arXiv subjects

Sanjay Gupta

Publications and source records attributed to Sanjay Gupta.

16 recordsLinked to original sources

arXiv2025

Study of Correlated Disorders and interaction in the Hofstadter Butterfly

We investigate the impact of several quasiperiodic disorders and their continuous interpolation with the Aubry-Andre (AA) potential on the Hofstadter butterfly using mean field approximation at zero temperature for a two-dimensional square lattice. Weak disorder mildly smears the fractal spectrum, while strong quasiperiodic potentials destroy the butterfly and generate multiple energy gaps. The AA potential produces the strongest spectral restructuring, creating prominent gaps near half-filling. Interpolating AA with other quasiperiodic potentials reveals competing gap-opening mechanisms, ranging from AA-dominated gaps at small interpolation parameters to a robust half-filling gap generated by the competing disorders at large parameters. Entanglement entropy follows the area law at low and high magnetic fields but shows pronounced deviations at intermediate fields, with opposite trends for strong AA versus other quasiperiodic potentials. Localization analysis using IPR and NPR confirms enhanced localization with increasing disorder; the AA potential yields the largest IPR, with notable field dependence. Interpolation produces smooth crossovers between distinct localization regimes.

cond-mat.str-el↗

arXiv2019

Interacting fermions in two dimension in simultaneous presence of disorder and magnetic field

We have studied the revival of Hofstadter butterfly due to the competition between disorder and electronic interaction using mean field approximation of unrestricted Hartree Fock method at zero temperature for two dimensional square and honeycomb lattices. Interplay of disorder and electronic correlation to nullify each other is corroborated by the fact that honeycomb lattice needs more strength of electronic correlation owing to its less co-ordination number which enhances the effect of disorder. The extent of revival of the butterfly is better in square than honeycomb lattice due to higher coordination number. The effect of disorder and interaction is also investigated to study entanglement entropy and entanglement spectrum. It has been observed that for the square lattice, area law of entanglement entropy is violated for intermediate strength magnetic and magnitude of such departure from area law depends on disorder and interaction as well. However such departure from area law is absence for honeycomb lattice. Moreover the entanglement spectrum for square lattice does have the symmetry of original Hofstadter butterfly and this symmetry is destroyed in the presence of disorder. The interaction opens up a gap in the entanglement spectrum as well. For the honeycomb lattice, the entanglement spectrum forms a continuous band without any symmetry and its feature is mostly unchanged in the presence of disorder as well as interaction.

cond-mat.str-el↗

arXiv2012

Electronic structure of a single vortex in d-wave superconductor revisited

The present work deals with the study of d-wave superconductor in presence of a single vortex placed at the centre of the 2D lattice using the $t-t'-J$ model within the renormalized mean field theory. It is found that the in absence of the vortex the ground state has a d-wave configuration. In presence of the vortex, the superconducting order parameter, above the critical doping, drops to a low non zero value within a few lattice points from the vortex (that is within the the vortex core) and beyond it converges to the constant value in absence of vortex. We observe that above the critical doping things are consistent with the experimental results while there is an anomalous rise in the superconducting order parameter at very low doping within the vortex core. This we feel is because of antiferromagnetic ordering taking place within the vortex core at low doping.

cond-mat.str-el↗

arXiv2011

Physics of interface: Strongly correlated barrier with chemical modulation sandwiched between two metallic planes

Barrier planes described by the Ionic Hubbard model and sandwiched between metallic planes on both sides are studied using unrestricted Hartree Fock. For zero onsite correlation, the presence of the metallic interface generates an additional gap in the energy spectrum away from half filling, if the chemically modulated potential in the barrier planes exceed a critical value. There is reentrant behaviour and an insulator-metal-insulator transition as we tune onsite correlation for fixed site potential. The metal is thus able to penetrate the barrier planes due to proximity effect, in a system that is otherwise an insulator throughout.

cond-mat.str-el↗

arXiv2011

Physics of interface: Mott insulator barrier sandwiched between two metallic planes

We consider a heterostructure of a metal and a barrier with onsite correlation at half filling using unrestricted Hartree Fock. We find that above a certain value of correlation strength in the barrier planes, the system is a Mott insulator, while below this value the system still behaves like a gapless insulator. The energy spectrum is found to be very novel with the presence of multiple gaps. Thus the system remains non metallic for any finite value of correlation.

cond-mat.str-el↗

arXiv2011

Physics of interface: Barrier with correlations and disorder sandwiched between two metallic planes

A Metal-Disordered Mott insulator-Metal heterostructure is studied at half-fiiling using unrestricted Hartree Fock method. The corresponding clean system has been shown to be an insulator for any finite on site correlation. Interestingly we find that introduction of explicit disorder induces a metal-insulator transition at a critical value of disorder. The critical value corresponds to the point at which disorder nullifies the effect of onsite correlation. The wavefunctions are found to delocalize by increasing disorder, rendering the system metallic.

cond-mat.str-el↗

arXiv2010

Dimensional and temperature dependence of metal insulator transition in correlated and disordered systems

We study the dimensional dependence of the interplay between correlation and disorder in two dimension at half filling using 2D $t-t'$ disordered Hubbard model with deterministic disorder both at zero and finite temperatures. Inclusion of $t'$ without disorder leads to a metallic phase at half filling below a certain critical value of $U$. Above this critical value $U_c$ correlation favours antiferromagnetic phase. Since disorder leads to double occupancy over the lower energy site, the competition between Hubbard $U$ and disorder leads to the emergence of a metallic phase, which can be quantified by the calculation of Kubo conductivity, gap at half-filling, density of states, spin order parameter, Inverse participation ratio (IPR) and bandwidth. We have studied the effect of disorder on the system in a very novel way through a deterministic disorder which follows a Fibonacci sequence. Behaviour of different parameters show interesting features on going from a two to quasi one dimensional system.

cond-mat.str-el↗

arXiv2009

Zero-spin-photon hypothesis: `Zero-spin-photon generation in pair-production and its subsequent decay into neutrino and antineutrino' - solves many-riddles of physics and universe

`What is work and what is heat' is re-investigated from the perspective of second law of thermodynamics. It is shown that the inevitable consequence of second law of thermodynamics and spin conservation necessitates the possible generation of zero spin photon in pair production process, and its subsequent decay explains the birth of neutrino and antineutrino. The proposed neutrino-genesis, solves many riddles of physics and universe. The riddles considered and explained are about: (i) mysterious neutrino (and antineutrino) and its bizarre properties such as handed-ness and parity-violation, (ii) questionable asymmetry/ excess of matter over antimatter, (iii) possibility of existence of antimatter world and (iv) parity (P) violation and aspects of CP and CPT violation or restoration in the universe.

physics.gen-ph↗

arXiv2005

Half-filled Hubbard ring with alternating site potentials in a magnetic field

We have studied a Hubbard ring with alternating site potentials for half filling in presence of a magnetic flux. Using a mean field approach we have calculated the conductivity of such a ring at low and high temperatures. The interplay of correlation, the polarizing field and the chemical modulation in the site potentials tune the conductivity in an interesting fashion. In presence of the modulation in the site energy an appreciable variation in the conductance is observed with the change in flux. Finite size effects are also identified and they are found to be quickly disappearing with increasing system size. Sharp changes in the magnetoconductance is found to disappear at higher temperatures.

cond-mat.str-el↗

arXiv2005

Effect of Fibonacci Modulation On Superconductivity

We have studied finite-sized single band models with short range pairing interactions between electrons in presence of diagonal Fibonacci modulation in one dimension. Two models, namely the attractive Hubbard model and the Penson-Kolb model, have been investigated at half-filling at zero temperature by solving the Bogoliubov-de Gennes equations in real space within a mean field approximation. The competition between ``disorder'' and the pairing interaction leads to a suppression of superconductivity (of usual pairs with zero centre-of-mass momenta) in the strong-coupling limit while an enhancement of the pairing correlation is observed in the weak-coupling regime for both the models. However, the dissimilarity of the pairing mechanisms in these two models brings about notable difference in the results. The extent to which the bond ordered wave and the $η$-paired (of pairs with centre-of-mass momenta = $π$) phases of the Penson-Kolb model are affected by the disorder has also been studied in the present calculation. Some finite size effects are also identified.

cond-mat.str-el↗

arXiv2005

On Possibility of Using High-Tc Ceramic-Superconductor as Junction-less Transistor towards Nano-miniaturization

High-Tc Type-II ceramic-superconductor at temperature T < Tc, under presence of magnetic-field B becomes non-superconducting if B exceeds a critical value Bc2. Thus at T < Tc, by application/absence of critical magnetic- field as a controlling device, these non-superconducting/superconductor states can be achieved for current-flow to two corresponding states of block/pass or off/on or 0/1. Thus it appears that there is a possibility of a new breed of transistors purely with high-Tc Type-II ceramic-superconductor; compact and without junctions & complexities. The proposed ceramic-superconductor-transistor (CST) seems in-principle to work well for switching purpose, but its use could also be extended for other electronic/computer devices too. The CST, being junction-less thus diffusion-less, could possibly be packed more closely (at nano-level) than the semi-conductor devices which has a limitation due to diffusion-layer-overlapping. A similar superconductor-device named Cryotron was invented at MIT half-a-century ago, but could not survive against semiconductor. CST is a rebirth of cryotron in different disguise & in new perspective.

physics.gen-ph↗

arXiv2005

A Novel General Theoretical Derivation of Newton-Experimental-Formula for Collision of Particles

An experimental formula, sometimes named as Newton-collision-formula, (v1-v2) = - e.(u1-u2) relating relative-velocities before & after impact of two bodies under linear-collision, is commonly used successfully for study of collision-dynamics. Although it seems possible as shown in text-books [1,2] to derive this relation, assuming (defining) e as ratio of impulses during restitution & deformation; but as yet, neither a good theoretical-basis nor a general-derivation of this formula based on obvious choice of energy-consideration, has been reported. In this brief-paper a relativistic-theoretical-basis is adopted and a general formula-derivation is given. It is shown, interestingly, that proof of the Newton-collision-formula is hidden in Einstein-special-relativity.

physics.gen-ph↗

arXiv2003

Fibonacci-Hubbard Chain at Zero and Finite Temperatures

We have studied finite-sized single band Hubbard chains with Fibonacci modulation for half filling within a mean field approximation. The ground state properties, together with the dc conductivity both at zero and non-zero temperatures, are calculated for such quasi-periodic Hubbard chains. While a reduction in the conductivity is found for strong electronic interaction or strong Fibonacci modulation, a competition between these two is observed to enhance the conductivity. The results at finite temperatures also illustrate some interesting features of such finite-sized systems.

cond-mat.str-el↗

arXiv2003

Is Second Law of Thermodynamics Violated for Electron Transition from Lower-Energy Level to Higher-Energy Level

Second law of thermodynamics is applied to a few electronic processes. It is seen that the second law of thermodynamics holds good for all except one mentioned here. The classical approach, based on exact equivalence of emission and absorption spectra, for electron transition from lower energy level (first orbit) to higher energy level (second orbit) violates the second law of thermodynamics. But since second law which implies irreversibility and is universally true, a new explanation of electron transition from lower to higher energy level is proposed which leads to better understanding of several topics such as Fraunhofer lines, Optical laser. Also, interestingly, it is shown that widely different fields such as second law of thermodynamics and special relativity are in fact closely linked to each other. Also, possible links between supersymmetry and new concept of quaternion mass are mentioned.

physics.gen-ph↗

arXiv2003

Predicting Response-Function Results of Electrical/Mechanical Systems Through Artificial Neural Network

In the present paper a newer application of Artificial Neural Network (ANN) has been developed i.e., predicting response-function results of electrical-mechanical system through ANN. This method is specially useful to complex systems for which it is not possible to find the response-function because of complexity of the system. The proposed approach suggests that how even without knowing the response-function, the response-function results can be predicted with the use of ANN to the system. The steps used are: (i) Depending on the system, the ANN-architecture and the input & output parameters are decided, (ii) Training & test data are generated from simplified circuits and through tactic-superposition of it for complex circuits, (iii) Training the ANN with training data through many cycles and (iv) Test-data are used for predicting the response-function results. It is found that the proposed novel method for response prediction works satisfactorily. Thus this method could be used specially for complex systems where other methods are unable to tackle it. In this paper the application of ANN is particularly demonstrated to electrical-circuit system but can be applied to other systems too.

cs.NE↗

arXiv2002

Quantum Neural Networks

This paper initiates the study of quantum computing within the constraints of using a polylogarithmic ($O(\log^k n), k\geq 1$) number of qubits and a polylogarithmic number of computation steps. The current research in the literature has focussed on using a polynomial number of qubits. A new mathematical model of computation called \emph{Quantum Neural Networks (QNNs)} is defined, building on Deutsch's model of quantum computational network. The model introduces a nonlinear and irreversible gate, similar to the speculative operator defined by Abrams and Lloyd. The precise dynamics of this operator are defined and while giving examples in which nonlinear Schrödinger's equations are applied, we speculate on its possible implementation. The many practical problems associated with the current model of quantum computing are alleviated in the new model. It is shown that QNNs of logarithmic size and constant depth have the same computational power as threshold circuits, which are used for modeling neural networks. QNNs of polylogarithmic size and polylogarithmic depth can solve the problems in \NC, the class of problems with theoretically fast parallel solutions. Thus, the new model may indeed provide an approach for building scalable parallel computers.

quant-ph↗