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.
Non-equilibrium control of electronic properties in condensed matter systems can result in novel phenomena. In this work, we provide a novel non-equilibrium route to realize half-metallic phases. We explore the periodically driven Hubbard model on a bipartite lattice and demonstrate that a specially designed sublattice dependent drive can transform a weakly interacting metal or insulator into a ferrimagnetic half-metal (HM). We consider a Fermi-Hubbard model with only nearest-neighbour hopping and Floquet engineer the elusive half-metal phase by driving the site potentials periodically. The drive induces staggered higher range hoppings and a staggered potential between two sublattices in the Floquet Hamiltonian. Close to the dynamical localization point, due to the suppression of nearest neighbor hopping in the driven system, an effective enhancement of various terms in the Floquet Hamiltonian, including the e-e interactions, occurs. This helps in stabilizing a broad ferrimagnetic HM phase for a wide range of drive parameters. This dynamically stabilized HM phase is a pristine platform for next-generation spintronics, topological quantum computing (specifically for engineering Majorana zero modes in hybrid nanowires) and ultrafast magnetic memory architectures.
Controlling and stabilising collective phases of many-body quantum systems is a problem of deep fundamental and technological interest. In this thesis, we perform a theoretical investigation on how useful quantum phases may be engineered in strongly correlated fermionic lattice systems, especially through periodic driving. We first compute the phase diagram of the one-dimensional t–J model with the addition of non-standard pair hopping terms. We show that at dilute fillings these terms enhance superconductivity while, counter- intuitively, suppressing it at large fillings. We argue that this is due to dynamical constraints originating from the fact that local pairs cannot overlap. We conjecture that these constraints may play a more significant role in the physics of two-dimensional systems where the t–J model is studied as a candidate model of high-Tc superconductivity. We begin to investigate these dynamical constraints on a ladder geometry. We then study the fermionic Hubbard model under periodic driving. We show that the driving induces a strong and robust singlet-pairing effect consistent with a superconducting state. This could provide a new mechanism for light-induced superconductivity in some classes of strongly cor- related materials. We show using Floquet theory that the dynamics of the driven Hubbard model are described precisely by the t–J model studied in the previous section. As the driven Hubbard model is also implementable with ultracold fermions in an optical lattice, our results could lead to their use as a quantum simulator for a broad class of candidate models for high-Tc superconductivity.
We study the interplay of magnetic order and superconductivity in the square-lattice Hubbard model under periodic driving with circularly polarized light. Formulating diagrammatic techniques based on the random-phase approximation in terms of Floquet Green's functions, allows us to analyze fluctuation-driven unconventional pairing for weak to moderate interactions. The interplay of repulsive interactions and photoassisted hopping of electrons gives rise to a rich magnetic phase diagram featuring an antiferromagnetic-to-ferromagnetic transition prior to a Floquet Lifshitz transition. Close to the antiferromagnetic transition, topological d + i d -wave superconductivity prevails in the phase diagram for a wide range of drive parameters. At intermediate- to high-frequency driving near the Floquet Lifshitz transition, superconducting orders are tuned from spin-singlet d -wave to spin-triplet p -wave character, providing an effective protocol for Floquet engineering topological superconductivity.
We propose a driven Lieb--Hubbard quantum simulator whose prethermal dynamics realize a square-lattice spin-1/2 fermion model with independently tunable repulsive on-site and attractive bond interactions. Periodically modulating the charge-transfer offset between the site (
d) and bond (
p) orbitals of the Lieb lattice brings a
p-orbital doublon energetically close to a pair in the
d manifold while keeping all
p-orbital singlons off resonance, thereby creating a synthetic ``negative-
U'' center on a Lieb-lattice bond site. Two controlled eliminations then generate a compact bond attraction in the reduced
d-only model on the square lattice, despite the microscopic repulsion in the
p orbital. The resulting interaction
J is tunable independently of the Hubbard repulsion
Ud on the
d orbitals, while interference between photon-assisted paths provides access to an intermediate-coupling regime in which
J and
Ud are both comparable to the effective hopping. At half filling, a mean-field calculation in this regime finds adjacent antiferromagnetic and
d-wave superconducting phases, as well as narrow coexistence regions, suggesting close competition between these orders. We discuss the branch-preparation, prethermal, and higher-band conditions required to translate the formal construction into an optical-lattice protocol. More broadly, our work identifies a structural similarity between Floquet systems and electron-phonon problems that may guide the design of novel quantum-simulation protocols.
Recent experiments performed on cuprates and alkali-doped fullerides have demonstrated that key signatures of superconductivity can be induced above the equilibrium critical temperature by optical modulation. These observations in disparate physical systems may indicate a general underlying mechanism. Multiple theories have been proposed, but these either consider specific features, such as competing instabilities, or focus on conventional BCS-type superconductivity. Here we show that periodic driving can enhance electron pairing in strongly correlated systems. Focusing on the strongly repulsive limit of the doped Hubbard model, we investigate in-gap, spatially inhomogeneous, on-site modulations. We demonstrate that such modulations substantially reduce electronic hopping, while simultaneously sustaining superexchange interactions and pair hopping via driving-induced virtual charge excitations. We calculate real-time dynamics for the one-dimensional case, starting from zero- and finite-temperature initial states, and we show that enhanced singlet-pair correlations emerge quickly and robustly in the out-of-equilibrium many-body state. Our results reveal a fundamental pairing mechanism that might underpin optically induced superconductivity in some strongly correlated quantum materials.
We study the interplay between electronic correlations and circularly polarized periodic driving in the Hubbard model on a Kagome lattice. Using Brillouin-Wigner perturbation theory, we derive an effective Floquet Hamiltonian in which the drive renormalizes the bare hopping and generates chiral nearest- and next-nearest-neighbor terms, producing repeated topological transitions and a flat band whose position is continuously tunable across the spectrum. Within slave-rotor mean-field theory, we show that the resulting Mott transition is strongly non-monotonic in the drive amplitude, yielding repeated metal-insulator transitions, and that the spinon excitations inside the Mott phase acquire a band topology distinct from that of the non-interacting Floquet bands. This correlation-driven topological reconstruction produces emergent flat-band spinon insulators inaccessible to either driving or interactions alone. Our results establish periodically driven Kagome systems as a platform for engineering correlated topological flat-band physics out of equilibrium, with proposed realizations in ultracold atomic lattices.