@article{IzquierdoKarolakPrabhakaranetal.2019, author = {Izquierdo, Manuel and Karolak, Michael and Prabhakaran, Dharmalingam and Boothroyd, Andrew T. and Scherz, Andreas O. and Lichtenstein, Alexander and Molodtsov, Serguei L.}, title = {Monitoring ultrafast metallization in LaCoO3 with femtosecond soft x-ray spectroscopy}, series = {Communications Physics}, volume = {2}, journal = {Communications Physics}, doi = {10.1038/s42005-019-0109-9}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-323265}, year = {2019}, abstract = {The study of ultrafast dynamics is a new tool to understand and control the properties of correlated oxides. By enhancing some properties and realizing new dynamically excited phrases, this tool has opened new routes for technological applications. LaCoO3 is one paradigmatic example where the strong electron, spin, and lattice coupling induced by electronic correlations results in a low-temperature spin transition and a high-temperature semiconductor-to-metal transition that is still not completely understood. Here, we monitor ultrafast metallization in LaCoO3 using time-resolved soft x-ray reflectivity experiments. While the process is entangled at the Co L3 edge, the time information of the different channels is decrypted at different resonant energies of the O K edge. Metallization is shown to occur via transient electronic, spin, and lattice separation. Our results agree with the thermodynamical model and demonstrate the potential of femtosecond soft x-ray experiments at the O K edge to understand correlated oxides.}, language = {en} } @article{HeDiSanteLietal.2018, author = {He, Jiangang and Di Sante, Domenico and Li, Ronghan and Chen, Xing-Qiu and Rondinelli, James M. and Franchini, Cesare}, title = {Tunable metal-insulator transition, Rashba effect and Weyl Fermions in a relativistic charge-ordered ferroelectric oxide}, series = {Nature Communications}, volume = {9}, journal = {Nature Communications}, doi = {10.1038/s41467-017-02814-4}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-227946}, year = {2018}, abstract = {Controllable metal-insulator transitions (MIT), Rashba-Dresselhaus (RD) spin splitting, and Weyl semimetals are promising schemes for realizing processing devices. Complex oxides are a desirable materials platform for such devices, as they host delicate and tunable charge, spin, orbital, and lattice degrees of freedoms. Here, using first-principles calculations and symmetry analysis, we identify an electric-field tunable MIT, RD effect, and Weyl semimetal in a known, charge-ordered, and polar relativistic oxide Ag2BiO3 at room temperature. Remarkably, a centrosymmetric BiO6 octahedral-breathing distortion induces a sizable spontaneous ferroelectric polarization through Bi3+/Bi5+ charge disproportionation, which stabilizes simultaneously the insulating phase. The continuous attenuation of the Bi3+/Bi5+ disproportionation obtained by applying an external electric field reduces the band gap and RD spin splitting and drives the phase transition from a ferroelectric RD insulator to a paraelectric Dirac semimetal, through a topological Weyl semimetal intermediate state. These findings suggest that Ag2BiO3 is a promising material for spin-orbitonic applications.}, 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{WagnerCrippaAmariccietal.2023, author = {Wagner, N. and Crippa, L. and Amaricci, A. and Hansmann, P. and Klett, M. and K{\"o}nig, E. J. and Sch{\"a}fer, T. and Di Sante, D. and Cano, J. and Millis, A. J. and Georges, A. and Sangiovanni, G.}, title = {Mott insulators with boundary zeros}, series = {Nature Communications}, volume = {14}, journal = {Nature Communications}, doi = {10.1038/s41467-023-42773-7}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-358150}, year = {2023}, abstract = {The topological classification of electronic band structures is based on symmetry properties of Bloch eigenstates of single-particle Hamiltonians. In parallel, topological field theory has opened the doors to the formulation and characterization of non-trivial phases of matter driven by strong electron-electron interaction. Even though important examples of topological Mott insulators have been constructed, the relevance of the underlying non-interacting band topology to the physics of the Mott phase has remained unexplored. Here, we show that the momentum structure of the Green's function zeros defining the "Luttinger surface" provides a topological characterization of the Mott phase related, in the simplest description, to the one of the single-particle electronic dispersion. Considerations on the zeros lead to the prediction of new phenomena: a topological Mott insulator with an inverted gap for the bulk zeros must possess gapless zeros at the boundary, which behave as a form of "topological antimatter" annihilating conventional edge states. Placing band and Mott topological insulators in contact produces distinctive observable signatures at the interface, revealing the otherwise spectroscopically elusive Green's function zeros.}, 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{UenzelmannBentmannFiggemeieretal.2021, author = {{\"U}nzelmann, M. and Bentmann, H. and Figgemeier, T. and Eck, P. and Neu, J. N. and Geldiyev, B. and Diekmann, F. and Rohlf, S. and Buck, J. and Hoesch, M. and Kall{\"a}ne, M. and Rossnagel, K. and Thomale, R. and Siegrist, T. and Sangiovanni, G. and Di Sante, D. and Reinert, F.}, title = {Momentum-space signatures of Berry flux monopoles in the Weyl semimetal TaAs}, series = {Nature Communications}, volume = {12}, journal = {Nature Communications}, number = {1}, doi = {10.1038/s41467-021-23727-3}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-260719}, year = {2021}, abstract = {Since the early days of Dirac flux quantization, magnetic monopoles have been sought after as a potential corollary of quantized electric charge. As opposed to magnetic monopoles embedded into the theory of electromagnetism, Weyl semimetals (WSM) exhibit Berry flux monopoles in reciprocal parameter space. As a function of crystal momentum, such monopoles locate at the crossing point of spin-polarized bands forming the Weyl cone. Here, we report momentum-resolved spectroscopic signatures of Berry flux monopoles in TaAs as a paradigmatic WSM. We carried out angle-resolved photoelectron spectroscopy at bulk-sensitive soft X-ray energies (SX-ARPES) combined with photoelectron spin detection and circular dichroism. The experiments reveal large spin- and orbital-angular-momentum (SAM and OAM) polarizations of the Weyl-fermion states, resulting from the broken crystalline inversion symmetry in TaAs. Supported by first-principles calculations, our measurements image signatures of a topologically non-trivial winding of the OAM at the Weyl nodes and unveil a chirality-dependent SAM of the Weyl bands. Our results provide directly bulk-sensitive spectroscopic support for the non-trivial band topology in the WSM TaAs, promising to have profound implications for the study of quantum-geometric effects in solids. Weyl semimetals exhibit Berry flux monopoles in momentum-space, but direct experimental evidence has remained elusive. Here, the authors reveal topologically non-trivial winding of the orbital-angular-momentum at the Weyl nodes and a chirality-dependent spin-angular-momentum of the Weyl bands, as a direct signature of the Berry flux monopoles in TaAs.}, language = {en} } @article{LundtKlembtCherotchenkoetal.2016, author = {Lundt, Nils and Klembt, Sebastian and Cherotchenko, Evgeniia and Betzold, Simon and Iff, Oliver and Nalitov, Anton V. and Klaas, Martin and Dietrich, Christof P. and Kavokin, Alexey V. and H{\"o}fling, Sven and Schneider, Christian}, title = {Room-temperature Tamm-plasmon exciton-polaritons with a WSe\(_{2}\) monolayer}, series = {Nature Communications}, volume = {7}, journal = {Nature Communications}, doi = {10.1038/ncomms13328}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-169470}, year = {2016}, abstract = {Solid-state cavity quantum electrodynamics is a rapidly advancing field, which explores the frontiers of light-matter coupling. Metal-based approaches are of particular interest in this field, as they carry the potential to squeeze optical modes to spaces significantly below the diffraction limit. Transition metal dichalcogenides are ideally suited as the active material in cavity quantum electrodynamics, as they interact strongly with light at the ultimate monolayer limit. Here, we implement a Tamm-plasmon-polariton structure and study the coupling to a monolayer of WSe\(_{2}\), hosting highly stable excitons. Exciton-polariton formation at room temperature is manifested in the characteristic energy-momentum dispersion relation studied in photoluminescence, featuring an anti-crossing between the exciton and photon modes with a Rabi-splitting of 23.5 meV. Creating polaritonic quasiparticles in monolithic, compact architectures with atomic monolayers under ambient conditions is a crucial step towards the exploration of nonlinearities, macroscopic coherence and advanced spinor physics with novel, low-mass bosons.}, language = {en} } @article{ShamimMahapatraScappuccietal.2017, author = {Shamim, Saquib and Mahapatra, S. and Scappucci, G. and Klesse, W. M. and Simmons, M. Y. and Ghosh, Arindam}, title = {Dephasing rates for weak localization and universal conductance fluctuations in two dimensional Si: P and Ge: P δ-layers}, series = {Scientific Reports}, volume = {7}, journal = {Scientific Reports}, number = {46670}, doi = {10.1038/srep46670}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-170934}, year = {2017}, abstract = {We report quantum transport measurements on two dimensional (2D) Si:P and Ge:P δ-layers and compare the inelastic scattering rates relevant for weak localization (WL) and universal conductance fluctuations (UCF) for devices of various doping densities (0.3-2.5 × 10\(^{18}\)m\(^{-2}\)) at low temperatures (0.3-4.2 K). The phase breaking rate extracted experimentally from measurements of WL correction to conductivity and UCF agree well with each other within the entire temperature range. This establishes that WL and UCF, being the outcome of quantum interference phenomena, are governed by the same dephasing rate.}, language = {en} } @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{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} }