arXiv subjects

Aniket Singha

Publications and source records attributed to Aniket Singha.

16 recordsLinked to original sources

arXiv2026

Phonon-Assisted Photoluminescence and Ultrafast Exciton Dynamics in Two-Dimensional Silicon Carbide

Phonon assisted photoluminescence provides a direct window into exciton phonon interactions in semiconductors. Using fully ab initio many-body perturbation theory, including finite momentum Bethe Salpeter calculations, we investigate phonon-assisted emission and exciton dynamics in two dimensional (2D) hexagonal silicon carbide (hSiC) and benchmark its response against 2D h boron nitride (hBN). By explicitly resolving exciton phonon matrix elements, we identify an electron-phonon scattering channel mediated by A$^\prime$ high energy longitudinal and transverse optical phonons as the dominant contributors to sideband formation and quantify their spectral weights. We find that h SiC exhibits pronounced phonon-assisted sidebands comparable to hBN, despite a smaller exciton phonon energy separation and fewer resolved replicas. The bright \textbf{K}\textbf{K} exciton governs near UV zero phonon emission, while intervalley excitons acquire radiative character through symmetry allowed optical phonon coupling. Temperature dependent scattering rates reveal an ultrashort bright exciton lifetime of approximately 300 fs at 10 K, highlighting rapid exciton relaxation driven by intrinsic phonon channels.

cond-mat.str-el↗

arXiv2026

Transition-Metal Tailored $Ga_{2}O_{2}$ Monolayer: From Room-Temperature Gas Sensing to Chemical Scavenging

Pristine $Ga_{2}O_{2}$ monolayers suffer from poor sensitivity and weak molecular capture, limiting their application in toxic gas detection and environmental detoxification. Here, we employ first-principles density functional theory (DFT) calculations to investigate the gas sensing and scavenging properties of $Ga_{2}O_{2}$ monolayers substitutionally tailored via seven transition-metals (TM): Pd, Zn, Zr, Mo, Ag, Ti, and Pt. All TM-substituted monolayers exhibit negative formation and binding energies, negligible lattice distortion, and structural stability in molecular dynamics simulations. Performance evaluation against eight toxic industrial and three environmental gases reveals functionalities ranging from selective, reusable room-temperature sensing to permanent molecular capture. Ag substitution exhibits exceptional selectivity for $NO$ with moderate adsorption strength (~-0.83eV), an up to eight-order-of-magnitude conductivity enhancement, besides facilitating reusable $O_2$ and $NO_2$ detection. Additionally, Pd-, Zn-, Zr-, and Mo substitutions tune selectivity toward $NO$, $NO_2$, $CO_2$, $CO$, and $O_2$. Coming to applications towards toxic gas capture, Zr- and Mo-substituted systems selectively scavenge oxidizing gases, whereas Ti and Pt act as universal scavengers. Further analysis reveals that Pd- and Ag-substituted monolayers remain selective for $NO$, while Zn substitution favors $NO_2$ detection even in ambient atmospheric conditions. Thus, these tailored $Ga_{2}O_{2}$ monolayers offer a practical platform for atmospheric monitoring and detoxification.

cond-mat.mtrl-sci↗

arXiv2025

Gas Sensing Properties of Novel Indium Oxide Monolayer: A First-Principles Study

We present a comprehensive first-principles investigation into the gas sensing capabilities of a novel two-dimensional Indium Oxide (In2O3) monolayer, using density functional theory (DFT) calculations. Targeting both resistive-type and work function based detection mechanisms, we evaluate interactions with ten hazardous gases (NH3, NO, NO2, SO2, CS2, H2S, HCN, CCl2O, CH2O, CO) as well as ambient molecules (O2, CO2, H2O). The monolayer shows pronounced sensitivity towards NO and H2S, and work function modulation enables detection of NH3 and HCN. Mechanical strain further broadens detection capability, enhancing adsorption and selectivity. These results establish 2D In2O3 as a tunable platform for next-generation miniaturized gas sensors for environmental monitoring and safety applications.

cond-mat.mtrl-sci↗

arXiv2021

Non-local triple quantum dot thermometer based on Coulomb-coupled systems

Recent proposals towards non-local thermoelectric voltage-based thermometry, in the conventional dual quantum dot set-up, demand an asymmetric step-like system-to-reservoir coupling around the ground states for optimal operation (Physica E, 114, 113635, 2019). In addition to such demand for unrealistic coupling, the sensitivity in such a strategy also depends on the average measurement terminal temperature, which may result in erroneous temperature assessment. In this paper, I propose non-local current based thermometry in the dual dot set-up as a practical alternative and demonstrate that in the regime of high bias, the sensitivity remains robust against fluctuations of the measurement terminal temperature. Proceeding further, I propose a non-local triple quantum dot thermometer, that provides an enhanced sensitivity while bypassing the demand for unrealistic step-like system-to-reservoir coupling and being robust against fabrication induced variability in Coulomb coupling. In addition, I show that the heat extracted from (to) the target reservoir, in the triple dot design, can also be suppressed drastically by appropriate fabrication strategy, to prevent thermometry induced drift in reservoir temperature. The proposed triple dot setup thus offers a multitude of benefits and could potentially pave the path towards the practical realization and deployment of high-performance non-local ``sub-Kelvin range" thermometers.

cond-mat.mes-hall↗

arXiv2021

Thermometry in dual quantum dot set-up with staircase ground state configuration

We propose and investigate thermometry of a setup employing dual quantum dots with staircase ground state configuration. The stair-case ground state configuration actuates thermally controlled inelastic tunnelling, which translates into a temperature sensitive conductance, thereby inducing thermometry. The performance of the set-up is then analyzed employing quantum master equation (QME) for such systems in the sequential tunnelling regime. In particular, it is demonstrated that the system performance, in terms of temperature sensitivity and efficiency, is maximum in the regime of low temperature, making such system suitable for cryogenic thermometry. The proposed set-up can pave the path towards realization of high performance cryogenic nano temperature sensors.

cond-mat.mes-hall↗

arXiv2021

A non-local cryogenic thermometer based on Coulomb-coupled systems

We investigate a quadruple quantum dot setup that can be employed to sense the temperature of an electrically isolated remote target reservoir. Such a setup was conceived earlier by Sánchez et. al. (New Journal of Physics, 19, 113040) as non-local thermodynamic engine and relies on the electrostatic interaction between Coulomb-coupled quantum dots. The conjugation of Coulomb-coupling and energy-filtering results in an overall change in conductance with remote reservoir temperature. The performance of the thermometer is then theoretically investigated using density matrix formulation, and it is demonstrated that the quadruple quantum dot design ensures a superior temperature sensitivity and noise robustness compared to a simple thermometer consisting of two Coulomb-coupled quantum dots. In the end, we investigate the regime of operation and comment on the ground state configuration for optimal performance of the thermometer. The setup investigated in this paper can be employed to construct highly efficient non-local cryogenic thermometers.

cond-mat.mes-hall↗

arXiv2020

Density matrix to quantum master equation (QME) model for arrays of Coulomb coupled quantum dots in the sequential tunneling regime

Coulomb coupled quantum dot arrays with staircase ground state configuration have been proposed in literature for enhancing heat-harvesting and refrigeration performance. However, due to their mutual Coulomb interaction, a performance analysis of such systems remains complicated and necessitates consideration of microscopic physics using density matrix formulation. However the path of device analysis starting from the system Hamiltonian to density matrix formulation is complicated and lacks the simplicity and intuitive aspect of sequential electron transport conveyed by the quantum master equation (QME) approach. In this paper, starting from the system Hamiltonian and employing the density matrix formulation, I derive the QME of a system of three quantum dots, two of which are electro-statically coupled. The framework formulated in this paper can be further extended to derive QME of systems with higher number of Coulomb coupled quantum dots.

physics.app-ph↗

arXiv2020

Realistic non-local refrigeration engine based on Coulomb coupled systems

Employing Coulomb-coupled systems, we demonstrate a cryogenic non-local refrigeration engine, that circumvents the need for a change in the energy resolved system-to-reservoir coupling, demanded by the recently proposed non-local refrigerators. We demonstrate that an intentionally introduced energy difference between the ground states of adjacent tunnel coupled quantum dots, associated with Coulomb coupling, is sufficient to extract heat from a remote target reservoir. Investigating the performance and operating regime using quantum-master-equation (QME) approach, we point out to some crucial aspects of the proposed refrigeration engine. In particular, we demonstrate that the maximum cooling power for the proposed set-up is limited to about $70\%$ of the optimal design. Proceeding further, we point out that to achieve a target reservoir temperature, lower compared to the average temperature of the current path, the applied voltage must be greater than a given threshold voltage $V_{TH}$, that increases with decrease in the target reservoir temperature. In addition, we demonstrate that the maximum cooling power, as well as the coefficient of performance deteriorates as one approaches a lower target reservoir temperature. The novelty of the proposed refrigeration engine is the integration of fabrication simplicity along with descent cooling power. The idea proposed in this paper may pave the way towards the realization of efficient non-local cryogenic refrigeration systems.

physics.app-ph↗

arXiv2020

A realistic non-local heat engine based on Coulomb coupled systems

Optimal non-local heat-engines, based on Coulomb-coupled systems, demand a sharp step-like change in the energy resolved system-to-reservoir coupling around the ground state of quantum-dots. Such a sharp step-like transition in the system-to-reservoir coupling cannot be achieved in a realistic scenario. Here, I propose realistic design for non-local heat engine based on Coulomb-coupled system, which circumvents the need for any change in the system-to-reservoir coupling, demanded by the optimal set-ups discussed in literature. I demonstrate that an intentionally introduced asymmetry (or energy difference) in the ground state configuration between adjacent tunnel coupled quantum dots, in conjugation with Coulomb coupling, is sufficient to convert the stochastic fluctuations from a non-local heat source into a directed flow of thermoelectric current. The performance, along with the regime of operation, of the proposed heat engine is then theoretically investigated using quantum-master-equation (QME) approach. It is demonstrated that the theoretical maximum power output for the proposed set-up is limited to about $50\%$ of the optimal design. Despite a lower performance compared to the optimal set-up, the novelty of the proposed design lies in the conjunction of fabrication simplicity along with reasonable power output. At the end, the sequential transport processes leading to a performance deterioration of the proposed set-up are analyzed and a method to alleviate such transport processes is discussed. The set-up proposed in this paper can be used to design and fabricate high-performance non-local cryogenic heat engines.

physics.app-ph↗

arXiv2019

Enhanced thermoelectric performance actuated by inelastic processes in the channel region

I propose a design strategy to enhance the performance of heat engine via absorption of thermal energy from the channel region. The absorption of thermal energy can be actuated by inelastic processes and may be accomplished by an energy restrictive flow of electrons into the channel. The proposed design strategy employs dual energy filters to inject and extract electrons through the contact to channel interface. The first filter injects a compressed stream of electrons from the hot contact, at an effective temperature much lower than the channel temperature. The compressed stream of injected electrons, then, absorb energy via inelastic scattering inside the channel and are finally extracted via a second filter at the cold contact interface. Rigorous mathematical derivations demonstrate that an optimized performance for the proposed design strategy demands the implementation of a box-car transmission function at the electron injecting terminal and a unit-step transmission function at the electron extracting terminal. Numerical simulation show that in the proposed design strategy, the heat engine performance, under optimal conditions, can surpass the ballistic limit when the required output power is low compared to the quantum bound. The proposed concept can be used to construct high efficiency thermoelectric generators in situations where the source of usable heat energy is limited, but insulated from environmental dissipation.

physics.app-ph↗

arXiv2018

Optimized Peltier cooling via an array of quantum dots with stair-like ground-state energy configuration

With the advancement in fabrication and scaling technology, the rising temperature in nano devices has attracted special attention towards thermoelectric or Peltier cooling. In this paper, I propose optimum Peltier cooling by employing an array of connected quantum dots with stair-like ground-state eigen energy configuration. The difference in ground state eigen energy between two adjacent quantum dots in the stair-like configuration is chosen to be identical with the optical phonon energy for efficient absorption of lattice heat. I show that in the proposed configuration, for a given optical phonon energy, one can optimize the cooling power by tuning the number of stages in the array of quantum dots. A further analysis demonstrates that the maximum cooling power at a given potential bias under optimal conditions doesnot depend strongly on the optical phonon energy or the number of stages at which the maximum cooling power is achieved, provided that the optical phonon energy is less than $kT$. The proposed concept can also be applied to $2-D$ or bulk resonant tunnel and superlattice structures with stair-like resonant energy configuration.

physics.app-ph↗

arXiv2018

Performance analysis of nanostructured Peltier coolers

Employing non-equilibrium quantum transport models, we investigate the details and operating conditions of nano-structured Peltier coolers embedded with an energy filtering barrier. Our investigations point out non-trivial aspects of Peltier cooling which include an inevitable trade-off between the cooling power and the coefficient of performance, the coefficient of performance being high at a low voltage bias and subsequently deteriorating with increasing voltage bias. We point out that there is an optimum energy barrier height for nanowire Peltier coolers at which the cooling performance is optimized. However, for bulk Peltier coolers, the cooling performance is enhanced with the height of the energy filtering barrier. Exploring further, we point out that a degradation in cooling performance with respect to bulk is inevitable as a single moded nanowire transitions to a multi-moded one. The results discussed here can provide theoretical insights for optimal design of nano Peltier coolers.

physics.app-ph↗

arXiv2018

Landauer-Büttiker approach for hyperfine mediated electronic transport in the integer quantum Hall regime

The interplay of spin-polarized electronic edge states with the dynamics of the host nuclei in quantum Hall systems presents rich and non-trivial transport physics. Here, we develop a Landauer-Büttiker approach to understand various experimental features observed in the integer quantum Hall set ups featuring quantum point contacts. The approach developed here entails a phenomenological description of spin resolved inter-edge scattering induced via hyperfine assisted electron-nuclear spin flip-flop processes. A self-consistent simulation framework between the nuclear spin dynamics and edge state electronic transport is presented in order to gain crucial insights into the dynamic nuclear polarization effects on electronic transport and in turn the electron-spin polarization effects on the nuclear spin dynamics. In particular, we show that the hysteresis noted experimentally in the conductance-voltage trace as well as in the resistively detected NMR lineshape results from a lack of quasi-equilibrium between electronic transport and nuclear polarization evolution. In addition, we present circuit models to emulate such hyperfine mediated transport effects to further facilitate a clear understanding of the electronic transport processes occurring around the quantum point contact. Finally, we extend our model to account for the effects of quadrupolar splitting of nuclear levels and also depict the electronic transport signatures that arise from single and multi-photon processes.

cond-mat.mes-hall↗

arXiv2017

Incoherent scattering can favorably influence energy filtering in nanostructured thermoelectrics

Investigating in detail the physics of energy filtering through a single planar energy barrier in nanostructured thermoelectric generators, we reinforce the non-trivial result that the anticipated enhancement in generated power at a given efficiency via energy filtering is a characteristic of systems dominated by incoherent scattering and is absent in ballistic devices. In such cases, assuming an energy dependent relaxation time $τ(E)=kE^r$, we show that there exists a minimum value $r_{min}$ beyond which generation can be enhanced by embedding nanobarriers. For bulk generators with embedded nanobarriers, we delve into the details of inter sub-band scattering and show that it has finite contribution to the enhancement in generation. We subsequently discuss the realistic aspects, such as the effect of smooth transmission cut-off and show that for $r>r_{min}$, the optimized energy barrier is just sufficiently wide enough to scatter off low energy electrons, a very wide barrier being detrimental to the performance. Analysis of the obtained results should provide general design guidelines for enhancement in thermoelectric generation via energy filtering. Our non-equilibrium approach is typically valid in the absence of local quasi-equilibrium and hence sets the stage for future advancements in thermoelectric device analysis, for example, Peltier cooling near a barrier interface.

cond-mat.mes-hall↗

arXiv2016

Role of incoherent scattering on energy filtering in nanostructured thermoelectric generators

The physics of energy filtering in electronic transport through nanoscale barriers is a fundamental aspect in the context of electronic engineering of nanostructured thermoelectrics. In the context of thermoelectric generators, it aims to engineer the Seebeck coefficient to favorably increase the power factor and ultimately the power generated. In this work, we employ the incoherent non-equilibrium Green's function formalism to investigate in detail the physics of energy filtering and how it leads to a direct enhancement in power generation across nanostructured thermoelectrics featuring a single planar energy barrier. In particular, we reinforce that the enhancement in the generated power via energy filtering at a particular operating efficiency is a characteristic of incoherent scattering and is absent in ballistic devices. In such cases, by assuming an energy dependent relaxation time, $τ(E)=kE^r$, we show that there exists a minimum value $r_{min}$ for which the thermoelectric power generation is enhanced and thereby leading to a degradation in power generation for $r<r_{min}$. For bulk generators, we delve into the details of intermode scattering and show that such scattering processes between electrons in higher energy modes and lower energy modes have a finite contribution to the enhancement in the generated power. We also discuss realistic aspects such as finite width of energy barriers and imperfect energy filtering due to partial reflections. In particular, we show that such imperfect filtering and partial transmission of electrons near the top of the barrier affects the enhancement in the generated power drastically in the high efficiency regime of operation. Analysis of the results obtained in this work should provide general design guidelines for nanostructured enhancement in power generation via energy filtering.

cond-mat.mes-hall↗

arXiv2015

Exploring Packaging Strategies of Nano-embedded Thermoelectric Generators

Embedding nanostructures within a bulk matrix is an important practical approach towards the electronic engineering of high performance thermoelectric systems. For power generation applications, it ideally combines the efficiency benefit offered by low dimensional systems along with the high power output advantage offered by bulk systems. In this work, we uncover a few crucial details about how to embed nanowires and nanoflakes in a bulk matrix so that an overall advantage over pure bulk may be achieved. First and foremost, we point out that a performance degradation with respect to bulk is inevitable as the nanostructure transitions to being multi moded. It is then shown that a nano embedded system of suitable cross-section offers a power density advantage over a wide range of efficiencies at higher packing fractions, and this range gradually narrows down to the high efficiency regime, as the packing fraction is reduced. Finally, we introduce a metric - \emph{the advantage factor}, to elucidate quantitatively, the enhancement in the power density offered via nano-embedding at a given efficiency. In the end, we explore the maximum effective width of nano-embedding which serves as a reference in designing generators in the efficiency range of interest.

cond-mat.mes-hall↗