226 research outputs found
Shubnikov-de Haas oscillations in SrTiO3\LaAlO3 interface
Quantum magnetic oscillations in SrTiO3/\LaAlO3 interface are observed. The
evolution of their frequency and amplitude at various gate voltages and
temperatures is studied. The data are consistent with the Shubnikov de-Haas
theory. The Hall resistivity rho exhibits nonlinearity at low magnetic field.
It is fitted assuming multiple carrier contributions. The comparison between
the mobile carrier density inferred from the Hall data and the oscillation
frequency suggests multiple valley and spin degeneracy. The small amplitude of
the oscillations is discussed in the framework of the multiple band scenario
Tuning spin-orbit coupling and superconductivity at the SrTiO3/LaAlO3 interface: a magneto-transport study
The superconducting transition temperature, Tc, of the SrTiO3/LaAlO3
interface was varied by the electric field effect. The anisotropy of the upper
critical field and the normal state magneto-transport were studied as a
function of gate voltage. The spin-orbit coupling energy is extracted. This
tunable energy scale is used to explain the strong gate dependence of the
mobility and of the anomalous Hall signal observed. The spin-orbit coupling
energy follows Tc for the electric field range under study
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.Comment: Submitted to Phys. Rev
Anomalous magneto-transport at the superconducting interface between LaAlO3 and SrTiO3
The magnetoresistance as a function of temperature and field for atomically
flat interfaces between 8 unit cells of LaAlO3 and SrTiO3 is reported.
Anomalous anisotropic behavior of the magnetoresistance is observed below 30 K
for superconducting samples with carrier concentration of 3.5\times10^13 cm^-2
. We associate this behavior to a magnetic order formed at the interface.Comment: 2 pages, 3 figures. Proceedings of the 9th International Conference
on Materials and Mechanisms of Superconductivit
Measuring Hall Viscosity of Graphene's Electron Fluid
Materials subjected to a magnetic field exhibit the Hall effect, a phenomenon
studied and understood in fine detail. Here we report a qualitative breach of
this classical behavior in electron systems with high viscosity. The viscous
fluid in graphene is found to respond to non-quantizing magnetic fields by
producing an electric field opposite to that generated by the classical Hall
effect. The viscous contribution is large and identified by studying local
voltages that arise in the vicinity of current-injecting contacts. We analyze
the anomaly over a wide range of temperatures and carrier densities and extract
the Hall viscosity, a dissipationless transport coefficient that was long
identified theoretically but remained elusive in experiment. Good agreement
with theory suggests further opportunities for studying electron
magnetohydrodynamics.Comment: 18 pages, 9 figure
Negative local resistance caused by viscous electron backflow in graphene
Graphene hosts a unique electron system in which electron-phonon scattering
is extremely weak but electron-electron collisions are sufficiently frequent to
provide local equilibrium above liquid nitrogen temperature. Under these
conditions, electrons can behave as a viscous liquid and exhibit hydrodynamic
phenomena similar to classical liquids. Here we report strong evidence for this
transport regime. We find that doped graphene exhibits an anomalous (negative)
voltage drop near current injection contacts, which is attributed to the
formation of submicrometer-size whirlpools in the electron flow. The viscosity
of graphene's electron liquid is found to be ~0.1 m /s, an order of
magnitude larger than that of honey, in agreement with many-body theory. Our
work shows a possibility to study electron hydrodynamics using high quality
graphene
Micromagnetometry of two-dimensional ferromagnets
The study of atomically thin ferromagnetic crystals has led to the discovery
of unusual magnetic behaviour and provided insight into the magnetic properties
of bulk materials. However, the experimental techniques that have been used to
explore ferromagnetism in such materials cannot probe the magnetic field
directly. Here, we show that ballistic Hall micromagnetometry can be used to
measure the magnetization of individual two-dimensional ferromagnets. Our
devices are made by van der Waals assembly in such a way that the investigated
ferromagnetic crystal is placed on top of a multi-terminal Hall bar made from
encapsulated graphene. We use the micromagnetometry technique to study
atomically thin chromium tribromide (CrBr3). We find that the material remains
ferromagnetic down to monolayer thickness and exhibits strong out-of-plane
anisotropy. We also find that the magnetic response of CrBr3 varies little with
the number of layers and its temperature dependence cannot be described by the
simple Ising model of two-dimensional ferromagnetism.Comment: 19 pages, 12 figure
A Universal Critical Density Underlying the Physics of Electrons at the LaAlO3/SrTiO3 Interface
The two-dimensional electron system formed at the interface between the
insulating oxides LaAlO3 and SrTiO3 exhibits ferromagnetism, superconductivity,
and a wide range of unique magnetotransport properties. A key challenge is to
find a unified microscopic mechanism that underlies these emergent phenomena.
Here we show that a universal Lifshitz transition between d-orbitals lies at
the core of the observed transport phenomena in this system. Our measurements
find a critical electronic density at which the transport switches from single
to multiple carriers. This density has a universal value, independent of the
LaAlO3 thickness and electron mobility. The characteristics of the transition,
its universality, and its compatibility with spectroscopic measurements
establish it as a transition between d-orbitals of different symmetries. A
simple band model, allowing for spin-orbit coupling at the atomic level,
connects the observed universal transition to a range of reported
magnetotransport properties. Interestingly, we also find that the maximum of
the superconducting transition temperature occurs at the same critical
transition, indicating a possible connection between the two phenomena. Our
observations demonstrate that orbital degeneracies play an important role in
the fascinating behavior observed so far in these oxides
- …