Dynamical swinging between the insulating and metallic phases induced by the coherent amplitude mode excitation in 1T-TaS2

Abstract

Abstract We investigate the nonequilibrium electronic structure of 1T-TaS2 by time- and angle-resolved photoemission spectroscopy. We observe that strong photo excitation induces the collapse of the Mott gap, leading to the photo-induced metallic phase. It is also found that the oscillation of photoemission intensity occurs as a result of the excitations of coherent phonons corresponding to the amplitude mode of the charge density wave (CDW). To study the dynamical change of the band dispersions modulated by the CDW amplitude mode, we perform analyses by using frequency-domain angle-resolved photoemission spectroscopy. We find that two different peak structures exhibit anti-phase oscillation with respect to each other. They are attributed to the minimum and maximum band positions in energy, where the single band is oscillating between them synchronizing with the CDW amplitude mode. We further find that the flat band constructed as a result of CDW band folding survives with the collapse of the Mott gap. Our results strongly suggest the CDW phase is more robust than the Mott insulating phase, and the lattice modulation corresponding to the CDW amplitude mode dynamically modulates the Mott gap.