Nonlinear Tunable Vibrational Response in Hexagonal Boron Nitride

Abstract

Nonlinear light-matter interactions in structured materials are the source of exciting properties and enable vanguard applications in photonics. However, the magnitude of nonlinear effects is generally small, thus requiring high optical intensities for their manifestation at the nanoscale. Here, we reveal a large nonlinear response of monolayer hexagonal boron nitride (hBN) in the mid-infrared phonon-polariton region, triggered by the strongly anharmonic potential associated with atomic vibrations in this material. We present robust first-principles theory predicting a threshold light field ∼ 40 MV/m to produce order-unity effects in Kerr nonlinearities and harmonic generation, which are made possible by a combination of the long lifetimes exhibited by optical phonons and the strongly asymmetric landscape of the configuration energy in hBN. We further foresee polariton blockade at the few-quanta level in nanometer-sized structures. In addition, by mixing static and optical fields, the strong nonlinear response of monolayer hBN gives rise to substantial frequency shifts of optical phonon modes, exceeding their spectral width for in-plane DC fields that are attainable using lateral gating technology. We therefore predict a practical scheme for electrical tunability of the vibrational modes with potential interest in mid-infrared optoelectronics. The strong nonlinear response, low damping, and robustness of hBN polaritons set the stage for the development of applications in light modulation, sensing, and metrology, while triggering the search for intense vibrational nonlinear response in other ionic materials.

Dynamics of optical vortices in 2D materials

“…The vast degrees of freedom of polaritons in 2D materials creates a unique advantage for simulating universal vortex phenomena. For example, recent demonstrations of quantum simulations 59 and analogies of gravity 60 with exciton-polaritons raise intriguing possibilities for similar prospects with PhPs, especially once higher excitation intensities unlock their nonlinear optical response 61 . It is possible that nonlinear effects had already affected our measurements here (see Fig.…”

Growth of Noncentrosymmetric Two-Dimensional Single Crystals

“…hBN is a well-established noncentrosymmetric 2D materials, characterized by an alternating arrangement of boron and nitrogen atoms in its lattice. Its exceptional properties, including strong insulation, large nonlinear susceptibility, excellent chemical inertness, high thermal conductivity, and atomic flatness without dangling bonds make it highly suitable for potential applications in nanoelectronics, integrated photonics, quantum optics, and metal-corrosion protection. − To realize such applications of hBN from lab to industry, the production of large-sized single-crystal hBN films is a prerequisite. Since the hBN films were synthesized through the CVD method on the nickel foils, significant efforts have been dedicated to produce hBN single crystals in the past decades. − …”