arXiv subjects

Santanu K. Maiti

Publications and source records attributed to Santanu K. Maiti.

At least 37 records · Page 2Linked to original sources

arXiv2025

Spintronics in antiferromagnetic helix: A new prescription

The occurrence of a finite mismatch between the up and down spin energy channels due to the application of an electric field, leading to the generation of a polarized spin current from an unpolarized beam in antiferromagnetic materials, has already been established. But, in this work, we report for the first time that even in the absence of any electric field, spin polarization can be achieved. We choose a tight-binding antiferromagnetic helix, where the strengths of magnetic moments at different lattice sites are non-uniform. The non-uniformity is introduced in two distinct forms, correlated and uncorrelated, and in each case we find a high degree of spin polarization. The Greens formalism is used to compute the results under various input conditions, and the results are valid for a broad range of physical parameters. Our analysis can open up a new direction of getting spin selectivity in different magnetic systems with zero net magnetization, in the absence of an electric field.

cond-mat.mes-hall↗

arXiv2025

Reentrant localization in a quasiperiodic chain with correlated hopping sequences

Quasiperiodic systems are known to exhibit localization transitions in low dimensions, wherein all electronic states become localized beyond a critical disorder strength. Interestingly, recent studies have uncovered a reentrant localization (RL) phenomenon: upon further increasing the quasiperiodic modulation strength beyond the localization threshold, a subset of previously localized states can become delocalized again within a specific parameter window. While RL transitions have been primarily explored in systems with simple periodic modulations, such as dimerized or long-range hopping integrals, the impact of more intricate or correlated hopping structures on RL behavior remains largely elusive. In this work, we investigate the localization behavior in a one-dimensional lattice featuring staggered, correlated on-site potentials following the Aubry-André-Harper model, along with off-diagonal hopping modulations structured according to quasiperiodic Fibonacci and Bronze Mean sequences. By systematically analyzing the fractal dimension, inverse participation ratio, and normalized participation ratio, we demonstrate the occurrence of RL transitions induced purely by the interplay between quasiperiodic on-site disorder and correlated hopping. We further examine the parameter space to determine the specific regimes that give rise to RL. Our findings highlight the crucial role of underlying structural correlations in governing localization-delocalization transitions in low-dimensional quasiperiodic systems, where the correlated disorder manifests in both diagonal and off-diagonal terms.

cond-mat.dis-nn↗

arXiv2025

Flux-Driven Circular Current in a Non-Hermitian Dimerized Aharonov-Bohm Ring: Impact of Physical Gain and Loss

In the present theoretical work, we numerically explore magnetic response of a tight-binding dimerized ring subjected to Aharonov-Bohm (AB) flux and environmental interactions. Specifically, we introduce an imaginary site potential on the odd lattice sites to represent physical gain and loss, while the even lattice sites remain unperturbed. We investigate the induced current resulting from the AB flux in both real and imaginary eigenspaces, aiming to enhance this current significantly by adjusting the gain/loss parameter ($d$). Our analysis focuses on how exceptional points in the real and imaginary eigenenergy spaces contribute to notable increases in current at specific $d$ values, and the emergence of purely real current when the imaginary current vanishes. We discuss how the dual behavior of energy spectrum (real and imaginary), converging to and diverging from zero energy, affects the enhancement of the current. Additionally, we study the interplay between the correlations of dimerized hopping integrals and the gain-loss parameter, which affects the current and highlights key features associated with these physical parameters. Furthermore, we consider how system size impacts our findings. Our study may reveal unconventional characteristics in various loop configurations, potentially paving the way for new research directions.

cond-mat.mes-hall↗

arXiv2025

Circular currents in a magnetic ring with zero net magnetization in presence of a side-coupled one-dimensional chain

We investigate persistent charge and spin currents in a magnetic quantum ring threaded by an Aharonov-Bohm flux, in the presence of a side-coupled one-dimensional non-magnetic chain. The neighboring magnetic moments in the ring are arranged in an antiparallel configuration. In the absence of the chain, the spin circular current vanishes exactly due to the symmetry between the up and down spin sub-Hamiltonians. Modeling the system within a tight-binding framework, we compute the currents using a second-quantized approach. Both charge and spin currents can be selectively tuned by adjusting the ring-chain coupling strength. Temperature plays a crucial role in modulating the currents, and interestingly, we find that they increase significantly with rising temperature--contrary to conventional expectations.

cond-mat.mes-hall↗

arXiv2025

Anomalous Power Factor Enhancement and Local Structural Transition in Ni-Doped TiCoSb

We report a significant enhancement (~269%) in the power factor (PF) and a local structural transition in Ni-doped TiCoSb samples (TiCo_{1-x}Ni_xSb, (x= 0.0, 0.01, 0.02, 0.03, 0.04, and 0.06). First-principles calculations reveal that even minute Ni doping induces a substantial shift in the Fermi level (EF) and alters the density of states (DOS). Structural analysis via Rietveld refinement of X-ray diffraction (XRD) data shows anomalous behavior at x = 0.02, supported by Williamson-Hall and modified methods. X-ray absorption spectroscopy (XAS) at the Ti and Co K-edges further confirms a pronounced local structural change at this composition. These structural transitions are consistent with temperature-dependent resistivity (ρ(T)) and thermopower (S(T)) data, which reflect changes in EF and disorder. Analysis of Lorentz number and scattering parameters reinforces the observed modifications in the electronic structure. The simultaneous enhancement of S and electrical conductivity at x = 0.02 is attributed to the disorder-to-order transition, leading to the marked rise in PF.

cond-mat.mtrl-sci↗

arXiv2025

Phonon mediated spin polarization in a one-dimensional Aubry-Andre-Harper chain

A comparative study of electronic transport and spin polarization between clean and Aubry-Andre-Harper chains in the presence of electron-electron (e-e) and electron-phonon (e-ph) interactions is presented. The entire system is simulated within a tight-binding framework based on the Hubbard-Holstein model. Trans-mission probability and spin polarization are evaluated using the Green's function method under the Hartree-Fock mean-field approximation through a self-consistent procedure. The transmission profile is found to be consistent with the band structure, which is also discussed. An overall enhancement of spin polariza-tion induced by e-ph interaction is reported for the first time, to the best of our knowledge. Our analysis may be useful for studying controlled spin-selective electron transmission in the presence of e-ph coupling.

cond-mat.mes-hall↗

arXiv2025

Drastic modification in thermal conductivity of TiCoSb Half-Heusler alloy: Phonon engineering by lattice softening and ionic polarization

A drastic variation (~47%) in thermal conductivity (\k{appa}) for synthesized samples (TiCoSb1+x, x=0.0, 0.01, 0.02, 0.03, 0.04, and 0.06) is observed. The lowest \k{appa} is reported for the TiCoSb1.02 sample. Thermal variation of \k{appa} is estimated from the temperature and power-dependent Raman spectroscopy data. Embedded phases and Co vacancy are analysed, employing scanning electron microscopy and transmission electron microscopy data. X-ray absorption fine structure (XAFS) spectroscopy reveals the Co vacancy in synthesized samples, and the most ordered phase is TiCoSb1.02 amid the synthesized samples. X-ray photoelectron spectroscopy measurement of the synthesized samples provides direct evidence of Co vacancies and their increase with Sb concentration (x). Lattice dynamics are revealed using Raman Spectroscopy (RS) measurements. RS data accomplishes that variation in \k{appa} as a function of Sb concentration is observed owing to an alteration in phonon group velocity, related to lattice softening. The polar nature of the TiCoSb half-Heusler (HH) sample is revealed. Longitudinal Optical and Transvers Optical phonon (LO-TO) splitting in RS is observed due to the polar nature of TiCoSb1+x synthesized samples. Tailoring in LO-TO splitting due to the screening effect, correlated with Co vacancies, is reported for TiCoSb1+x synthesized samples. Lattice softening and LO-TO splitting lead to a minimum \k{appa} for the TiCoSb1.02 synthesized sample.

cond-mat.mtrl-sci↗

arXiv2025

Anomalous persistent current in a 1D dimerized ring with aperiodic site potential: Non-interacting and interacting cases

In this work, we investigate the magnetic response by examining flux-driven circular currents in a Su-Schrieffer-Heeger (SSH) tight-binding (TB) ring threaded by an Aharonov-Bohm (AB) flux, $ϕ$. We consider both non-interacting and interacting electrons, where site energies are modulated by a slowly varying cosine form. Repulsive electron-electron interaction is incorporated through an on-site Hubbard term, and we analyze the system using the Hartree-Fock (HF) mean-field (MF) approximation. We discuss the characteristics of flux-driven circular currents to aperiodic potentials, dimerized hopping integrals, and Hubbard interactions. For the chosen aperiodic potential, both the strength and configuration play a crucial role, and we explore these aspects in depth. Interestingly, we observe a counterintuitive delocalizing effect as the aperiodic potential increases, unlike in conventional disordered rings. The effects of system size, filling factor, the presence of circular spin current, and the accuracy of MF results are also discussed. Finally, we provide a brief description of possible experimental realizations of our chosen quantum system. This investigation can be extended to explore additional properties in various loop substructures, promising further insights.

cond-mat.mes-hall↗

arXiv2025

Estimating critical disorder strength of an AAH system via thermal response

The Aubry-André-Harper (AAH) model provides a paradigmatic platform to study localization phenomena, where a transition from a conducting to an insulating phase occurs at a critical disorder strength equal to twice the nearest-neighbor hopping amplitude, $2t$. While this transition has been explored extensively through various probes, here we propose a fundamentally new approach based on thermal response. Specifically, we demonstrate that the electronic specific heat exhibits a distinctive signature across the transition, directly reflecting the anomalous evolution of the density of states with disorder strength. Our findings, supported by numerical analysis, establish specific heat measurement as a powerful and sensitive probe for detecting the critical point. This thermal characterization opens a new avenue for exploring disorder-induced phase transitions and paves the way for experimental realization in engineered quantum systems.

cond-mat.mes-hall↗

arXiv2025

Antiferromagnetic diamond network as an efficient spin filter: Proposition of a spin-specific semi-conducting behavior

We propose, for the first time, that an array of diamond plaquettes, each possessing vanishing net magnetization, can achieve complete spin polarization over a broad bias window. Furthermore, this system can be utilized to realize spin-specific semiconducting behavior. We describe the antiferromagnetic diamond network within a tight-binding framework, where spin-dependent scattering arises due to the interaction between itinerant electrons and local magnetic moments at different lattice sites. The mechanism underlying spin filtration relies on the specific arrangement of magnetic moments within individual plaquettes. We systematically investigate the spin polarization phenomenon under various input conditions, examining its dependence on network size, system temperature, and the magnetic flux threading each plaquette. Due to the network's geometry, we identify a sharply localized, highly degenerate energy level coexisting with conducting states. By tuning physical parameters, a small energy gap can be established between these degenerate localized states and the conducting energy band, enabling spin-specific $p$-type and $n$-type semiconducting behavior. Our findings offer a novel approach for designing future spintronic devices based on similar antiferromagnetic networks.

cond-mat.mes-hall↗

arXiv2025

Persistent current in a non-Hermitian Hatano-Nelson ring: Disorder-induced amplification

Non-reciprocal hopping induces a synthetic magnetic flux which leads to the non-Hermitian Aharonov-Bohm effect. Since non-Hermitian Hamiltonians possess both real and imaginary eigenvalues, this effect allows the observation of real and imaginary persistent currents in a ring threaded by the synthetic flux. Motivated by this, we investigate the behavior of persistent currents in a disordered Hatano-Nelson ring with anti-Hermitian intradimer hopping. The disorder is diagonal and we explore three distinct models, namely the Aubry-André-Harper model, the Fibonacci model, both representing correlated disorder, and an uncorrelated (random) model. We conduct a detailed analysis of the energy spectrum and examine the real and imaginary parts of the persistent current under various conditions such as different ring sizes and filling factors. Interestingly, we find that real and imaginary persistent currents exhibit amplification in the presence of correlated disorder. This amplification is also observed in certain individual random configurations but vanishes after configuration averaging. Additionally, we observe both diamagnetic and paramagnetic responses in the current behavior and investigate aspects of persistent currents in the absence of disorder that have not been previously explored. Interestingly, we find that the intradimer bonds host only imaginary currents, while the interdimer bonds carry only real currents. The bulk-boundary correspondence is investigated by analyzing the existence of localized edge states under the open boundary condition.

cond-mat.mes-hall↗

arXiv2025

Bias driven circular current in a ring nanojunction: Critical role of environmental interaction

The specific role of environmental interaction on bias driven circular current in a ring nanojunction is explored within a tight-binding framework based on wave-guide theory. The environmental interaction is implemented through disorder in backbone sites where these sites are directly coupled to parent lattice sites of the ring via single bonds. In absence of backbone disorder circular current becomes zero for a lengthwise symmetric nanojunction, while it increases with disorder which is quite unusual, and after reaching a maximum it eventually drops to zero in the limit of high disorder. The effects of ring-electrode interface configuration, ring-backbone coupling, different types of backbone disorder and system temperature are critically investigated. All the studied results are valid for a broad range of physical parameters, giving us confidence that the outcomes of this theoretical work can be verified experimentally. To make this study self-contained, we also discuss the feasibility of detecting bias-driven circular current and provide design guidelines for implementing our proposed quantum system in a laboratory.

cond-mat.mes-hall↗

arXiv2025

Enhanced thermoelectric properties of two-dimensional Janus ferromagnetic LaBrI with strain-induced valley degeneracy

Since the successful synthesis of the MoSSe monolayer, which violated the out-of-plane mirror symmetry of TMDs monolayers, considerable and systematic research has been conducted on Janus monolayer materials. By systematically analyzing the LaBrI monolayer, we are able to learn more about the novel Janus material by focusing on the halogen family next to group VIA (S, Se, Te). The structural optimizations have been carried out using pseudopotential based Quantum espresso code. Computed structural parameters are in good agreement with literature reports. The optimized crystal structures were used for computing effect of strain on electronic and thermoelectric properties. Dynamical stability predicts that this material can withstand up to 10% of tensile strain. Computed electronic structure reveals material to be indirect wide band gap ferromagnet with magnetic moment 1μB. With increase in the biaxial tensile strain the band gap decreases. Furthermore, the computed magneto-thermoelectric properties predict high Seebeck coefficient ~ 400 μV/K and low thermal conductivity of ~ 0.93 W/m.K in LaBrI which results in a high ZT ~ 1.84 for 4% strain at 800 K. The present study supports the fact that tensile strain on ferromagnetic LaBrI material can further enhance TE properties making it to be a promising material for TE applications at higher temperatures.

cond-mat.mtrl-sci↗

arXiv2025

Spin filtration in a single-stranded antiferromagnetic helix with slowly varying disorder: Higher order electron hopping

This work explores spin filtration in a helical magnetic system within a tight-binding framework, where neighboring magnetic moments are aligned antiparallel. The helix experiences a slowly-varying diagonal disorder, following a cosine form, which creates a finite energy mismatch between up and down spin channels. Unlike earlier studies that relied on external electric fields, this investigation demonstrates that disorder alone can achieve high spin filtration, even at low bias and high temperatures. Higher-order electron hopping in the helix leads to a non-uniform energy level distribution, facilitating favorable spin filtration, sometimes reaching $100\%$. The interplay between higher-order hopping and atypical disorder may enable selective spin transmission through various antiferromagnetic helices, potentially opening new avenues for functional elements.

cond-mat.mes-hall↗

arXiv2024

Critical analysis of multiple reentrant localization in an antiferromagnetic helix with transverse electric field: Hopping dimerization-free scenario

Reentrant localization (RL), a recently prominent phenomenon, traditionally links to the interplay of staggered correlated disorder and hopping dimerization, as indicated by prior research. Contrary to this paradigm, our present study demonstrates that hopping dimerization is not a pivotal factor in realizing RL. Considering a helical magnetic system with antiferromagnetic ordering, we uncover spin-dependent RL at multiple energy regions, in the {\em absence} of hopping dimerization. This phenomenon persists even in the thermodynamic limit. The correlated disorder in the form of Aubry-André-Harper model is introduced by applying a transverse electric field to the helical system, circumventing the use of traditional substitutional disorder. We conduct a finite-size scaling analysis on the observed reentrant phases to identify critical points, determine associated critical exponents, and examine the scaling behavior linked to localization transitions. Additionally, we explore the parameter space to identify the conditions under which the reentrant phases occur. Described within a tight-binding framework, present work provides a novel outlook on RL, highlighting the crucial role of electric field, antiferromagnetic ordering, and the helicity of the geometry. Potential applications and experimental realizations of RL phenomena are also explored.

cond-mat.dis-nn↗

arXiv2024

Modulation of charge and spin circular currents in a ring-wire hybrid setup

We present a comprehensive investigation into the charge and spin circular currents in a mesoscopic hybrid system, with a particular focus on the intricate interplay between the Aubry-André-Harper (AAH) potential, Aharonov-Bohm (AB) flux, chemical potential ($μ$), and antiferromagnetic (AF) ordering. The proposed quantum system comprises a composite structure of an AF ring coupled to an AAH chain. Utilizing a tight-binding model and operator method to calculate charge and spin circular currents, we uncover a range of intriguing phenomena. An interesting finding is that while the antiferromagnetic ring alone does not exhibit spin channel separation due to the symmetry between the up and down spin sub-Hamiltonians, the introduction of a dangling bond or chain can break this symmetry, leading to a spin separation effect. The AAH potential in the chain disrupts energy level symmetry, significantly impacting transport behavior. The charge circular current exhibits periodic oscillations with the AB flux, and its polarity changes with variations in $μ$. The AAH phase affects the charge current through the shifting of energy levels. Furthermore, the spin current displays oscillatory behavior as the AAH potential strength changes, with peaks emerging due to interference phenomena caused by disorder-induced localization. A possible experimental realization of our proposed quantum setup is also discussed, for the sake of completeness. This work may provide important insights into the complex physics of charge and spin transport in various hybrid mesoscopic systems, offering promising avenues for future research and technological applications.

cond-mat.mes-hall↗

arXiv2024

Thermolectricity in irradiated bilayer graphene flakes

We present a comprehensive study on enhancing the thermoelectric (TE) performance of bilayer graphene (BLG) through irradiation with arbitrarily polarized light, focusing on $AA$- and $AB$-stacked configurations with zigzag edges. Utilizing a combination of tight-binding theory and density functional theory (DFT), we systematically analyze the impact of light irradiation on electronic and phononic transport properties. Light irradiation alters the electronic hopping parameters, creating an asymmetric transmission function, which significantly increases the Seebeck coefficient, thereby boosting the overall {\it figure of merit} (FOM). For the phononic contribution, DFT calculations reveal that $AB$-stacked BLG exhibits lower lattice thermal conductivity compared to $AA$-stacked, attributed to enhanced anharmonic scattering and phonon group velocity. The combined analysis shows that FOM exceeds unity in both stacking types, with notable improvements near the irradiation-induced gap. Additionally, we explore the dependence of FOM on the system dimensions and temperature, demonstrating that light-irradiated BLG holds great promise for efficient thermoelectric energy conversion and waste heat recovery. Our results show favorable responses over a wide range of irradiation parameters. These findings provide crucial insights into optimizing BLG for advanced TE applications through light-induced modifications.

cond-mat.mes-hall↗

arXiv2024

Thermal signature of helical molecule: Beyond nearest-neighbor electron hopping

We investigate, for the first time, the thermal signature of a single-stranded helical molecule that is described beyond usual nearest-neighbor electron hopping, by analyzing electronic specific heat. Depending on the hopping of electrons, two different kinds of helical systems are considered. In one case the hopping is confined within a few neighboring lattice sites which is referred to as short-range hopping helix, while in the other case, electrons can hop in all possible sites making the system a long-range hopping one. These two helices accurately emulate the structures of single-stranded DNA and protein molecules, respectively. Each helix geometry is exposed to a transverse electric field applied perpendicular to the helix axis. The interplay among the helicity, higher-order hopping, and the electric field has significant impact on thermal response. Our comprehensive theoretical analysis reveals that, under low-temperature conditions, the short-range hopping helix exhibits greater sensitivity to temperature compared to the long-range hopping helix system. Conversely, the scenario reverses in the high-temperature limit. The thermal response of the helices can be modified selectively by means of the electric field, and the difference between the specific heats of the two helices gradually decreases with increasing the field strength. The molecular handedness, on the other hand, does not have any appreciable effect on the thermal signature. In addition, we also explore a significant application of electronic specific heat (ESH). Finally, we discuss the results of ESH by considering the spin degree of freedom and in the context of real biological helical systems.

cond-mat.mes-hall↗