arXiv subjects

Kaushal K. Kesharpu

Publications and source records attributed to Kaushal K. Kesharpu.

6 recordsLinked to original sources

arXiv2025

Quantum selection of order and dynamic properties of Kitaev-Heisenberg ferromagnet on a triangular lattice

Recent interest in monolayer materials motivated a search for two-dimensional ferromagnets with sizable spin-orbit coupling. Magnetic anisotropy of exchange Hamiltonian, induced by spin-orbit coupling, may not only stabilize long-range order, but also in turn can be a source of frustration and accidental degeneracy, which is the case for the Kitaev-Heisenberg model. Here we present an extensive study of ground state and excitations of ferromagnetic anisotropic-exchange Kitaev-Heisenberg model on a triangular lattice using order-by-disorder and augmented spin-wave theory calculations. It is shown that while bond-dependent terms of the model do not affect the ground state classically, quantum fluctuations select preferred magnetization direction of the ferromagnetic state and significantly alter classical phase diagram. Anisotropic terms of the magnetic Hamiltonian also give rise to magnon-magnon interactions that lead to spontaneous decay and spectral renormalization, which we illustrate using non-linear spin-wave theory.

cond-mat.str-el↗

arXiv2024

Anisotropic zero-resistance onset in organic superconductors

We study the coexistence of superconductivity (SC) and density-wave state and reconcile various puzzling experimental data in organic superconductors (TMTSF)$_{2}$PF$_{6}$ and (TMTSF)$_{2}$ClO$_{4}$. The anisotropic resistance drop above $T_c$ is qualitatively described by nascent isolated SC islands within a bulk analytical model. However, the observed anisotropic SC onset is explained only when the finite size and flat needle shape of samples is considered. Our results pave a way to estimate the volume fraction and the typical size of SC islands in far from the sample surface, and apply to many inhomogeneous superconductors, including high-$T_c$ cuprate or Fe-based ones.

cond-mat.supr-con↗

arXiv2023

Evolution of shape and volume fraction of superconducting domains with temperature and anion disorder in (TMTSF)$_2$ClO$_4$

In highly anisotropic organic superconductor (TMTSF)$_2$ClO$_4$, superconducting (SC) phase coexists with metallic and spin density wave phases in the form of domains. Using the Maxwell-Garnett approximation (MGA), we calculate the volume ratio and estimate the shape of these embedded SC domains from resistivity data at various temperature and anion disorder, controlled by the cooling rate or annealing time of (TMTSF)$_{2}$ClO$_{4}$ samples. We found that the variation of cooling rate and of annealing time affect differently the shape of SC domains. In all cases the SC domains have oblate shape, being the shortest along the interlayer $z$-axis. This contradicts the widely assumed filamentary superconductivity along $z$-axis, used to explain the anisotropic superconductivity onset. We show that anisotropic resistivity drop at the SC transition can be described by the analytical MGA theory with anisotropic background resistance, while the anisotropic $T_c$ can be explained by considering a finite size and flat shape of the samples. Due to a flat/needle sample shape, the probability of percolation via SC domains is the highest along the shortest sample dimension ($z$-axis), and the lowest along the sample length ($x$-axis). Our theory can be applied to other heterogeneous superconductors, where the size $d$ of SC domains is much larger than the SC coherence length $ξ$, e.g. cuprates, iron based or organic superconductors. It is also applicable when the spin/charge-density wave domains are embedded inside a metallic background, or vice versa.

cond-mat.supr-con↗

arXiv2023

Topological Hall effect induced by classical large-spin background: $su(2)$ path-integral approach

The $su(2)$ coherent-state path-integral technique is employed to study lattice electrons strongly coupled to a quantum spin background. In the large-spin limit it is replaced with its classical counterpart that breaks the time-reversal symmetry. The fermions propagating through a classical large-spin texture may then exhibit the topological Hall effect which arises even for a zero scalar spin chirality of the underlying spin background.

cond-mat.str-el↗

arXiv2019

The evolution of electron dispersion in the series of rare-earth tritelluride compounds obtained from their charge-density-wave properties and susceptibility calculations

We calculated electron susceptibility of rare-earth tritelluride compounds RTe$_3$ as a function of temperature, wave vector and electron-dispersion parameters. Comparison of results obtained with the available experimental data on the transition temperature and on the wave vector of a charge-density wave in these compounds allowed us to predict values and the evolution of electron-dispersion parameters with the variation of atomic number of rare-earth element R.

cond-mat.str-el↗

arXiv2018

Self-consistent and Maxwell approximations to describe the excess conductivity anisotropy in FeSe above superconducting transition temperature

Using the self-consistent approximation we calculate conductivity in an anisotropic heterogeneous media with superconducting inclusions and compare the results with those obtained previously using the Maxwell approximation and with available experimental data on excess conductivity above $ T_c= $~8K in FeSe. Advantages and drawbacks of these two approximations are discussed. The obtained analytical formulas can be applied to various other anisotropic heterogeneous superconductors, including high-Tc layered superconductors.

cond-mat.supr-con↗