Light-control of materials via nonlinear phononics

TL;DR

Nonlinear phononics involves using light to excite specific phonons in materials, causing lattice displacements that can control or alter material properties, including inducing transient phases and switching functionalities.

Contribution

This paper reviews recent experimental and theoretical advances in nonlinear phononics, highlighting how light-driven phonon interactions can manipulate material phases and properties.

Findings

Mid-infrared lasers enable control of material phases.

Theoretical models predict light-induced switching of ferroelectricity.

Experimental evidence shows ultrafast control of magnetic and electronic states.

Abstract

Nonlinear phononics is the phenomenon in which a coherent dynamics in a material along a set of phonons is launched after its infrared-active phonons are selectively excited using external light pulses. The microscopic mechanism underlying this phenomenon is the nonlinear coupling of the pumped infrared-active mode to other phonon modes present in a material. Nonlinear phonon couplings can cause finite time-averaged atomic displacements with or without broken crystal symmetries depending on the order, magnitude and sign of the nonlinearities. Such coherent lattice displacements along phonon coordinates can be used to control the physical properties of materials and even induce transient phases with lower symmetries. Light-control of materials via nonlinear phononics has become a practical reality due to the availability of intense mid-infrared lasers that can drive large-amplitude oscillations of the infrared-active phonons of materials. Mid-infrared pump induced insulator-metal transitions and spin and orbital order melting have been observed in pump-probe experiments. First principles based microscopic theory of nonlinear phononics has been developed, and it has been used to better understand how the lattice evolves after a mid-infrared pump excitation of infrared-active phonons. This theory has been used to predict light-induced switching of ferroelectric polarization as well as ferroelectricity in paraelectrics and ferromagnetism in antiferromagnets, which have been partially confirmed in recent experiments. This review summarizes the experimental and theoretical developments within this emerging field.