Mechanical Control of Individual Superconducting Vortices

Abstract

Manipulating individual vortices in a deterministic way is challenging; ideally, manipulation should be effective, local, and tunable in strength and location. Here, we show that vortices respond to local mechanical stress applied in the vicinity of the vortex. We utilized this interaction to move individual vortices in thin superconducting films via local mechanical contact without magnetic field or current. We used a scanning superconducting quantum interference device to image vortices and to apply local vertical stress with the tip of our sensor. Vortices were attracted to the contact point, relocated, and were stable at their new location. We show that vortices move only after contact and that more effective manipulation is achieved with stronger force and longer contact time. Mechanical manipulation of vortices provides a local view of the interaction between strain and nanomagnetic objects as well as controllable, effective, and reproducible manipulation technique.

Electrically Tunable Multiterminal SQUID-on-Tip

“…In contrast to conventional two-terminal/two-junction SQUIDs that display optimal sensitivity when flux biased to about a quarter of the flux quantum, the additional terminals and junctions allow optimal sensitivity at arbitrary applied flux, thus eliminating the magnetic field "blind spots". We demonstrate spin sensitivity of 5 to 8 µ B /Hz 1/2 over a continuous field range of 0 to 0.5 T, with promising applications for nanoscale scanning magnetic imaging.KEYWORDS: superconducting quantum interference device, SQUID on tip, nanoscale magnetic imaging, current-phase relations 2 In recent years, there has been a growing effort to develop and apply nanoscale magnetic imaging tools in order to address the rapidly evolving fields of nanomagnetism and spintronics.These include magnetic force microscopy (MFM) 1,2 , magnetic resonance force microscopy (MRFM) [3][4][5] , nitrogen vacancy (NV) centers sensors [6][7][8][9] , scanning Hall probe microscopy (SHPM) 10-12 , x-ray magnetic microscopy (XRM) 13 , and micro-or nano-superconducting quantum interference device (SQUID) [14][15][16][17][18][19][20] based scanning microscopy (SSM) [21][22][23][24][25][26][27][28][29][30][31][32] . Scanning micro-and nanoscale SQUIDs are of particular interest for magnetic imaging due to their high sensitivity and large bandwidth 15,19 .…”

The response of an individual vortex to local mechanical contact

“…Vortices moved in the direction of the scan, similar to their response to contact with the SQUID turned on. A possible magnetic influence caused by distortion of field lines by the superconducting field coil and pickup loop, was ruled out experimentally [1]. The motion of vortices in our contact experiments is visually different than vortex motion by local magnetic field.…”

“…Local mechanical deformation by a tip of a silicon chip can move individual vortices without causing damage to the sample [1]. We observed this behavior in two samples of Niobium (Nb) (50 and 100 nm) and nine samples of Niobium Nitride (NbN) (30 nm) and confirmed for thousands of individual, well-separated vortices.…”

“…Vortices can be controlled by electrical currents (Lorentz force) [2,6], by altering the pinning landscape [7,8] or by magnetic field [9,10]. Recently we found that vortices also respond to local mechanical contact [1]. Strain is known to affect electronic properties in various materials.…”

Scanning SQUID Study of Vortex Manipulation by Local Contact

“…The sample did not show memory of the manipulation; we observed no change in the diamagnetism of the sample, corresponding to the superfluid density, as well as no change to the topography of the sample. New vortex configurations created after reheating and cooling in the presence of magnetic field did not show memory of previous manipulations either 11 .…”