Does Vo2 Host a Transient Monoclinic Metallic Phase?

Abstract

Ultrafast phase transitions induced by femtosecond light pulses present a new opportunity for manipulating the properties of materials. Understanding how these transient states are different from, or similar to, their thermal counterparts is key to determining how materials can exhibit properties that are not found in equilibrium. In this paper, we reexamine the case of the light-induced insulator-metal phase transition in the prototypical, strongly correlated material VO 2 , for which a nonthermal Mott-Hubbard transition has been claimed. Here, we show that heat, even on the ultrafast timescale, plays a key role in the phase transition. When heating is properly accounted for, we find a single phase-transition threshold corresponding to the thermodynamic structural insulator-metal phase transition, and we find no evidence of a hidden transient Mott-Hubbard nonthermal phase. The interplay between the initial thermal state and the ultrafast transition may have implications for other transient states of matter.

Nanoscale self-organisation in Mott insulators: a richness in disguise

“…Experimentally, the present results justify the ongoing efforts to develop novel table-top and large-scale facility time-resolved microscopy techniques to investigate the intertwining between non-thermal properties and real-space morphology in quantum correlated materials. Addressing the role of real space inhomogeneities and intrinsic strain nanotexture will be crucial to finally clarify the long-standing issue about the possibility of fully decoupling and control the electronic and structural phase transitions in vanadates 3,25,26,29,30,69,[72][73][74] and other Mott materials.…”

“…Evidences of a monoclinic metal phase have been observed in V 2 O 3 at high pressure 38,39 . On the contrary, at ambient pressure the possible existence of a monoclinic metal phase remains so far controversial 30,35,37,[53][54][55][56][57][58] .…”

“…The experiment was carried out on the same sample, and in the same experimental conditions as the optical pump-probe results reported in Fig. 12d, in order to avoid possible artefacts related to different average heating in the two experiments 30 . The pump-probe spatial and temporal overlap was carefully checked by exploiting the non-linear photoemision from surface impurities, as explained in detail in the Supplementary Material 43 (see Sec.…”

“…Much activity has focused on developing strategies to decouple the electronic and structural changes, with the ultimate goal of achieving all-electronic switching for ultrafast Mottronics. The recent claim of a photoinduced metallic phase of monoclinic VO 2 25, 26 has triggered a huge effort to address to what extent the photoinduced transition is similar to the thermally driven one and whether the electronic and lattice degrees of freedom remain coupled at the nanoscale during and after the light excitation 3,[27][28][29][30] .…”

Photoinduced multistage phase transitions in Ta2NiSe5

“…Up to now, the PI insulator to steady metallic state is achieved only in few systems exhibiting competing orders or broken symmetry phases, e.g., manganites perovskites 3 , 4 , 9 , 13 and a charge density wave (CDW) crystal of 1T-TaS 2 8 , with their PI states only surviving at temperatures far below the room temperature. PI nonthermal insulator-metal phase transition was also reported in a strongly correlated material VO 2 14 , 15 , however, a recent study questioned the claim and found no evidence for a hidden transient Mott–Hubbard nonthermal phase in VO 2 16 . Here we report on distinct PI multistage phase transitions with insulator-to-metal transition (IMT) characteristics in Ta 2 NiSe 5 —the compound is currently known as an important candidate of excitonic insulator (EI) 17 – 19 .…”