An effective strategy for the dynamical tuning of k in solids would be critical for developing novel phononic devices able to perform logic operations with phonons, as well as for solid-state refrigeration, energy harvesting, and thermoelectrics. A promising approach consists in taking advantage of field-induced phase transitions, using electric or magnetic fields to manipulate the crystal lattice of polar and magnetic materials, respectively. Such electrophononic and magnetophononic effects can provide fast and dynamical manipulation of the heat carriers, thus yielding à la carte thermal properties for on-demand applications. On the other hand, the possibility of manipulating k with light has received very little attention. Light- driven control of the thermal conductivity could bypass some of the issues posed by the schemes described above (e.g., application of large driving fields) as well as simplify the design of logic devices (i.e., lack of electrical contacts).
Here we discuss this scenario in the archetypal ferroelectrics BaTiO3 and KNbO3, where by means of first-principles calculations, we show that photoinduced charge injection can trigger a ferro-to-paraelectric phase transition, yielding a (potentially ultrafast) reversible change in thermal transport properties [1,2]. Our results reveal a substantial reduction in lattice thermal conductivity, especially at low photoexcited charge densities, as the material undergoes a polar-to-nonpolar transformation. This reduction is primarily due to the suppression of low-frequency phonon modes, which limits heat flow as a result of enhanced phonon-phonon scattering.
We will also discuss the case of TiSe2, a van der Waals 2D material where a photoinduced phase transition can restore a more symmetric crystal phase [3], similar to what we report with ferroelectric oxides. In particular, photoexcited charges or electron/hole doping suppress the charge density wave (CDW, a periodical modulation of the electron density), which is the ground state below ~200 K. Such a CDW melting is accompanied by a sizable reduction in the thermal conductivity, a variation that also in this case almost entirely originate from the changes in the phonon-phonon scattering processes.
These findings underscore a step forward in tunable thermal conductivity, offering new prospects for efficient thermal management in phonon logic, advanced electronics and energy-harvesting applications.
[1] Adv. Funct. Mater. e2425424, in press (2025)
[2] Nanoscale, 16, 8335 (2024)
[3] npj 2D Mater Appl 8, 64 (2024)