Enhanced spin-orbit coupling and charge carrier density suppression in LaAl1-xCrxO3/SrTiO3 hetero-interfaces

We report a gradual suppression of the two-dimensional electron gas (2DEG) at the LaAlO(3)/SrTiO(3) interface on substitution of chromium at the Al sites. The sheet carrier density at the interface (n□) drops monotonically from ∼2.2 × 10(14) cm(-2) to ∼2.5 × 10(13) cm(-2) on replacing ≈60% of the Al sites by Cr and the sheet resistance (R□) exceeds the quantum limit for localization (h/2e(2)) in the concentrating range 40-60% of Cr. The samples with Cr ⩽40% show a distinct minimum (T(m)) 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 (H(SO)) and time scale (τ(SO)) 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 ⩽ T(m) 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.