| esults of direct measurements of the transverse force on moving vortices in single-crystal high-Tc superconductors using high-Q, double-torsional, single-crystal silicon mechanical oscillators are reported. The equation of motion for a vortex has been controversial for more than thirty years, with estimates of the transverse force differing by several orders of magnitude. Indirect measurements (e.g., Hall effect) have many complications. We have designed and built an apparatus to measure the force directly; our technique applies magnetic flux locally to the center of a single crystal, avoiding edge-pinning effects. For Bi2212, we have found that the upper limit of the transverse force per unit length is 2 x 10--12 N/m per vortex when the vortex velocity is 7.5... |
