arXiv subjects

Raymond Wiedmann

Publications and source records attributed to Raymond Wiedmann.

3 recordsLinked to original sources

arXiv2025

Quantum effects in the magnon spectrum of 2D altermagnets via continuous similarity transformations

We investigate quantum effects on magnon excitations in a minimal spin-1/2 Heisenberg model for 2D altermagnets on the square lattice. A continuous similarity transformation is applied in momentum space to derive an effective Hamiltonian that conserves the number of magnon excitations. This allows us to quantitatively calculate the one-magnon dispersion, the effects of magnon-magnon interactions, and the dynamic structure factor in a certain range of parameters. In particular, we focus on the altermagnetic spin splitting of the magnon bands and the size of the roton minimum. We further map out divergencies of the continuous similarity transformation for different types of generators, which signal either the breakdown of the N\'eel-ordered phase or the presence of significant magnon decay.

cond-mat.str-el↗

arXiv2025

Quantum geometry and low-frequency optical conductivity of nodal planes

Nodal planes, two-dimensional symmetry-enforced band crossings, can carry a topological charge, similar to Weyl points. While the transport properties of Weyl points are well understood, those of nodal planes remain largely unexplored. These properties are influenced not only by the Berry curvature, but also by other quantum geometric quantities. In this work we study the quantum geometry - specifically the Berry curvature and quantum metric - and the linear optical conductivity of topological nodal planes. We introduce a low-energy model and investigate its low-frequency optical responses to determine the unique signatures of nodal planes. By comparing these findings to the optical response in a tight-binding model with a topological nodal plane, we observe consistent low-frequency behavior with a cubic power law. This paves the way for the experimental detection of nodal planes through optical conductivity measurements for which we suggest suitable materials, most promisingly the material group $X$Mo$_3$S$_3$ ($X$ = Rb, K, Cs).

cond-mat.mes-hall↗

arXiv2024

Topological responses from gapped Weyl points in 2D altermagnets

We study the symmetry requirements for topologically protected spin-polarized Weyl points in 2D altermagnets. The topology is characterized by a quantized $\pi$-Berry phase and the degeneracy is protected by spin-space group symmetries. Gapped phases with finite Chern and/or spin/chirality Chern numbers emerge under different symmetry-breaking mass terms. We investigate the surface and transport properties of these gapped phases using representative electronic tight-binding and magnonic linear spin-wave models. In particular, we calculate the electronic and magnonic Hall currents and discuss implications for experiments.

cond-mat.mes-hall↗