquet-Magnus expansion in the high-frequency regime. We find that, in spin-singlet superconductors with spin-orbit coupling, triplet superconductivity can be induced in the first-order perturbation for dynamical gap functions and the second-order perturbation for static gap functions. We also show that, in unitary triplet superconductors with altermagnetism, nonunitary triplet superconductivity can emerge in the firstorder perturbation for dynamical gap function and in the second-order perturbation for static gap functions. These results indicate optical generation and control of triplet superconductivity.

Floquet engineering triplet superconductivity in superconductors with spin-orbit coupling or altermagnetism

TL;DR

This work investigates how high-frequency light can optically generate and control triplet superconductivity in systems with spin-orbit coupling or altermagnetism by applying the Floquet-Magnus expansion to a Bogoliubov–de Gennes framework. The authors show that dynamical gap oscillations generate triplet components at first order in the drive (Ω^{-1}) in spin-singlet superconductors with Rashba SOC and in unitary triplet superconductors with altermagnetism, while static gaps produce triplet channels only at second order (Ω^{-2}); explicit forms for the induced d-vectors and their magnitudes are derived, with illustrative parameter estimates. In spin-singlet Rashba systems, a triplet d-vector {\bf d}_b({\bf k}) and mixing Δ_a({\bf k}) arise, scaling as 1/Ω with J_2(Bessel) factors, while in altermagnetic triplets, nonunitary components appear via {\bf d}_a and related terms; second-order corrections for static gaps yield triplet components proportional to Re(ξ_2^* g_2)/Ω^2 or through exchange-field–driven terms that can produce nonunitarity. The results suggest a route to optically generate and tune triplet superconductivity and potentially realize Floquet-topological superconducting states, with experimental probes such as time-resolved ARPES or STM discussed as possible observations.

Abstract

We study superconductivitiy under light irradiation based on the Floquet-Magnus expansion in the high-frequency regime. We find that, in spin-singlet superconductors with spin-orbit coupling, triplet superconductivity can be induced in the first-order perturbation for dynamical gap functions and the second-order perturbation for static gap functions. We also show that, in unitary triplet superconductors with altermagnetism, nonunitary triplet superconductivity can emerge in the firstorder perturbation for dynamical gap function and in the second-order perturbation for static gap functions. These results indicate optical generation and control of triplet superconductivity.
Paper Structure (15 sections, 51 equations, 2 figures)

This paper contains 15 sections, 51 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Formulation
  3. Results
  4. Dynamical gap functions: $\Omega^{-1}$ terms
  5. Spin-singlet $s$-wave superconductor with Rashba type spin-orbit coupling
  6. Spin-triplet superconductor with $d$-wave exchange field
  7. Static gap functions: $\Omega^{-2}$ terms
  8. Spin-singlet $s$-wave superconductor with Rashba type spin-orbit coupling
  9. Spin-triplet superconductor with $d$-wave exchange field
  10. Summary
  11. ACKNOWLEDGMENTS
  12. Derivation of the Hamiltonian
  13. Validity of the approximation
  14. Triplet spin wave
  15. Inhomogeneous superconductors

Figures (2)

  • Figure 1: (Color online) Schematic of the model. (a) Irradiation of the superconductor can engineer triplet superconductivity. For spin-singlet superconductors with spin-orbit coupling, singlet Cooper pairs can be converted into triplet ones. (b) In triplet superconductor/altermagnet junctions, due to the proximity effect, triplet superconductivity and altermagnetism can coexist.
  • Figure 2: (Color online) $F(x,M)$ and $G(x,M)$ as a function of $x$.