Research Sara Conti

Abstract

The supersolid, an intriguing counter-intuitive quantum state in which a rigid lattice of particles flows without resistance, has attracted long-time interest but has to date not been unambiguously realised. Alternative approaches have been proposed to Chester's original idea of a supersolid, where within the macroscopic quantum condensate the single particles are localized on each lattice site by strong repulsion. These include periodic density-modulated superfluids or clusters of condensates observed in cold atoms gases in optical lattices. Most recently, we have revealed a supersolid in double-layer heterostructures with interlayer excitons: electrons confined in a layer, coupled with holes, confined in a separated layer. This exciton supersolid is a Chester-type supersolid with one exciton per site and it shows over a wide range of layer separations, well within reach of the experimental capabilities but outside the focus of recent experiments. In this project, we aim to theoretically investigate how the existence and the stability of an interlayer exciton supersolid can be controlled and enhanced, by providing the phase diagram augmented by all supersolid phases. By controlling the layer separation (length of the exciton dipole) and the exciton density of the system, the exciton repulsions can be tuned to stabilize the supersolid with respect to the other excitonic phases and rich novel phenomena can be explored in the vicinity of the phase transitions.

Researcher(s)

• Promoter: Milosevic Milorad
• Co-promoter: Tempere Jacques
• Fellow: Conti Sara

Research team(s)

• Condensed Matter Theory

Project type(s)

• Research Project

Abstract

Recent experimental results on superconductivity in twisted bilayer graphene indicates that flat bands are a key feature to explore strongly correlated phases. A straightforward access to quasi-flat bands has also been realised by means of twisting or periodic straining in van der Waals heterobilayers made of transition metal dichalcogenides. By controlling the doping in bilayer systems, it is possible to generate interlayer excitons: electrons are confined in a layer and couples with holes, confined in the opposite and separated layer. In this project, I propose to theoretically study the effects of tunable flat bands on interlayer excitons with the aim to investigate the emergence of excitonic strongly correlated phases. At low temperature, a number of competing phases have been predicted, including electron-hole superfluidity, exciton insulator, coupled Wigner crystallisation and charged density waves. The enhancement of the effective masses of the carriers increases of the excitonic binding energy and this makes the excitonic phases more robust. By tuning the flatness of the bands it will become possible to enhance the critical temperature for electron-hole superfluidity and to control the emergence of the competing strongly correlated phases that appear in the phase diagram.

Researcher(s)

• Promoter: Partoens Bart
• Co-promoter: Neilson David
• Fellow: Conti Sara

Research team(s)

• Condensed Matter Theory

Project type(s)

• Research Project