Electrically switchable ferron upconversion in a van der Waals ferroelectric

TL;DR

This paper demonstrates electrically controllable nonlinear phonon upconversion in a van der Waals ferroelectric, enabling dynamic lattice control and potential applications in quantum phononics and information processing.

Contribution

It introduces ferron upconversion in a ferroelectric as a new platform for tunable nonlinear phononics with electric-field control.

Findings

Resonant THz excitation drives upconversion from 3.1 THz to 7.0 THz.

Electric-field switching enables nonvolatile control of ferron dynamics.

Hysteretic behavior shows strong dependence on ferroelectric order parameter.

Abstract

Nonlinear phononics provides a powerful ultrafast route to control lattice excitations, enabling access to hidden quantum orders, phononic computing, and quantum transduction. However, dynamic control of anharmonic phonon interactions remains limited, as these interactions are typically fixed by the equilibrium crystal lattice and lack external tunability. Emergent ferrons in ferroelectrics, which are collective oscillations of the spontaneous electric polarization, may offer a promising platform to overcome this limitation by combining intrinsic phononic nonlinearity with direct electrical control of the ferroelectric order parameter. Here we report electrically controllable nonlinear ferron upconversion in the van der Waals ferroelectric NbOI2. We show that resonant THz excitation of a 3.1 THz ferron drives coherent upconversion to a 7.0 THz optical phonon. Using two-dimensional THz spectroscopy, we directly resolve off-diagonal coupling features and establish the nonlinear upconversion pathway. Supported by first-principles calculations and analytical modeling, we identify the microscopic origin as a cubic anharmonic lattice coupling. Importantly, in situ electric-field switching enables nonvolatile control of both the ferron dynamics and the associated upconversion process. The phase reversal and hysteretic behavior across the coercive fields establish that the ferron-mediated nonlinear phononic interaction is strongly dependent on the underlying ferroelectric order parameter. These results introduce ferron upconversion as a new and universal regime of nonlinear phononics in ferroelectrics and establish an electrically programmable platform for coherent lattice control, paving the way for ferronic information processing and quantum phononic transduction.