SCIENTIFIC ACHIEVEMENT
Using the Advanced Light Source (ALS), researchers demonstrated a new way to confine, or “squeeze,” infrared light by coupling photons with phonons (lattice vibrations) within a certain type of thin film.
SIGNIFICANCE AND IMPACT
The work heralds a new class of optical materials for controlling infrared light, with potential applications in photonics, sensors, and microelectronic heat management.
A light squeeze
Researchers have demonstrated that thin films of strontium titanate (SrTiO3, or STO) can confine, or “squeeze,” infrared light 10 times more than its bulk form can—a finding that holds promise for next-generation microelectronic and photonic devices. While this unusual behavior had been theoretically predicted for STO membranes, it had not yet been experimentally observed.
The researchers took advantage of advances in the synthesis of freestanding, large-scale crystalline oxide membranes, then used a combination of infrared micro- and nanospectroscopy to observe how infrared light couples to lattice vibrations in the membranes. They found that the coupling produced hybrid vibrational and electromagnetic waves (phonon polaritons) in the material, with different modes characterized by highly compressed wavelengths or greatly enhanced fields inside the sample.
Transferable membranes
Theoretical studies have suggested that ultrathin STO and other perovskite membranes can host highly confined surface phonon polaritons (SPhPs) with good propagation quality. Other compounds may have higher figures of merit, but because they are typically manually exfoliated, their lateral size is constrained to the micrometer range, which limits their potential for large-scale device fabrication.
Read more on ALS website
Image: In this experiment, an atomic force microscope tip focuses broadband synchrotron infrared light onto the surface of a strontium titanate (SrTiO3) membrane, just 100 nm thick. The infrared light excites phonon polaritons—quasiparticles that arise when light strongly interacts with dipole oscillations in the material’s lattice. Spectroscopic analysis of the scattered light enabled researchers to determine the properties of phonon polaritons on the material surface.
