Find the upcoming seminars below.

TQM seminar #20 : April 6 2023, 2pm (en visio: zoom link : ID de réunion : 924 2140 1721 Code secret : 5RTr40)

**François Dubin** (INSP, Sorbonne Université, Paris)

*Exploring extended Bose-Hubbard models with dipolar excitons*

The Bose-Hubbard (BH) model quantifies the quantum matter phases accessible to strongly correlated bosons confined in lattice potentials. In its elementary form the BH Hamiltonian is restricted to on-site interactions and a single lattice confined state. At sufficiently low temperatures, the transition from superfluid to Mott insulating phases is thus accurately quantified. Extending the BH model to additional degrees of freedom naturally provides a direct route to broaden the range of accessible quantum matter phases. In this presentation we introduce a new platform to experimentally emulate extended Bose-Hubbard models. In particular, we emphasise semiconductor excitons confined in electrostatic lattice potentials. By suitably tuning the lattice geometry we first probe experimentally a multi-orbital version of the BH model, i.e. the situation where excitons have access to a set of discrete (Wannier) states in every lattice site. In this regime, we show that a subtle competition between the on-site interaction strength and the energy separation between lattice confined states rules the buildup of Mott insulating phases [1]. We also evidence that electrostatic lattices can be designed to enter the regime the the BH Hamiltonian is extended to interactions between excitons confined in nearest neighbouring lattice sites. In this regime, we demonstrate that ordered insulating phases emerge at fractional lattice fillings, such as a checkerboard solid at half filling [2].

[1] C. Lagoin et al., Nat. Phys. 18, 149 (2022)

[2] C. Lagoin et al., Nature 609, 485 (2022)

TQM seminar #21 : April 13 2023, 2pm (LPTHE library, towers 13-14, 4th floor)

**Gian Marcello Andolina** (JEIP, CNRS – Collège de France, Paris)

*Can deep sub-wavelength cavities induce Amperean superconductivity in a 2D material?*

Amperean superconductivity is an exotic phenomenon stemming from attractive effective electron-electron interactions (EEEIs) mediated by a transverse gauge field. Originally introduced in the context of quantum spin liquids and high-Tc superconductors, Amperean superconductivity has been recently proposed to occur at temperatures on the order of 1-20 K in two-dimensional, parabolic-band, electron gases embedded inside deep sub-wavelength optical cavities.

I will first generalize the microscopic theory of cavity-induced Amperean superconductivity to the case of graphene and then argue that this superconducting state cannot be achieved in the deep sub-wavelength regime. In the latter regime, indeed, a cavity induces only EEEIs between density fluctuations rather than the current-current interactions which are responsible for Amperean pairing.

TQM seminar #22 : May 11 2023, 2pm (INSP great hall, towers 22-23, 3rd floor, room 317)

**Aurélien Schmitt** (LPENS, Ecole Normale Supérieure, Paris)

*Klein-Schwinger effect in graphene* (provisoire)

TQM seminar #23 : June 29 2023, 2pm (LPTHE library, towers 13-14, 4th floor)

**Serge Florens** (Institut Néel, Grenoble)

TBA