Correlations and topology are the cornerstones of modern condensed matter physics, and their coexistence is believed to lead to novel quantum electronic devices with built-in information protection. In the last three years 2D materials led to a revival of the field of strongly correlated materials. By placing two graphene sheets on top of each other, with a small, well-defined rotation angle, flat bands and novel phases form including superconducting and correlated insulator states. As the electron density of these materials is low, it can be tuned with gate electrodes and the phase diagram can be obtained in a single day, as opposed to conventional strongly correlated materials. Moreover, due to the topological nature of these materials new topological phases will be manifested. This has led to the discovery of a multitude of correlated phases including correlated insulators, orbital magnetic, non-conventional superconducting and ferroelectric phases, etc. To have a better understanding of these correlated phases novel experimental tools are required.

 

The goal of the PhD project is to investigate twisted van der Waals structures using pressure and strain. On the one hand pressure tunes the interlayer distance, which can heavily change the band structure parameters and lead to stronger correlations, on the other hand strain leads to symmetry breaking and it is expected that it can lead to the appearance of novel phases.

 

During the PhD work the candidate will be involved in the fabrication of novel 2D heterostructures using 2D layer assembly and electron-beam lithography. The samples will be studied at ultra-low temperatures under pressure at in-situ tunable strain. The work is done in close collaboration with several European universities.

 

Left: Pressure cell with a 2D heterostructure inside. Right: a van der Waals heterostructure, which is tuneable via electrostatic gating, hydrostatic pressure (green arrow) and strain (blue arrows).