Person:

Zhang, Jessie

We use a magnetic force microscope (MFM) to investigate single vortex pinning and penetration depth in NdFeAsO1−xFx, one of the highest-Tc iron-based superconductors. In fields up to 20 Gauss, we observe a disordered vortex arrangement, implying that the pinning forces are stronger than the vortex-vortex interactions. We measure the typical force to depin a single vortex, Fdepin ' 4.5 pN, corresponding to a critical current up to Jc ' 7×105 A/cm2. Furthermore, our MFM measurements allow the first local and absolute determination of the superconducting in-plane penetration depth in NdFeAsO1−xFx, λab = 320 ± 60 nm, which is larger than previous bulk measurements.

When chemists run reactions, what they are really doing is mixing up an enormous number of reacting partners and then hoping that they collide productively. It is possible to manipulate atoms more deliberately with a scanning tunneling microscope tip, but the process is then confined to a surface. Liu et al. directly manipulated individual atoms with light to form single molecules in isolation (see the Perspective by Narevicius). They used optical tweezers of two different colors to selectively steer ultracold sodium (Na) and cesium (Cs) atoms together. A subsequent optical excitation formed NaCs.