Two-dimensional excitonic insulators @ CMD30 – FisMat2023

A three half-days Mini Colloqiua during the Conference of the Condensed Matter Division of the European Physical Society (CMD30 – FisMat2023) dedicated to the field of the excitonic insulator, with dedicated discussion and posters sessions.

The organisers are Hope Bretscher (MPI, Germany), Elisa Molinari (UniMoRe, Italy) and Massimo Rontani (Cnr-Nano, Italy)

Abstract: The field of the excitonic insulator (EI) is moving fast. This research has its origin in a prediction formulated more than 50 years ago by a group of visionary physicists: If a narrow-gap semiconductor failed to screen its intrinsic charge carriers, then excitons---electron-hole pairs bound together by Coulomb attraction---would spontaneously form. This would destabilize the ground state, leading to a reconstructed ‘excitonic insulator’---a condensate of excitons at equilibrium. This chimeric phase shares similarities with the BCS superconductor: a distinctive broken symmetry, and collective modes of purely electronic origin. Its observation was deterred for decades by the trade-off between competing effects in the semiconductor: as the size of the energy gap decreases, favoring spontaneous exciton generation, the screening of the electron-hole interaction increases, suppressing the exciton binding energy. In the last two years, mounting evidence has been accumulating in 2d materials, as they combine truly long-ranged interactions and giant excitonic effects. New electron-hole bilayers hold promise of room-temperature superfluid behavior [1-4], whereas signatures of the bulk phase were found in monolayers [5-7]. Excitonic materials exhibit other kinds of order as well: a variety that includes topological insulators [6-8], ferroelectrics [8,9], unconventional superconductors [6-7,9]. This introduces new far-reaching questions, concerning the role of excitonic correlations in a plethora of allegedly unrelated phenomena, whose interplay is just beginning to be explored. At the same time, the long-term challenge of establishing the EI through the signatures of macroscopic quantum coherence is attracting renewed interest. By collecting the key actors of theoretical and experimental research, who are spread among different communities, we aim at in-depth analysis of common themes and novel challenges, to progress our understanding of 2d interacting systems.

To browse the detailed program open the link HERE and read the column MC_10: Two-dimensional excitonic insulators