Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session G15: Coupled Lattice and Electronic Phase Transitions: The Case of TaNiSe5Invited Live Streamed
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Sponsoring Units: DCMP DMP Chair: Antoine Georges, College de France Room: McCormick Place W-183C |
Tuesday, March 15, 2022 11:30AM - 12:06PM |
G15.00001: Photoinduced multistage phase transitions in Ta2NiSe5 Invited Speaker: Nan-Lin Wang Utrafast control of material physical properties represents a rapid developing field and has become one of the most attractive frontiers in condensed matter physics and materials science. Yet, accessing to the long-lived photoinduced electronic states is still in its early stage, especially with respect to the transition from an insulator to a steady metal phase. Here, by combing transport measurement with ultrashort photoexcitation and coherent phonon spectroscopy, we report on photoinduced multistage phase transitions in Ta2NiSe5. Upon excitation by weak pulse intensity, the system is triggered to a short-lived state accompanied by a structural change. Further increasing the excitation intensity beyond a threshold, a photoinduced steady new state is achieved where the resistivity drops by more than four orders at temperature 50 K. This new state is thermally stable up to at least 350 K and exhibits the lattice structure different from any of the thermally accessible equilibrium states. Transmission electron microscopy revealed a photoinduced structure transition showing in-chain Ta atoms displacement. We also found that nano-sheet samples with the thickness less than the optical penetration depth are required for attaining a complete transition with dramatic resistivity change, indicating an intrinsic cooperative multiple phase control of this electron-hole coupled system in an ultrafast fashion. |
Tuesday, March 15, 2022 12:06PM - 12:42PM |
G15.00002: Critical excitonic mode interacting with phonons in excitonic insulator Ta2Ni(Se1−xSx)5 Invited Speaker: Mai Ye Excitonic insulator is a quantum coherent phase resulting from formation of a macroscopic population of electron-hole pairs. For a semimetal with narrow overlap of the conduction and valence bands, a finite exciton binding energy could lead to excitonic instability. Candidate material Ta2NiSe5 shows a second-order structural phase transition at Tc=328K, with two mirror symmetries broken. |
Tuesday, March 15, 2022 12:42PM - 1:18PM |
G15.00003: Ab-initio theory of the symmetry-breaking transitions in Ta2NiS5 and Ta2NiSe5 Invited Speaker: Malte Roesner Ta2NiSe5 is one of the most promising materials for hosting an excitonic insulator ground state. While several experimental observations have been interpreted in this way, the precise nature of the symmetry breaking occurring in Ta2NiSe5, the electronic order parameter, and a realistic microscopic description of the transition mechanism are, however, missing and the role of structural and electronic instabilities on crystal symmetry breaking has yet to be disentangled. Meanwhile, the structural phase transition in its complementary material Ta2NiS5 does not show any experimental hints of an excitonic insulating phase. |
Tuesday, March 15, 2022 1:18PM - 1:54PM Withdrawn |
G15.00004: Direct observation of excitonic instability in Ta2NiSe5 Invited Speaker: BJ Kim
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