Terahertz electrodynamics of tunable graphene microcavities*

VdW heterostructures host a wide range of gate-tunable topological and strongly correlated quantum phenomena that fall on the THz energy scale. Capturing the THz electrodynamics of these systems could provide a unique window into their ground-state physics. However, far-field THz techniques cannot operate on microstructured samples. 

 

We present a generalizable platform for near-field on-chip THz spectroscopy that can access the electrodynamic response of gate-tunable vdW heterostructures from ~30 GHz - 1.2 THz (0.12 - 5 meV). Our results show that graphene heterostructures embedded in ultrafast circuitry act like microcavities, confining the electric field to excite coherent plasmon-polariton modes. We develop an analytical model to describe these cavity modes, which can be tuned by engineering the geometrical properties of the cavity, the dielectric environment, and the carrier density.  

 

These results illustrate the potential for this technique to operate at millikelvin temperatures and strong magnetic fields, bringing THz spectroscopy into the realm traditionally reserved for quantum transport.