In this talk, I will present our recent experimental observations of the large-scale mesoscopic transport in nanostructured graphene, and tunnelling spectroscopy in gate-induced superconductivity in MoS2.
I will first talk about the observation of Anderson localization in two dimensions through sample size scaling on nanostructured graphene. The localization length is observed to increase with applied magnetic field, in accurate agreement with the theoretical prediction. The large-scale mesoscopic transport is manifest as a parallel conduction channel to 2D variable range hopping, with a Coulomb quasigap around the Fermi level, which leads to an observed dephasing length of 10 μm.Then the study of gate-induced superconductivity in MoS2 by performing tunnelling spectroscopy through the van der Waals heterostructures will be presented. The ability to gate-induce superconductivity by electrostatic charge accumulation is a recent breakthrough in physics and nano-electronics, but experiments on gate-induced superconductors have been largely confined to resistance measurements, which provide very limited information about the superconducting state. We explore gate-induced superconductivity in MoS2 by performing tunnelling spectroscopy to determine the energy-dependent density of states (DOS) for different levels of electron density n. Our measurements reveal the presence of a DOS that vanishes linearly with energy, whose explanation requires going beyond a conventional, purely phonon-driven BCS mechanism.The bandstructure study of Transition metal dichalcogenides (TMDs) will also be discussed. By combining the in-plane transport, tunnelling spectroscopy and carrier density measurement, we are able to determine the valley occupation in TMDs, which is meaningful for understanding the microscopic mechanism of the gate-induced superconductivity.
Dr. Haijing Zhang received her Bachelor degree from Nanjing University in 2009 and got her Ph.D in physics from Hong Kong University of Science and Technology (HKUST) in 2014 under the supervision of Prof. Ping Sheng. From September 2014 to September 2016, she worked in the physics department of HKUST as a Post-doctoral Fellow. Starting from October 2016, she joined Prof. Alberto F. Morpurgo’s group as a Post-doctoral Fellow in the Department of Quantum Matter Physics at University of Geveva, Switzerland. Her research interests mainly focus on quantum and mesoscopic transport properties on nanostructured 2D materials and 2D gate-induced superconductivity.