arXiv subjects

Ritesh Das

Publications and source records attributed to Ritesh Das.

10 recordsLinked to original sources

arXiv2026

Strain-controlled magnetism and magnetoelasticity in monolayer NiPS$_3$ and CrPS$_4$

We develop a first-principles framework for magnetoelastic coupling in two-dimensional magnets based on a strain-dependent Heisenberg model. In this approach, strain derivatives of the exchange interactions provide direct access to magnetostriction and to the magnetic renormalization of the elastic tensor, establishing a microscopic link between spin interactions and elastic response. We apply the method to monolayer NiPS$_3$ and CrPS$_4$, which exhibit contrasting magnetoelastic behavior. NiPS$_3$ shows weak and nearly isotropic spin-lattice coupling, consistent with a robust zigzag antiferromagnetic ground state. In contrast, CrPS$_4$ displays strong anisotropic coupling, leading to strain-driven transitions between spin-spiral and ferromagnetic phases and significant changes in the critical temperature and elastic response. Our results demonstrate a general route to quantify magnetoelastic effects in low-dimensional magnets and highlight CrPS$_4$ as a promising platform for strain engineering of magnetic order.

cond-mat.mtrl-sci↗

arXiv2026

Magnetic ground states of CrPS$_4$ and NiPS$_3$ monolayers from long-range exchange interactions

We investigate the magnetic properties of monolayer CrPS$_4$ and NiPS$_3$ by combining first-principles calculations, second-principles spin models, and Monte Carlo simulations. Unlike conventional approaches that truncate exchange interactions after only a few shells and determine them by fitting total energies, we extract the magnetic exchange tensors directly from density functional theory using the LKAG formalism and include interactions until numerical convergence is achieved. We show that long-range exchange interactions qualitatively modify the magnetic behavior of both materials. In CrPS$_4$, they destabilize the previously predicted ferromagnetic ground state and stabilize a spin-spiral phase, reducing the critical temperature to about 21\,K, in agreement with available experiments. The resulting magnetic phase diagram contains multiple collinear and non-collinear phases that can be tuned by temperature and external magnetic fields. In NiPS$_3$, the experimentally observed zigzag antiferromagnetic order only emerges when exchange interactions up to the fifth shell are included. These results demonstrate that quantitatively predictive spin models for thiophosphate monolayers require long-range exchange interactions and provide a predictive framework for accurately describing two-dimensional van der Waals magnets.

cond-mat.mtrl-sci↗

arXiv2026

Magnon-polaron mediated spin Seebeck effect in altermagnets

Altermagnets, distinguished by compensated antiparallel spins yet nondegenerate magnon spectra, bridge the gap between ferromagnets and antiferromagnets. Although several probes such as anisotropic transport and spectroscopic measurements have been proposed to identify altermagnetic order, experimentally accessible transport signatures remain highly desirable. Here, we show that in altermagnets subject to an external magnetic field, the spin Seebeck effect exhibits pronounced directional anisotropy. Specifically, the spin Seebeck coefficient differs significantly along in-plane directions, and this anisotropy increases with field strength. Magnetoelastic interactions further produce resonant peaks whose positions with respect to an applied magnetic field reflect the intrinsic magnon band anisotropy, and provide localized features that enhance the distinguishability of the altermagnetic response. The peaks provide a robust experimental signature of altermagnetic order. Our findings serve as signatures of altermagnetic order while laying the groundwork for their application in spintronic devices.

cond-mat.mes-hall↗

arXiv2026

Magnomechanical Coupling in Suspended 2D van der Waals Ferromagnets

Magnomechanical systems provide a promising route for exploring coherent hybrid magnon-phonon interactions and hybrid information processing, but their realization has so far been limited by weak magnon-phonon coupling in conventional bulk platforms. We show that a suspended membrane of a two-dimensional van der Waals ferromagnet with in-plane magnetization and out-of-plane mechanical oscillations exhibits large magnomechanical coupling dominated by magnetoelastic interactions. The parametric single magnon-phonon coupling rate scales linearly with pre-strain and can reach hundreds of Hertz to low kiloHertz in suspended membranes of van der Waals ferromagnets such as CrGeTe_3 under experimentally realistic conditions. This rate exceeds typical values reported for YIG spheres by more than three orders of magnitude. Our results demonstrate that suspended membranes of van der Waals magnets provide a robust and highly tunable platform for magnomechanics.

cond-mat.mes-hall↗

arXiv2025

Spin Wave Dispersion of the van der Waals Antiferromagnet NiPS$_3$

We calculate the magnon dispersion spectra of the two-dimensional zigzag van der Waals antiferromagnet NiPS$_3$ for monolayer, bilayer, and bulk systems as a function of an external magnetic field. We calculate the exchange and anisotropy constants in our spin model by first principles. We can accurately explain the transition from a collinear to a canted ground state for a magnetic field applied normal to the (in-plane) easy-axis, and a spin-flop transition when the field is parallel to it. A topologically protected Dirac nodal line is present and robust with respect to both external and anisotropy fields.

cond-mat.mes-hall↗

arXiv2025

Dipolar-exchange spin waves in thin bilayers

We investigate the dipolar-exchange spin wave spectrum in thin ferromagnetic bilayers with inplane magnetization, incorporating interlayer exchange coupling and intra- and interlayer dipolar interactions. In the continuum approximation we analyze the nonreciprocity of propagating magnetic stray fields emitted by spin waves as a function of the relative orientation of the layer magnetizations that are observable by magnetometry of synthetic antiferromagnets or weakly coupled type-A van der Waals antiferromagnetic bilayers as a function of an applied magnetic field.

cond-mat.mes-hall↗

arXiv2025

Spin waves in the bilayer van der Waals magnet CrSBr

We derive analytical expressions for the spin wave frequencies and precession amplitudes in monolayer and antiferromagnetically coupled bilayer CrSBr under in-plane external magnetic fields. The analysis covers the antiferromagnetic, ferromagnetic, and canted phases, demonstrating that the spin wave frequencies in all phases are tunable by the applied magnetic field. We discuss the roles of intra- and interlayer exchange interactions, triaxial anisotropy, and intralayer dynamic dipolar fields in controlling the magnetization dynamics.

cond-mat.mes-hall↗

arXiv2023

Majorana fermion induced power-law scaling in the violations of the Wiedemann-Franz law

Violation of the Wiedemann-Franz law in a 2D topological insulator due to Majorana bound states is studied via the Lorenz ratio in the single-particle picture. We study the scaling of the Lorenz ratio in the presence and absence of Majorana bound states with inelastic scattering modeled using a Buttiker voltage-temperature probe. We compare our results with that seen in a quantum dot junction in the Luttinger liquid picture operating in the topological Kondo regime. We explore the scaling of the Lorentz ratio in our setup when either phase and momentum relaxation or phase relaxation is present. This scaling differs from that predicted by the Luttinger liquid picture for both uncoupled and coupled Majorana cases.

cond-mat.mes-hall↗

arXiv2023

Majorana Thermoelectrics and Refrigeration

A two-terminal quantum spin-Hall heat engine and refrigerator with embedded Majorana bound states (MBS) is analyzed for optimality in thermoelectric performance using the Landaeur-Buttiker approach. This investigation can be an effective tool to detect MBS. Furthermore, the occurrence of MBS can enhance the performance to rival, as well as outperform, some modern nanoscale quantum heat engines and quantum refrigerators. The optimal performance of this MBS quantum heat engine and quantum refrigerator can be further enhanced by an Aharonov-Bohm flux.

cond-mat.mes-hall↗

arXiv2022

Probing Majorana Bound States via Thermoelectric Transport

We propose a set of thermoelectric experiments based on Aharonov-Bohm interferometry to probe Majorana bound states (MBS), which are generated in 2D topological insulators (TI) in the presence of superconducting and ferromagnetic correlations via the proximity effect. The existence and nature (coupled or uncoupled) of these MBS can be determined by studying the charge and heat transport, specifically, the behavior of various thermoelectric coefficients like the Seebeck coefficient, Peltier coefficient, thermal conductance, and violations of Wiedemann-Franz law as a function of the Fermi energy and Aharonov-Bohm flux piercing the TI ring with the embedded MBS.

cond-mat.mes-hall↗