A joint fellowship, for an experimental PhD thesis, is available in the Quantum and Nanoelectronics group at the Department of Physics, Univ. of Basel and the Laboratory of Quantum physics at the Institute of Physics, EPFL, Lausanne.

In Van der Waals cystals atomically thin sheets can be isolated by “exfoliation” and randomly stacked on top of each another. This provides an opportunity to design new material properties. One such arrangement is stacking two graphene layers together, with a small twist angle. This gives rise to a new lattice periodicity and new electronic properties — and new means here radically new and in an unexpected way! At certain ‘magic angles’ twisted bilayer graphene exhibits phases such as superconductivity and correlated electronic states that are not present in the parent material. In this project you will investigate novel phases that appear in twisted bilayer graphene by creating gate tunable mesoscopic structures and studying their electronic transport properties.

The phenomenal transition of twisted bilayer into a superconducting state is believed to be due to so-called “flat bands”, which arise in superlattices, for example, in twisted bilayer. Instead of having a linear “Dirac spectrum”, like in monolayer graphene, the electronic bands assume a small curvature, and hence a large mass due to hybridization of the Dirac cones of the two layers. This increase the superconducting coupling strength. In our own research, we have studied superlattices in aligned h-BN encapsulated graphene and found van-Hove singularities in transport studies with superconducting contacts. These are also places where the bands become flat. Flat bands are not only the source for supeconductivity, but also a source for highly correlated states. This is due to the reduced carrier velocity which significantly increase interaction effects. There is an increasing  interest in these materials due to the wealth of new properties that are already knowns and that still need to be discovered.

(a) Encapsulated graphene Hall-bar devices with the inset showing a “Fraunhofer-pattern” of the critical current of a graphene Josephson junction (JJ). (b) Principle of superlattice with indicated superlattice unit-cell in the center. (c) Measurement of a JJ in an RF-SQUID by microwave reflectometry, the principle of which is shown in figure (d). The frequency shift of the microwave \lambda/4 resonator with a bare frequency of ~3GHz is shown as a function of phase tuned by an external flux-coil

You will design and fabricate your own devices made from 2D van der Waals heterostructures using state-of-the-art micro- and nanofabrication technologies including a glovebox stacking system. Electric measurements will be done down to mK temperatures and include DC to RF techniques based on modern cryogenic circuitry (for example rf-resonators) and cold amplifiers. We are looking for a highly motivated student (preferably a physicist) who is keen to explore fundamental aspects of quantum devices.

All PhD fellows are expected to work in a team and collaborate with other PhD and postdoctoral fellows, as well as bachelor and master students joining the lab part of their time. Start of the project latest by 1 of Sept. 2021. Duration 3-4 years. Requirement: you need to have a profound understanding of quantum and solid state physics as it is taught in a physics curriculum.

To apply, please email to Christian Schönenberger and/or Miatli Banerjee a short curriculum vitae, including names and contact info of referees and scanned copies of grades. Please add a short statement on your motivation and your education / background in quantum physics and solid-state physics.