Topological Quantum Devices

We discovered that highly disordered superconductors, such as indium oxide films, undergo abrupt first-order quantum phase transitions, challenging traditional theories that assume gradual transitions. Our findings, which reveal a sharp drop in superfluid stiffness at a critical disorder level, have significant implications for quantum circuits that use disordered superconductors as superinductors.

This study we have evidenced unusual electron pairing and tripling phenomena without attractive interactions in graphene quantum Hall Fabry–Pérot interferometers (QH FPIs). At a bulk filling factor of ν = 2, electron pairing occurs while at ν = 3, electron tripling emerges, characterized by a fractional Aharonov–Bohm flux period of h/2e and h/3e, respectively. Using plunger-gate spectroscopy, we show that charge transport in this pairing and tripling regime is correlated across two and three edge channels.

In this work we have tackled the complex challenge of associating two emblematic quantum phenomena of condensed matter: the quantum Hall effect and superconductivity. We demonstrated the existence of a chiral Josephson supercurrent with unprecedented properties flowing between two superconducting electrodes, connected by a graphene nanoribbon in the quantum Hall regime. This supercurrent is transported along the quantum Hall edge channels of the graphene, forming a chiral loop whose rotation direction depends on the sign of the magnetic field.

This study report on the first scanning tunneling spectroscopy of quantum Hall edge channels in graphene under a perpendicular magnetic field. Our work reveals that these edge channels are confined to a few magnetic lengths at crystal edges, confirming them as ideal 1D chiral channels without electrostatic reconstruction. The findings carry implications for electron and heat transport experiments in graphene and other 2D crystalline materials.

When electrons populate a flat band their kinetic energy becomes negligible, forcing them to organize in exotic many-body states to minimize their Coulomb energy. The zeroth Landau level of graphene under a magnetic field is a particularly interesting strongly interacting flat band because interelectron interactions are predicted to induce a rich variety of broken-symmetry states with distinct topological and lattice-scale orders, which we evidence in this work.

Electron interferometry with quantum Hall (QH) edge channels in semiconductor heterostructures can probe and harness the exchange statistics of anyonic excitations. In this work we show that high-mobility monolayer graphene constitutes an alternative material system, not affected by charging effects, for performing Fabry–Pérot QH interferometry in the integer QH regime.

This Review Article summarizes recent progress in understanding of the various pathways that lead to the destruction of superconductivity by the interplay of disorder, localization and interactions, including experiments in low dimensional materials and application in superconducting quantum devices.

We unveiled a new interaction-induced topological phase in the zeroth Landau level of graphene. This phase is insulating in the bulk and exhibits a pair of spin-filtered, helical edge channels. It emerges under moderate perpendicular magnetic field when graphene is placed in proximity to a high-k dielectric substrate. In this work we demonstrated a remarkably robust quantum spin Hall effect that withstands up to 110 K over micron-long distances which opens a new avenue for spintronics and topological superconductivity.

The search for experimental evidence of Majorana modes is an area of intense research in condensed matter and quantum physics and uncovering clear evidence is complicated. We investigate the impact of Joule heating which can influence the analysis of experimental features related to Majorana bound states in topological Josephson junctions.

Strongly disordered superconductors in a magnetic field exhibit many characteristic properties of type-II superconductivity—except at low temperatures, where an anomalous linear temperature dependence of the resistive critical field Bc2 is routinely observed. Here we report systematic measurements of the critical magnetic field and current on amorphous indium oxide films which show that the Bc2 anomaly is accompanied by mean-field-like scaling of the critical current. Based on a comprehensive theoretical study we demonstrate that these observations are a consequence of the vortex-glass ground state and its thermal fluctuations.

Transport measurements performed on MoGe superconducting nanowires reveal a quantitative agreement with quantum critical behaviour driven by a pair-breaking mechanism.

High mobility graphene van der Waals heterostructures equipped with split-gate electrodes enable to control the transmission of integer and fractional quantum Hall edge channels in a gate tunable fashion, demonstrating Quantum Point Contact operation in the quantum Hall regime of graphene.