Fig. 3: Confocal Raman spectroscopy study of the induced polar moment.
From: Non-collinear and asymmetric polar moments at back-gated SrTiO3 interfaces
a Sketch of the measurement geometry. b Gate-voltage-dependent spectra of an AlOx/SrTiO3 heterostructure at 10 K. A Stokes/Anti-Stokes comparison yields a temperature offset of max. ∼20 K, caused by laser heating. Black stars mark the R-modes at 15, 45, 144, 229 and 447 cm−1 that become Raman-active below the antiferrodistortive transition temperature T* = 105 K. Green arrows show the field-induced infrared-active phonon modes at 25, 175, 540 and 795 cm−1. c Magnified view of the field-induced soft mode (TO1) and its asymmetry with respect to ±V. Inset: Corresponding spectra taking in s-polarization (normalized to the multi-phonon background). d Depth profile of the normalized peak area of the soft mode for +V and −V. e Field-dependence of the soft mode of a LaAlO3/SrTiO3 heterostructure. f Temperature dependence of the peak area of the soft mode for +V and −V. g–i Low-frequency Raman spectra of an AlOx/KTaO3 (KTO) heterostructure, showing a weak and rapidly decaying (within minutes) soft mode signal that occurs only after the voltage has been decreased, i.e. either from +V to 0 V (g) or from 0 V to −V (h), but is absent after a corresponding voltage increase from 0 V to +V or from −V to 0 V (i).
