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 vortexcoresdisplayastrongparticle-holeasymmetrywithspatialoscillation,characteristicofthequantum-limit vortex core. Furthermore, a quasihexagonal vortex lattice at low magnetic field undergoes noticeable rhombic distortionsaboveacertainfield∼1.5T.ThisfieldH∗ alsorevealsitselfasakinkinthemagneticfielddependence 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 tomultiple-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.
Vortex-core properties and vortex-lattice transformation in FeSe
Di Giorgio, C.;
2019-01-01
Abstract
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 vortexcoresdisplayastrongparticle-holeasymmetrywithspatialoscillation,characteristicofthequantum-limit vortex core. Furthermore, a quasihexagonal vortex lattice at low magnetic field undergoes noticeable rhombic distortionsaboveacertainfield∼1.5T.ThisfieldH∗ alsorevealsitselfasakinkinthemagneticfielddependence 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 tomultiple-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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
