Fig. 1: Infrared ellipsometry study of phonon anomalies due to the electric-field-induced polar moment.
From: Non-collinear and asymmetric polar moments at back-gated SrTiO3 interfaces
a Spectra of the optical conductivity, σ1, showing the asymmetric R-mode splitting due to an in-plane polarization Pab for gate-voltage cycles 0 V → + V → −V and b the corresponding hysteresis loops for the magnitude of the R-mode splitting (and thus of Pab) at 10 K. c Spectra and d hysteresis loops of the R-mode splitting for the reverse voltage cycling direction, i.e. 0 V → −V → + V. e, f Anomaly at the longitudinal optical (LO4) edge. e The difference spectra of the ellipsometric angle ΔΨ = Ψexp – Ψ0V, pristine at the LO4 edge show the signatures of an infrared-active transverse optical (TO) mode that is induced at −V. This new TO mode can only be modeled by assuming a polarization with a sizeable vertical component (dashed purple), instead of a polarization of pure horizontal character (dashed dark blue). f Corresponding voltage loops of the oscillator strength, S, of the field-induced TO mode. g, h Temperature dependence of the LO4 anomaly. g Spectra of the field-induced TO mode (cyan) together with the fit (dashed purple) at selected temperatures. h Temperature dependence of S for the field-induced TO mode (at −8 kV/cm).
