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arXiv:2607.02717

Correlation-Induced Topological Reconstruction in a Periodically Driven Kagome Mott Insulator

Rahul Ghosh, Subhajyoti Pal, Ganesh C. Paul

Published Jul 2, 2026• 0 citations
arXivHTMLPDF

Abstract

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.

DOI
10.48550/arxiv.2607.02717

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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.
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.
We construct a systematic high-frequency expansion for periodically driven quantum systems based on the Brillouin-Wigner (BW) perturbation theory, which generates an effective Hamiltonian on the projected zero-photon subspace in the Floquet theory, reproducing the quasienergies and eigenstates of the original Floquet Hamiltonian up to desired order in $1/\ensuremath{\omega}$, with $\ensuremath{\omega}$ being the frequency of the drive. The advantage of the BW method is that it is not only efficient in deriving higher-order terms, but even enables us to write down the whole infinite series expansion, as compared to the van Vleck degenerate perturbation theory. The expansion is also free from a spurious dependence on the driving phase, which has been an obstacle in the Floquet-Magnus expansion. We apply the BW expansion to various models of noninteracting electrons driven by circularly polarized light. As the amplitude of the light is increased, the system undergoes a series of Floquet topological-to-topological phase transitions, whose phase boundary in the high-frequency regime is well explained by the BW expansion. As the frequency is lowered, the high-frequency expansion breaks down at some point due to band touching with nonzero-photon sectors, where we find numerically even more intricate and richer Floquet topological phases spring out. We have then analyzed, with the Floquet dynamical mean-field theory, the effects of electron-electron interaction and energy dissipation. We have specifically revealed that phase transitions from Floquet-topological to Mott insulators emerge, where the phase boundaries can again be captured with the high-frequency expansion.
Kagome metals exhibit a rich interplay of topology, electronic correlations, and lattice dynamics. Recent discoveries of Kagome materials with a flat band near the Fermi level have revealed a variety of correlated electronic phases. However, elucidating their microscopic origin remains challenging, as realistic descriptions require accounting for multiple orbitals and competing interactions on an equal footing. To disentangle correlation effects from material-specific details and identify the essential physics of the flat-band regime, we study the single-orbital Kagome-Hubbard model at flat-band fillings using dynamical mean-field theory. We find strong signatures of flat-band ferromagnetism, consistent with exact and mean-field ground-state results. Moreover, we uncover an unconventional quasi-ordered phase in which a partially filled spin-polarized flat band pinned at the Fermi level gives rise to persistent local spin fluctuations down to zero temperature, in striking contrast to the classical behavior expected for a conventional ferromagnet. Our results demonstrate that these anomalous fluctuations are an intrinsic consequence of the flat-band degeneracy and establish a minimal framework for understanding correlation effects in flat-band Kagome systems.
We propose a simple scheme for the realization of a topological quasienergy band structure with ultracold atoms in a periodically driven optical square lattice. It is based on a circular lattice shaking in the presence of a superlattice that lowers the energy on every other site. The topological band gap, which separates the two bands with Chern numbers $\ifmmode\pm\else\textpm\fi{}1$, is opened in a way characteristic of Floquet topological insulators, namely, by terms of the effective Hamiltonian that appear in subleading order of a high-frequency expansion. These terms correspond to processes where a particle tunnels several times during one driving period. The interplay of such processes with particle interactions also gives rise to new interaction terms of several distinct types. For bosonic atoms with on-site interactions, they include nearest-neighbor density-density interactions introduced at the cost of weakened on-site repulsion as well as density-assisted tunneling. Using exact diagonalization, we investigate the impact of the individual induced interaction terms on the stability of a bosonic fractional Chern insulator state at half filling of the lowest band.
Higher-order topological insulators have attracted significant interest in both static single-particle and many-body lattice systems. While periodically driven (Floquet) higher-order topological phases have been explored at the single-particle level, the role of interactions in such systems remains less understood. In this paper, we extend previous studies by investigating interaction-induced higher-order topological phases through Floquet engineering. To achieve this, we construct an extended Bose-Hubbard model on a square lattice subjected to periodic driving. We demonstrate the emergence of interaction-induced normal Floquet second-order topological corner states for doublons (i.e., bound boson pairs) from a trivial phase, which exhibit robustness against disorder. Notably, beyond the normal phase, we reveal an interaction-induced anomalous Floquet second-order topological phase, where in-gap corner states of doublons emerge within the $\ensuremath{\pi}/T$ gap (TTT being the driving period). Our model, accessible with state-of-the-art ultracold atom techniques, provides a platform for realizing interaction-driven higher-order topological phases uniquely enabled by periodic driving, with no direct counterparts in static or single-particle systems.
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.