arXiv subjects

Ranjini Bhattacharya

Publications and source records attributed to Ranjini Bhattacharya.

6 recordsLinked to original sources

arXiv2026

Interplay of Quasiperiodicity, Hubbard Interactions, and Staggered Magnetism in a 1D Ring: Localization and Re-entrant Characteristics

We study interaction-induced localization in a spinful quasiperiodic Hubbard ring with quasiperiodically modulated hopping and a staggered spin-dependent Zeeman field using a self-consistent Hartree-Fock approach. We characterize localization through the inverse participation ratio, normalized participation ratio, and multifractal analysis, and further examine its signatures in self-consistent real-space observables, including double occupancy, density fluctuations, local entropy, spin-density-wave order, and related correlation measures. As the Hubbard interaction is increased, we find a nonmonotonic evolution of the eigenstates: an initially extended regime gives way to an intermediate localized phase, followed by reentrant delocalization at stronger interactions. The width of this intermediate regime grows systematically with both the quasiperiodic hopping amplitude and the staggered Zeeman-field strength, indicating a cooperative enhancement of localization by these two ingredients. In the localized regime, the self-consistent interaction produces pronounced spin dependence in both the spectra and localization properties, resulting in distinct responses of the spin-up and spin-down sectors. The interaction-driven crossover is consistently captured by the real-space observables and further corroborated by real-time wave-packet dynamics, which reveal successive ballistic, confined, and reentrant-transport regimes consistent with the underlying eigenstate character. These results provide a unified framework for understanding the interplay of quasiperiodicity, electronic interactions, and spin-dependent fields in controlling localization, criticality, and quantum transport in correlated quasiperiodic systems.

cond-mat.mes-hall↗

arXiv2026

Quasiperiodicity-Engineered Re-entrant Localization-Delocalization aspects in a Diamond Lattice

We investigate localization in a quasiperiodically engineered diamond lattice with strand-dependent Aubry-André-Harper onsite modulations, highlighting the decisive roles of the modulation ratio $s$ and the averaged potential on the middle strand. The upper strand hosts the primary potential $λ$, the lower strand carries a weaker modulation $λ/s$, and the middle strand follows their average, generating a correlated quasiperiodic landscape across each plaquette. By tuning $λ$ for selected values of $s$, we probe spectral and eigenstate properties via the inverse participation ratio (IPR), normalized participation ratio (NPR), and fractal dimension $D_2$. We uncover a pronounced re-entrant localization behavior, where eigenstates repeatedly switch between extended and localized regimes, which persists only within a finite range of $s$ and crucially relies on the averaged potential construction. This unconventional sequence arises from the interplay of $s$, the correlated potential, and the intrinsic diamond geometry, producing a highly nontrivial interference landscape. Our results reveal localization physics beyond the standard Aubry-André paradigm, further supported by the evolution of extended states, system-size scaling of $\langle \mathrm{NPR} \rangle$ and $\langle D_2 \rangle$, and dynamical signatures from the time-dependent root-mean-square displacement, confirming the robustness of the re-entrant transitions.

cond-mat.mes-hall↗

arXiv2026

Energy-Selective Complete Spin Polarization in an Extended Su-Schrieffer-Heeger Ferromagnetic Chain

We study spin-dependent transport in an extended Su-Schrieffer-Heeger chain with cosine modulated nearest- and next-nearest-neighbor hopping using the nonequilibrium Green's function formalism. Suitable tuning of the hopping parameters yields a complete separation of spin channels and perfect spin polarization over broad energy windows. The inclusion of next-nearest-neighbor hopping enhances both tunability and robustness, while systematic phase-diagram analyses reveal quantized polarization across extended regions of parameter space rather than at isolated fine-tuned points. These characteristics persist for larger system sizes, establishing the extended SSH model as a versatile platform for controllable spin-polarized transport.

cond-mat.mes-hall↗

arXiv2025

Thermoelectric Enhancement via Electronic and Phononic Channels in Staggered and Non-Staggered Dimerized Quantum Ring

Harnessing the quantum coherence and tunability of molecular-scale structures, we theoretically explore thermoelectric transport in ring-shaped molecular junctions featuring dimerized hopping integrals. By engineering alternating strong and weak bonds in both staggered and non-staggered configurations, we reveal a marked transmission asymmetry that drives a substantial enhancement in the thermoelectric figure of merit, ZT. To further steer transport behavior, we introduce controlled aperiodicity via site-energy modulations in unit cell format governed by the Aubry-André-Harper (AAH) potential, a quasiperiodic landscape that enables tunable localization-delocalization transitions. This interplay between hopping dimerization and AAH-type disorder gives rise to energy filtering effects and a rich spectrum where extended and critical states coexist, amplifying the Seebeck coefficient while preserving finite electrical conductance. Through a comprehensive non-equilibrium Green's function analysis, we uncover how key device parameters, including disorder strength, dimerization amplitude, and lead-ring connectivity, collectively shape transport characteristics. Notably, asymmetric lead couplings are shown to enhance performance by leveraging quantum interference pathways. Our findings highlight a robust design strategy for optimizing nanoscale thermoelectric functionality, providing actionable insights for experimental realization in molecular electronic platforms.

cond-mat.other↗

arXiv2025

Spin-Selective Thermoelectric Transport in a Triangular Spin Ladder

We theoretically investigate spin-resolved thermoelectric transport in a triangular ladder geometry hosting antiferromagnetic spin alignment, where lattice topology and magnetic ordering jointly enable highly efficient spin-selective energy conversion. The inherent geometric frustration of the ladder, together with intrinsic spin-filtering mechanisms, is shown to promote a pronounced separation between spin channels. Implementing spin-dependent onsite modulations, such as binary asymmetric potentials, induces pronounced spin splitting in the transmission spectrum, enabling controlled spin-selective transport and highlighting the role of lattice engineering in tailoring spin-dependent thermoelectric response. Additional control is achieved through modulation of the hopping amplitudes, which activates multiple transport pathways and allows fine tuning of spin-dependent conduction. A detailed evaluation of charge and spin thermoelectric coefficients reveals a strong enhancement of the thermoelectric performance, with the dimensionless figure of merit ZT reaching large values in optimized parameter regimes. Notably, the spin figure of merit systematically surpasses its charge counterpart, underscoring the decisive role of lattice geometry and antiferromagnetic order in amplifying spin thermoelectric efficiency. Our findings provide a versatile theoretical platform for designing low-dimensional spin-caloritronic devices with enhanced functionality.

cond-mat.mes-hall↗

arXiv2025

Fibonacci-Engineered Spin and Charge Thermoelectrics in a Long Range Su-Schrieffer-Heeger Chain: A Pathway to Giant Figure of Merit

In this work, we present a novel investigation into the spin-dependent thermoelectric performance of an extended Su-Schrieffer-Heeger (SSH) model, showcasing for the first time how its intrinsic spin filtration mechanism can be strategically harnessed to function as an efficient spin thermoelectric generator. By introducing a Fibonacci-type aperiodic modulation in the onsite energies, we engineer a deterministic disorder that mimics realistic aperiodic systems and profoundly influences transport characteristics. Furthermore, we incorporate both nearest-neighbor (NN) and next-nearest-neighbor (NNN) hopping amplitudes with tunable cosine dependencies, enabling us to meticulously explore the intricate interplay between these hopping processes and its implications on thermoelectric behavior. Our analysis reveals a remarkable enhancement in the dimensionless thermoelectric figure of merit ZT for both charge and spin transport channels, under carefully optimized conditions. Notably, the spin thermoelectric response exhibits distinct advantages, opening a new frontier in the design of next-generation thermoelectric materials and devices. This qualitative study not only deepens our understanding of aperiodic topological systems but also establish a foundational framework for exploiting spin-based thermoelectricity in low-dimensional platforms.

cond-mat.mes-hall↗