M. Ben Shalom

Tuning spin-orbit coupling and superconductivity at the SrTiO{3}/LaAlO{3} interface: a magnetotransport study.

The superconducting transition temperature T{c} of the SrTiO{3}/LaAlO{3} interface was varied by the electric field effect. The anisotropy of the upper critical field and the normal-state magnetotransport were studied as a function of gate voltage. The spin-orbit coupling energy epsilon{SO} is extracted. This tunable energy scale is used to explain the strong gate dependence of the mobility and of the anomalous Hall signal observed. Epsilon{SO} follows T{c} for the electric field range under study.

Shubnikov-de Haas oscillations in SrTiO3/LaAlO3 interface.

Quantum magnetic oscillations in SrTiO3/LaAlO3 interface are observed in the magnetoresistance. We study their frequency as a function of gate voltage and the evolution of their amplitude with temperature. The data are consistent with the Shubnikov-de Haas theory. The Hall resistivity ρ(xy) is nonlinear at low magnetic fields. ρ(xy) is fitted assuming multiple carrier contributions. We infer the density of the mobile charge carriers from the oscillations frequency and from Hall measurements. The comparison between these densities suggests multiple valley and spin degeneracy. The small amplitude of the oscillation is discussed in the framework of the multiple band scenario.

Shubnikov–De Haas Oscillations inSrTiO3/LaAlO3Interface

Quantum magnetic oscillations in SrTiO3/LaAlO3 interface are observed in the magnetoresistance. We study their frequency as a function of gate voltage and the evolution of their amplitude with temperature. The data are consistent with the Shubnikov-de Haas theory. The Hall resistivity ρ(xy) is nonlinear at low magnetic fields. ρ(xy) is fitted assuming multiple carrier contributions. We infer the density of the mobile charge carriers from the oscillations frequency and from Hall measurements. The comparison between these densities suggests multiple valley and spin degeneracy. The small amplitude of the oscillation is discussed in the framework of the multiple band scenario.

Anisotropic magneto-transport effects at SrTiO3\LaAlO3 interfaces

a two dimensional electron gas isformed at the interface between these insulators [1]. Thisinterface was latter shown to be superconducting [2] andmagnetic [3]. Recently Caviglia et al. have shown thatthe superconducting transition temperature can be con-trolled by solely varying the number of charge carriers atthe interface using a gate voltage.[4] These unexpectedresults and the potential for development of high per-formance oxide based electronics motivated an effort tounderstand the properties of this interface [5, 6, 7] andto improve it.The origin of the large carrier concentration at the in-terface remains under debate. When depositing mono-layers of LaAlO

Nature of weak magnetism in SrTiO3/LaAlO3 multilayers.

We report the observation of weak magnetism in superlattices of LaAlO(3)/SrTiO(3) using β-detected nuclear magnetic resonance. The spin lattice relaxation rate of ^{8}Li in superlattices with a spacer layers of 8 and 6 unit cells of LaAlO(3) exhibits a strong peak near ~35 K, whereas no such peak is observed in a superlattice with spacer layer thickness of 3 unit cells. We attribute the observed temperature dependence to slowing down of weakly coupled electronic moments at the LaAlO(3)/SrTiO(3) interface. These results show that the magnetism at the interface depends strongly on the thickness of the spacer layer, and that a minimal thickness of ~4-6 unit cells is required for the appearance of magnetism. A simple model is used to determine that the observed relaxation is due to small fluctuating moments (~0.002μ(B)) in the two samples with a larger LaAlO(3) spacer thickness.

Low-temperature dependence of the thermo-magnetic transport properties of the SrTiO3/LaAlO3 interface.

We report transport measurements, including: Hall, Seebeck and Nernst Effect. All these transport properties exhibit anomalous field and temperature dependences, with a change of behavior observed at about H 1.5T and T 15K. We were able to reconcile the low-temperature-low-field behavior of all transport properties using a simple two band analysis. A more detailed model is required in order to explain the high magnetic field regime.

Phase coherent transport in SrTiO3/LaAlO3 interfaces

The two dimensional electron gas formed between the two band insulators SrTiO3 and LaAlO3 exhibits a variety of interesting physical properties which make it an appealing material for use in future spintronics and/or quantum computing devices. For this kind of applications electrons have to retain their phase memory for sufficiently long times or length. Using a mesoscopic size device we were able to extract the phase coherence length, and its temperature variation. We find the dephasing rate to have a power law dependence on temperature. The power depends on the temperature range studied and sheet resistance as expected from dephasing due to strong electron-electron interactions.

Anomalous response to gate voltage application in mesoscopic LaAlO3/SrTiO3devices

We report on resistivity and Hall measurements performed on a series of narrow mesa devices fabricated from LaAlO_3/SrTiO_3 single interface heterostructure with a bridge width range of 1.5-10 microns. Upon applying back-gate voltage of the order of a few Volts, a strong increase in the sample resistance (up to factor of 35) is observed, suggesting a relatively large capacitance between the Hall-bar and the gate. The high value of this capacitance is due to the device geometry, and can be explained within an electrostatic model using the Thomas Fermi approximation. The Hall coefficient is sometimes a non-monotonic function of the gate voltage. This behavior is inconsistent with a single conduction band model. We show that a theoretical two-band model is consistent with this transport behavior, and indicates a metal to insulator transition in at least one of these bands.

Magnetotransport effects in polar versus non-polar SrTiO3 based heterostructures

Anisotropic magnetoresistance and negative magnetoresistance for in-plane fields are compared for the LaAlO3 /SrTiO3 interface and the symmetric Nb-doped SrTiO3 heterostructure. Both effects are exceptionally strong in LaAlO3 /SrTiO3 . We analyze their temperature, magnetic field and gate voltage dependencies and find them to arise from a Rashba type spin-orbit coupling with magnetic scatterers that have two contributions to their potential: spin exchange and Coulomb interaction. Atomic spin-orbit coupling is sufficient to explain the small effects observed in Nb-doped SrTiO3 . These results clarify contradicting transport interpretations in SrTiO3 -based heterostructures.