Vortex-core properties and vortex-lattice transformation in FeSeстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 17 июля 2019 г.
Аннотация:Low-temperature scanning tunneling microscopy and spectroscopy has been used to image the vortex core
and the vortex lattice in FeSe single crystals. The local tunneling spectra acquired at the center of elliptical
vortex cores display a strong particle-hole asymmetry with spatial oscillation, characteristic of the quantum-limit
vortex core. Furthermore, a quasihexagonal vortex lattice at low magnetic field undergoes noticeable rhombic
distortions above a certain field∼1.5 T. This field H∗ also reveals itself as a kink in themagnetic field dependence
of the specific heat. The observation of a nearly hexagonal vortex lattice at low field is very surprising for
materials with an orthorhombic crystal structure and it is in apparent contradiction with the elliptical shape of
the vortex cores. These observations can be directly connected to the multiband nature of superconductivity
in this material, provided we attribute them to the suppression of superconducting order parameter in one of
the energy bands. Above the field H∗ the superconducting coherence length for this band can well exceed the
intervortex distance which strengthens the nonlocal effects. Therefore, in addition to multiple-band effects, other
possible sources that can contribute to the observed evolution of the vortex-lattice structure include nonlocal
effects which cause the field-dependent interplay between the symmetry of the crystal and vortex lattice or the
magnetoelastic interactions due to the strain field generated by vortices.