A skyrmion-based spin-torque nano-oscillator

A model for a spin-torque nano-oscillator based on the self-sustained oscillation of a magnetic skyrmion is presented. The system involves a circular nanopillar geometry comprising an ultrathin film free magnetic layer with a strong Dzyaloshinkii-Moriya interaction and a polariser layer with a vortex-like spin configuration. It is shown that spin-transfer torques due to current flow perpendicular to the film plane leads to skyrmion gyration that arises from a competition between geometric confinement due to boundary edges and the vortex-like polarisation of the spin torques. A phenomenology for such oscillations is developed and quantitative analysis using micromagnetics simulations is presented. It is also shown that weak disorder due to random anisotropy variations does not influence the main characteristics of the steady-state gyration.Comment: 15 pages, 6 figure

Electric field effect modulation of transition temperature, mobile carrier density and in-plane penetration depth in NdBa2Cu3O(7-delta) thin films

We explore the relationship between the critical temperature, T_c, the mobile areal carrier density, n_2D, and the zero temperature magnetic in-plane penetration depth, lambda_ab(0), in very thin underdoped NdBa2Cu3O{7-delta} films near the superconductor to insulator transition using the electric field effect technique. We observe that T_c depends linearly on both, n_2D and lambda_ab(0), the signature of a quantum superconductor to insulator (QSI) transition in two dimensions with znu-bar where z is the dynamic and nu-bar the critical exponent of the in-plane correlation length.Comment: 4 pages, 4 figure

Tunable Rashba spin-orbit interaction at oxide interfaces

The quasi-two-dimensional electron gas found at the LaAlO3/SrTiO3 interface offers exciting new functionalities, such as tunable superconductivity, and has been proposed as a new nanoelectronics fabrication platform. Here we lay out a new example of an electronic property arising from the interfacial breaking of inversion symmetry, namely a large Rashba spin-orbit interaction, whose magnitude can be modulated by the application of an external electric field. By means of magnetotransport experiments we explore the evolution of the spin-orbit coupling across the phase diagram of the system. We uncover a steep rise in Rashba interaction occurring around the doping level where a quantum critical point separates the insulating and superconducting ground states of the system

Seebeck effect in the conducting LaAlO_{3}/SrTiO_{3} interface

The observation of metallic behavior at the interface between insulating oxides has triggered worldwide efforts to shed light on the physics of these systems and clarify some still open issues, among which the dimensional character of the conducting system. In order to address this issue, we measure electrical transport (Seebeck effect, Hall effect and conductivity) in LaAlO_{3}/SrTiO_{3} interfaces and, for comparison, in a doped SrTiO_{3} bulk single crystal. In these experiments, the carrier concentration is tuned, using the field effect in a back gate geometry. The combined analysis of all experimental data at 77 K indicates that the thickness of the conducting layer is ~7 nm and that the Seebeck effect data are well described by a two-dimensional (2D) density of states. We find that the back gate voltage is effective in varying not only the charge density, but also the thickness of the conducting layer, which is found to change by a factor of ~2, using an electric field between -4 and +4MV/m at 77K. No enhancement of the Seebeck effect due to the electronic confinement and no evidence for two-dimensional quantization steps are observed at the interfaces.Comment: 15 pages, 5 figure

Two-dimensional quantum oscillations of the conductance at LaAlO3/SrTiO3 interfaces

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 $m^{*}\simeq1.45$\,$m_{e}$. An electric field applied in the back-gate geometry increases the mobility, the carrier density and the oscillation frequency.Comment: 4 pages, 4 figure

Superconductivity at the LaAlO3/SrTiO3interface

We report on the structural characterization of LaAlO3/SrTiO3 interfaces and on their transport properties. LaAlO3 films were prepared using pulsed laser deposition onto TiO2 terminated (001) SrTiO3 substrates inducing a metallic conduction at the interface. Resistance and Hall effect measurements reveal a sheet carrier density between 0.4 and 1.2·10 14 electrons/cm 2 at room temperature and mobility of ∼ 300 cm 2 V −1 s −1 at low temperatures. A transition to a superconducting state is observed at a temperature of ∼ 200 mK. The superconducting characteristics display signatures of 2D superconductivity