Low-Energy Muons at PSI: Examples of Investigations of Superconducting Properties in Near-Surface Regions and Heterostuctures

Abstract

With the advent of polarized low-energy muons, with tunable energy in the kiloelectronvolt range, it is possible to use the sensitivity and the local-probe character of µSR to perform depth-dependent investigations on the nanometer scale of magnetic and superconducting properties of materials. Here, after a brief summary of the present status of LE-μSR at PSI, we give some examples of investigations of superconducting properties in the near-surface regions of single crystals and thin-film materials.

A segmented conical electric lens for optimization of the beam spot of the low-energy muon facility at PSI: a Geant4 simulation analysis

“…To overcome these limitations and to extend µSR to the investigation of thin films, PSI developed and operates the low energy muons beam facility (LEM) where a cryogenic moderation method [2,3,4,5,6] is used to generate nearly fully polarized positive muons with tunable energies in the range of eV to several keV. Up to now the LEM facility at PSI has played a leading role in low energy muon experiments, extending the µSR technique to the investigation of nano-materials, layer interfaces, thin films and near-surface regions [7,8,9,10,11,12,13,14,15,16,17,18,19].…”

“…The moderation of the muons from about 4 MeV to 10 eV is achieved within 10 ps, such that their initial high polarization is conserved [5]. The moderator consists of a 200-300 nm thick Ar layer (capped by a 10 nm thin N 2 layer) deposited on a thin Ag foil (∼125 µm) [20] which is held by a cryostat at a temperature below 20 K. The mean energy of the moderated muons is about 15 eV with a width of about 20 eV (full width at half maximum, FWHM) [21].…”