Abstract-Momentum shift current at terahertz frequencies in twisted bilayer graphene

 

Daniel Kaplan, Tobias Holder, Binghai Yan

https://arxiv.org/abs/2101.07539

The detection of terahertz (THz) radiation promises intriguing applications in biology, telecommunication, and astronomy but remains a challenging task so far. For example, semiconductor infrared detectors (e.g., HgCdTe) utilize photo-excited electrons across the bandgap and hardly reach the far-infrared terahertz regime because they are vulnerable to thermally excited carriers. In this work, we propose the THz sensing by the bulk photovoltaic effect (BPVE) in the twisted bilayer graphene (TBG). The BPVE converts light into a coherent DC at zero bias or an open-circuit voltage. As a quantum response from the wave function's geometry (different from the p-n junction), BPVE is more robust against temperature excitation and disorders. We predict that the TBG (bandgap of several meV) exhibits a sizeable BPVE response in a range of 0.2 -- 1 THz. Beyond the ordinary shift current scenario, BPVE in TBG comes from a momentum-space shift of flat bands. Our work provides a pathway to design twisted photonics for resonant terahertz detection.