R. Stumberger | Searcharxiv

arXiv2024

Chiral electronic excitations and strong electron-phonon coupling to Weyl fermions in the Kagome semimetal Co$_3$Sn$_2$S$_2$

We present results of a Raman scattering study of the Kagome ferromagnet Co$_3$Sn$_2$S$_2$, with a focus on electronic and phononic excitations and their interplay. We provide a theoretical analysis of the electronic band structure, enabling a semi-quantitative explanation of the spectra. A prominent feature in the electronic spectra is a redistribution of spectral weight from low to high energies in all polarization configurations starting at the Curie temperature T$_C$. In the symmetry-resolved spectra, the suppression of the A$_{1g}$ continuum in the ferromagnetic state arises from the redistribution of electronic states below T$_C$, while a strong enhancement of the A$_{2g}$ continuum is linked to the dynamics of fermions near the Fermi level $E_{\rm F}$ being characterized by spin-momentum locking near Weyl points. The A$_{1g}$ phonon modulates the position of these Weyl points and couples strongly to the related fermions close to $E_{\rm F}$. These results allow a comprehensive understanding of the bulk band structure evolution as a function of temperature in Co$_3$Sn$_2$S$_2$, offering key insights for further studies of the driving force behind the long-range magnetic order and novel topological states in this compound.

cond-mat.str-el↗

arXiv2022

Evolution of lattice, spin, and charge properties across the phase diagram of FeSe$_{1-x}$S$_x$

A Raman scattering study covering the entire substitution range of the FeSe$_{1-x}$S$_x$ solid solution is presented. Data were taken as a function of sulfur concentration $x$ for $0\le x \le 1$, of temperature and of scattering symmetry. All type of excitations including phonons, spins and charges are analyzed in detail. It is observed that the energy and width of iron-related B$_{1g}$ phonon mode vary continuously across the entire range of sulfur substitution. The A$_{1g}$ chalcogenide mode disappears above $x=0.23$ and reappears at a much higher energy for $x=0.69$. In a similar way the spectral features appearing at finite doping in A$_{1g}$ symmetry vary discontinuously. The magnetic excitation centered at approximately 500 cm$^{-1}$ disappears above $x=0.23$ where the A$_{1g}$ lattice excitations exhibit a discontinuous change in energy. The low-energy mode associated with fluctuations displays maximal intensity at the nemato-structural transition and thus tracks the phase boundary.

cond-mat.supr-con↗