Optical Control of Multistage Phase Transition via Phonon Coupling in MoTe2

Photoinduced Structural Dynamics of 2H-MoTe2Under Extremely High-Density Excitation Conditions

“…Saturable absorption at an incident pump fluence of ∼4 mJ/cm 2 (∼0.4% electronic excitation) and sample damage in the high fluence regime indicate that it is challenging to realize the electronic excitation of more than several percent of valence electrons only via photoexcitation with ultrashort pulsed laser, which is necessary for the 2H-to-1T′ phase transition, as predicted by theoretical calculations. − To further investigate the structural phase transition, other steps are needed, e.g., the preparation of a sample encapsulated by h-BN, the use of THz pulses, and the use of single-shot measurements…”

“…T d is a low-temperature (<250 K) phase of 1T′. To date, ultrafast transient spectroscopic measurements have demonstrated the structural phase transition between the 1T′ and T d phases and the emergence of the intermediate T* phase. − Theoretical calculations have predicted the 2H-to-1T′ phase transition in the presence of a transient metallic 2H* phase under electronic excitation conditions at a magnitude of several percent. − Therefore, it is essential to investigate the structural dynamics of MoTe 2 in the experiment, which comprehensively interferes with photoexcited dense electron–hole plasma . However, there are few experimental studies on intense electronic excitation because photothermal and heat-accumulation effects often lead to permanent ablation and tellurium segregation .…”

Optically Induced Multistage Phase Transition in Coherent Phonon-Dominated a-GeTe

“…One can assume that optical excitation flattens the double-valley PES along the ⟨001⟩ direction and reverses the motion of Ge and Te atoms, triggering a structural transition from a rhombohedral to cubic geometry. Instead of the emergence of transferable PES required for transition-metal dichalcogenide in photoexcited events, i.e., the excitation of the ground state begins with the transfer of certain valence electrons manually to the conduction band bottom for supplementing the activation energy required for the phase transition . We determine a phase transition behavior triggered by a change in its own potential energy landscape in the photoexcited scenario of GeTe, which certainly identifies an energetically favorable way of phase changing.…”

“…Instead of the emergence of transferable PES required for transition-metal dichalcogenide in photoexcited events, i.e., the excitation of the ground state begins with the transfer of certain valence electrons manually to the conduction band bottom for supplementing the activation energy required for the phase transition. 37 We determine a phase transition behavior triggered by a change in its own potential energy landscape in the photoexcited scenario of GeTe, which certainly identifies an energetically favorable way of phase changing. Typically, the femtosecond laser excitation invites flattening of the double-valley PES followed by suppression of structural aberrations, verifying higher crystal symmetry in many material systems.…”

Photoinduced Ultrafast Phase Transition in Bilayer CrI3

“…The maximum widths of the forbidden bands of the R-stacked and M-stacked BLC are 1.21 and 1.16 eV, respectively. Based on the semiconductor nature of BLC and previous works, − we simulated the real-time evolution of the structure and electronic states of the R-stacked BLC under a series of Gaussian light fields with a given frequency of ℏω = 1.55 eV and different electric field strengths. More comparisons of parameters are discussed in Note S1 of the Supporting Information.…”