Yearbook of the Max Planck Society

Yearbook of the Max Planck Society

2019

  • Sensors at the quantum limit

    2019 Wrachtrup, Jörg; Kern, Klaus
    Nanoscale quantum sensors open new perspectives in material science as well as bio- or medical diagnostics. The research group at MPI for Solid State Research in Stuttgart recently successfully detected single proteins with a diamond quantum sensor and was able to measure its dynamics.
  • The kinetics of compositional changes

    2019 Merkle, Rotraut; Maier, Joachim
    Within certain bounds, solids can change their chemical composition. As in such typically narrow ranges the ionic and electronic carriers can vary by orders of magnitude, this process is not only of fundamental interest but also highly relevant for applications such as sensors, fuel cells, and batteries. The understanding of the kinetics of such compositional changes is indispensable for a targeted materials functionalization.

2018

  • Flexible organic transistors and integrated circuits with extremely small supply voltages of 0.7 V

    2018 Klauk, Hagen
    Compared with transistors based on inorganic semiconductors, organic transistors can be fabricated at much lower temperatures of about 100 degrees Celsius. This makes it possible to manufacture electronic systems on a variety of unconventional substrates, such as plastics, paper and textiles. As this type of electronic systems is of interest for mobile applications, it is critical that the transistors and circuits can be operated at very low supply voltages. We have therefore developed an ultra-thin gate dielectric that reduces the required supply voltage to 0.7 Volt.
  • Higgs spectroscopy of superconductors in nonequilibrium

    2018 Schwarz, Lukas; Fauseweh, Benedikt; Manske, Dirk

    In superconductors, a collective excitation of Cooper pairs exists which is known as the Higgs mode. If the system is excited out of equilibrium, Higgs oscillations can arise. From these, properties of the superconducting energy gap can be deduced. In conventional superconductors the system oscillates with a frequency corresponding to two times the energy gap. In the case of unconventional superconductors multiple Higgs modes can arise. As a consequence, Higgs oscillations can serve as a spectroscopic method to retrieve information about the symmetry of the energy gap.

2017

  • Quantum chemical approaches to electronic structure theory for materials

    2017 Grüneis, Andreas; Alavi, Ali
    Quantum chemical approaches to the description of the electronic structure of real materials can be used to predict even strong electronic correlation effects with high accuracy. However, the scaling of the computational complexity to calculate and store the true many-electron wave function often makes these methods intractable. In this review we report on recent progress to reduce the computational complexity of wave function based methods for the study of molecules and solids.
  • Ultrafast Lithium between two graphene layers

    2017 Kühne, Matthias; Paolucci, Federico; Popovic, Jelena; Maier, Joachim; Smet, Jurgen H.
    In analogy to lithium-ion technology, bilayer graphene is employed as an electrode in an electrochemical cell for the first time. An innovative cell design allows for the application of electronic transport methods known from the field of nanostructures and low-dimensional systems. This unusual combination offers unprecedented direct access to the motion of lithium-ions that may be reversibly inserted in between the two carbon sheets of bilayer graphene. An ionic mobility much higher than in bulk graphite can thus be revealed.

2016

  • Magnetism at the limit

    2016 Loth, Sebastian

    Atomically small magnets behave drastically different compared to macroscopic magnets. Quantum mechanical phenomena determine their stability and dynamics. Scanning probe methods can be used to create individual quantum magnets atom by atom. The atomically precise magnetic structures enable the exploration of new concepts for ultra-dense data storage and magnetic sensors for atomic-scale environments.

  • The exotic faces of entangled electrons in solids

    2016 Takagi, Hidenori

    In transition metal compounds, electrons are strongly entangled (correlated) by Coulomb interaction and forms a rich variety of solid, liquid and gas phases. We are aiming to explore exotic electronic phases formed by spin, charge and orbital degrees of freedom of entangled electrons. In this review, we report that by incorporating relativistic spin-orbit coupling, entanglement of spin and motion of electrons, in complex iridium oxides, even richer phases of correlated electrons emerge including spin orbital electron solid (Mott insulator), Dirac electron gas and Quantum spin liquid.

2015

  • Oxide electronics

    2015 Mannhart, Jochen
    The rich array of conventional and exotic electronic properties that can be generated by oxide heterostructures is of great potential value for device applications. However, transistors with voltage gain have not yet been realized from complex oxides. Here we report on the fabrication of such transistors and on monolithically integrated NMOS logic circuits that utilize a two-dimensional electron liquid generated at an oxide interface as channel material. These results illustrate the practicability and the potential of oxide electronics.
  • Polymers go solar – molecular materials for artificial photosynthesis

    2015 Lotsch, Bettina
    The efficient conversion of solar energy into useful chemical fuels has been identified as one of the major challenges facing modern materials science. In the quest for powerful, abundant and economic photocatalysts capable of light-induced hydrogen evolution, a new generation of porous polymers has recently been brought to fruition. The molecular structure of these materials enables the rational design of photocatalysts with tailor-made properties according to Nature's blueprint.

2014

  • Epitaxial graphene on silicon carbide with taylor-made electronic properties

    2014 Starke, Ulrich

    Graphene, a single atom thick carbon layer, is grown on top of silicon carbide (SiC). When the topmost silicon atoms are sublimated by annealing the SiC substrate, the remaining carbon forms the graphene layer. In order to retrieve the extraordinary electronic properties of the graphene, it must be chemically decoupled from the substrate. This is achieved by inserting hydrogen between graphene and SiC, so-called intercalation, which passivates the substrate. Intercalation of other materials, such as germanium allows to functionalize the graphene, so that a taylor-made doping is possible.

  • Molecules under a sharp tip

    2014 Rauschenbach, Stephan; Kern, Klaus

    Non-evaporable functional molecules such as proteins and peptides can be converted into intact gas phase ions by electrospray ionization. This allows the deposition on surfaces in a vacuum, and thus the atomically resolving analysis by scanning tunneling microscopy. In addition to a detailed insight into the structure of these large molecules, electrospray ion beam deposition allows steering of the molecular conformation into folded, unfolded or two-dimensionally folded structures.

2013

  • 100 years after Max von Laue – Phase transitions and parametric symmetry modes: innovative methods in crystallography

    2013 Dinnebier, Robert. E.; Etter, Martin
    Since the first diffraction patterns by Max von Laue 100 years ago, crystallography underwent an enormous development. Today's position sensitive detectors and radiation intensive synchrotron and neutron sources allow to measure powder diffractograms with high time resolution. This possibility and innovative analysis methods such as the coupling of symmetry modes with parametric Rietveld refinement allow for direct observation and investigation of phase transitions in solids.
  • High-resolution neutron spectroscopy

    2013 Keller, Thomas; Keimer, Bernhard
    The neutron spectrometer TRISP constructed by the MPI-FKF at the FRM II in Garching allows measurements of the lifetimes of lattice vibrations (phonons) and of spin excitations (magnons) in solids as a function of energy and momentum. The data generated by TRISP throw new light on several prominent problems in solid state physics. This article describes measurements of phonon lifetimes in the superconductors niobium and lead, and of magnon lifetimes in the antiferromagnet MnF2. In addition, the thermal expansion of MnSi was determined under extreme conditions by the Larmor-diffraction method.

2012

  • Exploitation of size effects for electrochemical energy conversion

    2012 Maier, Joachim
    Recent activities of our Department showed how crucial the parameter "size" is with respect to electrochemical overall properties. This paper highlights experimental contributions of our department in this respect, which are based on predictions that we made and succeeded to verify.
  • Large scale numerical simulations to understand and predict the properties of nanostructures

    2012 Bester, Gabriel
    The demands on the numerical methods to calculate the electronic and optical properties of nanostructures are presented. It is emphasized that a connection to experimental results requires to take many atoms into account, while considering the effects of correlations in the excited exciton states. A modern approach to this difficult challenge is presented along with an application of the method to predict the feasibility of a scheme aimed at the generation of entangled photon pairs.

2011

  • Iron arsenide superconductors – an example of the central role of crystal growth in solid state research

    2011 Keimer, Bernhard; Lin, Chengtian
    The synthesis of high-grade single crystals plays a key role in solid state research, because the significance of experimental results depends critically on the sample quality. We will illustrate this relationship by highlighting experiments on the recently discovered high-temperature superconducting iron arsenides.
  • Nematic order of electrons in solids

    2011 Metzner, Walter
    Theoretical considerations indicated that, under suitable circumstances, conduction electrons in metallic solids may assume an ordered state with a preferred direction for the electron motion. This nematic order breaks an orientational symmetry of the underlying crystal, but not the translation invariance. Nematic order of electrons has now been observed in a high temperature superconductor and another transition metal oxide compound.

2010

  • Missing light signals the presence of a nanoparticle

    2010 Lippitz, Markus
    Seemingly identical nanoobjects such as molecules, proteins, or nanoparticles differ in size, shape, and local environment. Averaging over many nanoobjects blurs the result one gets. Only measurements on single nanoobjects give the full picture. Optical spectroscopy of a single absorbing nanoparticle has to detect a small variation on a large, noisy background. Coupling the particle under investigation to a larger antenna particle simplifies the task and will allow experiments on tiny nanoparticles.
  • The quest for high-temperature superconductivity: Can theory help?

    2010 Andersen, Ole Krogh
    To find materials which superconduct at normal temperatures is an enormous challenge. So-far the discoveries of new superconductors were nearly always empirical and often surprising. The high-temperature superconductivity in cuprates has not been understood, but for all known cuprates it has been found that the experimental critical temperatures correlate with the calculated dispersions of the conduction band. Although it seems impossible to find cuprates with "better" bandstructures, this might be achieved with man-made heterostructures of alternating nickelates and insulating oxides.

2009

  • Superconductivity in Intercalated Graphite

    2009 Kremer, Reinhard K.; Kim, Jun Sung
    Elementary properties of the recently discovered alkali-earth intercalated graphite compounds AC6 (A = Ca, Sr, Yb) will be described. These new superconductors with critical temperatures of up to 11.6 K can be described as electron-phonon coupled superconductors with a weakly anisotropic order parameter. Experimental results and ab-initio calculations are in good agreement.
  • Symmetries and Spins

    2009 Ast, Christian R.; Kern, Klaus
    Symmetries play an important role in science as well as in every day life. They are regarded as esthetic and they can be used to simplify problems. On the other hand, a reduction of symmetries may lead to the consequence that certain properties of a system become discernable. In the field of spintronics this is used to manipulate the electron spin without the use of magnetic fields. The design and characterization of nanostructures relevant for spintronics are studied in the Department of Prof. Kern and the Emmy-Noether-Research-Group "Electronic structure at surfaces and interfaces".

2008

  • Electronic properties of metal oxide interfaces

    2008 Keimer, Bernhard; Habermeier, Hanns-Ulrich
    Bulk metal oxides exhibit a large variety of unusual electronic properties, such as high-temperature superconductivity and magnetic order. This article describes the synthesis of heterostructures of complex metal oxides as well as the characterization of interfaces contained in these structures by different experimental methods. The results may lead to a new generation of electronic devices.
  • Organic Electronics

    2008 Klauk, Hagen
    Unlike transistors based on single-crystalline silicon, organic thin-film transistors can be processed entirely at temperatures below 100°C. This allows the manufacturing of flexible or rollable flat panel displays. Of particular importance for the performance of the transistors are the properties of the gate dielectric.

2007

  • A Concept for Synthesis Planning in Solid State and Materials Chemistry

    2007 Schön, J. Christian; Putz, Holger; Wevers, Marcus A. C.; Hannemann, Alexander; ¿an¿arevi¿, ¿eljko; Pentin, Ilya; Fischer, Dieter; Jansen, Martin
    Rational synthesis planning in solid state chemistry is presented as a self-consistent concept. The unbiased prediction of new compounds followed by an analysis of their properties allows the selection of the most appropriate route for their synthesis.
  • Ferromagnetism and superconductivity – the combination of the antagonistic in complex oxides

    2007 Habermeier, Hanns-Ulrich; Cristiani, Georg; Soltan, Soltan; Albrecht, Joachim
    Heterostructures consisting of superconducting and ferromagnetic oxides open a new field of research to study the mutual interaction of incompatible ground states in solids. As an example spin-polarized quasiparticle injection into high-temperature superconductors is used to study non-equilibrium effects and thus to contribute to the understanding of superconductivity in cuprates.

2006

  • Atomic and electronic properties of solid state surfaces and interfaces

    2006 Starke, Ulrich
    The investigation of surfaces, interfaces and thin films represents a major subject of state of the art solid state research. The morphology of surfaces on an atomic scale can be measured in real space using a variety of microscopy methods. The detailed atomic structure of the surface is determined using a combination of electron spectroscopy methods, low-energy electron diffraction and scanning tunneling microscopy. An overview of research in surface and interface analysis is demonstrated by a set of exemplary experiments.
  • Carbon Nanotubes

    2006 Roth, Siegmar
    Carbon nanotubes are presented as prototype nanostructure objects. Experiments on charge transport and methods to identify individual nanotubes are described. Applications as transistors, electrical leads ("VIAs"), and electromechanical devices are discussed.

2005

  • Interplay of Electrons in Metal-Rich Compounds

    2005 Simon, Arndt; Ryazanov, Mikhail; Mattausch, Hansjürgen; Kremer, Reinhard K.
    Two examples out of the extended new chemistry of metal-rich lanthanoid compounds illustrate the mutual influence of different electronic systems leading to interesting physical properties.
  • Solids under high pressure

    2005 Loa, Ingo; Wang, Xin; Syassen, Karl
    Progress in high pressure research has resulted in tremendous gains in knowledge on materials behavior over a wide range of pressures. Experimental high pressure research takes advantage of numerous recent developments in diamond-anvil-cell techniques, mainly with respect to advances in analytical methods that utilize synchrotron x-ray radiation (diffraction and inelastic scattering), optical spectroscopy, and synchrotron infrared spectroscopy. Our subjects of interest range from illuminating the interplay between subtle changes in atomic arrangements, electron delocalization, magnetism, and superconductivity to fundamental questions about phase transformations, crystal structure, and the nature of interatomic bonding. Some of our recent results are briefly highlighted here.

2004

  • Ion Transport and electrical storage in small systems ("Nano-ionics")

    2004 Balaya, Palani; Bhattacharyya, Aninda; Fleig, Jürgen; Kim, Sangtae; De Souza, Roger; Sata, Noriko; Maier, Joachim
    The investigation of electrochemical phenomena in the nanometer range reveals a variety of exciting anomalies of fundamental significance and technological relevance. This applies to anomalies of mass transport and mass storage in nanocrystalline materials and nanocomposites. A bunch of examples are discussed including mesoscopic ionic heterostructures, mesoscopic accumulation and depletion layers at grain boundaries, novel soft matter electrolytes, the appearance of ferroelectricity in nanocrystalline SrTiO3 and a new storage mode in nanocrystalline Li-battery electrodes.
  • Strained semiconductor nanostructures

    2004 Heidemeyer, Henry; Kiravittaya, Suwit; Deneke, Christoph; Jin-Phillipp, Neng Yun; Stoffel, Mathieu; Schmidt, Oliver G.
    We apply strained layer heteroepitaxial growth to create two- and three-dimensional quantum dot (QD) crystals, SiGe heterostructures with unique optical and electronic properties as well as radial superlattices and accurately positioned semiconductor nanopipelines. The high degree of structural perfection of the QD crystals allows us to observe novel phenomena such as lateral strain field interferences. SiGe based heterostructures and interband tunnelling diodes, grown at extremely low temperatures (≈300°C), emit at wavelengths beyond 2 µm and experience peak-to-valley current ratios larger than 7:1. Furthermore, we roll up strained semiconductor bilayers and show that the walls of these structures consist of novel radial superlattices. Individual rolled-up nanotubes are filled up with red dye fluid.
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