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Dynamics of charge density waves in semi-metallic metal chalcogenides

Lunedì 9 dicembre 2019, ore 12.00, aula Seminari, terzo piano, edificio Fisica, Dipartimento FIM, Modena

Relatore: Prof. Enrico Da Como (University of Bath United Kingdom)

Abstract: Most semimetallic transition metal dichalcogenides (TMDs) exhibit phase transitions to a charge density wave (CDW) phase driven by different phenomena: exciton condensation, Jahn-Teller distortion, and Fermi surface nesting. In this talk I will address two material systems: single crystals of Titanium Selenide (TiSe2) and Vanadium Selenide VSe2. The layered TMD 1T-TiSe2 has been suggested to host a unique CDW phase transition driven by cooperative excitonic and electron-phonon interactions [1].Ultrafast spectroscopy uses optical pulses below hundred fs to generate non-equilibrium states where electronic and lattice degrees of freedom respond on different time scales. This possibility is used here to observe a phonon bottleneck in the recovery of the CDW in 1T-TiSe2 after transient perturbation of the CDW excitons optical excitation. Using a suitable combination of energy and time resolution provided by an angle-resolved photoemission spectroscopy (tr-ARPES) setup I will show how to estimate the excitonic and lattice contributions to the CDW gap [2].

In VSe2, the CDW mechanism is discussed in terms of Fermi surface nesting and I will discuss the role of defects in tuning the CDW transition temperature by combining ARPES and x-ray photoemission spectroscopy results [3].

[1] P. Knowles, B. Yang, T. Muramatsu, O. Moulding, J. Buhot, C. Sayers, E. Da Como, S. Friedemann, arXiv:1911.01945 (2019)
[2] H. Hedayat, C. J. Sayers, D. Bugini, C. Dallera, D. Wolverson, T. Batten, S. Karbassi, S. Friedemann, G. Cerullo, J. van Wezel, S. R. Clark, E. Carpene, and E. Da Como, Physical Review Research, 1, 023029, (2019)
[3] C. J. Sayers, L. S. Farrar, S. J. Bending, M. Cattelan, A. J. H. Jones, N. A. Fox, G. Kociok-Kohn, K. Koshmak, J. Laverock, L. Pasquali, and E. Da Como, under review (2019)

Host: Elisa Molinari e Massimo Rontani e-mail: elisa.molinari@unimore.it

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