5 research outputs found
Imaging vortex dynamics in Josephson arrays using magnetic force microscopy
Vortices and vortex lattices play a major role in determining the transport properties of type-II superconductors[1ā3], and enable a platform to investigate exotic superconducting physics[4,5]. The study of vortex matter has generally focused on novel states in 2D ļ¬lms and structures, and has recently moved to investigating systems with constrained dimensions and smaller vortex numbers[6ā11]. Vortices are responsible, for example, for some electrical transport regimes in superconducting ļ¬lms, as well as the Berezinkskii-Kosterlitz-Thouless phase transition in superconducting ļ¬lms[12]. Unconventional forms of superconductivity, such as the spin triplet pairing predicted in Sr2RuO4, or in topological insulators paired to s-wave superconductors, contain two condensates that may support two vortex lattices, and may display Majorana modes, signatures of which may have been seen in other superconducting systems[13ā17]. The vortex-vortex interactions, or inter and intra-condensate couplings in multicondensate systems, are important parameters that characterize the behavior of the systems that display such phenomena[18ā20]. In investigating these parameters, a technique that can both probe the energies in a system, as well as manipulate the vortices therein, has long been desired.
In this work, we report on progress in determining the energy scales of vortex systems, as well as limited control over the vortex motion. Using a technique based on magnetic force microscopy, we can directly measure the resonant motion of vortices present in a superconducting lattice. We use a scanning magnetic tip to trap a small number of vortices in a superconducting Josephson junction array near the tip. By observing the resonant motion of the conļ¬guration of vortices, a map of the location of energy degeneracies between diļ¬erent stable conļ¬gurations is generated. From this data, we use a simulation to extract the relative strengths of the characteristic energy scales for the system, including the vortex-magnetic ļ¬eld interaction, the vortex-vortex interaction strength, and the chemical potential for the vortices. The simulations for small numbers of vortices ļ¬ts the data well for multiple ļ¬eld proļ¬les and lattice spacings. The ability to tune the vortex number and conļ¬gurations by changing the magnetic ļ¬eld proļ¬le from the tip, as well as the lattice parameters of the superconducting surface, are key portions of this technique. We demonstrate that the relative strengths of the chemical potential and vortex-vortex interactions can be tuned relative to the vortex-magnetic ļ¬eld energy by changing the lattice spacing of the array. We also show that by moving the tip farther from or closer to the surface, which changes the potential well from the tip, that the conļ¬gurations of vortices can be modiļ¬ed. From the experiments, we show that this technique can be used to both extract the strengths of the relative energy scales in this system and other superconducting systems, as well as for manipulating the vortex conļ¬gurations for quantum computation applications
Nanoscale Fourier-Transform Magnetic Resonance Imaging
We report a method for nanometer-scale pulsed nuclear magnetic resonance imaging and spectroscopy. Periodic radio-frequency pulses are used to create temporal correlations in the statistical polarization of a solid organic sample. The spin density is spatially encoded by applying a series of intense magnetic field gradient pulses generated by focusing electric current through a nanometer-scale metal constriction. We demonstrate this technique using a silicon nanowire mechanical oscillator as a magnetic resonance sensor to image ^{1}H spins in a polystyrene sample. We obtain a two-dimensional projection of the sample proton density with approximately 10-nm resolution