Lab News & Scientific Highlights

For decades, the mechanism of Mott phase in Ca₂RuO₄ has puzzled researchers. This material is a paradigmatic case of multi-band Mott physics including spin-orbit and Hund's coupling. Progress has been impeded by the lack of knowledge about the low-energy electronic structure. With our recent contribution, we provided-- using angle-resolved photoemission electron spectroscopy -- the band structure of the paramagnetic insulating phase of Ca₂RuO₄.

Turning the semimetal graphene into a technologically useful semiconductor is challenging. One way of opening a band gap is to cut graphene into nanometre-wide ribbons, but even atomic-level roughness at the ribbon edges can seriously degrade the mobility of charge carriers. Recent advances in on-surface chemistry have made it possible to obtain graphene nanoribbons with atomically precise edges through direct synthesis from molecular building blocks. Here, we report the synthesis, full structural and electronic characterization of 9-atom wide graphene nanoribbons with significantly improved electronic properties.

Researchers at PSI have developed a new unique miniaturized biaxial deformation rig, which allows to apply in-plane biaxial stress states with arbitrary stress ratios and to perform strain path changes on thin-sheet metals. The device is optimized for in situ usage inside a scanning electron microscope and at synchrotron beam lines.

Single holmium atoms adsorbed on few monolayers of magnesium oxide are extraordinarily stable magnets. They retain a significant fraction of their magnetization when the external magnetic field is switched off. This has been shown recently in a study combining x-ray magnetic circular dichroism performed at the Swiss Light Source (SLS) and at the European Synchrotron Radiation Facility (ESRF) as well as scanning tunneling microscopy. The results open perspectives of storing and processing information at ultrahigh density.

The first example of an insulating phase which is close to the superconducting phase in an iron-pnictide system has been recently observed in heavy Cu-doped NaFe_1-xCuxAs (x > 0.3). A combined study by angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations revealed that on-site Coulomb repulsion and enhanced Hund’s rule coupling are responsible for the insulating behavior. The results show that the insulating phase in NaFe_0.5Cu_0.5As resembles the situation in the parent compounds of the high-T_c cuprate superconductors.

The use of spin-wave signals in future information processing devices can substantially reduce power consumption over present charge current based technologies. As part of an international research venture, scientists at PSI now introduced a concept to generate spin waves with nanoscale wavelengths exploiting the driven dynamics of magnetic vortex cores in magnetic heterostructures.

Researchers from PSI and EPFL have demonstrated that the magnetization hysteresis and remanence of TbPc₂ single-molecule magnets drastically depends on the substrate on which they are deposited. If a few atomic layers thick magnesium oxide film grown on a silver substrate is used, a record wide hysteresis and record large remanence can be obtained. Single-molecule magnets are attractive for molecular spintronics applications such as information processing or storage.

Researchers have overcome a number of challenges in order to employ an advanced probe in the study of an unusual material, barium bismuth oxide (BaBiO3) – an insulating parent compound of a family of high-temperature superconductors known since the late 80s. In order to finally realize the experiments, the researchers grew and studied thin films of the material completely in situ under ultrahigh vacuum conditions. The results show that superconductivity in bismuth oxides emerges out of a novel insulating phase, where hole pairs located on combinations of the oxygen orbitals are coupled with distortions of the crystal lattice.

Resonant magnetic scattering performed at the x-ray free electron laser facility LCLS (USA) has been used to investigate the magnetization dynamics of elemental Holmium. It is found that the demagnetization of conduction electrons and localized 4f magnetic moments have the same temporal evolution showing a strong coupling between the different magnetic moments.

The Angle Resolved Photoemission Spectroscopy (ARPES) measurements performed on 2DEL at STO surface revealed that, at low carrier density, electrons are always accompanied by a quantized dynamic lattice deformation. Together with the electron, these phonon-cloud formed a new composite quasiparticle called Fröhlich polaron.

The study of nontrivial topological semimetals (TSM) is an emerging subject, providing a new frontier in topological aspects beyond insulators. Here, we have investigated the spin texture of surface Fermi arcs in the recently discovered Weyl semimetal TaAs using spin- and angle-resolved photoemission spectroscopy. The experimental results demonstrate that the Fermi arcs are spin polarized. The measured spin texture fulfills the requirement of mirror and time-reversal symmetries and is well reproduced by our first-principles calculations, which gives strong evidence for the topologically nontrivial Weyl semimetal state in TaAs. The consistency between the experimental and calculated results further confirms the distribution of chirality of the Weyl nodes determined by first principles calculations.

At the PEARL beamline, metal-supported ultrathin oxide films have been studied which are a class of materials of technological importance in various research fields such as catalysis, spintronics, or nanoelectronics.

Quasicrystals (QCs) are intermetallic alloys where excellent long-range order coexists with lack of translational symmetry in one or more dimensions. These materials have a high potential in application as a material for a solar cells, hydrogen storage applications, heat insulating layers, and others.

Recent advances in fabrication techniques to create mesoscopic 3D structures have led to significant developments in a variety of fields including biology, photonics, and magnetism. Further progress in these areas benefits from their full quantitative and structural characterization.

Vortices are fundamental magnetic topological structures characterized by a curling magnetization around a highly stable nanometric core.

Very small superparamagnetic iron oxide nanoparticles were characterized by innovative synchrotron X-ray total scattering methods and Debye function analysis, developed at the X04SA Materials Science beamline of SLS.

The surface-induced changes of the oxidation state and magnetic properties of Mn ion clusters have been probed by X-ray absorption spectroscopy and X-ray magnetic circular dichroism.

The spin of electron plays a crucial role in many physical phenomena, ranging from the obvious example of magnetism, via novel materials for spintronics applications, to high-temperature superconductivity. Spin- and angle-resolved photoelectron spectroscopy (SARPES) gives the most direct access to the spin aspects of the electronic structure, but the one-channel detection principle of all presently available SARPES spectrometers severely limits their efficiency. A team of Swiss and Russian scientists has developed a revolutionary concept of a multichannel electron spin detector based on Mott scattering as the spin selective process and imaging-type electron optics.

A research team led by scientists from the Swiss Light Source has for the first time established three-dimensional (3D) electronic structure of the perovskite compound La1−xSrxMnO3 connected with its colossal magnetoresistance. Instrumental for this study has been the use of the new experimental technique of soft-x-ray ARPES, available at the ADRESS beamline, with its intrinsically sharp definition of 3D electron momentum.

Understanding the interplay of the various degrees of freedom such as the electrons, spins and lattice is essential for many complex materials, including the high-temperature superconductors.