Description
Moiré superlattices, formed by twisting two-dimensional atomic crystals, provide a powerful platform for engineering the underlying quantum geometry of electrons, particularly the Berry curvature. This capability opens new avenues for exploring and harnessing the valley degree of freedom. Here, we report the direct observation of a giant photo-induced valley Hall effect in twisted double bilayer graphene. Using mid-infrared optical pumping, we generate and detect a valley-polarized photovoltage, achieving an ultra-high valley Hall conductivity up to 0.125 e^2/h at 78 K—orders of magnitude larger than that observed in transition metal dichalcogenides-based systems. This substantial response originates from a massively enhanced Berry curvature, induced by symmetry breaking via the moiré potential. Combined experimental and theoretical analyses reveal the evolution of this valley Hall conductivity with an external displacement field, demonstrating its full electrical tunability. Furthermore, the valley Hall measurement geometry effectively suppresses additional noise voltage under a longitudinal bias, yielding an exceptionally low noise voltage floor of 29.7 nV/√Hz at 105 Hz. With outstanding responsivity and inherent low‑noise configuration, our devices enable circular-polarization-resolved mid‑infrared imaging, offering unique advantages over commercial thermal detectors at 10.6 μm. Our findings establish moiré engineering as a powerful route to harnessing the valley degree of freedom and point towards new architectures for ultra-low-noise optoelectronic and valleytronic devices.
