arXiv subjects

Sapta Sindhu Paul Chowdhury

Publications and source records attributed to Sapta Sindhu Paul Chowdhury.

7 recordsLinked to original sources

arXiv2026

Extreme Suppression of Thermal Conductivity in Monolayer Beryllene

We demonstrate an extreme suppression of thermal conductivity in monolayer beryllene through first-principles solutions of the phonon Boltzmann transport equation. While the fully converged three-phonon calculation predicts a room-temperature lattice thermal conductivity of 154.3 W/(m$\cdot$K), inclusion of four-phonon interactions suppresses it to 10.7 W/(m$\cdot$K), a reduction of more than 90\%. This exceptionally large reduction of the thermal conductivity is amongst the highest reported in two-dimensional materials. The microscopic origin of this breakdown is traced to the strong sensitivity of the low-frequency flexural ZA phonons to four-phonon scattering: mode-resolved scattering rates reveal a pronounced enhancement of ZA scattering, which substantially shortens their lifetimes and suppresses their dominant contribution to heat conduction. Moreover, the temperature dependence of the thermal conductivity changes from $κ\propto T^{-0.86}$ to $κ\propto T^{-1.38}$ upon inclusion of four-phonon processes. Our results establish $α$-beryllene as an unusually strong case of four-phonon-controlled thermal transport amongst two-dimensional materials. These findings identify selective higher-order scattering of flexural phonons as a key mechanism for controlling thermal transport in strongly anharmonic low-dimensional systems.

cond-mat.mtrl-sci↗

arXiv2025

Anomalous Temperature Induced Transition and Convergence of Thermal Conductivity in Germanene Monolayer

We report an anomalous temperature-induced transition in thermal conductivity in germanene monolayer around a critical temperature $T_c = 350 \, \text{K}$. Equilibrium molecular dynamics simulations reveal a transition from $κ\sim T^{-2}$ scaling below $T_c$ to $κ\sim T^{-1/2}$ above, contrasting with conventional $κ\sim T^{-1}$ behavior. This anomalous scaling correlates with the long-scale characteristic timescale $τ_2$ obtained from double exponential fitting of the heat current autocorrelation function. Phonon mode analysis using normal mode decomposition indicates that a redshift in ZO phonons reduces the acoustic-optical phonon gap, causing an overlap, enhances the phonon-phonon scattering, driving the anomalous scaling behavior. Moreover, nonequilibrium simulations find a convergent thermal conductivity of germanene with sample size, in agreement with mode coupling theory, owing to the high scattering of ZA phonons due to the inherent buckling of germanene.

cond-mat.mes-hall↗

arXiv2025

Tunable Interfacial Thermal Conductance in Graphene/Germanene van der Waals Heterostructure using an Optimized Interlayer Potential

Accurately modeling interfacial thermal transport in van der Waals heterostructures is challenging due to the limited availability of interlayer interaction potentials. We develop a pairwise interlayer potential for graphene/germanene van der Waals heterostructure using the binding energy obtained from ab-initio density functional theory calculations and use it to calculate the interfacial thermal conductivity. Our calculations reveal that the interfacial thermal conductivity shows superior tunability with external strain. The phonon density of states calculations show a blueshift in the phonon spectra with an applied compressive strain in the direction of heat flow, increasing the interfacial thermal conductance to $\sim$136% of the unstrained value. In contrast, a tensile strain is found to cause an opposite effect, reducing the conductance to $\sim$70% of the unstrained value. Moreover, due to increased availability of phonons for heat transfer, both temperature and interaction strength are found to correlate positively with the interfacial thermal conductance for both directions of heat flow.

cond-mat.mes-hall↗

arXiv2024

Salt Effects on Ionic Conductivity Mechanisms in Ethylene Carbonate Electrolytes: Interplay of Viscosity and Ion-ion Relaxations

The intricate role of shear viscosity and ion-pair relaxations on ionic conductivity mechanisms and the underlying changes induced by salt concentration ($c$) in organic liquid electrolytes remain poorly understood despite their widespread technological importance. Using molecular dynamics simulations employing nonpolarizable force fields for $c$ ranging between 10$^{-3}$ to 10$^1$ M, we show that the low and high $c$ regimes of the EC-LiTFSI electrolytes are distinctly characterized by $η\simτ_c^{1/2}$ and $η\simτ_c^{1}$, where $η$ and $τ_c$ are shear viscosity and cation-anion relaxation timescales, respectively. Our extensive simulations and analyses suggest a universal relationship between the ionic conductivity and $c$ as $σ(c)\sim c^αe^{-c/c_{0}} (α>0)$. The proposed relationship convincingly explains the ionic conductivity over a wide range of $c$, where the term $c^α$ accounts for the uncorrelated motion of ions and $e^{-c/c_0}$ captures the salt-induced changes in shear viscosity. Our simulations suggest vehicular mechanism to be dominant at low $c$ regime which transitions into a structural diffusion mechanism at high $c$ regime, where structural relaxation is the dominant form of ion transport mechanism. Our findings shed light on some of the fundamental aspects of the ion conductivity mechanisms in liquid electrolytes, offering insights into optimizing the ion transport in EC-LiTFSI electrolytes.

cond-mat.soft↗

arXiv2023

Modeling Interlayer Interactions and Phonon Thermal Transport in Silicene Bilayer

We develop an accurate interlayer pairwise potential derived from the \textit{ab-initio} calculations and investigate the thermal transport of silicene bilayers within the framework of equilibrium molecular dynamics simulations. The electronic properties are found to be sensitive to the temperature with the opening of the band gap in the $Γ$$\rightarrow$M direction. The calculated phonon thermal conductivity of bilayer silicene is surprisingly higher than that of monolayer silicene, contrary to the trends reported for other classes of 2D materials like graphene and hBN bilayers. This counterintuitive behavior of the bilayer silicene is attributed to the interlayer interaction effects and inherent buckling, which lead to a higher group velocity in the LA$_1$/LA$_2$ phonon modes. The thermal conductivity of both the mono- and bilayer silicene decreases with temperature as $κ\sim T^{-0.9}$ because of the strong correlations between the characteristic timescales of heat current autocorrelation function and temperature ($τ\sim T^{-0.75}$). The mechanisms underlying phonon thermal transport in silicene bilayers are further established by analyzing the temperature induced changes in acoustic group velocity.

cond-mat.mtrl-sci↗

arXiv2023

Ion Transport Mechanisms in Pectin-containing EC-LiTFSI Electrolytes

Using all-atom molecular dynamics simulations, we report the structure and ion transport characteristics of a new class of solid polymer electrolytes that contain biodegradable and mechanically stable biopolymer pectin. We simulate a highly conducting ethylene carbonate (EC) as a solvent for lithium-trifluoromethanesulfonimide (LiTFSI) salt containing different weight percentages of pectin. Our simulations reveal that the pectin chains reduce the coordination numbers of lithium ions around the counterions (and vice-versa) because of stronger lithium-pectin interactions compared to lithium-TFSI interactions. Further, the pectin is found to promote smaller ionic aggregates over larger ones, contrary to results typically reported for liquid and polymer electrolytes. We observe that the loading of pectin in EC-LiTFSI electrolytes increases the viscosity ($η$) and relaxation timescales ($τ_c$), indicating higher mechanical stability and, consequently, the mean squared displacements, diffusion coefficients (D), and the Nernst-Einstein conductivity ($σ_{NE}$) decrease. Interestingly, while the lithium diffusivities are related to the ion-pair relaxation timescales as $D_+\sim τ_c^{-3.1}$, the TFSI$^-$ diffusivities exhibit excellent correlations with ion-pair relaxation timescales as $D_-\sim τ_c^{-0.95}$. On the other hand, the NE conductivities are dictated by distinct transport mechanisms and scales with ion-pair relaxation timescale as $σ_{NE}\sim τ_c^{-1.85}$.

cond-mat.soft↗

arXiv2019

Proximity effects in Graphene and Ferromagnetic CrBr3 van der Waals Heterostructure

We report on first-principle calculations on magnetic proximity effect in a van der Waals heterostructure formed by a graphene monolayer induced by its interaction with a two-dimensional (2D) ferromagnet (chromium tribromide, CrBr3). We observe that the magnetic proximity effect arising from the spin-dependent interlayer coupling depends sensitively on the interlayer electronic configuration. The proximity effect results in spin polarization of graphene orbital by up to 63.6 %, together with a miniband splitting band gap of about 73.4 meV and 8% enhancement in magnetic moment (3.47$μ$B/cell) in heterostructure. The position of the Fermi level in the Dirac cone is shown to depend strongly on the graphene-CrBr3 interlayer separation of 3.77 Angstrom. Consequently, we also show that a perpendicular electric field can be used to control the miniband spin splitting and transmission spectrum. Also, the interfacial polarization effect due to the existence of two different constituents reinforces the conductivity via electrostatic screening in the heterolayer. These findings point toward potential nanoscale devices where the electric field driven magnetic proximity effect can lead to unique spin controllability and possible engineering of spin gating.

cond-mat.mes-hall↗