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Register a new userHopping Transport in SrTiO3/Nd1-xTiO3/SrTiO3 Heterostructures
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Electronic transport near the insulator-metal transition is investigated in the molecular beam epitaxy-grown SrTiO3/Nd1-xTiO3/SrTiO3 heterostructures using temperature dependent magnetotransport measurements. It was found that Nd-vacancies introduce localized electronic states resulting in the variable range hopping transport at low temperatures. At a fixed Nd-vacancies concentration, a crossover from Mott to Efros-Shklovskii (ES) variable range hopping transport was observed with decreasing temperature. With increasing disorder, a sign reversal of magnetoresistance from positive to negative was observed revealing interplay between intra-state interaction and the energy dependence of the localization length as a function of disorder. These findings highlight the important role of stoichiometry when exploring intrinsic effect using heterostructure and interfaces in addition to offering broad opportunity to tailor low temperature transport using non-stoichiometry defects.
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Interface engineering is an extremely useful tool for systematically investigating materials and the various ways materials interact with each other. We describe different interface engineering strategies designed to reveal the origin of the electric and magnetic dead-layer at La0.67Sr0.33MnO3 interfaces. La0.67Sr0.33MnO3 is a key example of a strongly correlated peroskite oxide material in which a subtle balance of competing interactions gives rise to a ferromagnetic metallic groundstate. This balance, however, is easily disrupted at interfaces. We systematically vary the dopant profile, the disorder and the oxygen octahedra rotations at the interface to investigate which mechanism is responsible for the dead layer. We find that the magnetic dead layer can be completely eliminated by compositional interface engineering such that the polar discontinuity at the interface is removed. This, however, leaves the electrical dead-layer largely intact. We find that deformations in the oxygen octahedra network at the interface are the dominant cause for the electrical dead layer.
The hysteretic piezoelectric response in LaAlO3/SrTiO3 heterostructures can provide important insights into the mechanism for interfacial conductance and its metastability under various conditions. We have performed a variety of nonlocal piezoelectric force microscopy experiments on 3 unit cell LaAlO3/SrTiO3 heterostructures. A hysteretic piezoresponse is observed under various environmental and driving conditions. The hysteresis is suppressed when either the sample is placed in vacuum or the interface is electrically grounded. We present a simple physical model which can account for the observed phenomena.
Using polarized neutron reflectometry (PNR) we measured the neutron spin dependent reflectivity from four LaAlO3/SrTiO3 superlattices. This experiment implies that the upper limit for the magnetization induced by an 11 T magnetic field at 1.7 K is 2 emu/cm3. SQUID magnetometry of the superlattices sporadically finds an enhanced moment, possibly due to experimental artifacts. These observations set important restrictions on theories which imply a strongly enhanced magnetism at the interface between LaAlO3 and SrTiO3.
The low-temperature resistance of a conducting LaAlO3/SrTiO3 interface with a 10 nm thick LaAlO3 film decreases by more than 50% after illumination with light of energy higher than the SrTiO3 band-gap. We explain our observations by optical excitation of an additional high mobility electron channel, which is spatially separated from the photo-excited holes. After illumination, we measure a strongly non-linear Hall resistance which is governed by the concentration and mobility of the photo-excited carriers. This can be explained within a two-carrier model where illumination creates a high-mobility electron channel in addition to a low-mobility electron channel which exists before illumination.
We demonstrate a current tunable Rashba spin orbit interaction in LaAlO3/SrTiO3 (LAO/STO) quasi two dimensional electron gas (2DEG) system. Anisotropic magnetoresistance (AMR) measurements are employed to detect and understand the current-induced Rashba field. The effective Rashba field scales with the current and a value of 2.35 T is observed for a dc-current of 200 uA. The results suggest that LAO/STO heterostructures can be considered for spin orbit torque based magnetization switching.
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