51 research outputs found
Inhomogeneous multi-carrier superconductivity at LaXO3/SrTiO3 (X=Al or Ti) oxide interfaces
Several experiments reveal the inhomogeneous character of the superconducting
state that occurs when the carrier density of the two-dimensional electron gas
formed at the LaXO3/SrTiO3 (X=Al or Ti) interface is tuned above a threshold
value by means of gating. Re-analyzing previous measurements, that highlight
the presence of two kinds of carriers, with low and high mobility, we shall
provide a description of multi-carrier magneto-transport in an inhomogeneous
two-dimensional electron gas, gaining insight into the properties of the
physics of the systems under investigation. We shall then show that the
measured resistance, superfluid density, and tunneling spectra result from the
percolative connection of superconducting "puddles" with randomly distributed
critical temperatures, embedded in a weakly localizing metallic matrix. We
shall also show that this scenario is consistent with the characteristics of
the superconductor-to-metal transition driven by a magnetic field. A
multi-carrier description of the superconducting state, within a weak-coupling
BCS-like model, will be finally discussed.Comment: 12 pages 10 figure
Multi-band superconductivity and nanoscale inhomogeneity at oxide interfaces
The two-dimensional electron gas at the LaTiO3/SrTiO3 or LaAlO3/SrTiO3 oxide
interfaces becomes superconducting when the carrier density is tuned by gating.
The measured resistance and superfluid density reveal an inhomogeneous
superconductivity resulting from percolation of filamentary structures of
superconducting "puddles" with randomly distributed critical temperatures,
embedded in a non-superconducting matrix. Following the evidence that
superconductivity is related to the appearance of high-mobility carriers, we
model intra-puddle superconductivity by a multi-band system within a weak
coupling BCS scheme. The microscopic parameters, extracted by fitting the
transport data with a percolative model, yield a consistent description of the
dependence of the average intra-puddle critical temperature and superfluid
density on the carrier density.Comment: 7 pages with 3 figures + supplemental material (4 pages and 5
figures
Non-linear characteristics in two-dimensional superconductors: Berezinskii-Kosterlitz-Thouless physics vs inhomogeneity
One of the hallmarks of the Berezinskii-Kosterlitz-Thouless (BKT) transition
in two-dimensional (2D) superconductors is the universal jump of the superfluid
density, that can be indirectly probed via the non-linear exponent of the
current-voltage characteristics. Here, we compare the experimental
measurements of characteristics in two cases, namely NbN thin films and
SrTiO-based interfaces. While the former display a paradigmatic example of
BKT-like non-linear effects, the latter do not seem to justify a BKT analysis.
Rather, the observed characteristics can be well reproduced theoretically
by modelling the effect of mesoscopic inhomogeneity of the superconducting
state. Our results offer an alternative perspective on the spontaneous
fragmentation of the superconducting background in confined 2D systems.Comment: Final version, as publishe
Quantized conductance in a one-dimensional ballistic oxide nanodevice
Electric-field effect control of two-dimensional electron gases (2-DEG) has
enabled the exploration of nanoscale electron quantum transport in
semiconductors. Beyond these classical materials, transition metal-oxide-based
structures have d-electronic states favoring the emergence of novel quantum
orders absent in conventional semiconductors. In this context, the
LaAlO3/SrTiO3 interface that combines gate-tunable superconductivity and
sizeable spin-orbit coupling is emerging as a promising platform to realize
topological superconductivity. However, the fabrication of nanodevices in which
the electronic properties of this oxide interface can be controlled at the
nanoscale by field-effect remains a scientific and technological challenge.
Here, we demonstrate the quantization of conductance in a ballistic quantum
point contact (QPC), formed by electrostatic confinement of the LaAlO3/SrTiO3
2-DEG with a split-gate. Through finite source-drain voltage, we perform a
comprehensive spectroscopic investigation of the 3d energy levels inside the
QPC, which can be regarded as a spectrometer able to probe Majorana states in
an oxide 2-DEG
Field-effect control of superconductivity and Rashba spin-orbit coupling in top-gated LaAlO3/SrTiO3 devices
The recent development in the fabrication of artificial oxide
heterostructures opens new avenues in the field of quantum materials by
enabling the manipulation of the charge, spin and orbital degrees of freedom.
In this context, the discovery of two-dimensional electron gases (2-DEGs) at
LAlO3/SrTiO3 interfaces, which exhibit both superconductivity and strong Rashba
spin-orbit coupling (SOC), represents a major breakthrough. Here, we report on
the realisation of a field-effect LaAlO3/SrTiO3 device, whose physical
properties, including superconductivity and SOC, can be tuned over a wide range
by a top-gate voltage. We derive a phase diagram, which emphasises a
field-effect-induced superconductor-to-insulator quantum phase transition.
Magneto-transport measurements indicate that the Rashba coupling constant
increases linearly with electrostatic doping. Our results pave the way for the
realisation of mesoscopic devices, where these two properties can be
manipulated on a local scale by means of top-gates
magnetic field induced transition in superconducting latio3 srtio3 interfaces
Superconductivity at the LaTiO3/SrTiO3 interface is studied by low temperature and high magnetic field measurements as a function of a back-gate voltage. We show that it is intimately related to the appearance of a low density (a few 1012 cm−2) of high mobility carriers, in addition to low mobility ones always present in the system. These carriers form superconducting puddles coupled by a metallic two-dimensional electron gas, as revealed by the analysis of the phase transition driven by a perpendicular magnetic field. Two critical fields are evidenced, and a quantitative comparison with a recent theoretical model is made
Effect of disorder on superconductivity and Rashba spin-orbit coupling in LaAlO3/SrTiO3 interfaces
A rather unique feature of the two-dimensional electron gas formed at the interface between the two insulators LaAlO3 and SrTiO3 is to host both gate-tunable superconductivity and strong spin-orbit coupling. In the present work, we use the disorder generated by Cr substitution of Al atoms in LaAlO3 as a tool to explore the nature of superconductivity and spin-orbit coupling in these interfaces. We analyze the transport properties of three different samples whose only relevant difference is their elastic scattering time tau(e). A reduction of the superconducting T-c is observed with Cr doping consistent with an increase of electron-electron interaction in the presence of disorder. In addition, the evolution of spin-orbit coupling with gate voltage and Cr doping evidences a Dyakonov-Perel mechanism of spin relaxation (tau(SO) proportional to tau(-1)(e)) in the presence of a Rashba-type spin-orbit interaction
- …