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Moumita Patra

Publications and source records attributed to Moumita Patra.

At least 19 recordsLinked to original sources
arXiv2026

Transport characteristics of bulk and edge states in an off-diagonal Aubry--Andr\'e--Harper chain

We investigate quantum transport in an off-diagonal Aubry--Andr\'e--Harper chain. The periodic hopping modulation generates effective internal boundaries that strongly influence the transmission characteristics. We show that edge, in-band bulk, and band-edge bulk states can be clearly distinguished through their transport signatures. In particular, bulk states near the band edges exhibit behavior similar to edge states, with weak dependence on system size, whereas in-band bulk states display pronounced size-dependent oscillations. We further demonstrate that the chain--electrode coupling strength controls the broadening of transmission resonances and drives a crossover from tunneling-dominated to nearly ballistic transport. In addition, dephasing introduces distinct sensitivity across different state classes, depending on their degree of spatial localization. These results highlight the key role of internal boundaries and quantum coherence in governing transport in modulated one-dimensional systems.

cond-mat.mes-hall↗
arXiv2024

Beyond-ballistic transport in an open quantum ring

In an open quantum ring (OQR), an asymmetric ring-to-electrode configuration, where the upper and lower arms have unequal lengths, generates antiresonances in the junction transmission spectrum around the doubly degenerate eigenenergies of the isolated ring Hamiltonian. The asymmetric OQR also gives rise to a net circular current transmission within the ring, specifically around these doubly degenerate eigenenergies. We investigate the system-size scaling properties of the transmission within the ring and the overall junction transmission of an OQR. Ballistic transport refers to the unhindered flow of charge carriers within a conductor, where transmission is independent of the system size. Here, we find beyond-ballistic behavior, characterized by an anomalous increase of the transmission with increasing system size, near both the degenerate and non-degenerate eigenenergies of the ring Hamiltonian, depending on the ring-to-electrode configuration. This phenomenon is unique to OQRs and is associated with the quantum interference effect between two counter-propagating electronic waves with nearly equal and opposite momenta. Consequently, there is no equivalent phenomenon in open quantum junctions with linear conductors.

cond-mat.mes-hall↗
arXiv2023

Circular current in a one-dimensional open quantum ring in the presence of magnetic field and spin-orbit interaction

In an open quantum system having a channel in the form of loop geometry, the current inside the channel, namely circular current, and overall junction current, namely transport current, can be different. A quantum ring has doubly degenerate eigen energies due to periodic boundary condition that is broken in an asymmetric ring where the ring is asymmetrically connected to the external electrodes. Kramers' degeneracy and spin degeneracy can be lifted by considering non-zero magnetic field and spin-orbit interaction (SOI), respectively. Here, we find that symmetry breaking impacts the circular current density vs energy ($E$) spectra in addition to lifting the degeneracy. For charge and spin current densities, the corresponding effects are not the same. Under symmetry-breaking they may remain symmetric or anti-symmetric or asymmetric around $E = 0$ whereas the transmission function (which is proportional to the junction current density) vs energy characteristic remains symmetric around $E = 0$. This study leads us to estimate the qualitative nature of the circular current and the choices of Fermi-energy/chemical potential to have a net non-zero current. As a result, we may manipulate the system to generate pure currents of charge, spin, or both, which is necessary for any spintronic and electronic applications.

cond-mat.mes-hall↗
arXiv2022

Effect of spin-orbit interaction on circular current: Pure spin current phenomena within a ring conductor

A net circulating current may appear within a quantum ring under finite bias. We study the characteristic features of the circular current in the presence of Rashba spin-orbit interaction (RSOI). Both charge and spin currents appear within the ring. Whereas when the ring is symmetrically connected to the external leads, we can get a pure charge current at non-zero Fermi-energy. On the other hand, for asymmetric ring-to-leads configuration, at zero Fermi-energy, the spin current vanishes but a pure charge current flows within the ring. Tuning RSOI, we demonstrate a way to control the pure spin current externally. This new perspective of the generation of the pure spin circular current can open a new basis for the highly efficient, low energy cost spintronic devices.

cond-mat.mes-hall↗
arXiv2021

Superconformal Index for $\mathcal{N}=3$ $\hat{ADE}$ Chern-Simons Quiver Gauge Theories

We compute superconformal indices for $\mathcal{N} = 3$ $\hat{ADE}$ Chern-Simons quiver gauge theories with a product gauge group $\prod_i U(N)_i$, using the method of supersymmetric localization. We also perform a large $N$ analysis of the index. This index includes contribution from non zero magnetic flux sector. The fact that these theories have a weakly coupled UV completion in terms of $\mathcal{N}= 3$ supersymmetric Chern-Simons Yang-Mills theories enables us to apply the localization technique. Such theories have dual M-theory description on $\mathrm{AdS}_4\times M_7$, where $M_7$ is a tri-Sasaki Einstein manifold.

hep-th↗
arXiv2021

Spin half-adder

A new proposal is given to design a spin half-adder in a nano-junction. It is well known that at finite voltage a net circulating current (known as circular current) appears within a mesoscopic ring under asymmetric ring-to-electrode interface configuration. This circular current induces a finite magnetic field at the center of the ring. We utilize this phenomenon to construct a spin half adder. The circular current induced magnetic field is used to regulate the alignments of local free spins, by their orientations we specify the output states of the `sum' and `carry'. All the outputs are spin based, therefore the results get atomically stored in the system. We also illustrate the experimental possibilities of our proposed model.

cond-mat.mes-hall↗
arXiv2021

Non-volatile reconfigurable spin logic device: parallel operations

A new proposal is given for designing a non-volatile, completely spin logic device, that can be reprogrammed for different functional classical logical operations. We use the concept of bias driven spin dependent circular current and current induced magnetic field in a quantum ring under asymmetric ring-to-electrode interface configuration to implement all the Boolean operations. We extend our idea to build two kinds of parallel computing architectures for getting parallelized operations, all at a particular time. For one case, different kinds of parallel operations are performed in a single device, whereas in the other type all the possible inputs of a logic gate are processed in parallel and all the outputs are read simultaneously. The performance and reliability are investigated in terms of power, delay and power-delay-product and finally the system temperature. We find that both the individual and simultaneous logic operations studied here are much superior compared to the operations performed in different conventional logic families like complementary metal oxide semiconductor logic, transistor-transistor logic, etc. The key advantage is that we can perform several logic operations, as many as we wish, repeating the same or different logic gates using a single setup, which indeed reduces wiring in the circuits and hence consumes much less power. Our analysis can be utilized to design optimized logic circuits at nano-scale level.

cond-mat.mes-hall↗
arXiv2020

Charges of Monopole Operators in $\widehat{ADE}$ Chern-Simons Quiver Gauge Theories

We compute R-charges of the BPS-monopole operators in $\mathcal{N} = 3$ $\widehat{ADE}$ Chern-Simons quiver gauge theories, along the lines of the work of Benna, Klebanov and Klose in \cite{bkk}. These theories have a weakly coupled UV completion in terms of $\mathcal{N}=3$ supersymmetric Chern-Simons Yang-Mills theories. In the UV limit the monopole operators are well approximated by classical solutions. We construct classical BPS and anti-BPS monopole solutions to these theories which preserve $\frac{1}{3}$ supersymmetry all along the RG flow. We compute the $SU(2)_R$ charges in these backgrounds and show that the smallest possible value of quantised $SU(2)_R$ charge is zero in each quiver theory.

hep-th↗
arXiv2019

Bias induced circular spin current: Effects of environmental dephasing and disorder

Analogous to circular spin current in an isolated quantum loop, bias induced spin circular current can also be generated under certain physical conditions in a nanojunction having single and/or multiple loop geometries which we propose first time, to the best of our concern, considering a magnetic quantum system. The key aspect of our work is the development of a suitable theory for defining and analyzing circular spin current in presence of environmental dephasing and impurities. Unlike transport current in a conducting junction, circular current may enhance significantly in presence of disorder and phase randomizing processes. Our analysis provides a new spin dependent phenomenon, and can give important signatures in designing suitable spintronic devices as well as selective spin regulations.

cond-mat.mes-hall↗
arXiv2019

Classical Monopole Solutions to $\mathcal{N}=3$ Chern-Simons-Yang-Mills Theories

We construct the component action and supersymmetry transformations of the $\mathcal{N} = 3$ Chern-Simons-Yang-Mills theory that flows in the infra red to the $\mathcal{N} = 3$ super conformal quiver Chern-Simons gauge theory obtained by Jafferis and Tomasiello in \cite{Jafferis:2008qz}. We then obtain classical $\frac{1}{3}$-BPS (and anti-BPS) solutions all along the RG flow. The solutions display a rich structure, for example, there is a non-trivial moduli space. Various properties of supersymmetric monopole operators in the infra red super conformal field theory, such as global charges and scaling dimensions can be derived from the monopole solutions we obtain in this paper; along the lines of the work of Benna, Klebanov and Klose in \cite{Benna:2009xd}.

hep-th↗
arXiv2019

Engineering magnetoresistance: A new perspective

A new proposal is given to achieve high degree of magnetoresistance (MR) in a magnetic quantum device where two magnetic layers are separated by a non-magnetic (NM) quasiperiodic layer that acts as a spacer. The NM spacer is chosen in the form of well-known Aubry-André or Harper (AAH) model which essentially gives the non-trivial features in MR due to its gaped spectrum and yields the opportunities of controlling MR selectively by tuning the AAH phase externally. We also explore the role of dephasing on magnetotransport to make the model more realistic. Finally, we illustrate the experimental possibilities of our proposed quantum system.

cond-mat.mes-hall↗
arXiv2019

Controlled charge and spin current rectifications in a spin polarized device

Quasicrystals have been the subject of intense research in the discipline of condensed matter physics due to their non-trivial characteristic features. In the present work we put forward a new prescription to realize both charge and spin current rectifications considering a one-dimensional quasicrystal whose site energies and/or nearest-neighbor hopping (NNH) integrals are modulated in the form of well known Aubry-André or Harper (AAH) model, a classic example of an aperiodic system. Each site of the chain contains a finite magnetic moment which is responsible for spin separation, and, in presence of finite bias an electric field is generated along the chain which essentially makes the asymmetric band structures under forward and reverse biased conditions, yielding finite rectification. Rectification is observed in two forms: (i) positive and (ii) negative, depending on the sign of currents in two bias polarities. These two forms can only be observed in the case of spin current rectification, while charge current shows conventional rectification operation. Moreover, we discuss how rectification ratio and especially its direction can be controlled by AAH phase which is always beneficial for efficient designing of a device. Finally, we critically examine the role of dephasing on rectification operations. Our study gives a new platform to analyze current rectification at nano-scale level, and can be verified in different quasi-crystals along with quantum Hall systems.

cond-mat.mes-hall↗
arXiv2018

Charge-based re-programmable logic device with built-in memory: New era in molecular electronics

We put forward a new proposal of designing charge-based logic devices considering a cyclic molecule that can be programmed and re-programmed for different functional logical operations and suitably engineered for data storage as well. The key idea is based on the appearance of bias induced circular current under asymmetric molecule-to-electrode interface configuration which does not dissipate even when the bias is off. Our results are valid for a broad range of parameter values, and provide a boost in the field of storage mechanism, reconfigurable computing, charge-based logic functions and other nano-scale applications.

cond-mat.mes-hall↗
arXiv2018

Analytical study of nano-scale logical operations

A complete analytical prescription is given to perform three basic (OR, AND, NOT) and two universal (NAND, NOR) logic gates at nano-scale level using simple tailor made geometries. Two different geometries, ring-like and chain-like, are taken into account where in each case the bridging conductor is coupled to a local atomic site through a dangling bond whose site energy can be controlled by means of external gate electrode. The main idea is that when injecting electron energy matches with site energy of local atomic site transmission probability drops exactly to zero, whereas the junction exhibits finite transmission for other energies. Utilizing this prescription we perform logical operations, and, we strongly believe that the proposed results can be verified in laboratory. Finally, we numerically compute two-terminal transmission probability considering general models and the numerical results matches exactly well with our analytical findings.

cond-mat.mes-hall↗
arXiv2018

Logical operations using phenyl ring

Exploiting the effects of quantum interference we put forward an idea of designing three primary logic gates, OR, AND and NOT, using a benzene molecule. Under a specific molecule-lead interface geometry, anti-resonant states appear which play the crucial role for AND and NOT operations, while for OR gate no such states are required. Our analysis leads to a possibility of designing logic gates using simple molecular structure which might be significant in the area of molecular electronics.

cond-mat.mes-hall↗
arXiv2018

Externally controlled high degree of spin polarization and spin inversion in a conducting junction: Two new approaches

We propose two new approaches for regulating spin polarization and spin inversion in a conducting junction within a tight-binding framework based on wave-guide theory. The system comprises a magnetic quantum ring with finite modulation in site potential is coupled to two non-magnetic electrodes. Due to close proximity an additional tunneling is established between the electrodes which regulates electronic transmission significantly. At the same time the phase associated with site potential, which can be tuned externally yields controlled transmission probabilities. Our results are valid for a wide range of parameter values which demonstrates the robustness of our proposition. We strongly believe that the proposed model can be realized in the laboratory.

cond-mat.mes-hall↗
arXiv2018

All-spin logic operations: Memory device and Reconfigurable computing

Exploiting spin degree of freedom of electron a new proposal is given to characterize spin-based logical operations using a quantum interferometer that can be utilized as a programmable spin logic device (PSLD). The ON and OFF states of both inputs and outputs are described by {\em spin} state only, circumventing spin-to-charge conversion at every stage as often used in conventional devices with the inclusion of extra hardware that can eventually diminish the efficiency. All possible logic functions can be engineered from a single device without redesigning the circuit which certainly offers the opportunities of designing new generation spintronic devices. Moreover we also discuss the utilization of the present model as a memory device and suitable computing operations with proposed experimental setups.

cond-mat.mes-hall↗