Phase coherent transport in SrTiO_{3}/LaAlO_{3} interfaces

The European Physical Journal B, 1999

Localization and dephasing of conduction electrons in a low carrier density ferromagnet due to scattering on magnetic fluctuations is considered. We claim the existence of the "mobility edge", which separates the states with fast diffusion and the states with slow diffusion; the latter is determined by the dephasing time. When the "mobility edge" crosses the Fermi energy a large and sharp change of conductivity is observed. The theory provides an explanation for the observed temperature dependence of conductivity in ferromagnetic semiconductors and manganite pyrochlores. PACS. 75.50.Pp Magnetic semiconductors -75.70.Pa Giant magnetoresistance -72.10.-d Theory of electronic transport; scattering mechanisms -72.10.Di Scattering by phonons, magnons, and other nonlocalized excitations

Physical Review Letters, 2010

We report on a study of magnetotransport in LaAlO3/SrTiO3 interfaces characterized by mobilities of the order of several thousands cm 2 /Vs. We observe Shubnikov-de Haas oscillations that indicate a two-dimensional character of the Fermi surface. The frequency of the oscillations signals a multiple sub-bands occupation in the quantum well or a multiple valley configuration. From the temperature dependence of the oscillation amplitude we extract an effective carrier mass m * 1.45 me. An electric field applied in the back-gate geometry increases the mobility, the carrier density and the oscillation frequency.

Physical Review B, 2005

We study, both theoretically and experimentally, the negative magnetoresistance (MR) of a twodimensional (2D) electron gas in a weak transverse magnetic field B. The analysis is carried out in a wide range of zero-B conductances g (measured in units of e 2 /h), including the range of intermediate conductances, g ∼ 1. Interpretation of the experimental results obtained for a 2D electron gas in GaAs/InxGa1−xAs/GaAs single quantum well structures is based on the theory which takes into account terms of higher orders in 1/g. We show that the standard weak localization (WL) theory is adequate for g 5. Calculating the corrections of second order in 1/g to the MR, stemming from both the interference contribution and the mutual effect of WL and Coulomb interaction, we expand the range of a quantitative agreement between the theory and experiment down to significantly lower conductances g ∼ 1. We demonstrate that at intermediate conductances the negative MR is described by the standard WL "digamma-functions" expression, but with a reduced prefactor α. We also show that at not very high g the second-loop corrections dominate over the contribution of the interaction in the Cooper channel, and therefore appear to be the main source of the lowering of the prefactor, α ≃ 1 − 2/πg. The fitting of the MR allows us to measure the true value of the phase breaking time within a wide conductance range, g 1. We further analyze the regime of a "weak insulator", when the zero-B conductance is low g(B = 0) < 1 due to the localization at low temperature, whereas the Drude conductance is high, g0 ≫ 1, so that a weak magnetic field delocalizes electronic states. In this regime, while the MR still can be fitted by the digamma-functions formula, the experimentally obtained value of the dephasing rate has nothing to do with the true one. The corresponding fitting parameter in the low-T limit is determined by the localization length and may therefore saturate at T → 0, even though the true dephasing rate vanishes.

Applied Physics Express, 2013

We report the fabrication and electrical measurements for LaAlO 3 /SrTiO 3 (LAO/STO) heterostructures having various lateral sizes. When the sample size is reduced to the sub-micrometer range, the magnetoconductance (MC) curve deviates from classical parabolic behavior. Instead, a negative MC behavior appears with superimposed conductance fluctuations, which is attributed to weak antilocalization and universal conductance fluctuations. Using the Maekawa-Fukuyama model, the spin-orbit scattering and phase coherence lengths are estimated from the MC data, which are dependent on the gate voltage and temperature. Our comprehensive study shows that LAO/STO heterointerfaces provide a useful platform to explore quantum coherent transport of strongly correlated electrons. #

Physical review, 2016

We present a time-resolved terahertz spectroscopic study of the half-metallic ferromagnet CrO 2. The ultrafast conductivity dynamics excited by an optical pump displays a very short (several picoseconds) and a very long (several hundred picoseconds) characteristic time scales. We attribute the former to the electron-phonon relaxation and the latter to the spin-lattice relaxation. We use this distinction to quantify the relative contribution of the scattering by spin fluctuations to the resistivity of CrO 2 : we find that they contribute less than one half of all scattering events below room temperature. This contribution rises to ∼ 70% as the temperature approaches T C =390 K. The small effect of spin fluctuations on the resistivity is unexpected in the light of the proposed double-exchange nature of the electronic and magnetic properties of CrO 2. jela,

2008

We present low-temperature and high-field magnetotransport data on SrTiO3-LaAlO3 interfaces. The resistance shows hysteresis in magnetic field and a logarithmic relaxation as a function of time. Oscillations in the magnetoresistance are observed, showing a √ B periodicity, both in large-area unstructured samples as well as in a structured sample. An explanation in terms of a commensurability condition of edge states in a highly mobile two-dimensional electron gas between substrate step edges is suggested.

Advanced Materials Interfaces, 2013

We report the fabrication and electrical measurements for LaAlO 3 /SrTiO 3 (LAO/STO) heterostructures having various lateral sizes. When the sample size is reduced to the sub-micrometer range, the magnetoconductance (MC) curve deviates from classical parabolic behavior. Instead, a negative MC behavior appears with superimposed conductance fluctuations, which is attributed to weak antilocalization and universal conductance fluctuations. Using the Maekawa-Fukuyama model, the spin-orbit scattering and phase coherence lengths are estimated from the MC data, which are dependent on the gate voltage and temperature. Our comprehensive study shows that LAO/STO heterointerfaces provide a useful platform to explore quantum coherent transport of strongly correlated electrons. #

Journal of Applied Physics, 2004

IEEE Transactions on Magnetics, 2000

We study the magnetoresistance (MR) of the quasi-2-D electron liquid at the interface that forms between SrTiO 3 and LaAlO 3 as a function of the magnitude and orientation of the magnetic field. We find that at T 60K, the MR is described by a + b cos 2 + c sin 2 cos 2 ', where is the angle between the field and the film normal and ' is the angle between the in-plane component of the field and the current. For = 0 (field perpendicular to the plane), we show that the MR obeys Kohler's rule while for = 90 (field in the plane) the MR is significantly smaller, and it is almost temperature independent, suggesting it is dominated by interface scattering.