A5002034980- Iron-based superconductors research
- Physics of Superconductivity and Magnetism
- Rare-earth and actinide compounds
- Superconductivity in MgB2 and Alloys
- Superconducting Materials and Applications
- Topological Materials and Phenomena
- Molecular Junctions and Nanostructures
- Electric Motor Design and Analysis
- Advanced Thermoelectric Materials and Devices
- Intellectual Capital and Performance Analysis
- Magnetic properties of thin films
- Advanced Condensed Matter Physics
- Surface and Thin Film Phenomena
- Quantum, superfluid, helium dynamics
- Thermal properties of materials
Universidad Autónoma de Madrid
2013-2025
Consejo Superior de Investigaciones Científicas
2013
We present very low-temperature scanning tunneling microscopy (STM) experiments on single-crystalline samples of the superconductor $\ensuremath{\beta}\ensuremath{-}{\mathrm{Bi}}_{2}\mathrm{Pd}$. find a single superconducting gap from zero-field conductance. However, magnetic field dependence intervortex conductance is higher than one expected in single-gap superconductor. Such an increase has been found superconductors with multiple gaps. also that hexagonal vortex lattice locked to square...
Measurements of the London penetration depth and tunneling conductance in single crystals recently discovered stoicheometric, iron - based superconductor, CaKFe$_4$As$_4$ (CaK1144) show nodeless, two effective gap superconductivity with a larger about 6-9 meV smaller 1-4 meV. Having critical temperature, $T_{c,onset}\approx$35.8 K, this material behaves similar to slightly overdoped Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ (e.g. $x=$0.54, $T_c \approx$ 34 K)---a known multigap $s_{\pm}$ superconductor....
We study the superconducting density of states and vortex lattice single crystals CaKFe$_4$As$_4$ using a scanning tunneling microscope (STM). This material has critical temperature $T_c= 35\,$ K, which is one highest among stoichiometric iron based superconductors (FeBSC) comparable to $T_c$ found near optimal doping in other FeBSC. Using quasi-particle interference we identify hole sheets around zone center find that two gaps open these sheets. The scattering centers are small defects can...
We study the spatial distribution of density states (DOS) at zero bias N(r) in mixed state single and multigap superconductors. provide an analytic expression for based on deGennes' relation between DOS order parameter that reproduces well Scanning Tunneling Microscopy (STM) data several superconducting materials. In gap superconductor $\beta$-Bi$_2$Pd, we find is governed by a length scale $\xi_H=\sqrt{\phi_0/2\pi H}$, which decreases rising fields. The vortex core size $\cal C$, defined...
The layered rare-earth diantimonides $R{\mathrm{Sb}}_{2}$ are anisotropic metals with generally low electronic densities whose properties can be modified by substituting the rare earth. ${\mathrm{LaSb}}_{2}$ is a nonmagnetic metal residual resistivity presenting low-temperature magnetoresistance that does not saturate magnetic field. It has been proposed latter associated to charge density wave (CDW), but no CDW yet found. Here we find kink in above room temperature (at 355 K) and show...
Many structural phase transitions are of first order, and many superconducting second order. Some iron-based materials have a first-order (magneto)structural transition then cross over to at low temperatures. Using nanoscale imaging, the authors show that this results in separated normal regions, each showing different crystalline structure. In systems having phases, it can be energetically favorable separate superconductor into patches.
A Scanning Tunneling Microscope (STM) is one of the most important scanning probe tools available to study and manipulate matter at nanoscale. In a STM, tip scanned on top surface with separation few Å. Often, tunneling current between sample maintained constant by modifying distance apex through feedback mechanism acting piezoelectric transducer. This produces very detailed images electronic properties surface. The nearly always made using digital processing circuit separate from user...
Abstract Bound states in superconductors are expected to exhibit a spatially resolved electron-hole asymmetry which is the hallmark of their quantum nature. This manifests as oscillations at Fermi wavelength, usually tiny and thus washed out by thermal broadening or scattering defects. Here we demonstrate theoretically confirm experimentally that, when coupled magnetic impurities, bound vortex core an emergent axial on much longer scale, set coherence length. We study vortices 2H-NbSe 2 1.8...
We study vortex lattices (VLs) in superconducting weak-pinning platelet-like crystals of $\beta$-Bi$_{2}$Pd tilted fields with a Scanning Tunneling Microscope. show that vortices exit the sample perpendicular to surface and are thus bent beneath surface. The structure orientation VL bulk are, for large tilt angles, strongly affected by Coulomb-type intervortex repulsion at due stray fields.
Scanning tunneling microscopy (STM) has been by now made in many pnictide layered superconductors. In AFe2As2 (A=Ca, Sr, Ba), surface reconstructions dominate the STM topographic images and no termination with bulk atomic lattice reported. Here, we present measurements on of Ca(Fe0.965Co0.035)2As2 cleaved in-situ below liquid helium temperatures. We observe ubiquitous reconstruction consisting 1D stripes that can adopt two degenerate orientations respect to crystal lattice. By searching over...