Depth-Sensitive Visualization of Irradiation-Induced Columnar Defects in the Layered Superconductor 2H-NbSe₂via Scanning Probe Microscopy

Abstract

For the first time irradiation-induced columnar defects have been visualized in a classical superconductor by means of scanning probe microscopy (SPM). These defects manifest themselves as hillocks or hollows in atomic-force microscope (AFM) images, depending on the scan direction. Using lateral-force microscopy (LFM) the observed structures can be identified as higher lateral forces within the defects. Depth-dependent measurements show that the mean diameter of the tracks decreases inside the NbSe2 crystals as a result of a reduction of the electronic energy loss Se. The comparison of magnetization measurements before and after the irradiation with 500 MeV 127I show an enhancement of the critical current density as it is known for pinning active columnar defects in high-Tc materials after the irradiation with swift heavy ions.