Structural involvement in the melting of the charge density wave in 1T-TiSe2

The authors find using resonant and non-resonant x-ray diffraction on an x-ray free electron laser that the structural distortion and the underlying electronic structure of the charge density wave in TiSe₂ show different energetics at ultrafast timescales. This indicates that the lattice distortion stabilizes the charge density wave.

It is commonly assumed that electronic phenomena occur at faster time scales than structural rearrangements. Here, we show the opposite: weak electronic excitations induce atomic displacements that outpace purely electronic charge carrier-interactions and hence are the dominant contribution in melting of the charge-density wave (CDW) in TiSe₂. This divergence of electronic and structural order is directly observed in experimental data from a transient ultrafast resonant/non-resonant X-Ray diffraction experiment. Our results create a  paradigm shift that constitute a different, mechanistic pathway for phase transitions in the ultrafast regime.