Eur. Phys. J. Special Topics 228, 669–673 (2019)
https://doi.org/10.1140/epjst/e2019-800145-7

Regular Article

Infrared spectroscopy of two-dimensional electron systems

¹ CNR-SPIN and Dipartimento di Fisica, Universitá di Roma “La Sapienza”, Roma, Italy
² Department of Microtechnology & Nanoscience, Chalmers University, Gothenburg, Sweden
³ Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA
⁴ Dipartimento di Fisica, Universitá di Roma La Sapienza, Roma, Italy
⁵ CNR-SPIN UOS Napoli, Complesso Universitario di Monte Sant’Angelo, Napoli, Italy
⁶ Synchrotron SOLEIL, Gif-sur-Yvette, France

^a e-mail: paolo.calvani@roma1.infn.it

Received: 19 September 2018
Received in final form: 27 November 2018
Published online: 3 July 2019

Abstract

We have used grazing-angle infrared spectroscopy with polarized radiation to detect the Berreman effect (BE) in the two-dimensional electron systems (2DES) which form spontaneously at two interfaces: one between an amorphous film LaAlO₃ and its SrTiO₃ substrate (LAO/STO), and another at the interface between the topological insulator (TI) Bi₂Se₃ and its sapphire substrate. In both systems we have thus extracted the 2DES parameters at different temperatures. In the quasi-2DES under amorphous LAO, the surface density n_s is higher than under crystalline LAO, while the mobility is nearly the same and the thickness d is 7 nm. In ultrapure Bi₂Se₃ on sapphire, preliminary data provided d < 1 nm and n_s ≈ 10¹³ cm⁻², indicating, by comparison with existing estimates, that the BE indeed detects the topological surface states.