Technical advances in high pressure measurements of twisted graphene heterostructures

Hydrostatic pressure can modify the band structure of twisted graphene by reducing the interlayer separation, thus enabling the generation of flat bands even at non-optimal twist angles. Previously, pressure has been used to tune superconductivity and other correlated states in twisted bilayer graphene. However, despite being a valuable tuning knob, pressure measurements are still quite challenging due to the limited sample space inside the pressure cell, and difficulties in mounting the sample and establishing electrical connections to numerous contacts and gates. To address these issues, we have designed a custom printed circuit board (PCB) with gold pads on one side and solder cups on the other. The sample is mounted in the center of the PCB, and electrical connection is established by wire bonding rather than hand-pasting wires. The PCB additionally acts as a connection terminal that routes 16 wires to the device within a tight sample space of 3 mm diameter. The PCB has a central through hole enabling the sample to be anchored in place with a stiff tungsten wire. We will additionally report the status of ongoing work enabled by these technical advances, in which we investigate the pressure-tuned properties of various graphene-based moiré heterostructures.