Periodic drive induced unconventional superconductivity in a half-filled system

Abstract

The non-equilibrium control of electronic properties has emerged as a transformative paradigm for engineering novel quantum phases. The most intriguing example of such a phase is light-induced superconductivity (SC) in non-superconducting materials. However, realizing unconventional SC at commensurate half-filling remains a formidable challenge even in non-equilibrium, as the regime is typically dominated by the robust stability of the antiferromagnetic (AFM) Mott insulating (MI) state. Here, we provide a novel non-equilibrium route to realize unconventional d-wave SC in a half-filled system through Floquet engineering. We analyze the periodically driven Fermi-Hubbard model on a bipartite lattice and demonstrate that a high-frequency drive can transform a weakly interacting insulator into a regime of strong correlations by the drive-induced renormalization of nearest-neighbor hopping. Furthermore, the drive induces staggered higher range hoppings that can frustrate the AFM order while simultaneously generate staggered potential that lifts the kinetic constraints inherent to the half-filled system, fostering the charge dynamics required to stabilize d-wave pairing against the competing AFM state. The resulting SC phase is protected by high-frequency prethermalization, maintaining stability over timescales exponentially large in the drive frequency. This protocol circumvents the need for chemical doping, offering a 'disorder-free' alternative for realizing unconventional pairing with direct applications in optimizing the performance of superconducting quantum computers, qubit arrays and other upcoming quantum technologies.

Figures (5)

• Figure 1: Panel[a]: A possible implementation of the periodic drive explored in this work in ultracold experiments. The right panel shows the drive induced 2nd and 3rd neighbour hoppings on 2-dimentional square lattice. Panel [b] shows how time lag between the drive of A and B sublattices can induce the required phase difference $\Phi$.
• Figure 2: Effective couplings in periodically driven Hubbard model in $\Omega-\Phi$ plane for the drive with amplitude $A=2.5\Omega$. Here $U_{eff}=U/t_{eff}$ is the effective Hubbard interaction, $V_{eff}=2V/t_{eff}$ is the effective staggered potential between two sublattices and $\pm t^\prime_{eff}=\pm t^\prime_{ind}/t_{eff}$ is staggered higher range intra-sublattice hopping. The right bottom panel shows the effective correlated hopping $t^{eff}_{cor}$ on nearest neighbour bonds. The data shows are for $U_0=1$ and $V_0=0.5$ in units of $t_0$.
• Figure 3: Top panels: Phase diagram of periodically driven Hubbard model with drive frequency $\Omega=15$ and drive amplitude $A=2.5\Omega$. As the phase $\Phi$ is tuned, at a threshold $\Phi_c$ where $U_{eff}+2V_{eff}\gg 1$, and the higher range hoppings $t^\prime_{eff}$ are significantly large, the system shows d-wave superconductivity. On increasing $\Phi$ further, dwave pairing amplitude goes to zero with a sharp drop and the staggered magnetization turns on such that the system transits into an AFM Mott Insulator. The phase diagram in the right panel shows the colormap of d-wave pairing amplitude in $\Omega-\Phi$ plane. The d-wave superconductivity exists for a broad range of drive frequencies(with $A=2.5\Omega$). Bottom panels shows the basic plots of the d-wave pairing amplitude $\Delta_{AB}$ and the staggered magnetization $m_s$ vs $\Phi$ for a range of drive parameters. The data shown are for $U=1.0t_0$ and staggered potential $V_0=0.5t_0$ in the undriven Hamiltonian.
• Figure 4: Panel[a] shows the d-wave pairing amplitude $\Delta_{AB}$ vs $\Phi$ for a range of initial values of the staggered potential $V_0$ for a fixed value of the Hubbard interaction $U=1.0$. Panel [b] shows the staggered magnetization $m_s$ vs $\Phi$ for various values of $V_0$ for $U=1.0$. Panel[c] shows the consolidated phase diagram in $V_0-\Phi$ plane for the periodic drive with $\Omega=10$ and $A=2.5\Omega$ based on the results shown in panel[a]. The d-wave superconducting phase survives for a broad range of staggered potential $V_0$. Panel[c] and [d] shows the results for the system with $V_0=0$ and $U=0.55t_0$. The d-wave superconductivity survives even in this case for a range of drive parameters.
• Figure 5: Left Panel shows d-wave pairing amplitude vs the drive frequency $\Omega$ for various values of the phase $\Phi$. The right panel shows the staggered magnetization $m_s$ vs phase $\Omega$ of the drive for the same set of $\Phi$ values. The data shown are for $A= 2.5\Omega$, $U=1.0t_0$ and $V_0=0.5$.