Experimental study of the magnetic field distribution and shape of domains near the surface of type-I superconductors in the intermediate state

TL;DR

This study uses depth-resolved measurements to investigate magnetic field distribution and domain shapes near the surface of type-I superconductors, revealing deviations from classical theory at high fields.

Contribution

It provides new experimental insights into the surface domain structures of type-I superconductors, highlighting differences from traditional theoretical models at high magnetic fields.

Findings

Field distribution agrees with Tinkham's model at low fields

At high fields, superconducting laminae expand near the surface

Maximum magnetic field observed outside the sample at high fields

Abstract

The importance of accounting for the inhomogeneity of the magnetic field distribution and roundness of domain walls near the surface of type-I superconductors in the intermediate state for forming the equilibrium flux structure was predicted by Landau eight decades ago. Further studies confirmed this prediction and extended it to all equilibrium properties of this state. Here we report on direct depth-resolved measurements of the field distribution and shape of domains near the surface of high-purity type-I (indium) films in a perpendicular field using Low-Energy Muon Spin Rotation spectroscopy. We find that at low applied fields (in about half of the field range of the intermediate state) the field distribution and domains' shape agrees with that proposed by Tinkham. However, for high fields our data suggest that reality differs from theoretical expectations. In particular, the width of the superconducting laminae can expand near the surface leading to formation of a maximum in the static magnetic field in the current-free space outside the sample. A possible interpretation of these experimental results is discussed.