arXiv subjects

Kingshuk Sarkar

Publications and source records attributed to Kingshuk Sarkar.

7 recordsLinked to original sources

arXiv2026

Universal Scaling of the Magnetocaloric Effect in 2D Ising Monolayers and Bilayer

We report a Monte Carlo study of the magnetocaloric effect (MCE) in two-dimensional ferromagnetic Ising models on square, honeycomb, and triangular lattices with monolayer and bilayer configurations. Using Binder cumulant analysis, we determine the critical temperature ($T_c$) of each structure and find that $T_c$ increases with coordination number, from the honeycomb ($r=3$) to the triangular ($r=6$) lattice. In contrast, the magnetic entropy change ($-\Delta S_M$) decreases with coordination number, reaching its maximum for the honeycomb lattice. After normalization by their peak values and appropriate temperature scaling, both $-\Delta S_M$ and the field exponent $n$ collapse onto universal master curves for different magnetic fields and across all six lattice structures at a fixed low field. This demonstrates universal MCE scaling independent of coordination number and layer count. Critical scaling analysis further supports the observed universality and power-law behavior. Unlike $-\Delta S_M$, the adiabatic temperature change ($\Delta T_{ad}$) increases with coordination number, whereas the magnetic Gr\"{u}neisen parameter ($\Gamma_M$) follows the same trend as $-\Delta S_M$. Although the peak value of $-\Delta S_M$ decreases with coordination number, the relative cooling power and cooling capacity remain nearly unchanged due to compensating broadening of the $-\Delta S_M$ curves. The field dependence of $-\Delta S_M$, relative cooling power, and cooling capacity follows power laws up to $\sim2.6$ T (assuming $J\approx1$ meV). Hysteresis analysis shows that lattices with lower coordination numbers exhibit a faster reduction in loop width with increasing temperature. These results establish the universal scaling behavior of the magnetocaloric effect in two-dimensional monolayer and bilayer magnetic lattices and provide guidelines for designing magnetic refrigerants.

cond-mat.stat-mech↗

arXiv2024

Mott and Wiedemann Franz Law for Monolayer Graphene for Different Scattering Mechanisms

In this study, we conducted a comprehensive review and analysis of the thermoelectric responses exhibited by monolayer pristine graphene in response to temperature variations. Employing the Boltzmann transport theory, we rigorously examined and evaluated various thermoelectric coefficients, with particular emphasis on elucidating their behavior under different scattering mechanisms. We derived the analytical expressions for electrical conductivity, thermopower, and thermal conductivity at low temperatures by Sommerfeld expansion of the Fermi integral. We demonstrated that our numerically obtained values are consistent with the analytical calculations at low temperatures and hence obeying Mott and Wiedeman Franz law. However, the deviation was observed at higher temperatures. Furthermore, we performed theoretical calculations of chemical potential at both low and high temperatures and compared them with our numerically evaluated results at all temperatures. Through extensive calculations and meticulous evaluation, our study contributes to a deeper understanding of the intricate thermoelectric properties inherent in monolayer pristine graphene.

cond-mat.mes-hall↗

arXiv2024

Monte Carlo Simulation of Anisotropic Ising Model Using Metropolis and Wolff Algorithm

We employ Monte Carlo techniques, utilizing the Metropolis and Wolff algorithms, to investigate phase behavior and phase transitions in anisotropic Ising models. Our study encompasses the thermodynamic properties, evaluating energy, magnetization, specific heat, magnetic susceptibility, magnetic entropy, and the Binder cumulant. Additionally, we examine the impact of external fields on these thermodynamic quantities at different externally applied field values. We accurately determine the critical temperature for various model scenarios by analyzing the Binder cumulant. Our investigations also include an analysis of the hysteresis loop for the model for different an-isotropic cases. In particular, our study presents the magnetocaloric effect, which is the change in temperature of magnetic material when exposed to a changing magnetic field, in the different anisotropic cases of the Ising model.

cond-mat.stat-mech↗

arXiv2018

High Temperature Superconductivity in the Cuprates: Materials, Phenomena and a Mechanism

Superconductivity in the cuprates, discovered in the late 1980s and occurring at unprecedentedly high temperatures (up to about 140K) in about thirty chemically distinct families, continues to be a major problem in physics. In this article, after a brief introduction of these square planar materials with weak interlayer coupling, we mention some of the salient electronic properties of hole doped cuprates such as the pseudogap phase and the Fermi arc . We then outline a phenomenological, Ginzburg Landau like theory developed by some of us for the emergent d-wave symmetry superconductivity in these materials, and confronted successfully with a large amount of experimental information. A more recent application of the approach to fluctuation diamagnetism and to the anomalously large Nernst effect is also discussed.

cond-mat.str-el↗

arXiv2018

Seebeck Coefficient of a Single van der Waals Junction in Twisted Bilayer Graphene

When two planar atomic membranes are placed within the van der Waals distance, the charge and heat transport across the interface are coupled by the rules of momentum conservation and structural commensurability, leading to outstanding thermoelectric properties. Here we show that an effective "interlayer phonon drag" determines the Seebeck coefficient (S) across the van der Waals gap formed in twisted bilayer graphene (tBLG). The cross-plane thermovoltage, which is non-monotonic in both temperature and density, is generated through scattering of electrons by the out-of-plane layer breathing (ZO'/ZA2) phonon modes and differs dramatically from the expected Landauer-Buttiker formalism in conventional tunnel junctions. The tunability of the cross-plane Seebeck effect in van der Waals junctions may be valuable in creating a new genre of versatile thermoelectric systems with layered solids.

cond-mat.mes-hall↗

arXiv2017

The correlation between the Nernst effect and fluctuation diamagnetism in strongly fluctuating superconductors

We study the Nernst effect in fluctuating superconductors by calculating the transport coefficient $α_{xy}$ in a phenomenological model where relative importance of phase and amplitude fluctuations of the order parameter is tuned continuously to smoothly evolve from an effective XY model to more conventional Ginzburg-Landau description. To connect with a concrete experimental realization we choose the model parameters appropriate for cuprate superconductors and calculate $α_{xy}$ and the magnetization ${\bf M}$ over the entire range of experimentally accessible values of field, temperature and doping. We argue that $α_{xy}$ and ${\bf M}$ are both determined by the equilibrium properties of the superconducting fluctuations (and not their dynamics) despite the former being a transport quantity. Thus, the experimentally observed correlation between the Nernst signal and the magnetization arises primarily from the correlation between $α_{xy}$ and ${\bf M}$. Further, there exists a dimensionless ratio ${\bf M}/(T α_{xy})$ that quantifies this correlation. We calculate, for the first time, this ratio over the entire phase diagram of the cuprates and find it agrees with previous results obtained in specific parts of the phase diagram. We conclude that that there appears to be no sharp distinction between the regimes dominated by phase fluctuations and Gaussian fluctuations for this ratio in contrast to $α_{xy}$ and ${\bf M}$ individually. The utility of this ratio is that it can be used to determine the extent to which superconducting fluctuations contribute to the Nernst effect in different parts of the phase diagram given the measured values of magnetization.

cond-mat.supr-con↗

arXiv2015

Doping dependence of fluctuation diamagnetism in High Tc superconductors

Using a recently proposed Ginzburg-Landau-like lattice free energy functional due to Banerjee et al. Phys. Rev. B 83, 024510 (2011) we calculate the fluctuation diamagnetism of high-Tc superconductors as a function of doping, magnetic field and temperature. We analyse the pairing fluctuations above the superconducting transition temperature in the cuprates, ranging from the strong phase fluctuation dominated underdoped limit to the more conventional amplitude fluctuation dominated overdoped regime. We show that a model where the pairing scale increases and the superfluid density decreases with underdoping produces features of the observed magnetization in the pseudogap region, in good qualitative and reasonable quantitative agreement with the experimental data. In particular, we explicitly show that even when the pseudogap has a pairing origin the magnetization actually tracks the superconducting dome instead of the pseudogap temperature, as seen in experiment. We discuss the doping dependence of the `onset' temperature for fluctuation diamagnetism and comment on the role of vortex core-energy in our model.

cond-mat.supr-con↗