Thermal and electrostatic tuning of surface phonon-polaritons in LaAlO<sub>3</sub>/SrTiO<sub>3</sub> heterostructures.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 38001108.
- Also identified by DOI 10.1038/s41467-023-43464-z and PMC identifier 10673882.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Phonon polaritons are promising for infrared applications due to a strong light-matter coupling and subwavelength energy confinement they offer. Yet, the spectral narrowness of the phonon bands and difficulty to tune the phonon polariton properties hinder further progress in this field. SrTiO<sub>3</sub> - a prototype perovskite oxide - has recently attracted attention due to two prominent far-infrared phonon polaritons bands, albeit without any tuning reported so far. Here we show, using cryogenic infrared near-field microscopy, that long-propagating surface phonon polaritons are present both in bare SrTiO<sub>3</sub> and in LaAlO<sub>3</sub>/SrTiO<sub>3</sub> heterostructures hosting a two-dimensional electron gas. The presence of the two-dimensional electron gas increases dramatically the thermal variation of the upper limit of the surface phonon polariton band due to temperature dependent polaronic screening of the surface charge carriers. Furthermore, we demonstrate a tunability of the upper surface phonon polariton frequency in LaAlO<sub>3</sub>/SrTiO<sub>3</sub> via electrostatic gating. Our results suggest that oxide interfaces are a new platform bridging unconventional electronics and long-wavelength nanophotonics.