Luca PERFETTI. Electronic states and in-plane chirality in 1T-TaS2
Luca PERFETTI, LSI, Ecole Polytechnique
Le résumé :
The transition metal compound 1T-TaS₂ is a layered insulator with a rich phase diagram that depends on both pressure and temperature. Its broken symmetry phases include the Incommensurate (IC), Nearly Commensurate (NC), and Commensurate (C) Charge Density Wave (CDW) states. Time-resolved ARPES measurements in the insulating C phase reveal new insights into the photoinduced phase transition. By utilizing different probe pulse polarizations, it becomes possible to visualize the dispersion of electronic states both below and above the chemical potential. Within a few hundred femtoseconds, the energy from the pump pulse suppresses the dispersion of these states near the chemical potential, effectively compressing them into flat bands within half a period of the coherent CDW oscillation.
In the second part of the talk, I will instead show that the in-plane chirality of the CDW undergoes a configuration switch at the NC-C transition. This phenomenon occurs only in samples free of intrinsic or externally induced strain and results from the nucleation of CDWs with opposite chirality in the mixed phase. Interestingly, the chirality can also be manipulated by applying shear stress to the sample while cooling it through the IC–NC transition. Based on these findings, we propose a protocol for reliable chirality switching in bulk 1T-TaS₂ crystals. These results pave the way for novel functional devices in which in-plane chirality can be programmed on demand.