Expérimental
Discovery of topological matter has triggered an intense research work motivated by the emergence of promising features among which the existence of helical ballistic edge states. For 2D systems or 3D high order topological insulators (TI), they form one dimensional conducting channels on the edges with two time-reversed spin-momentum-locked states which do not backscatter. The topological protection manifests itself in the supercurrent which appears when the TI is connected to superconducting electrodes. Our project aims at investigating the poorly understood dynamics of helical edge states, determining their relaxation mechanisms and the robustness of their topological protection in superconducting junctions as well as in isolated TI. We have proved that finite-frequency supercurrent response to a magnetic flux as well as the supercurrent noise at equilibrium contain clear signature of the relaxation mechanism in the GHz regime for non-topological junctions. For topological edge states, the expected millisecond lifetime calls for experiments below the MHz to detect the current fluctuations. We propose for the internship to use our new ultrasensitive GMR-based (Giant Magnetoresistance) magnetic field sensor to detect the supercurrent carried by the helical edge states as well as its fluctuations at equilibrium.