Light Control of Triplet Pairing in Correlated Electrons with Mixed-Sign Interactions

TL;DR

The paper addresses the challenge of realizing and controlling spin-triplet superconductivity in strongly correlated materials with mixed-sign interactions. It employs Floquet engineering of anisotropic spin exchange within a quarter-filled extended Hubbard model and ultrafast linearly polarized optical pulses to transiently flip exchange along the pump direction, thereby enhancing $p$-wave correlations. A two-pulse, orthogonal-polarization scheme demonstrates ultrafast switching between $p_x$ and $p_y$ channels, made possible by many-body fluctuations that distribute pairing correlations across the Bloch sphere. The approach provides a concrete route to dynamically stabilize and toggle spin-triplet superconducting tendencies in correlated oxides and cuprates, leveraging prethermal nonequilibrium dynamics and polarization-selective Floquet effects.

Abstract

Spin-triplet superconductivity is a key platform for topological quantum computing, yet its experimental realization and control in solid-state materials remain a significant challenge. For this purpose, we propose an ultrafast optical strategy to manipulate spin-triplet superconductivity by leveraging $p$-wave pairing instabilities in the extended Hubbard model, a framework applicable to transition-metal oxides. Utilizing Floquet engineering, we demonstrate that transient flipping of the effective spin-exchange interaction can enhance $p$-wave pairing correlations under linearly polarized optical pulses. Furthermore, we reveal that this emergent spin-triplet pairing in strongly correlated systems can be selectively switched by an orthogonal optical pulse. This work provides a pathway for stabilizing and controlling spin-triplet superconductivity in correlated materials.

Figures (5)

• Figure 1: Schematic of light-controlled spin-triplet pairing.a Correlated electrons on a 2D lattice, characterized by hopping $t$, on-site Coulomb interaction $U$, and nearest-neighbor interaction $V$. An external pump pulse transiently induces a ferromagnetic spin-exchange interaction along the pump polarization direction. b Bloch sphere representation of pairing correlations. c Schematic illustrating the redistribution of the pairing correlations across the Bloch sphere, following an optical pump and a subsequent second pump.
• Figure 2: Time evolution of spin-triplet pairing correlations under a single pump.a-c Dynamics of pairing correlations in the a$p_x$, b$p_y$, and c$p_x+p_y$ channels, in response to a $\Omega=9.2t_h$ pump pulse with amplitudes $A_0=0.2$, 0.4, 0.6 and 0.8, respectively. The top inset displays the time-dependent vector potential of the pump field. d Distribution of pairing correlations projected onto the equatorial plane of the Bloch sphere at four representative time points (marked by gray dashed lines in the inset of a). Colors from light to dark indicate increasing pump strengths from $A_0=0.2$ to 0.8. The arrows at the center indicate the magnitude of $\Phi_x -\Phi_y$ for each pump strength.
• Figure 3: Pump frequency and amplitude dependence.a Pump-induced changes in $p_x$ (upper) and $p_y$ (lower) pairing correlations at $t=0$ (center of the pump field), relative to their equilibrium values, plotted as a function of pump frequency and amplitude. The two distinct regimes of $p_x$ enhancement correspond to the single- and two-photon resonances. b Same as a but evaluated at $t = 10 t_h^{-1}$.
• Figure 4: Floquet-engineered anisotropic spin exchange.a Schematic depiction of the spin exchange process in a Floquet system. The effective superexchange interaction $J$ originates from second-order virtual hopping processes that involve multiple intermediate states, with their energies set by the equilibrium intermediate-state energy $E_{\text{int}}$ and integer multiples of the pump frequency $\Omega$. b Effective spin exchange interaction $J_{\alpha}^{\rm eff}$ at a transient state, calculated using the Floquet theory, as a function of the pump frequency $\Omega$. The red and blue regions indicate ferromagnetism (FM) and antiferromagnetism (AFM) exchange interactions, respectively. The solid lines correspond to calculations assuming homogeneous electron occupations, while the translucent extended $J_{\alpha}^{\rm eff}$ resonance area due to occupation imbalances, as illustrated in c. The single- and two-photon resonances are determined by the variation of FM regions. c Schematic illustration of various intermediate state configurations with distinct electron occupations and their corresponding intermediate-state energies $E_{\text{int}}$.
• Figure 5: Ultrafast switch between pairing correlations.a Dynamics of the $p_x$, $p_y$, and $p_x+p_y$ pairing correlations induced by two sequential pulses with $x$ and $y$ polarizations. Solid lines represent the phase-averaged pairing correlation $\overline{\Phi}_\alpha$, while the translucent lines correspond to results with a fixed phase $\phi = 0$. The upper inset shows the vector potential of the pump field. b Redistribution of pairing correlations on the equatorial plane of the Bloch sphere at the three selected time points (marked in a). The central arrows indicate the relative magnitude of $\Phi_x - \Phi_y$ at the corresponding time.