Superconducting vortex profile from fixed point measurements the “Lazy Fisherman” tunneling microscopy method

Abstract

We introduce a mode of operation for studying the vortex phase in superconductors using scanning tunnelling microscopy (STM). While in the conventional STM method, the tip is scanned over a sample in which a fixed vortex pattern is prepared, in our "Lazy Fisherman" method the STM tip is kept fixed at a selected location while the vortices are being moved by varying the applied magnetic field. By continuously acquiring the local tunnelling conductance spectra, dI/dV(V), we detect the changes in the local density of states under the tip due to the vortex motion. With no need for scanning, the method permits one to extend the study of vortices to samples in which scanning is difficult or even impossible due to surface nonuniformity and allows one to study vortex dynamics. Using a statistical analysis of the spectra, we reconstruct the single vortex zero bias conductance profile. We apply the method to the c-axis face of an MgB2 single crystal sample and obtain a vortex profile with a coherence length, ξ of 57±2 nm.

Type II superconductivity in SrPd2Ge2

“…This behavior can be explained by the dynamics of superconducting vortices, magnetic flux quanta penetrating the SrPd 2 Ge 2 sample, which locally disrupt superconductivity and suppress the superconducting order parameter. In analogy to the "Lazy Fisherman" method introduced by Kohen et al [27], by changing the value of the applied magnetic field, vortex motion below the stationary Au tip was induced. As a result, different points within the vortex lattice were accessed, leading to an increase of the ZBC in the vicinity of a vortex core and a decrease of the ZBC far from the vortex core.…”

Imaging superconducting vortex cores and lattices with a scanning tunneling microscope

“…A compromise must be found between imaging speed and resolution [52,172], depending on the experiment to be made. Taking data at a single position as a function of time may be useful to study some dynamic behavior [173]. For imaging, highest resolution is obtained by taking the whole I-V curve, which gives good images up to T c [63].…”

Flow and Tilt-Induced Orientation of the Moving Vortex Lattice in Amorphous NbGe Superconducting Thin Films

“…1) Within the London approximation for isotropic superconductors all the possible orientations of the vortex lattice are degenerate in energy, 2,3) while this is lifted not simply by tilting an applied magnetic field, 4,5) but also when driven by applying a transport current. In experiments various imaging techniques such as Bitter decoration, 6) small angled neutron scattering 7,8) and scanning tunneling microscopy [9][10][11] have provided structural evidence for the hexagonal order in moving VLs, and some of them have shown that the lattice orientation (one of close-packed directions of the hexagonal VL) is aligned to be either parallel or perpendicular to the flow direction. These flow-induced orientations, including a reorientation between them, have been observed on both crystalline 6,10) and non-crystalline weak pinning superconductors, [12][13][14] and thus underlying crystallographic orientations are not at play.…”

“…In experiments various imaging techniques such as Bitter decoration, 6) small angled neutron scattering 7,8) and scanning tunneling microscopy [9][10][11] have provided structural evidence for the hexagonal order in moving VLs, and some of them have shown that the lattice orientation (one of close-packed directions of the hexagonal VL) is aligned to be either parallel or perpendicular to the flow direction. These flow-induced orientations, including a reorientation between them, have been observed on both crystalline 6,10) and non-crystalline weak pinning superconductors, [12][13][14] and thus underlying crystallographic orientations are not at play. It is rather essential to understand how quenched disorder affects the orientation of moving VLs.…”