Scientific Highlights

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Watching electrons and switching bits on

Micro- and Nanotechnology Energy and Climate Future Technologies Materials Research Industrial co-operation Research Using Synchrotron Light Research Using Neutrons

Electronics should get smaller, faster, and above all more energy-efficient. These themes are also present in several research groups at PSI. From incremental improvements to complete rethinking – who is currently working on what?

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Electronic structure of overdoped La1.77Sr0.23CuO4. (left) dx2-y2 and dz2 band structure 
along the nodal direction. (middle) Light polarization analysis of the dx2-y2 and dz2 bands.
(right) Anti-nodal Fermi surface warping along the kz direction.

Cuprate Trilogy

In a trio of recent papers, a research group from the University of Zürich has made a number of new discoveries about the nature of cuprates' electronic structure and orbital composition. The results have important implications for superconductivity and pseudogaps in cuprates, and even the existence of type-II Dirac fermions in oxides.

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Evidence of a Coulomb-Interaction-Induced Lifshitz Transition and Robust Hybrid Weyl Semimetal in Td-MoTe2

Using soft x-ray angle-resolved photoemission spectroscopy we probed the bulk electronic structure of Td-MoTe2. We found that on-site Coulomb interaction leads to a Lifshitz transition, which is essential for a precise description of the electronic structure. A hybrid Weyl semimetal state with a pair of energy bands touching at both type-I and type-II Weyl nodes is indicated by comparing the experimental data with theoretical calculations.

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On the path to new high-performance transistors

Media Releases Research Using Synchrotron Light Large Research Facilities Materials Research Future Technologies

The electronics industry expects a novel high-performance transistor made of gallium nitride to offer considerable advantages over present-day high-frequency transistors. Yet many fundamental properties of the material remain unknown. Now, for the first time, researchers at the Paul Scherrer Institute PSI have observed electrons while they were flowing in this promising transistor. For that they used one of the world's best sources of soft X-rays at PSI's Swiss Light Source SLS.

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Dr. Nan Xu

Dr. Nan Xu awarded SPS 2017 Prize in Condensed Matter Physics

The SPS 2017 Prize in Condensed Matter Physics, sponsored by IBM, has been awarded to Dr. Nan Xu for his excellent work on topological quantum states. Dr. Nan Xu is a joint postdoc of Paul Scherrer Institute (PSI) and the École Polytechnique Fédérale de Lausanne (EPFL).

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ARPES recorded with right-handed circularly polarized (C+) 65 eV photons in the paramagnetic (150 K) insulating state of Ca2RuO4. Incident direction of the light is indicated by the blue arrow. Dark colours correspond to high intensities. (a) Constant energy map displaying the photoemission spectral weight at binding energy ε=E−EF=−5.2 eV. Solid and dashed lines mark the in-plane projected orthorhombic and tetragonal zone boundaries, respectively. Γi with i=1, 2, 3 label orthorhombic zone centres. S and X …

Realization of a combined band-Mott insulator

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.

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Better graphene nanoribbons for electronics applications

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.

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Novel insulating phase in iron-pnictide materials

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 NaFe1-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 NaFe0.5Cu0.5As resembles the situation in the parent compounds of the high-Tc cuprate superconductors.

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Selectively conductive or insulating

Media Releases Future Technologies Materials Research Research Using Synchrotron Light

The material neodymium nickel oxide is either a metal or an insulator, depending on its temperature. The possibility to control this transition electrically makes the material a potential candidate for transistors in modern electronic devices. By means of a sophisticated development of X-ray scattering, researchers at the Paul Scherrer Institute PSI have now been able to track down the cause of this transition: electrons around the oxygen atoms are rearranging.

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