Lerf A.,Walther - Meissner Institute
Dalton Transactions | Year: 2014
Intercalation chemistry will soon be a hundred years old. The period of greatest activity in this field of solid state chemistry and physics was from about 1970 to 1990. The intercalation reactions are defined as topotactic solid state reactions and the products-the intercalation compounds-are clearly distinguished from inclusion and interstitial compounds. After a short historical introduction emphasizing the pioneering work of Ulrich Hofmann, the central topics and concepts will be reviewed and commented on. The most important ones, in my view, are: dichalcogenide intercalation compounds, the electrochemical intercalation and the search for new battery electrodes, the physics of graphite intercalation compounds, and the staging and interstratification phenomena. The relation to other fields of actual research and the demands for forthcoming research will also be addressed. This journal is © the Partner Organisations 2014.
Nembach H.T.,U.S. National Institute of Standards and Technology |
Shaw J.M.,U.S. National Institute of Standards and Technology |
Weiler M.,U.S. National Institute of Standards and Technology |
Weiler M.,Walther - Meissner Institute |
And 2 more authors.
Nature Physics | Year: 2015
Proposals for novel spin-orbitronic logic and memory devices are often predicated on assumptions as to how materials with large spin-orbit coupling interact with ferromagnets when in contact. Such interactions give rise to a host of novel phenomena, such as spin-orbit torques, chiral spin structures and chiral spin torques. These chiral properties are related to the antisymmetric exchange, also referred to as the interfacial Dzyaloshinskii-Moriya interaction (DMI; refs,). For numerous phenomena, the relative strengths of the symmetric Heisenberg exchange and the DMI are of great importance. Here, we use optical spin-wave spectroscopy (Brillouin light scattering) to directly determine the volume-averaged DMI vector D for a series of Ni 80 Fe 20 /Pt thin films, and then compare the nearest-neighbour DMI coupling energy with an independently measured value of the Heisenberg exchange for each sample. We show that the dependence on Ni 80 Fe 20 thickness of both the microscopic symmetric and antisymmetric exchange are nearly identical, consistent with the notion that the fundamentals of the DMI and Heisenberg exchange essentially share the same underlying physics, albeit with different symmetries, as was originally proposed by Moriya for superexchange in magnetic oxides, and by Fert and Levy for RKKY coupling in metallic spin glasses. Indeed, our result demonstrates the generality of the original DMI theory, insofar as the proportionality of the symmetric and antisymmetric exchange is robust with regard to the details of spin coupling for the material system in question. Although of significant fundamental importance, this result also leads us to a deeper understanding of DMI and how it could be optimized for spin-orbitronic applications. © 2015 Macmillan Publishers Limited. All rights reserved.
Muschler B.,Walther - Meissner Institute
Journal of physics. Condensed matter : an Institute of Physics journal | Year: 2010
Raman scattering cross sections depend on photon polarization. In the cuprates, nodal and antinodal directions are weighted more strongly in B(2g) and B(1g) symmetries, respectively. On the other hand, in angle-resolved photoemission spectroscopy (ARPES), electronic properties are measured along well-defined directions in momentum space rather than their weighted averages being taken. In contrast, the optical conductivity involves a momentum average over the entire Brillouin zone. Newly measured Raman response data on high-quality Bi(2)Sr(2)CaCu(2)O(8 + δ) single crystals up to high energies have been inverted using a modified maximum entropy inversion technique to extract from B(1g) and B(2g) Raman data corresponding electron-boson spectral densities (glue), and these are compared to the results obtained with known ARPES and optical inversions. We find that the B(2g) spectrum agrees qualitatively with nodal direction ARPES while the B(1g) results look more like the optical spectrum. A large peak around 30-40 meV in B(1g) and a much less prominent one in B(2g) are taken as support for the importance of (π, π) scattering at this frequency.
Hoehne F.,TU Munich |
Dreher L.,TU Munich |
Huebl H.,Walther - Meissner Institute |
Stutzmann M.,TU Munich |
Brandt M.S.,TU Munich
Physical Review Letters | Year: 2011
We demonstrate the electrical detection of pulsed X-band electron nuclear double resonance (ENDOR) in phosphorus-doped silicon at 5 K. A pulse sequence analogous to Davies ENDOR in conventional electron spin resonance is used to measure the nuclear spin transition frequencies of the P31 nuclear spins, where the P31 electron spins are detected electrically via spin-dependent transitions through Si/SiO2 interface states, thus not relying on a polarization of the electron spin system. In addition, the electrical detection of coherent nuclear spin oscillations is shown, demonstrating the feasibility to electrically read out the spin states of possible nuclear spin qubits. © 2011 American Physical Society.
Hackl R.,Walther - Meissner Institute
Zeitschrift fur Kristallographie | Year: 2011
The discovery of superconductors on copperoxygen basis in 1986 was one of the most celebrated events in condensed matter physics. The maximal transition temperature Tc close to 150 K was observed in HgBa2Ca 2Cu3O8+δ at high pressure. In spite of enormous progress in both the experimental knowledge and theoretical understanding, the origin of the high Tc remains elusive. Although the materials properties require unexpectedly complicated technical solutions several applications have been commercialized. © by Oldenbourg Wissenschaftsverlag, München.