arXiv subjects

Atanu Nandy

Publications and source records attributed to Atanu Nandy.

At least 19 recordsLinked to original sources

arXiv2026

Reentrant localization transition, quantum butterfly and robust edge modes in aperiodic zig-zag ladder

Low dimensional tight-binding lattices in presence of quasiperiodic disorder generally exhibits localization transition. The system supports diffusive modes upto a limiting strength of disorder and all the eigenstates become localized beyond that critical strength thereby quenching the kinetic signature of the wavepacket. However, moving away from this situation, we demonstrate that with minimal long-range off-diagonal modulation, the eigenspectrum again may offer delocalization of electronic states for some subtle combination of kinetic parameters of the Hamiltonian leading to a second quantum phase change. The localization transitions are associated with the obvious presence of single-particle mobility edges. Multifractal energy landscape also shows quantum butterfly pattern with the in-gap robust edge modes. The re-emerging localization transition is manifested through the evaluation of inverse participation ratio, eigenspectrum and a pertinent quantum dynamical study.

cond-mat.other↗

arXiv2025

Localization, transport, flux induced extended modes and mobility edge in a self-similar corral substrate

We address that a single-band tight-binding Hamiltonian defined on a self-similar corral substrate can give rise to a set of non-diffusive localized modes that follow the same hierarchical distribution. As the lattice, the spatial extent of quantum prison containing a cluster of atomic sites is dependent on the generation of fractal structure. Apart from the quantum imprisonment of the excitation, a magnetic flux threading each elementary plaquette is shown to destroy the boundedness and generate an absolutely continuous sub-band populated by resonant eigen functions. Flux induced engineering of quantum states is corroborated through the evaluation of inverse participation ratio and quantum transport. Moreover, the robustness of the extended states has been checked in presence of diagonal disorder and off-diagonal anisotropy. Flux modulated single-particle mobility edge is characterized through mutlifractal analysis. Quantum interference is the essential issue, reported here, that manipulates the kinematics of the excitation and this is manifested by the workout of persistent current.

cond-mat.mes-hall↗

arXiv2025

Quantum Spin Hall Effect and Su-Schrieffer-Heeger Model Implementation in Novel C3N-based Dumbbell Morphologies

Two-dimensional carbon nitride materials have been the center of attention for their diverse usage in energy harvesting, environmental remediation and nanoelectronic applications. A broad range of utilities with decent synthetic plausibility have made this family a sweet spot to dive into, whereas the underlying analytical aspects are yet to have prominence. Recently, using the machinaries of first principles, we reported a family of six different structures C3NX with a unique dumbbell-shaped morphology, functionalizing the recently synthesized monolayer of C3N. Here we have critically explored the non-trivial topological phases of the semimetallic Dumbbell C3NX sheets and nanoribbons. Spin-orbit coupling induced gap across the Fermi level, its subsequent tuning via an external electric field, portrayal of band inversion from the Berry curvature distribution and the evaluation of topological index using the Wannier charge center (WCC) firmly establishes the traces of topological footprint. The real space decimation scheme and Green function technique evaluate the underlying spectral information with corresponding transport characteristics. Fascinating features of these quasi-1D systems are observed utilizing the Su-Schrieffer-Heeger (SSH) model where different twisted phases reveal distinct topological signatures even in a low atomic mass system like DB C4N.

cond-mat.mes-hall↗

arXiv2024

Unified strategy of flat band engineering, electronic transport and other spectral properties for different kagome ribbon variants

We address the problem of flat band engineering in different prototypes of quasi-one dimensional kagome network through a generalized analytical proposition worked out within the tight-binding formalism. Exact fabrication of single particle eigenstates with localized as well as diffusive modes is reported through the demonstration of such unified methodology by virtue of a simple real space decimation formalism in such interesting variants of ribbon shaped geometry. The description provides a common platform to investigate the band dispersion including the overall spectral portrait and associated physical aspects of those quasi-one dimensional lattices. Exact detection of dispersionless flat band mode and its tunability are reported as a direct consequence of the analytical prescription. Analytical work out is justified through the numerical evaluation of density of eigenstates, electronic transmission behavior, inverse participation ratio, persistent current study, Aharanov-Bohm oscillation in the transmittance and other related issues. An obvious analogous extension in the context photonics concludes our description.

cond-mat.mes-hall↗

arXiv2023

Localization property of a periodic chain of atoms with aperiodically coupled quantum dots

The spectral landscape and the transport property of a translationally invariant network with side-coupled quantum dots are demonstrated within the tight-binding framework. For periodic environment band structure is demonstrated analytically in details. Moreover, if the side-coupling here follows a typical quasiperiodic Aubry-Andre-Harper type of modulation then such off-diagonal disorder invites an exotic spectral feature for this model quantum system. We perform an in-depth numerical analysis followed by the evaluation of the density of eigenstates and the inverse participation ratio. The description shows that this network creates a typical self-similar kind of multifractal pattern in the energy landscape. The impacts of the strength of such aperiodic connectivity and the slowness parameter are reported in this analysis. In the present era of advanced technology and lithography techniques all such non-trivial results definitely throw an achievable challenge to the experimentalists to study the localization of excitation in such network

cond-mat.mes-hall↗

arXiv2023

Tunable caging of excitation in decorated Lieb-ladder geometry with long range connectivity

Controlled Aharonov-Bohm caging of wave train is reported in a quasi-one dimensional version of Lieb geometry with next nearest neighbor hopping integral within the tight-binding framework. This longer wavelength fluctuation is considered by incorporating periodic, quasi-periodic or fractal kind of geometry inside the skeleton of the original network. This invites exotic eigenspectrum displaying a distribution of flat band states. Also a subtle modulation of external magnetic flux leads to a comprehensive control over those non-resonant modes. Real space renormalization group method provides us an exact analytical prescription for the study of such tunable imprisonment of excitation. The non-trivial tunability of external agent is important as well as challenging in the context of experimental perspective.

cond-mat.mes-hall↗

arXiv2021

Tailoring flat bands and topological phases in a multi-strand Creutz network

We prove that, a suitable correlation between the system parameters can trigger topological phase transition and flat bands in a multi strand Creutz ladder network, when a staggered second neighbor interaction is included along the x axis. An appropriate change of basis maps such a finite N strand mesh into N or N 1 decoupled Su Schrieffer Heeger chains, depending onNeven or odd. A simple intuitive method, using a real space decimation scheme turns out to be very powerful in analytically extracting the flat bands, explaining their degeneracy or a lifting of the same. Our results are analytically exact, and may inspire experiments in photonics and ultracold atomic systems.

cond-mat.quant-gas↗

arXiv2020

Ring-localized states, radial aperiodicity and quantum butterflies on a Cayley tree

We present an analytical method, based on a real space decimation scheme, to extract the exact eigenvalues of a macroscopically large set of pinned localized excitations in a Cayley tree fractal network. Within a tight binding scheme we exploit the above method to scrutinize the effect of a deterministic deformation of the network, first through a hierarchical distribution in the values of the nearest neighbor hopping integrals, and then through a radial Aubry Andre Harper quasiperiodic modulation. With increasing generation index, the inflating loop less tree structure hosts pinned eigenstates on the peripheral sites that spread from the outermost rings into the bulk of the sample, resembling the spread of a forest fire, lighting up a predictable set of sites and leaving the rest unignited. The penetration depth of the envelope of amplitudes can be precisely engineered. The quasiperiodic modulation yields hitherto unreported quantum butterflies, which have further been investigated by calculating the inverse participation ratio for the eigenstates, and a multifractal analysis. The applicability of the scheme to photonic fractal waveguide networks is discussed at the end.

cond-mat.dis-nn↗

arXiv2020

Engineering topological phase transition and Aharonov-Bohm caging in a flux-staggered lattice

A tight binding network of diamond shaped unit cells trapping a staggered magnetic flux distribution is shown to exhibit a topological phase transition under a controlled variation of the flux trapped in a cell. A simple real space decimation technique maps a binary flux staggered network into an equivalent Su-Shrieffer-Heeger (SSH) model. In this way, dealing with a subspace of the full degrees of freedom, we show that a topological phase transition can be initiated by tuning the applied magnetic field that eventually simulates an engineering of the numerical values of the overlap integrals in the paradigmatic SSH model. Thus one can use an external agent, rather than monitoring the intrinsic property of a lattice to control the topological properties. This is advantageous from an experimental point of view. We also provide an in-depth description and analysis of the topologically protected edge states, and discuss how, by tuning the flux from outside one can enhance the spatial extent of the Aharonov-Bohm caging of single particle states for any arbitrary period of staggering. This feature can be useful for the study of transport of quantum information. Our results are exact.

cond-mat.mes-hall↗

arXiv2020

Controlled imprisonment of wave packet and flat bands in a fractal geometry

The explicit construction of non-dispersive flat band modes and the tunability of has been reported for a hierarchical 3-simplex fractal geometry. A single band tight binding Hamiltonian defined for the deterministic self-similar non-translationally invariant network can give rise to a countably infinity of such self localized eigenstates for which the wave packet gets trapped inside a characteristic cluster of atomic sites. An analytical prescription to detect those dispersionless states has been demonstrated elaborately. The states are localized over clusters of increasing sizes, displaying the existence of a multitude of localization areas. The onset of localization can, in principle, be delayed in space by an appropriate choice of the energy of the electron. The response of the system with the modulation of the anisotropy parameter is also studied. Supportive calculation of spectral landscape and demonstration of band dispersion plot are presented to solidify the analytical results. Variation of effective mass tensor cites re-entrant behavior with respect to the modulation of off-diagonal anisotropy. The tunability of those states leads to the controlled decay of wave function envelope. The impact of uniform magnetic perturbation on the bound states has also been discussed. Continuous variation of flux modulates the position of the flat band modes. The macroscopic degeneracy associated with the modes is retained with respect to the application of perturbation.

cond-mat.mes-hall↗

arXiv2019

Analytical study of quasi-one dimensional flat band networks and slow light analogue

Exact method of analytical solution of flat, non-dispersive eigenstates in a class of quasi-one dimensional structures is reported within the tight-binding framework. The states are localized over certain sublattice sites. One such finite size cluster of atomic sites is decoupled from the rest of the system by the special non-permissible vertex having zero amplitude. This immediately leads to the self-trapping of the incoming excitation. We work out an analytical scheme to discern the localizing character of the diffraction free dispersionless modes using real space renormalization group technique. Supportive numerical calculations of spectral profile and transport are demonstrated to substantiate the essence of compact localized states. Possible experimental scope regarding the photonic analogue of the tight-binding electronic case is also discussed elaborately. This eventually unfolds the concepts of slow light and the related re-entrant mode switching from the study of optical dispersion.

cond-mat.dis-nn↗

arXiv2019

Flux modulated flat band engineering in square-kagome ladder network

The origin of non-dispersive flat band modes for a quasi-one dimensional square-kagome ladder network is explored analytically by virtue of the real space renormalization group (RSRG) technique. A section of the eigenstates is non-diffusive i.e., localized within a cluster of sub-lattice sites partly by the destructive type of quantum interference and partly by the physical divider formed by the sites with zero wave function amplitude. By making the amplitude vanish at the selective sites it becomes possible to confine the incoming excitation within the trapping cell leading to the formation of compact localized states. The effective mass of the particle becomes infinitely large corresponding to those self-localized modes and hence the mobility of the wave train becomes vanishingly small. This quenched kinetic energy leads to a momentum independent contribution to a dispersion curve. The present analysis is corroborated by numerical calculation of spectral landscape and the corresponding dispersion profile. The application of uniform magnetic flux may lead to a comprehensive engineering of the position as well as the curvature of the band. Also, one-to-one mapping between electronic case and photonic case within the tight-binding framework helps us to study the photonic localization in an analogous single mode wave guide system. The concept of slow light eventually introduces the possibility of spatial compression of light energy.

cond-mat.dis-nn↗

arXiv2018

Spectral engineering and tunable thermoelectric behavior in a quasiperiodic ladder network

Double stranded quasiperiodic copper mean arrangement has been studied in respect of their electronic property and thermoelectric signature. The two-arm network is demonstrated by a tight binding Hamiltonian. The eigenspectrum of such aperiodic mesh that does not convey translational invariance, is significantly dependent on the parameters of the Hamiltonian. It is observed that specific correlation between the parameters obtained from the commutation relation between the on-site energy and overlap integral matrices can eventually modify the spectral nature and generate absolutely continuous energy spectrum. This part is populated by atypical extended states that has a large localization length substantiated by the flow of the hopping integral under successive real space renormalization group method steps. This sounds delocalization of single particle energy states in such nontranslationally invariant networks. Further this can be engineered at will by selective choice of the relative strengths of the parameters. This precise correlation has a crucial impact on the thermoelectric behavior. Anomalous nature of thermoelectric coefficient may inspire the experimentalists to frame tunable thermodevices. Specific correlations can help us to tune the continuous band and determine the band position at will.

cond-mat.dis-nn↗

arXiv2017

Controlled trapping of single particle states on a periodic substrate by deterministic stubbing

A periodic array of atomic sites, described within a tight binding formalism is shown to be capable of trapping electronic states as it grows in size and gets stubbed by an atom or an atomic clusters from a side in a deterministic way. We prescribe a method based on a real space renormalization group method, that unravels a subtle correlation between the positions of the side coupled atoms and the energy eigenvalues for which the incoming particle finally gets trapped. We discuss how, in such conditions, the periodic backbone gets transformed into an array of infinite quantum wells in the thermodynamic limit. We present a case here, where the wells have a hierarchically distribution of widths, hosing standing wave solutions in the thermodynamic limit.

cond-mat.dis-nn↗

arXiv2016

Engineering electronic states of periodic and quasiperiodic chains by buckling

The spectrum of spinless, non-interacting electrons on a linear chain that is buckled in a non- uniform manner giving it a flavor of a topologically disordered lattice, is investigated within a tight binding formalism. We have addressed two specific cases, viz., a perfectly periodic chain wrinkled in a quasiperiodic Fibonacci pattern, and a quasiperiodic Fibonacci chain, where the buckling also takes place in a Fibonacci pattern. The buckling brings distant neighbors in the parent chain to close proximity, which is simulated by a tunnel hopping amplitude. It is seen that, in the perfectly ordered case, increasing the strength of the tunnel hopping (that is, bending the segments more) absolutely continuous density of states is retained towards the edges of the band, while the central portion becomes fragmented and host subbands of narrowing widths containing extended, current carrying states, and multiple isolated bound states formed as a result of the bending. A switching on and off of the electronic transmission can thus be engineered by buckling. On the other hand, in the second example of a quasiperiodic Fibonacci chain, imparting a quasiperiodic buckling is found to generate continuous subband(s) destroying the usual multifractality of the energy spectrum. We present exact results based on a real space renormalization group analysis, that is corroborated by explicit calculation of the two terminal electronic transport.

cond-mat.dis-nn↗

arXiv2016

Controlled delocalization of electronic states in a multi-strand quasiperiodic lattice

Finite strips, composed of a periodic stacking of infinite quasiperiodic Fibonacci chains, have been investigated in terms of their electronic properties. The system is described by a tight binding Hamiltonian. The eigenvalue spectrum of such a multi-strand quasiperiodic network is found to be sensitive on the mutual values of the intra-strand and inter-strand tunnel hoppings, whose distribution displays a unique three-subband self-similar pattern in a parameter subspace. In addition, it is observed that special numerical correlations between the nearest and the next-nearest neighbor hopping integrals can render a substantial part of the energy spectrum absolutely continuous. Extended, Bloch like functions populate the above continuous zones, signalling a complete delocalization of single particle states even in such a non-translationally invariant system, and more importantly, a phenomenon that can be engineered by tuning the relative strengths of the hopping parameters. A commutation relation between the potential and the hopping matrices enables us to work out the precise correlation which helps to engineer the extended eigenfunctions and determine the band positions at will.

cond-mat.dis-nn↗

arXiv2016

Tight-binding chains with off-diagonal disorder: Bands of extended electronic states induced by minimal quasi-one dimensionality

It is shown that, an entire class of off-diagonally disordered linear lattices composed of two basic building blocks and described within a tight binding model can be tailored to generate absolutely continuous energy bands. It can be achieved if linear atomic clusters of an appropriate size are side coupled to a suitable subset of sites in the backbone, and if the nearest neighbor hopping integrals, in the backbone and in the side coupled cluster bear a certain ratio. We work out the precise relationship between the number of atoms in one of the building blocks in the backbone, and that in the side attachment. In addition, we also evaluate the definite correlation between the numerical values of the hopping integrals at different subsections of the chain, that can convert an otherwise point spectrum (or, a singular continuous one for deterministically disordered lattices) with exponentially (or power law ) localized eigenfunctions to an absolutely continuous spectrum comprising one or more bands (subbands) populated by extended, totally transparent eigenstates. The results, which are analytically exact, put forward a non-trivial variation of the Anderson localization [P. W. Anderson, Phys. Rev. 109, 1492 (1958)], pointing towards its unusual sensitivity to the numerical values of the system parameters and, go well beyond the other related models such as the Random Dimer Model (RDM) [Dunlap et al., Phys. Rev. Lett. 65, 88 (1990)].

cond-mat.dis-nn↗

arXiv2015

Engineering slow light and mode crossover in a fractal-kagome waveguide network

We present an analytically exact scheme of unraveling a multitude of flat, dispersionless photonic bands in a kagome waveguide strip where each elementary plaquette hosts a deterministic fractal geometry of arbitrary size. The number of non-dispersive eigenmodes grows as higher and higher order fractal geometry is embedded in the kagome motif. Such eigenmodes are found to be localized with finite support in the kagome strip and exhibit a hierarchy of localization areas. The onset of localization can, in principle, be delayed in space by an appropriate choice of frequency of the incident wave. The length scale at which the onset of localization for each mode occurs, can be tuned at will as prescribed here using a real space renormalization method. Conventional methods of extracting the non-dispersive modes in such geometrically frustrated lattices fail as a non-translationally invariant fractal decorates the unit cells in the transverse direction. The scheme presented here circumvents this difficulty, and thus may inspire the experimentalists to design similar fractal incorporated kagome or Lieb class of lattices to observe a multifractal distribution of flat photonic bands.

cond-mat.dis-nn↗