@article{HausoelKarolakŞaşιoğluetal.2017, author = {Hausoel, A. and Karolak, M. and Şa{\c{s}}ιoğlu, E. and Lichtenstein, A. and Held, K. and Katanin, A. and Toschi, A. and Sangiovanni, G.}, title = {Local magnetic moments in iron and nickel at ambient and Earth's core conditions}, series = {Nature Communications}, volume = {8}, journal = {Nature Communications}, number = {16062}, doi = {10.1038/ncomms16062}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-170681}, year = {2017}, abstract = {Some Bravais lattices have a particular geometry that can slow down the motion of Bloch electrons by pre-localization due to the band-structure properties. Another known source of electronic localization in solids is the Coulomb repulsion in partially filled d or f orbitals, which leads to the formation of local magnetic moments. The combination of these two effects is usually considered of little relevance to strongly correlated materials. Here we show that it represents, instead, the underlying physical mechanism in two of the most important ferromagnets: nickel and iron. In nickel, the van Hove singularity has an unexpected impact on the magnetism. As a result, the electron-electron scattering rate is linear in temperature, in violation of the conventional Landau theory of metals. This is true even at Earth's core pressures, at which iron is instead a good Fermi liquid. The importance of nickel in models of geomagnetism may have therefore to be reconsidered.}, language = {en} } @article{GottschollDiezSoltamovetal.2021, author = {Gottscholl, Andreas and Diez, Matthias and Soltamov, Victor and Kasper, Christian and Krauße, Dominik and Sperlich, Andreas and Kianinia, Mehran and Bradac, Carlo and Aharonovich, Igor and Dyakonov, Vladimir}, title = {Spin defects in hBN as promising temperature, pressure and magnetic field quantum sensors}, series = {Nature Communications}, volume = {12}, journal = {Nature Communications}, number = {1}, doi = {10.1038/s41467-021-24725-1}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-261581}, year = {2021}, abstract = {Spin defects in solid-state materials are strong candidate systems for quantum information technology and sensing applications. Here we explore in details the recently discovered negatively charged boron vacancies (V\(_B\)\(^-\)) in hexagonal boron nitride (hBN) and demonstrate their use as atomic scale sensors for temperature, magnetic fields and externally applied pressure. These applications are possible due to the high-spin triplet ground state and bright spin-dependent photoluminescence of the V\(_B\)\(^-\). Specifically, we find that the frequency shift in optically detected magnetic resonance measurements is not only sensitive to static magnetic fields, but also to temperature and pressure changes which we relate to crystal lattice parameters. We show that spin-rich hBN films are potentially applicable as intrinsic sensors in heterostructures made of functionalized 2D materials.}, language = {en} } @article{CiuchiDiSanteDobrosavljevićetal.2018, author = {Ciuchi, Sergio and Di Sante, Domenico and Dobrosavljević, Vladimir and Fratini, Simone}, title = {The origin of Mooij correlations in disordered metals}, series = {npj Quantum Materials}, volume = {3}, journal = {npj Quantum Materials}, doi = {10.1038/s41535-018-0119-y}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-223148}, year = {2018}, abstract = {Sufficiently disordered metals display systematic deviations from the behavior predicted by semi-classical Boltzmann transport theory. Here the scattering events from impurities or thermal excitations can no longer be considered as additive-independent processes, as asserted by Matthiessen's rule following from this picture. In the intermediate region between the regime of good conduction and that of insulation, one typically finds a change of sign of the temperature coefficient of resistivity, even at elevated temperature spanning ambient conditions, a phenomenology that was first identified by Mooij in 1973. Traditional weak coupling approaches to identify relevant corrections to the Boltzmann picture focused on long-distance interference effects such as "weak localization", which are especially important in low dimensions (1D and 2D) and close to the zero-temperature limit. Here we formulate a strong-coupling approach to tackle the interplay of strong disorder and lattice deformations (phonons) in bulk three-dimensional metals at high temperatures. We identify a polaronic mechanism of strong disorder renormalization, which describes how a lattice locally responds to the relevant impurity potential. This mechanism, which quantitatively captures the Mooij regime, is physically distinct and unrelated to Anderson localization, but realizes early seminal ideas of Anderson himself, concerning the interplay of disorder and lattice deformations.}, language = {en} } @article{AnisimovSiminSoltamovetal.2016, author = {Anisimov, A. N. and Simin, D. and Soltamov, V. A. and Lebedev, S. P. and Baranov, P. G. and Astakhov, G. V. and Dyakonov, V.}, title = {Optical thermometry based on level anticrossing in silicon carbide}, series = {Scientific Reports}, volume = {6}, journal = {Scientific Reports}, number = {33301}, doi = {10.1038/srep33301}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-147809}, year = {2016}, abstract = {We report a giant thermal shift of 2.1 MHz/K related to the excited-state zero-field splitting in the silicon vacancy centers in 4H silicon carbide. It is obtained from the indirect observation of the optically detected magnetic resonance in the excited state using the ground state as an ancilla. Alternatively, relative variations of the zero-field splitting for small temperature differences can be detected without application of radiofrequency fields, by simply monitoring the photoluminescence intensity in the vicinity of the level anticrossing. This effect results in an all-optical thermometry technique with temperature sensitivity of 100 mK/Hz\(^{1/2}\) for a detection volume of approximately 10\(^{-6}\) mm\(^3\). In contrast, the zero-field splitting in the ground state does not reveal detectable temperature shift. Using these properties, an integrated magnetic field and temperature sensor can be implemented on the same center.}, language = {en} }