Defect Control of Conventional and Anomalous Electron Transport at Complex Oxide Interfaces

Abstract

Using low-temperature electrical measurements, the interrelation between electron transport, magnetic properties, and ionic defect structure in complex oxide interface systems is investigated, focusing on NdGaO 3 =SrTiO 3 (100) interfaces. Field-dependent Hall characteristics (2-300 K) are obtained for samples grown at various growth pressures. In addition to multiple electron transport, interfacial magnetism is tracked exploiting the anomalous Hall effect (AHE). These two properties both contribute to a nonlinearity in the field dependence of the Hall resistance, with multiple carrier conduction evident below 30 K and AHE at temperatures ≲10 K. Considering these two sources of nonlinearity, we suggest a phenomenological model capturing the complex field dependence of the Hall characteristics in the low-temperature regime. Our model allows the extraction of the conventional transport parameters and a qualitative analysis of the magnetization. The electron mobility is found to decrease systematically with increasing growth pressure. This suggests dominant electron scattering by acceptor-type strontium vacancies incorporated during growth. The AHE scales with growth pressure. The most pronounced AHE is found at increased growth pressure and, thus, in the most defective, low-mobility samples, indicating a correlation between transport, magnetism, and cation defect concentration.

Insulator-to-Metal Transition at Oxide Interfaces Induced by WO3 Overlayers

“…The (4, 2) heterostructure presents two channels of electrons: one with lower-mobility µ I = 3600 cm 2 V −1 s −1 , n I = 1.7 × 10 13 cm −2 and one with higher mobility µ II = 80 000 cm 2 V −1 s −1 , n II = 9.3 × 10 12 cm −2 . Higher mobility values are observed for lower carrier densities, consistent with previous studies of STO-based 2DES [30]. We note that the sheet resistance of the higher-mobility channel ρ II is one order of magnitude smaller than ρ I , suggesting that it dominates the low-temperature transport.…”

“…Upon warming, n I maintains an almost constant value, while n II undergoes a sharp drop above 10 K and subsequently disappears. This disappearance might be due to the activation of interband scattering processes at higher temperatures, which cause a mixing of ρ I , ρ II , so that their populations cannot be independently resolved in Hall effect measurements [30]. Another possible interpretation for this trend is that the two conduction channels are situated in STO at two different distances from the interface.…”

Magnetic two-dimensional electron gas at the manganite-buffered LaAlO3/SrTiO3 interface

“…It is this feature that leads to the deep pit of the Hall coefficient. This is in sharp contrast to NdGaO 3 /STO [24] [blue curves in Fig. 2(d)] or LAO/EuTiO 3 /STO [23], for which R AHE owns the same sign as the applied field.…”

“…2(a) of Ref. [24]. The normal and anomalous Hall resistances have been determined by the technique described there.…”

“…Then, a spin-polarized 2DEG below 8 K was declared by Stornaiuolo et al [23], who inserted a 1-uc EuTiO 3 spacer between LAO and STO and observed AHE. Through optimizing the density of Sr and O vacancies in NdGaO 3 /STO, recently Gunkel et al [24] obtained the highest temperature of ∼10 K for the AHE. Obviously, the magnetic ordering temperature suggested by the AHE is much lower than that expected from the macroscopic [21] and microscopic [17] magnetic measurements.…”