Scanning near-field optical microscopy of LaAlO3/SrTiO3 heterostructures

The interface between LaAlO3 and SrTiO3 hosts a conducting two dimensional electron system with many interesting properties. Since its discovery in 2004, this system has been intensively studied but there are still several open questions mainly related to the presence of local modulations of the electronic properties. Visualizing these effects remains challenging as it requires the use of a non-invasive local probe with nanometric resolution and sensitive to the electronic properties of the interface buried by a film of insulating LaAlO3.

Luo and collaborators investigated the use of the scanning near field optical microscopy (SNOM) technique, now available at the DQMP, to study the properties of the interfacial system in LaAlO3/SrTiO3 heterostructures. SNOM combines an optics experiment with an atomic force microscope resulting in the possibility to probe the properties of a material with sub-wavelength resolution. The authors showed that the near-field component of the signal is sensitive to the presence of the conducting interface and that the optical response is modified by changes of the interfacial properties induced by temperature and electric field. They also compared the experiments with theoretical calculations of the optical response of the system revealing the physical origin of their observations: the plasmon-phonon coupling happening at the interface. Finally, they used this technique to image conducting nanowires patterned in insulating heterostructures.

These results show that the near-field optical response is a good observable to map the local electronic properties of LaAlO3/SrTiO3 interfaces and are a promising starting point for the use of SNOM to investigate emergent phenomena at oxides interfaces and surfaces.

The work is published in Nature Communications

Contact: Weiwei Luo, Margherita Boselli