Abstract
Alike materials in the solid state, the phase diagram of type-II superconductors exhibit crystalline, amorphous, liquid and spatially inhomogeneous phases. The multitude of different phases of vortex matter has thence proven to act as almost ideal model system for the study of both the underlying properties of superconductivity but also of general phenomena such as domain nucleation and morphology. Here we show how neutron grating interferometry yields detailed information on the vortex lattice and its domain structure in the intermediate mixed state of a type-II niobium superconductor. In particular, we identify the nucleation regions, how the intermediate mixed state expands, and where it finally evolves into the Shubnikov phase. Moreover, we complement the results obtained from neutron grating interferometry by small-angle neutron scattering that confirm the spatially resolved morphology found in the intermediate mixed state, and very small-angle neutron scattering that confirm the domain structure of the vortex lattice.
Highlights
Alike materials in the solid state, the phase diagram of type-II superconductors exhibit crystalline, amorphous, liquid and spatially inhomogeneous phases
To exclude effects arising from slightly different magnetic field or temperature conditions, the same sample environment was used for the nGI, small-angle neutron scattering (SANS) and the very small-angle scattering (VSANS) measurements
A comprehensive interpretation of the vortex lattice (VL) domain structure of the intermediate mixed state (IMS) and its evolution with increasing field based on the combination of nGI, SANS and VSANS data are given in the following paragraphs
Summary
Alike materials in the solid state, the phase diagram of type-II superconductors exhibit crystalline, amorphous, liquid and spatially inhomogeneous phases. The multitude of different phases of vortex matter has thence proven to act as almost ideal model system for the study of both the underlying properties of superconductivity and of general phenomena such as domain nucleation and morphology. We show how neutron grating interferometry yields detailed information on the vortex lattice and its domain structure in the intermediate mixed state of a type-II niobium superconductor. All these systems feature similar domain morphologies including stripe, bubble or dendritic patterns Their theoretical treatment is mostly based on the universal idea developed 80 years ago by Landau and Lifschitz[2]. In samples with a non-zero demagnetization coefficient N, an intermediate mixed state (IMS) phase is formed in which isolated Shubnikov domains with a typical diameter dIMS are nucleated, surrounded by the field-free Meissner state. In contrast to domains in other systems the vortex density, the vortex interaction and the volume filling of the sample can be ideally tuned by varying magnetic field and temperature
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