arXiv subjects

Suparna Sarkar

Publications and source records attributed to Suparna Sarkar.

10 recordsLinked 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

Localization transitions in an open quasiperiodic ladder

We investigate localization transition in an open quasiperiodic ladder where the quasiperiodicity is described by the Aubry-André-Harper model. While previous studies have shown that higher-order hopping or constrained quasiperiodic potentials can induce a mixed-phase zone in one dimension, we demonstrate that the dissipation can induce mixed phase zone in a one dimensional nearest-neighbor system without imposing any explicit constraints on the quasiperiodic potential or hopping parameter. Our approach exploits an exact correspondence between the eigenspectrum of the Liouvillian superoperator and that of the non-Hermitian Hamiltonian, valid for quadratic fermionic systems under linear dissipation. Using third quantization approach within Majorana fermionic representation, we analyze two dissipation configurations: alternating gain and loss at every site, and at alternate sites under balanced and imbalanced conditions. By computing the inverse and normalized participation ratios, we show that dissipation can drive the system into three distinct phases: delocalizd, mixed, and localized. Notably, the mixed-phase zone is absent for balanced dissipation at every site but emerges upon introducing imbalance, while for alternate site dissipation it appears in both balanced and imbalanced cases. Furthermore, the critical points and the width of the mixed-phase window can be selectively tuned by varying the dissipation strength. These findings reveal that the dissipation plays a decisive role in reshaping localization transitions in quasiperiodic systems, offering new insight into the interplay between non-Hermitian effects and quasiperiodic order.

cond-mat.mes-hall↗

arXiv2025

Phases and phase transtions in one-dimensional alternating mixed spin (1/2-1) chain: effects of frustration and anisotropy

We investigate the phases and phase-transitions in one-dimensional alternating mixed-spin (1/2-1) chain in the presence of both frustration and anisotropy. Frustration is introduced via next-nearest-neighbor interactions, while single-ion anisotropy is incorporated at each lattice site. Our results show that moderate frustration can drive a phase transition from a ferrimagnetic state to an anti-ferromagnetic ground state. Remarkably, the presence of a weak easy-plane anisotropy destabilizes the ferrimagnetic order, also leading to the emergence of an antiferromagnetic phase. Interestingly, under strong frustration and anisotropy, the system exhibits signatures of a novel phase with spin density wave (SDW)-like modulation . We explore these anomalous phase transitions by employing exact diagonalization (ED) for small system sizes and the density matrix renormalization group (DMRG) method to characterize ground state properties for larger system sizes. We also investigate the finite-temperature behavior across various phases using the ancilla-based time-evolving block decimation (TEBD) approach. The primary objective of this work is to elucidate the phase structure of alternating mixed-spin chains under the combined effects of frustration and anisotropy. The primary objective of this work is to elucidate the intricate interplay between frustration and anisotropy in identifying the exotic phases and phase-transitions in alternating mixed-spin chains. Our findings contribute to a deeper understanding of mixed-spin quantum systems and may offer insights for future theoretical and experimental studies.

cond-mat.str-el↗

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

Enhancement of persistent current in a non-Hermitian disordered ring

We have studied the Aharonov-Bohm flux-induced magnetic response of a disordered non-Hermitian ring. The disorder is introduced through an on-site quasiperiodic potential described by the Aubry-André-Harper (AAH) model, incorporating a complex phase that renders the model non-Hermitian. Our findings reveal that this form of non-Hermiticity enhances the persistent current, without requiring hopping dimerization. We explore both non-interacting and interacting scenarios. In the former, we examine spinless fermions, while in the latter, we consider fermions with Hubbard interactions. The Non-Hermitian phase induces both the real and imaginary components of the current. We thoroughly analyze the energy eigenspectrum, ground state energy, and persistent current in both real and imaginary spaces for various system parameters. Our primary goal is to investigate the combined effects of non-Hermiticity and disorder strength on persistent currents. We find an enhancement in both the real and imaginary components of the persistent current with increasing disorder strength, as well as the non-Hermiticity, up to a critical value. Furthermore, we observe an enhancement in persistent current in the presence of Hubbard correlation. Our findings may provide a new route to get nontrivial characteristics in persistent current for a special type of non-Hermitian systems.

cond-mat.mes-hall↗

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

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↗

arXiv2023

Phenomenon of multiple reentrant localization in a double-stranded helix with transverse electric field

The present work explores the potential for observing multiple reentrant localization behavior in a double-stranded helical (DSH) system, extending beyond the conventional nearest-neighbor hopping interaction. The DSH system is considered to have hopping dimerization in each strand, while also being subjected to a transverse electric field. The inclusion of an electric field serves the dual purpose of inducing quasiperiodic disorder and strand-wise staggered site energies. Two reentrant localization regions are identified: one exhibiting true extended behavior in the thermodynamic limit, while the second region shows quasi-extended characteristics with partial spreading within the helix. The DSH system exhibits three distinct single-particle mobility edges linked to localization transitions present in the system. The analysis in this study involves examining various parameters such as the single-particle energy spectrum, inverse participation ratio, local probability amplitude, and more. Our proposal, combining achievable hopping dimerization and induced correlated disorder, presents a unique opportunity to study phenomenon of reentrant localization, generating significant research interest.

cond-mat.mes-hall↗

arXiv2021

Localization to delocalization transition in a double stranded helical geometry: Effects of conformation, transverse electric field and dynamics

Conformational effect on electronic localization is critically investigated for the first time considering a double-stranded helical geometry (DSHG) subjected to an electric field. In the presence of electric field the DSHG behaves like a correlated disordered system whose site potentials are modulated in a cosine form like the well known Aubry-Andre-Harper (AAH) model. The potential distribution can be modulated further by changing the orientation of the incident field. A similar kind of cosine modulation is also introduced in the inter-strand hopping integrals of the DSHG. Suitably adjusting the orientation of the electric field, we can achieve fully extended energy eigenstates or completely localized ones or a mixture of both. The effects of short-range and long-range hopping integrals along with the chirality on localization are thoroughly studied. Finally, we inspect the role of helical dynamics to make the model more realistic. The interplay between the helical geometry and electric field may open up several notable features of electronic localization and can be verified by using different chiral molecules.

cond-mat.mes-hall↗

arXiv2019

Spin-selective transmission through a single-stranded magnetic helix

Magnetic helix (MH) structure can be a role model for future spintronic devices. Utilizing the advantage of constructing possible magnetic configurations, in the present work first time we investigate spintronic behavior, to the best of our knowledge, in a helical geometry with finite magnetic ordering. The interplay between short-range and long-range hopping of electrons yields many non-trivial features which are thoroughly studied. Quite interestingly we see that the MH exhibits the strong chiral-induced spin selectivity effect, like what is observed in chiral molecules. Finally, to make the model more realistic we also examine the effect of helical dynamics. All the results are valid for a wide range of physical parameters, which prove the robustness of our analysis.

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