On-chip multi-degree-of-freedom control of two-dimensional quantum and nonlinear materials

Abstract: Two-dimensional materials (2DM) and their derived heterostructures have electrical and optical properties that are widely tunable via several approaches, most notably electrostatic gating and interfacial engineering such as twisting. While electrostatic gating is simple and has been ubiquitously employed on 2DM, being able to tailor the interfacial properties in a similar real-time manner represents the next leap in our ability to modulate the underlying physics and build exotic devices with 2DM. However, all existing approaches rely on external machinery such as scanning microscopes, which often limit their scope of applications, and there is currently no means of tuning a 2D interface that has the same accessibility and scalability as electrostatic gating. Here, we demonstrate the first on-chip platform designed for 2D materials with in situ tunable interfacial properties, utilizing a microelectromechanical system (MEMS). Each compact, cost-effective, and versatile device is a standalone micromachine that allows voltage-controlled approaching, twisting, and pressurizing of 2DM with high accuracy. As a demonstration, we engineer synthetic topological singularities, known as merons, in the nonlinear optical susceptibility of twisted hexagonal boron nitride (h-BN), via simultaneous control of twist angle and interlayer separation. The chirality of the resulting moire pattern further induces a strong circular dichroism in the second-harmonic generation. A potential application of this topological nonlinear susceptibility is to create integrated classical and quantum light sources that have widely and real-time tunable polarization. Our invention pushes the boundary of available technologies for manipulating low-dimensional quantum materials, which in turn opens up the gateway for designing future hybrid 2D-3D devices for condensed-matter physics, quantum optics, and beyond.