arXiv subjects

Ashirbad Padhan

Publications and source records attributed to Ashirbad Padhan.

12 recordsLinked to original sources

arXiv2025

Topological phases of bosons with local parity coupling on a dimerized lattice

Symmetry-protected topological (SPT) phases in interacting bosonic systems have been widely explored, with many realizations emerging from the interplay of interactions, lattice geometry, and occupancy constraints. Here we investigate a dimerized bosonic lattice model with a local parity coupling and demonstrate that it supports a rich phase diagram containing topological phases at various fillings. Using density matrix renormalization group simulations, we identify two distinct topological regimes absent in the purely dimerized limit: an SPT phase at half filling stabilized by positive parity coupling and a paired-boson topological phase at unit filling, stabilized by negative parity coupling. While the latter is adiabatically connected to a trivial phase and is not symmetry protected in the conventional sense, it exhibits nontrivial topological signatures associated with paired bosons in the constrained Hilbert space. Our results establish local parity coupling as a useful framework for understanding and characterizing topological phases in one-dimensional bosonic systems.

cond-mat.str-el↗

arXiv2025

Long-range resonances in quasiperiodic many-body localization

We investigate long-range resonances in quasiperiodic many-body localized (MBL) systems. Focusing on the Heisenberg chain in a deterministic Aubry-Andr\'{e} potential, we complement standard diagnostics by analyzing the structure of long-distance pairwise correlations at high energy. Contrary to the expectation that the ergodic-MBL transition in quasiperiodic systems should be sharper due to the absence of Griffiths regions, we uncover a broad unconventional regime at strong quasiperiodic potential, characterized by fat-tailed distributions of longitudinal correlations at long distance. This reveals the presence of atypical eigenstates with strong long-range correlations in a regime where standard diagnostics indicate stable MBL. We further identify these anomalous eigenstates as quasi-degenerate pairs of resonant cat states, which exhibit entanglement at long distance. These findings advance the understanding of quasiperiodic MBL and identify density-correlation measurements in ultracold atomic systems as a probe of long-range resonances.

cond-mat.dis-nn↗

arXiv2025

Correlated hopping induced topological order in an atomic mixture

The large majority of topological phases in one dimensional many-body systems are known to inherit from the corresponding single-particle Hamiltonian. In this work, we go beyond this assumption and find a new example of topological order induced through specific interactions couplings. Specifically, we consider a fermionic mixture where one component experiences a staggered onsite potential and it is coupled through density dependent hopping interactions to the other fermionic component. Crucially, by varying the sign of the staggered potential, we show that this latter fermionic component can acquire topological properties. Thanks to matrix product state simulations, we prove this result both at the equilibrium by extracting the behavior of correlation functions and in an out-of-equilibrium scheme by employing a Thouless charge pumping. Notably, we further discuss how our results can be probed in quantum simulators made up of ultracold atoms. Our results reveal an important and alternative mechanism that can give rise to topological order.

cond-mat.quant-gas↗

arXiv2024

Phases and phase transitions in a dimerized spin-$\mathbf{\frac{1}{2}}$ XXZ chain

We revisit the phase diagram of the dimerized XXZ spin-$\frac{1}{2}$ chain with nearest-neighbor couplings which was studied numerically in Phys. Rev. B 106, L201106 (2022). The model has isotropic $XY$ couplings which have a uniform value and $ZZ$ couplings which have a dimerized form, with strengths $J_a$ and $J_b$ on alternate bonds. We find a rich phase diagram in the region of positive $J_a, ~J_b$. We provide a detailed understanding of the different phases and associated quantum phase transitions using a combination of mean-field theory, low-energy effective Hamiltonians, renormalization group calculations employing the technique of bosonization, and numerical calculations using the density-matrix renormalization group (DMRG) method. The phase diagram consists of two Ising paramagnetic phases called IPM$_0$ and IPM$_\pi$, and a phase with Ising Neel order called IN; all these phases are gapped. The phases IPM$_0$ and IPM$_\pi$ are separated by a gapless phase transition line given by $0 \le J_a = J_b \le 1$ which is described by a conformal field theory with central charge $c=1$. There are two gapless phase transition lines separating IPM$_0$ from IN and IPM$_\pi$ from IN; these are described by conformal field theories with $c=\frac{1}{2}$ corresponding to quantum Ising transitions. The $c=1$ line bifurcates into the two $c=\frac{1}{2}$ lines at the point $J_a = J_b = 1$; the shape of the bifurcation is found analytically using RG calculations. A symmetry analysis shows that IPM$_0$ is a topologically trivial phase while IPM$_\pi$ is a time-reversal symmetry-protected topological phase (SPT) with spin-$\frac{1}{2}$ states at the two ends of an open system. The numerical results obtained by the DMRG method are in good agreement with the analytical results. Finally we propose experimental platforms for testing our results.

cond-mat.str-el↗

arXiv2024

Interaction driven topological phase transitions of hardcore bosons on a two-leg ladder

We investigate the topological properties of hardcore bosons possessing nearest-neighbor repulsive interactions on a two-leg ladder. We show that by allowing nearest neighbour dimerized interactions instead of hopping dimerization, the system exhibits topological phases and phase transitions under proper conditions. First, by assuming uniform hopping throughout the ladder, we show that when interaction along the legs are dimerized and the dimerization pattern is different in the legs, a trivial rung-Mott insulator to a topological bond order phase transition occurs as a function of the dimerization strength. However, for a fixed dimerization strength, the system exhibits a topological to trivial phase transition with increase in the rung hopping. A completely different scenario appears when the rung interaction is turned on. We obtain that for a ladder with uniform hopping, the repulsive interaction either turns the topological phase into a trivial rung-Mott insulator or a charge density wave phase. Such topological features are absent when the dimerization pattern in the nearest neighbour interaction is considered to be identical in both the legs of the ladder. We numerically obtain the ground state properties and also show the signatures of topological phase transitions through Thouless charge pumping.

cond-mat.quant-gas↗

arXiv2024

Quasiperiodic and periodic extended Hatano-Nelson model: Anomalous complex-real transition and non-Hermitian skin effect

We study the effect of quasiperiodic and periodic onsite potentials in a Hatano-Nelson model with next-nearest-neighbour hopping. By considering a non-reciprocal next-nearest-neighbour hopping and a quasiperiodic onsite potential under periodic boundary conditions, we show a breakdown of the typical correspondence between the delocalization-localization and complex-real transitions as a function of the potential strength. Moreover, we reveal that in the delocalized regime, when the potential strength increases, the eigenstates under open boundary conditions exhibit a bidirectional non-Hermitian skin effect, i.e., they tend to localize on both the edges instead of localizing on either of the edges. However, when a periodic onsite potential is considered, the system not only exhibits a bidirectional skin effect but also shows a complete direction reversal of the skin effect as a function of the onsite periodic potential.

cond-mat.quant-gas↗

arXiv2023

Disorder driven Thouless charge pump in a quasiperiodic chain

Thouless charge pump enables a quantized transport of charge through an adiabatic evolution of the Hamiltonian exhibiting topological phase. While this charge pumping is known to be robust against the presence of weak disorder in the system, it often breaks down with the increase in disorder strength. In this work, however, we show that in a one dimensional Su-Schrieffer-Heeger lattice, a unit cell-wise staggered quasiperiodic disorder favors a quantized charge pump. Moreover, we show that such quantized Thouless charge pump is achieved by following the standard single cycle pumping protocol which usually leads to a breakdown of charge pump in other known models. This unusual property is found to be due to an emergence of a trivial gapped phase from a topological phase as the quasiperiodic disorder is tuned. This emergent gapped to gapped transition also allows us to propose a non-standard pumping scheme where a modulated disorder favors a quantized Thouless charge pump.

cond-mat.quant-gas↗

arXiv2023

Re-entrant topological phase transition in a non-Hermitian quasiperiodic lattice

We predict a re-entrant topological transition in a one dimensional non-Hermitian quasiperiodic lattice. By considering a non-Hermitian generalized Aubry-André-Harper (AAH) model with quasiperiodic potential, we show that the system first undergoes a transition from the delocalized phase to the localized phase and then to the delocalized phase as a function of the hermiticity breaking parameter. This re-entrant delocalization-localization-delocalization transition in turn results in a re-entrant topological transition identified by associating the phases with spectral winding numbers. Moreover, we find that these two transitions occur through intermediate phases hosting both extended and localized states having real and imaginary energies, respectively. We find that these phases also possess non-trivial winding numbers which are different from that of the localized phase.

cond-mat.quant-gas↗

arXiv2023

Interacting bosons on a Su-Schrieffer-Heeger ladder: Topological phases and Thouless pumping

We study the topological properties of hardcore bosons on a two-leg ladder consisting of two Su-Schrieffer-Heeger (SSH) chains that are coupled via hopping and interaction. We chart out the phase diagram for the system and show that based on the relative hopping dimerization pattern along the legs, distinctly different topological phases and phase transitions can occur. When the dimerization along the legs are uniform, we find that the topological nature vanishes for even the slightest rung hopping. For staggered dimerization, the system exhibits a well defined topological character and a topological phase transition as a function of rung hopping. While the topological phase shows bond order character, the trivial phase shows the behavior of a rung-Mott insulator. For this case, the topological nature is found to survive even in the presence of finite inter-leg interactions. Moreover, we find that the critical point of the topological phase transition shifts to a higher or a lower rung hopping strength depending on the attractive or repulsive nature of the interaction. To highlight the marked effects of interactions, we propose a scheme involving a Thouless charge pump that provides insights for the topological phases characterized by a quantised particle transport through a periodic modulation of appropriate system parameters. In our studies, we show an interaction induced charge pumping following specific pumping protocols in the case of staggered dimerization.

cond-mat.quant-gas↗

arXiv2023

Quantum phases of constrained bosons on a two-leg Bose-Hubbard ladder

Bosons in periodic potentials with very strong local interactions, known as the constrained bosons often exhibit interesting physical behavior. We investigate the ground state properties of a two-leg Bose-Hubbard ladder by imposing three-body constraint in one leg and hardcore constraint in the other. By using the cluster-mean-field theory approximation and the density matrix renormalization group method, we show that at unit filling, for strong two-body attraction among the three-body constrained bosons, the system becomes a gapped pair-Mott insulator where all the bosons form strong bound pairs and occupy the leg with three-body constraint. With increase in hopping strength this pair-Mott insulator phase undergoes a phase transition to the gapless superfluid phase for equal leg and rung hopping strengths. However, when the rung hopping is stronger compared to the leg hopping, we obtain a crossover to another gapped phase which is called the rung-Mott insulator phase where the bosons prefer to delocalize on the rungs than the legs. By moving away from unit filling, the system remains in the superfluid phase except for a small region below the gapped phase where a pair superfluid phase is stabilized in the regime of strong attractive interaction. We further extend our studies by considering three-body constraint on both the legs and find that the crossover from the gapped to gapped phase does not occur rather the system undergoes a transition from a pair-rung-Mott insulator phase to the superfluid phase at unit filling. Moreover, in this case we find the signature of the pair superfluid phase on either sides of this gapped phase.

cond-mat.quant-gas↗

arXiv2022

Realizing a symmetry protected topological phase through dimerized interactions

We show that in a system of one dimensional spinless fermions a topological phase and phase transition can emerge only through interaction. By allowing a dimerized or bond-alternating nearest neighbour interaction we show that the system exhibits a symmetry protected topological phase while its non-interacting limit is a gapless state. The non-trivial topological character appears due to the onset of two degenerate bond-order phases as a function of dimerized interaction which are found to be topologically distinct from each other. As a result a topological phase transition occurs between these bond order phases through a gap closing point. However, in the limit of strong interaction, the bond order phases are connected through a gapped charge density wave phase possessing local antiferromagnetic order. The topological nature is characterized by the edge states, Berry phase and non-local string order parameter. At the end we provide possible experimental signatures of the emergent symmetry protected topological phase transition in terms of Thouless charge pumping and density-density correlation.

cond-mat.str-el↗

arXiv2022

Emergence of multiple localization transitions in a one-dimensional quasiperiodic lattice

Low dimensional quasiperiodic systems exhibit localization transitions by turning all quantum states localized after a critical quasidisorder. While certain systems with modified or constrained quasiperiodic potential undergo multiple localization transitions in one dimension, we predict an emergence of multiple localization transitions without directly imposing any constraints on the quasiperiodic potential. By considering a one-dimensional system described by the Aubry-Andŕe (AA) model, we show that an additional staggered onsite potential can drive the system through a series of localization transitions as a function of the staggered potential. Interestingly, we find that the number of localization transitions strongly depends on the strength of the quasiperiodic potential. Moreover, we obtain the signatures of these localization transitions in the expansion dynamics and propose an experimental scheme for their detection in the quantum gas experiment.

cond-mat.quant-gas↗