Thermoelectric transport measurements in dual-gated Bernal bilayer graphene

A cascade of correlated phases in dual-gated, hexagonal boron-nitride (hBN) encapsulated BLG devices has been identified by magnetoconductance measurements. [1-3] The correlated phases emerge close to Lifshitz-transitions, where the density of states (Dos) is high and the kinetic energy gets quenched. While conductance measurements alone can be used to study the correlated phases, it is difficult to precisely connect the Dos with said phases.

Thermoelectric transport measurements on the other hand provide a simpler and more direct probe of the Dos through the Seebeck coefficient. The Seebeck coefficient is defined as the ratio of the thermal voltage to its inducing temperature difference. We demonstrate measurements of the Seebeck coefficient at 4 K up to a calibration factor. For the measurements we employed an on-chip heater next to an hBN-encapsulated BLG device with graphite contacts and dual graphite gates to simultaneously tune the Fermi-level and an out-of-plane electric field. The source-drain contacts were simultaneously used as quasi-4-point-probe on-chip resistance thermometers to determine the local temperature differences between them. The device was fabricated by dry-transfer of flakes, e-beam lithography, reactive ion etching as well as thermal evaporation of contact leads.



References

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de la Barrera, S. C. et al. Nat. Phys 18, 771-775 (2022)