Low-dimensional (super)conductors at low temperature or high magnetic field are a fantastic playground for experimentalists. Our research activities aim at unveiling new quantum phenomena related to 2d superconductivity, quantum localization, and quantum Hall effect. We are currently focusing on:

  • Control of quantum coherence in the quantum Hall effect in graphene
  • Strongly disordered superconductors and the Cooper-pair insulator
  • Topological Josephson junctions
  • Ionic liquid gating

Our fields of expertise cover state-of-the-art nanofabrication, quantum transport of mesoscopic devices, and low-temperature/high field STM spectroscopy.



When Joule poisons Majorana in topological Josephson junctions

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.

K. Le Calvez, L. Veyrat, F. Gay, P. Plaindoux, C. Winkelmann, H. Courtois, B. Sacépé, Communications Physics, 2:4 (2019)


Low-temperature anomaly in disordered superconductors near Bc2 as a vortex-glass property
Strongly disordered superconductors in a magnetic field exhibit many characteristic properties of type-II superconductivityexcept 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.
 B. Sacépé, J. Seidemann, F. Gay, K. Davenport, A. Rogachev, M. Ovadia, K. Michaeli, M. V. Feigel’man Nature Physics 15, 48-53 (2019) 
 See also CNRS press release: http://www.cnrs.fr/inp/spip.php?article6274

Pair-breaking quantum phase transition in superconducting nanowires

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

Hyunjeong Kim, Frédéric Gay, Adrian Del Maestro, Benjamin Sacépé, Andrey Rogachev. Nature Physics 14, 912-917 (2018)



Pinching off electron edge-channels in graphene

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.

Anna Jordan, Frédéric Gay, Kenji Watanabe, Takashi Taniguchi, Zheng Han, Vincent Bouchiat, Hermann Sellier, Benjamin Sacépé, Nature Communications 8:14983 (2017)