arXiv subjects

K. Navamani

Publications and source records attributed to K. Navamani.

6 recordsLinked to original sources

arXiv2026

A Flickering Resonance Degeneracy on Entropy-Ruled Charge Transport in the Extended Hopping Sites for Biological Systems: Role of Static-to-Dynamic Disorder Transition

Charge transport (CT) in biological systems is of great interest due to its role in various functional activities like photobiology, bioenergetics, redox catalytic and other metabolic activities, etc. It has been observed by various studies that the presence of a dynamic disorder in biomolecules facilitates charge dynamics in the intermediate transport regime, i.e., far from hopping and towards a bank-like mechanism. Hitherto, the dynamic disorder (in a time scale, coupling between electronic and nuclear dynamics) weightage on CT in molecules is not well-established for the measurement of molecular conductivity from small to long-range ordering. With this motivation, we propose the flickering resonance-coupled entropy-ruled charge transport theory for transfer-rate and diffusion-based mobility (D/{\mu}) calculations. The proposed analytical formalism incorporates the impact of dynamic disorder-correlated degeneracy (in a flickering-resonance manner) on the entropy-ruled electron transfer rate and diffusion-mobility, which are valid for localized hopping, delocalized band transport, and regimes in between. By this approach, it has been observed that the dynamics-driven electronic site matching probability enhances the degeneracy, which is quantified by the differential entropy. The analysis clearly shows that for ultra-fast dynamical and degenerate cases, the entropy-ruled mobility is transformed as band mobility, rather than the thermally activated hopping or diffusion process.

cond-mat.dis-nn↗

arXiv2023

Unified Entropy-Ruled Einstein Relation for Bulk and Low-Dimensional Systems: A Hopping to Band Shift Analysis

In this letter, we present the unified paradigm on entropy-ruled Einstein diffusion-mobility relation ({\mu}/D ratio) for all dimensional systems (1D, 2D and 3D) of molecules and materials. The different dimension-associated fractional value of the variation in differential entropy with respect to the chemical potential ({\Delta}h/{\Delta}{\eta}) gives the quantum-classical transition version of {\mu}/D relation. This is a new alternative version for quantum devices, instead of Einstein original relation of {\mu}/D = q/kT; where q, k and T are the electric charge, Boltzmann constant and temperature, respectively. It is found that the fractional value of {\Delta}h/{\Delta}{\eta} for {\mu}/D ratio for different dimensional systems or devices is a direct consequences with the average energy-Fermi energy relation, which can varies with the typical dimensions, whether the system belongs to 1D or 2D or 3D. This unified entropy-ruled transport formalism works well for both the quantum and classical systems with equilibrium as well as non-equilibrium conditions. Based on the dimensional dependent entropy-ruled {\mu}/D factor, the Navamani-Shockley diode equation is transformed.

cond-mat.mes-hall↗

arXiv2019

Extended Einstein diffusion-mobility equation for two-dimensional Schrödinger-type quantum materials

We present the exact analytical equation of diffusion-mobility for two-dimensional (2D) Schrödinger type transport systems, from molecules to materials. The density of electronic states in such Schrödinger systems pertains to the 2D non-relativistic carrier dynamics. We implement the Gaussian function into carrier density derivation; accordingly we develop the electronic compressibility and diffusion-mobility for both the generic and the degenerate Fermi systems. This model is originally developed from generalized Einstein relation, along with concern about the thermodynamic effects on many-body interactions. The effect of interactions is included through the imperfect Fermi-gas entropy function. Our extended model explains the cooperative behavior of thermal and electronic counterparts on diffusion-mobility in disordered systems at wide temperature range. Using earlier experimental and theoretical results, we have shown the validity of our extended Einstein model for different 2D degenerate systems. The results validate the original Einstein equation at certain sets of temperature and chemical potential values for different Gaussian variances. Beyond those combinations, the deviation is observed. At very low temperature, the diffusion-mobility depends only on chemical potential, which is the extended Einstein equation for ideal quantum materials.

cond-mat.stat-mech↗

arXiv2017

Generalized Charge Energy Rate for Organic Solids and Biomolecular Aggregates Through Drift-Diffusion and Hopping Transport Equations: A Unified Theory

We derive generalized charge energy rate equations for organic solids and biomolecular aggregates, even when these are dynamically disordered. These equations suggest that the transport in such cases rely on both drift and diffusion phenomena. The presence of disorder and field effects makes the equations nonlinear and together with cooperativity, these enhance the charge and energy transport. The generalized drift diffusion expression connects the adiabatic band and nonadiabatic hopping transport mechanisms, well suited for any complex organic semiconductors or assemblies of bio molecular systems. Here we have proposed donor-acceptor (DA) reaction state model, which examines the probability of charge transfer and the rate between two distinct transition state identities. From our analytical equations, we suggest that charge and energy transport property in DA states can be tuned by only a single parameter, i.e., the chemical potential. Importantly, we find the non-equilibrium assisted drift-diffusion transport at non- steady state regime in 2D and 3D semiconducting devices. The numerical results clearly support our unified analytical equations, which goes beyond Einstein's diffusion law even in quasi- equilibrium cases.

cond-mat.mes-hall↗

arXiv2017

Effect of Dynamic Disorder on Charge Transport in Organic Molecules

The charge transfer integral, site energy and the stacking angle fluctuations are used to study the hole and electron transport in recently synthesized dialkyl substituted thienothiophene caped benzobisthiazole (BDHTT-BBT) and methyl-substituted dicyanovinyl-capped quinquethiophene (DCV5T-Me) molecules. The charge transfer parameters, such as coherent and incoherent rate coefficients, hopping conductivity, mobility, disorder drift time, drift force, potential equilibrium rate and density flux rate are calculated and discussed. It has been observed that the charge decay up to the crossover point (or disorder drift time) is exponential, non-dispersive and charge transport follows the band-like transport. Beyond the disorder drift time, the charge decay is not fully exponential, dispersive and it follows the incoherent hopping transport. The proposed expressions for density flux and diffusion shows their dependency on dynamic disorder and is in agreement with the Troisi model on diffusion limited by thermal disorder. The density flux rate is directly related with the drift force which facilitates the charge transfer. Calculated electron hopping conductivity in the BDHTT-BBT and DCV5T-Me is 0.8 and 0.18 S/cm, respectively. Molecule BDHTT-BBT has good electron mobility of 0.36 cm^2/V s, which has larger electron density flux rate and drift force of 1.7 x10^20 C/m^3 s and 1.44x10^-12 N.

cond-mat.soft↗

arXiv2017

Unified Quantum Classical Theory of Einstein Diffusion-Mobility Relationship for Ordered and Disordered Semiconductors

We propose a unified diffusion-mobility relation which quantifies both quantum and classical levels of understanding on electron dynamics in ordered and disordered materials. This attempt overcomes the inability of classical Einstein relation (diffusion-mobility ratio) to explain the quantum behaviors, conceptually well-settles the dimensional effect, phase transition and nonlinear behavior of electronic transport. Our proposed theory relies on the chemical potential which provides the coupling mechanism of charge-heat current, due to electron-phonon coupling. We have derived expressions which explain charge transport in both degenerate and nondegenerate materials, and also provide the linear and nonlinear relationship between the charge density and chemical potential. Theoretically, we find that the symmetrical nature of electron-hole transport in strongly correlated two-dimensional semiconductors indicates linear dispersion. We also observe the broken symmetry in the nonlinear regime. This generalized diffusion-mobility relation explains both the strongly and weakly correlated systems from low temperature to high temperature, in both the relativistic as well as nonrelativistic domains. In vanishing charge density limit of nondegenerate cases, the nonlinear transport reduces to linear like transport, which is the classical Einstein relation.

cond-mat.other↗