Enhanced spin–orbit coupling and charge carrier density suppression in LaAl1−xCrxO3/SrTiO3hetero-interfaces

Abstract

We report a gradual suppression of the two-dimensional electron gas (2DEG) at the LaAlO3/SrTiO3 interface on substitution of chromium at the Al sites. The sheet carrier density at the interface (n□) drops monotonically from ∼2.2 × 1014 cm−2 to ∼2.5 × 1013 cm−2 on replacing ≈60% of the Al sites by Cr and the sheet resistance (R□) exceeds the quantum limit for localization (h/2e2) in the concentrating range 40–60% of Cr. The samples with Cr ⩽40% show a distinct minimum (Tm) in metallic R□(T) whose position shifts to higher temperatures on increasing the substitution. Distinct signatures of Rashba spin–orbit interaction (SOI) induced magnetoresistance (MR) are seen in R□ measured in out of plane field (H⊥) geometry at T ⩽ 8 K. Analysis of these data in the framework of Maekawa–Fukuyama theory allows extraction of the SOI critical field (HSO) and time scale (τSO) whose evolution with Cr concentration is similar as with the increasing negative gate voltage in LAO/STO interface. The MR in the temperature range 8 K ⩽ T ⩽ Tm is quadratic in the field with a +ve sign for H⊥ and −ve sign for H∥. The behaviour of H∥ MR is consistent with Kondo theory which in the present case is renormalized by the strong Rashba SOI at T < 8 K.