On-Chip Terahertz Spectroscopy for Dual-Gated van der Waals Heterostructures at Cryogenic Temperatures

TL;DR

This paper presents an on-chip THz spectroscopy technique for dual-gated bilayer graphene at cryogenic temperatures, enabling detailed study of electronic excitations and bandgap phenomena without gate-induced absorption interference.

Contribution

It introduces a novel on-chip THz spectroscopy method combining semiconducting and optically controlled gates to measure dual-gated 2D materials at cryogenic temperatures.

Findings

Detected electric-field-induced bandgap opening in graphene.

Measured Drude conductivities across different charge densities.

Extracted effective masses and scattering rates.

Abstract

Van der Waals heterostructures have emerged as a versatile platform to study correlated and topological electron physics. Spectroscopy experiments in the THz regime are crucial, since the energy of THz photons matches that of relevant excitations and charge dynamics. However, their micron-size and complex (dual-)gated structures have challenged such measurements. Here, we demonstrate on-chip THz spectroscopy on a dual-gated bilayer graphene device at liquid helium temperature. To avoid unwanted THz absorption by metallic gates, we developed a scheme of operation by combining semiconducting gates and optically controlled gating. This allows us to measure the clean THz response of graphene without being affected by the gates. We observed the THz signatures of electric-field-induced bandgap opening at the charge neutrality. We measured Drude conductivities at varied charge densities and extracted key parameters, including effective masses and scattering rates. This work paves the way for studying novel emergent phenomena in dual-gated two-dimensional materials.