Henrik Till Lemke | Searcharxiv

arXiv2026

Chemical and optical control of chiral-domain dynamics in 1T-TaS$_2$

Optical control of symmetry-breaking quantum phases is often constrained when one domain is strongly favored in equilibrium. This limitation is exemplified by the chiral charge-density-wave (CDW) order in 1T-TaS$_2$, where pristine samples predominantly select a single chirality. Here we show that free-energy landscape engineering through Ti substitution enables a distinct nonthermal pathway for ultrafast chiral-domain redistribution. Ti doping stabilizes coexisting chiral domains and tunes their relative stability, allowing femtosecond excitation to drive an asymmetric and anisotropic redistribution from the dominant toward the minority chirality. The subpicosecond response follows a $\sim2$ THz amplitude mode and is consistent with a phonon-assisted pathway involving transient domain-wall configurations. Our results establish free-energy landscape engineering as a strategy for selecting nonequilibrium transition pathways.

cond-mat.str-el↗

arXiv2023

Non-equilibrium dynamics of spin-lattice coupling

Interactions between the different degrees of freedom form the basis of many manifestations of intriguing physics in condensed matter. In this respect, quantifying the dynamics of normal modes that themselves arise from these interactions and how they interact with other excitations is of central importance. Of the different types of coupling that are often important, spin-lattice coupling is relevant to several sub-fields of condensed matter physics; examples include spintronics, high-TC superconductivity, and topological materials. While theories of materials where spin-lattice coupling is relevant can sometimes be used to infer the magnitude and character of this interaction, experimental approaches that can directly measure it are rare and incomplete. Here we use time-resolved X-ray diffraction to directly access the spin-lattice coupling by measuring both ultrafast atomic motion and the associated spin dynamics following the excitation of a coherent electromagnon by an intense THz pulse in a multiferroic hexaferrite. Comparing the dynamics of the two different components, one striking outcome is the different phase shifts relative to the driving field. This phase shift provides insight into the excitation process of such a coupled mode. This direct observation of combined lattice and magnetization dynamics paves the way to access the mode-selective spin-lattice coupling strength, which remains a missing fundamental parameter for ultrafast control of magnetism and is relevant to a wide variety of correlated electron physics.

cond-mat.str-el↗