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Many practical applications of high Tc superconductors involve layered materials and magnetic fields applied on an arbitrary direction with respect to the layers. When the anisotropy is very large, Cooper pair currents can circulate either within or perpendicular to the layers. Thus, tilted magnetic fields lead to intertwined lattices of Josephson and Abrikosov vortices, with quantized circulation across and within layers, respectively. Transport in such intertwined lattices has been studied in detail, but direct observation and manipulation of vortices remains challenging. Here we present magnetic force microscopy experiments in tilted magnetic fields in the extremely quasi-two dimensional superconductor Bi2Sr2CaCu2O8. We trigger Abrikosov vortex motion in between Josephson vortices, and find that Josephson vortices in different layers can be brought on top of each other. Our measurements suggest that intertwined lattices in tilted magnetic fields can be intrinsically easy to manipulate thanks to the mutual interaction between Abrikosov and Josephson vortices., Quantum Internet Division, QuTech

Many practical applications of high T superconductors involve layered materials and magnetic fields applied on an arbitrary direction with respect to the layers. When the anisotropy is very large, Cooper pair currents can circulate either within or perpendicular to the layers. Thus, tilted magnetic fields lead to intertwined lattices of Josephson and Abrikosov vortices, with quantized circulation across and within layers, respectively. Transport in such intertwined lattices has been studied in detail, but direct observation and manipulation of vortices remains challenging. Here we present magnetic force microscopy experiments in tilted magnetic fields in the extremely quasi-two dimensional superconductor BiSrCaCuO. We trigger Abrikosov vortex motion in between Josephson vortices, and find that Josephson vortices in different layers can be brought on top of each other. Our measurements suggest that intertwined lattices in tilted magnetic fields can be intrinsically easy to manipulate thanks to the mutual interaction between Abrikosov and Josephson vortices.

Tuning the electronic properties of two-dimensional (2D) layers is a current focus of interdisciplinary research. Here, we show that the electronic properties of a surface- supported 2-dimensional (2D) layer structure can spontaneously self-texturize at nanoscale. Specifically, we have characterized the 2D layer GdAu2 forming a mismatched interface on Au(111). We demonstrate that the variable adsorption stacking configurations causes local structural relaxation processes which result in a spatially modulated layer-buckling. This is sufficient to periodically open, at the Fermi level, an energy gap of ~0.5 eV at well-defined stacking configurations on an otherwise metallic layer. Additionally, this out-of-plane displacement of the Gd atoms patterns the character of the hybridized Gd-d states and shifts the center of mass of the Gd 4f multiplet proportionally to the lattice distortion. These findings demonstrate the close correlation between the electronic properties of the 2D-layer and its planarity. We demonstrate that the resulting template shows different chemical reactivity which may find important applications. We will compare the properties of the 2D-layer of GdAu2/Au(111) with the previously reported GdAg2/Ag(111).

Here, we show that the electronic properties of a surface-supported 2-dimensional (2D) layer structure can self-texturize at nanoscale. The local electronic properties are determined by structural relaxation processes through variable adsorption stacking configurations. We demonstrate that the spatially modulated layer-buckling, which arises from the lattice mismatch and the layer/substrate coupling at the GdAu/Au(111) interface, is sufficient to locally open an energy gap of ∼0.5 eV at the Fermi level in an otherwise metallic layer. Additionally, this out-of-plane displacement of the Gd atoms patterns the character of the hybridized Gd-d states and shifts the center of mass of the Gd 4f multiplet proportionally to the lattice distortion. These findings demonstrate the close correlation between the electronic properties of the 2D-layer and its planarity. We demonstrate that the resulting template shows different chemical reactivities which may find important applications.

[ES]: El trabajo experimental, en que se fundamenta esta tesis, tiene como objetivo la caracterización de las propiedades estructurales y electrónicas de aleaciones 2-dimensionales de gadolinio con las superficies de plata y oro. Estas aleaciones forman estructuras estequiometricas con una constante de red distinta a los sustratos de soporte; Ag(111) y Au(111). A pesar de esto, su débil interacción permite la formación de una estructura continua, pero descomensurada, que resulta en una superestructura llamada patrón de Moiré. En estas superredes, la geometría de empaquetamiento de los átomos varía periódicamente y así su acoplamiento con el sustrato. Esto se refleja en un pandeo perpendicular al plano de la aleación, debido al relajamiento atómico. Con la caracterización de estas aleaciones a nanoescala se demuestra que estos efectos determinan su estructura electrónica. La aleación 2-dimensional resulta así texturizada con la periodicidad del patrón de la Moiré. Además, la constante de red atómica varia también en el plano controlando la temperatura de crecimiento, y por consiguiente su estructura electrónica. Específicamente, en la aleación de GdAg2, donde la fuerza del acoplamiento con el sustrato de soporte es más débil que en GdAu2, se demuestra una relación lineal de la densidad de estados electrónicos con la constante reticular. Asimismo, esta define la periodicidad de la superred de la aleación y de su texturización a nanoescala. Las propiedades electrónicas, definidas por el apilamiento de los átomos de las aleaciones con el sustrato de soporte, determinan también la posición preferente de adsorción de moléculas de ftalocianina. Esta posición se mantiene desde recubrimientos muy bajos, es decir, moléculas aisladas, hasta la finalización de una capa. Esto sugiere que el empaquetamiento atómico de la aleación determina también su reactividad química. Para la demostración de las propiedades locales de estas redes nanoestructuradas ha sido necesaria la adquisic, [EN]: The aim of the experimental work presented in this thesis is the structural and electronic characterization of the two-dimensional alloys formed when Gd is deposited on Ag(111) and Au(111) surfaces. These alloys form stoichiometric structures with unit cell size different from that of the clean substrate. This lattice mismatch, combined with a weak interaction between the alloy layer and the underlying substrate, causes the formation of a continuous but incommensurate superstructure on the surface, called a Moiré pattern. The Moiré is characterized by a periodic variation in the alloy’s atoms and its coupling to the substrate. This is reflected in a buckling perpendicular out-of-plane of the alloy, due to atomic relaxation. The nanoscale characterization of the alloys reveals that these structural effects determine the electronic structure. The bi-dimensional alloys have a texturization with the Moiré pattern periodicity. In addition, the lattice constant atomic, change in-plane by controlling growth temperature and therefore its electronic structure. Particularly, in the GdAg2 alloy where coupling force with the substrate is weaker than in GdAu2. Moiré pattern GdAg2 has a linear relationship of the density of the state whit reticular constant. Additionally, this defines the periodicity of the alloy’s superlattice and its texturization at nanoscale. Electronic properties are defined by the alloy staking atoms with the support substrate that stablish the preferred adsorption position phthalocyanines molecules. This position is maintained from the very low coatings, i.e. isolates molecules, up to a monolayer. This suggests that atomic staking of the alloy also determine its chemical reactivity. For demonstration of the local properties of these nanostructures networks, it has been acquired and it´s perfectly working (installed and optimized) a scanning tunnelling microscope in ultra-high vacuum at temperature variable up to 1 Kelvin (K), located on the material

We report on the structural, electronic and magnetic properties of a monolayer of GdAg2, forming a moiré pattern on Ag(111). Combining scanning tunneling microscopy and ab initio spin-polarized calculations, we show that the electronic band structure can be shifted linearly via thermal controlled strain of the intra-layer atomic distance in the range of 1-7%, leading to lateral hetero-structuring. Furthermore, the coupling of the incommensurable GdAg2 alloy layer to the Ag(111) substrate leads to spatially varying atomic relaxation causing subsurface layer buckling, texturing of the electronic and spin properties, and inhomogeneity of the magnetic anisotropy energy across the layer. These results provide perspectives for control of electronic properties and magnetic ordering in atomically-thin layers.

Controlling anisotropy and exchange coupling in patterned magnetic nanostructures is the key for developing advanced magnetic storage and spintronic devices. We report on the antiferromagnetic interaction between a Co nanodot array and its supporting GdAu2 nanotemplate that induces large anisotropy values in individual Co nanodots. In clear contrast with nonmagnetic Au substrates, GdAu2 triggers an earlier switch from out-of-plane anisotropy in monatomic high dots to in-plane when the dot height becomes biatomic. © 2014 American Chemical Society.