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Two-dimensional excitonic insulators Workshop

C.C.

Following the two previous workshops organised in 2018, 2021 and 2023, we are organising the fourth edition of the Two-dimensional excitonic insulators  Workshop.

The focus of this new edition will be the frantic hunt for macroscopic quantum coherence, the search of new candidate materials and the prediction of experimental fingerprints of the condensed excitonic phase, the understanding of the relation between excitonic and other unconventional phases. 

Building on the discussion of common themes and novel challenges, both theoretical and computational, this Workshop will progress our understanding of interacting systems in low dimensions.

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

Modena, Italy

1-3 September 2025

Invited Speakers:

  • Peter Abbamonte* (Illinois)
  • Richard Averitt* (San Diego)
  • Kamran Behnia (Paris)
  • Leonid Butov (San Diego) 
  • Massimo Capone (Trieste)
  • David Cobden (Seattle)
  • Sara Conti (Antwerp)
  • Denis Golež (Ljubljana)
  • Ataç İmamoğlu (Zurich)
  • Luis A. Jauregui (Irvine)
  • Peter B. Littlewood* (Chicago)
  • Steven Louie (Berkeley)
  • Marios Michael (Hamburg)
  • Raquel Queiroz (Columbia)
  • Giorgio Sangiovanni (Würzburg)
  • Ajit Srivastava (Geneva)
  • Kristian Thygesen (Denmark)
  • Dai Xi (Hong Kong)
  • Xiaoyang Zhu (Columbia)

* to be confirmed

The Workshop

This event follows two workshops organised at CECAM in 2018, 2021 and 2023 [Lausanne 2018, ‘Excitonic insulator: New perspectives in long-range interacting systems’; online 2021, ‘Excitonic and competing orders in low-dimensional materials’, Milan 2023, ‘Two-dimensional excitonic insulators’], which are now recognized as a turning point in shaping this research domain, and helped establishing a community by collecting the key actors of theoretical and experimental research. This new edition aims at in-depth analysis of recent breakthroughs –which include significant experimental fingerprints of the excitonic phase, new candidate materials, advances in computational methods, and of the current challenges and perspectives.

This research has its origin in a heretic prediction formulated more than 50 years ago: If a narrow-gap semiconductor, or a semimetal with slightly overlapping conduction and valence bands, failed to fully 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 thermodynamic equilibrium. This chimeric phase shares fascinating similarities with the Bardeen-Cooper-Schrieffer superconductor: a distinctive broken symmetry, inherited by the exciton character, and collective modes of purely electronic origin. Its observation was deterred for many 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.

Starting from 2018, our workshops have witnessed mounting evidence of the excitonic insulator phase in layered materials, as they combine optimal band structures, poor screening behavior, truly long-ranged interactions, and giant excitonic effects. The presence of excitons in the ground state has now been reported in different materials and devices. Intriguingly, mono- and bi-layer candidates often exhibit also other kinds of order: a variety that includes topological insulators, ferroelectrics, unconventional superconductors, typically depending on tiny variations of tunable parameters, such as doping, pressure, strain. This has introduced new urgent and far-reaching questions, concerning the role of excitonic correlations in a plethora of allegedly unrelated phenomena, whose interplay is just beginning to be explored.