arXiv subjects

Shreya Debnath

Publications and source records attributed to Shreya Debnath.

4 recordsLinked to original sources

arXiv2026

Topological Magnons and Giant Orbital Nernst Effect in a Zigzag Kitaev Antiferromagnet

The exploration of topological and transport properties of collinear antiferromagnets and the role of Kitaev interactions in realising topological states therein have rarely been systematically addressed in literature. In this context, we consider a zigzag-ordered antiferromagnet with both extended Kitaev and Dzyaloshinskii-Moriya interactions (DMI) in presence of an external magnetic field to focus on the topological phases demonstrated by the magnon band structure and validated by the transport properties. The hybridization between the up- and down-spin sectors carries evidences of opening bulk gaps in the magnon band structure, giving rise to nontrivial topological phases characterized by finite Chern numbers, chiral edge modes, and a nonzero thermal Hall conductivity. Furthermore, generally speaking, a finite magnon orbital moment can exist and contribute to the Nernst response even when the net spin moment vanishes owing to the fundamental independence of the spin and orbital magnetizations. This motivates us to investigate the magnon orbital moment, orbital Berry curvature, and the resulting orbital Nernst conductivity associated with the magnon bands. We find that a giant orbital Nernst conductivity emerges even in the absence of an external magnetic field. Moreover, the distinction between different topological phases is more lucidly manifested via the orbital Nernst conductivity, thereby highlighting an enhanced sensitivity of the orbital transport to the underlying band topology. For completeness, we briefly discuss the scenario corresponding to a Néel-ordered spin alignment, which leads to a vanishing Chern number and consequently suppressed thermal Hall and orbital Nernst conductivities compared to the zigzag-ordered case, even in the presence of DMI and Kitaev interactions.

cond-mat.mes-hall↗

arXiv2025

Topological characterization of magnon-polaron bands and thermal Hall conductivity in a frustrated kagome antiferromagnet

Spin-phonon coupling and its efficacy in inducing multiple topological phase transitions in a frustrated kagome antiferromagnet have been rare in literature. To this end, we study the ramifications of invoking optical phonons in such a system via two different coupling mechanisms, namely, a local and a non-local one, which are distinct in their microscopic origin. In case of the local spin-phonon coupling, a single phonon mode affects the magnetic interactions, whereas in the non-local case, two neighbouring phonon modes are involved in the energy renormalization, and it would be worthwhile to compare and contrast between the two. To tackle these phonons, we propose an analytic approach involving a canonical spin-Peierls transformation applied to magnons. The formalism renders a hybridization between the magnons and the phonon modes, yielding magnon-polaron quasiparticles. In both the coupling regimes, validations for the topological signatures are systematically derived from the bulk and edge spectral properties of the magnon-polaron bands that are characterized by their corresponding Chern numbers. Thereafter, we investigate transitions from one topological phase to another solely via tuning the spin-phonon coupling strength. Moreover, these transitions significantly impact the behavior of the thermal Hall conductivity that aids in discerning distinct topological phases. Additionally, the explicit dependencies on the temperature and the external magnetic field are explored in inducing topological phase transitions associated with the magnon-polaron bands. Thus, our work serves as an ideal platform to probe the interplay of frustrated magnetism and polaronic physics.

cond-mat.mes-hall↗

arXiv2024

Magnons on a dice lattice: topological features and transport properties

In this paper, we study the topological properties of magnons on a dice lattice, also known as the dual of a more widely studied kagome lattice. This structure has a central atom at the center of the honeycomb lattice, which leads to the formation of a flat band. Magnetic Hamiltonians associated with the magnon bands are scarcely studied in this flat band system, which motivates us on examining an interplay of different magnetic spin interactions, such as the Heisenberg exchange, Dzyaloshinskii-Moriya interaction (DMI), pseudodipolar interaction (PDI) and magnetocrystalline anisotropies in a dice lattice. In particular, the objective is to ascertain their roles in inducing various topological phases and the phase transitions therein. The competing effects of the DMI and the PDI in inducing transitions from either topological to topological or topological to trivial phases are noted and the corresponding results are supported via the magnon band structures, presence (or absence) of edge modes in a nanoribbon geometry, and the transport characteristic, namely the discontinuities in the thermal Hall conductivities. Meanwhile, the magnetocrystalline anisotropy also plays an intriguing role, where distinct (nonuniform) values at the different sublattice sites result in a richer topological landscape with Chern numbers $C = \pm 2$, $\pm 1$, and $0$, while a uniform anisotropy yields only $C = \pm 2$ and $0$. This discrepancy arises from the broken valley symmetry in the nonuniform case. Finally, we have enriched our understanding on the role of the flat band in impacting the topological features by comparing some of the key results with that of a honeycomb structure.

cond-mat.mes-hall↗

arXiv2024

Studying magnon band topology through low-energy magnon excitations: role of anisotropic Dzyaloshinskii-Moriya interaction

In this work, we study topological properties of magnons via creating spin excitations in both ferromagnets and antiferromagnets in presence of an external magnetic field on a two-dimensional square lattice. It is known that Dzyaloshinskii-Moriya interaction (DMI) plays an important role in coupling between different particle (spin excitation) sectors, here we consider an anisotropic DMI and ascertain the role of the anisotropy parameter in inducing topological phase transitions. While the scenario, for dealing with ferromagnets, albeit with isotropic DMI is established in literature, we have developed the formalism for studying magnon band topology for the antiferromagnetic case. The calculations for the ferromagnetic case are included to facilitate a comparison between the two magnetically ordered systems. Owing to the presence of a two-sublattice structure of an antiferromagnet, a larger number of magnon bands participate in deciding upon the topological properties. However, in both the cases, an extended trivial region is observed even with the DMI to be non-zero, which is surprising since the DMI is the origin of the finite Berry curvature in presence of external magnetic field. Furthermore, in an antiferromagnet, a smaller anisotropy is capable of inducing a gap-closing transition from a topological to a trivial phase compared to that for a ferromagnet. The nature of the phases in both the cases and the phase transitions therein are characterized by the band structure, presence (or absence) of the chiral edge modes observed in a semi-infinite nano-ribbon geometry, computation of the thermal Hall effect, etc. Moreover, the strength of the magnetic field is found to play a decisive role in controlling the critical point that demarcates various topological phases.

cond-mat.mes-hall↗