Electronic excitation induced non-thermal phase transition of tungsten

Abstract

The electronically excited states of tungsten (W) material tuned by ultrafast laser irradiation cause intriguing jumps between different Born-Oppenheimer surfaces. This may give rise to a structural phase transformation of BCC-to-FCC or BCC-to-HCP on a very short time scale, which is still debated. By performing calculations on W with both density functional theory and a tight-binding approach, a martensitic phase transformation from BCC phase to HCP phase in bulk W is predicted at a threshold (15,500 ± 500 K) of electronic temperatures, where the HCP phase is found to be more stable than both BCC and FCC phases under intense electronic excitations. Additionally, it is proposed that the non-thermal phase transition could potentially be probed through experimental measurements of the c/a ratio of system in the future. The mechanism underlying the BCC-to-HCP transformation in the electronically excited bulk W system is analyzed under the level of electronic structure. It is found that the irradiation-induced changes of the density of states at the Fermi level could drive the structural phase transformation. This provides new insight into the atomic-level non-thermal phase transition process of W under intense electronic excitations.