Thermal and electrostatic tuning of surface phonon-polaritons in LaAlO3/SrTiO3 heterostructures

Yixi Zhou; Adrien Waelchli; Margherita Boselli; Iris Crassee; Adrien Bercher; Weiwei Luo; Jiahua Duan; J L M van Mechelen; Dirk van der Marel; Jérémie Teyssier; Carl Willem Rischau; Lukas Korosec; Stefano Gariglio; Jean-Marc Triscone; Alexey B Kuzmenko

doi:10.1038/s41467-023-43464-z

Thermal and electrostatic tuning of surface phonon-polaritons in LaAlO₃/SrTiO₃ heterostructures

Nat Commun. 2023 Nov 24;14(1):7686. doi: 10.1038/s41467-023-43464-z.

Authors

Yixi Zhou^{1

2}, Adrien Waelchli¹, Margherita Boselli¹, Iris Crassee¹, Adrien Bercher¹, Weiwei Luo^{1

3}, Jiahua Duan⁴, J L M van Mechelen⁵, Dirk van der Marel¹, Jérémie Teyssier¹, Carl Willem Rischau¹, Lukas Korosec¹, Stefano Gariglio¹, Jean-Marc Triscone¹, Alexey B Kuzmenko⁶

Affiliations

¹ Department of Quantum Matter Physics, University of Geneva, CH-1211, Geneva, 4, Switzerland.
² Beijing Key Laboratory of Nano-Photonics and Nano-Structure (NPNS), Department of Physics, Capital Normal University, 100048, Beijing, China.
³ The Key Laboratory of Weak-Light Nonlinear Photonics, Ministry of Education, School of Physics and TEDA Applied Physics Institute, Nankai University, Tianjin, 300457, China.
⁴ Department of Physics, University of Oviedo, Oviedo, 33006, Spain.
⁵ Department of Electrical Engineering, Eindhoven University of Technology, 5600 MB, Eindhoven, Netherlands.
⁶ Department of Quantum Matter Physics, University of Geneva, CH-1211, Geneva, 4, Switzerland. Alexey.Kuzmenko@unige.ch.

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. SrTiO₃ - 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 SrTiO₃ and in LaAlO₃/SrTiO₃ 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 LaAlO₃/SrTiO₃ via electrostatic gating. Our results suggest that oxide interfaces are a new platform bridging unconventional electronics and long-wavelength nanophotonics.