Dresden, Germany

The Leibniz Institute for Solid State and Materials Research in Dresden – in short IFW Dresden – is a non-university research institute and a member of the Gottfried Wilhelm Leibniz Scientific Community. It is concerned with modern materials science and combines explorative research in physics, chemistry and materials science with technological development of new materials and products. Wikipedia.


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Ament L.J.P.,Leiden University | Van Veenendaal M.,Argonne National Laboratory | Van Veenendaal M.,Northern Illinois University | Devereaux T.P.,SLAC | And 2 more authors.
Reviews of Modern Physics | Year: 2011

In the past decade, resonant inelastic x-ray scattering (RIXS) has made remarkable progress as a spectroscopic technique. This is a direct result of the availability of high-brilliance synchrotron x-ray radiation sources and of advanced photon detection instrumentation. The technique's unique capability to probe elementary excitations in complex materials by measuring their energy, momentum, and polarization dependence has brought RIXS to the forefront of experimental photon science. Both the experimental and theoretical RIXS investigations of the past decade are reviewed, focusing on those determining the low-energy charge, spin, orbital, and lattice excitations of solids. The fundamentals of RIXS as an experimental method are presented and then the theoretical state of affairs, its recent developments, and the different (approximate) methods to compute the dynamical RIXS response are reviewed. The last decade's body of experimental RIXS data and its interpretation is surveyed, with an emphasis on RIXS studies of correlated electron systems, especially transition-metal compounds. Finally, the promise that RIXS holds for the near future is discussed, particularly in view of the advent of x-ray laser photon sources. © 2011 American Physical Society.


Grant
Agency: GTR | Branch: EPSRC | Program: | Phase: Research Grant | Award Amount: 472.52K | Year: 2013

The ability to generate strong and stable magnetic fields is a critical enabling technology for a broad range of sustainable engineering applications. Almost invariably, more compact field sources and higher magnetic field densities lead directly to more efficient and cost effective devices. One example of this can be found in the widespread applications of small, high power DC electric motors, which have proliferated since the development of the cheap high energy density family of NdFeB materials in the 1980s. Wire-wound superconducting magnets, on the other hand, may offer the potential to generate large magnetic fields, but they are extremely expensive and are difficult to manufacture. A cheaper, simpler and more robust option is the use of magnetised bulk superconductors. The (RE)BCO (where RE = rare earth element such as Y, Nd, Sm, Gd, etc.) family of bulk, melt processed high temperature superconductors (HTS), in particular, is the subject of extensive world-wide developmental research. Bulk HTS materials offer considerable potential to both improve the performance of existing devices that incorporate permanent magnets and to develop new, high field and sustainable energy storage applications, in particular. Indeed, these materials represent a direct link between the physical sciences and the development of sustainable applications in the energy needs sector that will be fundamental to growth of the UK economy in the short to medium term. A number of important scientific and technical challenges to the incorporation of (RE)BCO bulk superconducting materials into practical engineering applications remain. These include improving process efficiency, sample properties, yield, reducing the cost of raw materials, recycling, processing larger samples with conformal geometries, development of a practical magnetisation process and the development of bespoke cryogenic systems for specific applications. The main objective of this proposal is to address and overcome the critical aspects of these challenges to gain a fundamental understanding of the single grain growth process. This will enable the cost-effective processing of (RE)BCO materials with conformal geometries that will be fundamental to their application in a range of sustainable engineering devices within the energy sector and healthcare industry. Specific emphasis of the project will be placed on the development of an effective recycling process to enable a new secondary bulk sample source for low to medium field applications, the development of a novel multi-seeding technique for fabricating large samples of conformal geometry and the development of a novel fabrication process based on a graded composition to produce bulk samples with homogeneous superconducting properties throughout the bulk microstructure.


Nussinov Z.,Washington University in St. Louis | Nussinov Z.,Leibniz Institute for Solid State and Materials Research | Nussinov Z.,TU Dresden | Van Den Brink J.,Washington University in St. Louis | And 2 more authors.
Reviews of Modern Physics | Year: 2015

Compass models are theories of matter in which the couplings between the internal spin (or other relevant field) components are inherently spatially (typically, direction) dependent. A simple illustrative example is furnished by the 90° compass model on a square lattice in which only couplings of the form τixτjx (where {τia}a denote Pauli operators at site i) are associated with nearest-neighbor sites i and j separated along the x axis of the lattice while τiyτjy couplings appear for sites separated by a lattice constant along the y axis. Similar compass-type interactions can appear in diverse physical systems. For instance, compass models describe Mott insulators with orbital degrees of freedom where interactions sensitively depend on the spatial orientation of the orbitals involved as well as the low-energy effective theories of frustrated quantum magnets, and a host of other systems such as vacancy centers, and cold atomic gases. The fundamental interdependence between internal (spin, orbital, or other) and external (i.e., spatial) degrees of freedom which underlies compass models generally leads to very rich behaviors, including the frustration of (semi-)classical ordered states on nonfrustrated lattices, and to enhanced quantum effects, prompting, in certain cases, the appearance of zero-temperature quantum spin liquids. As a consequence of these frustrations, new types of symmetries and their associated degeneracies may appear. These intermediate symmetries lie midway between the extremes of global symmetries and local gauge symmetries and lead to effective dimensional reductions. In this article, compass models are reviewed in a unified manner, paying close attention to exact consequences of these symmetries and to thermal and quantum fluctuations that stabilize orders via order-out-of-disorder effects. This is complemented by a survey of numerical results. In addition to reviewing past works, a number of other models are introduced and new results established. In particular, a general link between flat bands and symmetries is detailed. © 2015 American Physical Society.


Popov A.A.,Leibniz Institute for Solid State and Materials Research | Yang S.,Hefei University of Technology | Dunsch L.,Leibniz Institute for Solid State and Materials Research
Chemical Reviews | Year: 2013

One of the attractive properties of the hollow carbon clusters, known as fullerenes, is the possibility to use them as robust containers for other species. The field of chemical derivatization of EMFs has flourished in the past decade. Many cyclo- as well as radical addition reactions of EMFs are described forming a basis for the targeted synthesis of EMF-based functional materials. The a plications for EMFs as MRI contrasting agents and as electron-accepting blocks in photovoltaic devices are now considered as the most promising. Importantly, the reactivity and addition patterns of EMFs are significantly different from those of empty fullerenes. Advanced synthetic approaches and the progress in separation techniques dramatically improved the situation with availability of the EMF samples, which resulted in more dedicated and detailed studies of their structural, electronic, physical, and chemical properties. In the 1990s the field of the EMFs remained in the shadow of the empty fullerenes, which often resulted in the blind transfer of the guidelines, structural and chemical properties revealed for the empty fullerenes onto EMFs.


Dunsch L.,Leibniz Institute for Solid State and Materials Research
Journal of Solid State Electrochemistry | Year: 2011

To consider the past, present and future of in situ spectroelectrochemistry, a review on the recent state of modern spectroelectrochemistry and trends in the development of spectroelectrochemcial techniques is presented for the combined application of different in situ spectroelectrochemcial methods like ESR spectroelectrochemistry, NMR spectroelectrochemistry, Raman spectroelectrochemistry or IR spectroelectrochemistry to electrode systems. Starting with a discussion of the first steps in spectroelectrochemistry in the past, the main part of this review is focused on the advantages of the combined application of spectroelectrochemical techniques in the analysis of electrode reactions. The spectroelectrochemical methods are demonstrated to be successful in electrode reactions both for solid structures like polymers or carbon nanotubes and for molecular structures like fullerenes and oligothiophenes. The final outlook is attributed to future developments in spectroelectrochemistry. © 2011 Springer-Verlag.


Deng Q.,Leibniz Institute for Solid State and Materials Research | Popov A.A.,Leibniz Institute for Solid State and Materials Research
Journal of the American Chemical Society | Year: 2014

Endohedral clusters in metallofullerenes can vary in a broad range of geometrical parameters following the size and shape of the host carbon cage. Obviously, distortions of the cluster may increase its energy and even destabilize the whole clusterfullerene molecule. However, direct evaluation of the magnitude of cluster strain energies has not been done because of the lack of a suitable computational scheme that would allow one to decouple cluster and fullerene distortions and hence estimate individual components. In this work we offer a simple and efficient scheme to calculate cluster distortion energies in endohedral metallofullerenes (EMFs). Using this scheme, we analyze distortions in three classes of EMFs with nitride, sulfide, and carbide clusters and different metal atoms (Sc, Y, Ti). © 2014 American Chemical Society.


Eschrig H.,Leibniz Institute for Solid State and Materials Research
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

A logical foundation of equilibrium state density functional theory in a Kohn-Sham-type formulation is presented on the basis of Mermin's treatment of the grand canonical state by exploiting functional Legendre transforms. It is simpler and more satisfactory compared to the usual derivation of the ground-state theory and free of most remaining open points of the latter. The existence of the functional derivative of the corresponding density functional F [n] at all densities of grand canonical equilibrium states is proved even in the spin-density matrix version of the theory. It may, in particular, be relevant with respect to cases of spontaneous symmetry breaking such as noncollinear magnetism and orbital order. © 2010 The American Physical Society.


Magdanz V.,Leibniz Institute for Solid State and Materials Research | Sanchez S.,Leibniz Institute for Solid State and Materials Research | Schmidt O.G.,Leibniz Institute for Solid State and Materials Research
Advanced Materials | Year: 2013

A new biohybrid micro-robot is developed by capturing bovine sperm cells inside magnetic microtubes that use the motile cells as driving force. These micro-bio-robots can be remotely controlled by an external magnetic field. The performance of micro-robots is described in dependence on tube radius, cell penetration, and temperature. The combination of a biological power source and a microdevice is a compelling approach to the development of new microrobotic devices with fascinating future applications. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Borisenko S.,Leibniz Institute for Solid State and Materials Research
Nature Materials | Year: 2013

Two teams, led by Xinjiang Zhou and Donglai Feng, respectively were able to study the behavior of the electrons in an almost ideal model setting, and confirm earlier indications of a record-high superconducting temperatures (Tc) of 65 K for an iron-based superconductor. The object of their studies was just a single monolayer of iron selenide (FeSe) deposited on strontium titanate (SrTiO3). The two collaborations studied the electronic structure of FeSe in great detail, and by recording the energy (E) and momentum (k) distributions of the electrons they obtained the electronic band dispersions and their energy gaps as a function of various parameters, in such a way that theoretical concepts can be tested.


Nishimoto S.,Leibniz Institute for Solid State and Materials Research
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

The von Neumann entanglement entropy is studied with the density-matrix renormalization-group technique. We propose a simple approach to calculate the central charge using the entanglement entropy for a one-dimensional (1D) quantum system. This approach is applied to a couple of quantum systems: (i) a 1D frustrated spin model and (ii) a 1D half-filled spinless fermions with nearest-neighbor repulsion; it is confirmed that the central charge is estimated very accurately for the both systems. Also, a new method to determine the critical point between Tomonaga-Luttinger-liquid and gapped (or ordered) phases from the proposed approach is suggested. Furthermore, we mention that the Tomonaga-Luttinger parameter can be obtained in a like manner as the central charge, using the charge-density fluctuation of a part of the 1D system. © 2011 American Physical Society.

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