TY  - JOUR
A1  - Zusan, Andreas
A1  - Gieseking, Björn
A1  - Zerson, Mario
A1  - Dyakonov, Vladimir
A1  - Magerle, Robert
A1  - Deibel, Carsten
T1  - The Effect of Diiodooctane on the Charge Carrier Generation in Organic Solar Cells Based on the Copolymer PBDTTT-C
JF  - Scientific Reports
N2  - Microstructural changes and the understanding of their effect on photocurrent generation are key aspects for improving the efficiency of organic photovoltaic devices. We analyze the impact of a systematically increased amount of the solvent additive diiodooctane (DIO) on the morphology of PBDTTT-C:PC71BM blends and related changes in free carrier formation and recombination by combining surface imaging, photophysical and charge extraction techniques. We identify agglomerates visible in AFM images of the 0% DIO blend as PC71BM domains embedded in an intermixed matrix phase. With the addition of DIO, a decrease in the size of fullerene domains along with a demixing of the matrix phase appears for 0.6% and 1% DIO. Surprisingly, transient absorption spectroscopy reveals an efficient photogeneration already for the smallest amount of DIO, although the largest efficiency is found for 3% DIO. It is ascribed to a fine-tuning of the blend morphology in terms of the formation of interpenetrating donor and acceptor phases minimizing geminate and nongeminate recombination as indicated by charge extraction experiments. An increase in the DIO content to 10% adversely affects the photovoltaic performance, most probably due to an inefficient free carrier formation and trapping in a less interconnected donor-acceptor network.
KW  - electronic properties and materials
KW  - photonic devices
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-125022
VL  - 5
ER  - 
TY  - JOUR
A1  - Gottscholl, Andreas
A1  - Diez, Matthias
A1  - Soltamov, Victor
A1  - Kasper, Christian
A1  - Krauße, Dominik
A1  - Sperlich, Andreas
A1  - Kianinia, Mehran
A1  - Bradac, Carlo
A1  - Aharonovich, Igor
A1  - Dyakonov, Vladimir
T1  - Spin defects in hBN as promising temperature, pressure and magnetic field quantum sensors
JF  - Nature Communications
N2  - 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.
KW  - electronic properties and materials
KW  - qubits
Y1  - 2021
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-261581
VL  - 12
IS  - 1
ER  - 
TY  - JOUR
A1  - Lundt, Nils
A1  - Klembt, Sebastian
A1  - Cherotchenko, Evgeniia
A1  - Betzold, Simon
A1  - Iff, Oliver
A1  - Nalitov, Anton V.
A1  - Klaas, Martin
A1  - Dietrich, Christof P.
A1  - Kavokin, Alexey V.
A1  - Höfling, Sven
A1  - Schneider, Christian
T1  - Room-temperature Tamm-plasmon exciton-polaritons with a WSe\(_{2}\) monolayer
JF  - Nature Communications
N2  - 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.
KW  - optics and photonics
KW  - two-dimensional materials
KW  - electronic properties and materials
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-169470
VL  - 7
ER  - 
TY  - JOUR
A1  - Anisimov, A. N.
A1  - Simin, D.
A1  - Soltamov, V. A.
A1  - Lebedev, S. P.
A1  - Baranov, P. G.
A1  - Astakhov, G. V.
A1  - Dyakonov, V.
T1  - Optical thermometry based on level anticrossing in silicon carbide
JF  - Scientific Reports
N2  - 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.
KW  - electronic and spintronic devices
KW  - electronic properties and materials
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-147809
VL  - 6
IS  - 33301
ER  - 
TY  - JOUR
A1  - Wagner, N.
A1  - Crippa, L.
A1  - Amaricci, A.
A1  - Hansmann, P.
A1  - Klett, M.
A1  - König, E. J.
A1  - Schäfer, T.
A1  - Di Sante, D.
A1  - Cano, J.
A1  - Millis, A. J.
A1  - Georges, A.
A1  - Sangiovanni, G.
T1  - Mott insulators with boundary zeros
JF  - Nature Communications
N2  - 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.
KW  - electronic properties and materials
KW  - topological insulators
Y1  - 2023
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-358150
VL  - 14
ER  - 
TY  - JOUR
A1  - Ünzelmann, M.
A1  - Bentmann, H.
A1  - Figgemeier, T.
A1  - Eck, P.
A1  - Neu, J. N.
A1  - Geldiyev, B.
A1  - Diekmann, F.
A1  - Rohlf, S.
A1  - Buck, J.
A1  - Hoesch, M.
A1  - Kalläne, M.
A1  - Rossnagel, K.
A1  - Thomale, R.
A1  - Siegrist, T.
A1  - Sangiovanni, G.
A1  - Di Sante, D.
A1  - Reinert, F.
T1  - Momentum-space signatures of Berry flux monopoles in the Weyl semimetal TaAs
JF  - Nature Communications
N2  - 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.
KW  - electronic properties and materials
KW  - topological insulators
Y1  - 2021
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-260719
VL  - 12
IS  - 1
ER  - 
TY  - JOUR
A1  - Hausoel, A.
A1  - Karolak, M.
A1  - Şaşιoğlu, E.
A1  - Lichtenstein, A.
A1  - Held, K.
A1  - Katanin, A.
A1  - Toschi, A.
A1  - Sangiovanni, G.
T1  - Local magnetic moments in iron and nickel at ambient and Earth's core conditions
JF  - Nature Communications
N2  - 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.
KW  - ferromagnetism
KW  - electronic properties and materials
KW  - magnetic properties and materials
KW  - nickel
KW  - iron
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-170681
VL  - 8
IS  - 16062
ER  - 
TY  - JOUR
A1  - Shamim, Saquib
A1  - Mahapatra, S.
A1  - Scappucci, G.
A1  - Klesse, W. M.
A1  - Simmons, M. Y.
A1  - Ghosh, Arindam
T1  - Dephasing rates for weak localization and universal conductance fluctuations in two dimensional Si: P and Ge: P δ-layers
JF  - Scientific Reports
N2  - 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.
KW  - two-dimensional materials
KW  - quantum information
KW  - electronic properties and materials
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-170934
VL  - 7
IS  - 46670
ER  - 
TY  - JOUR
A1  - Kraus, Hannes
A1  - Heiber, Michael C.
A1  - Väth, Stefan
A1  - Kern, Julia
A1  - Deibel, Carsten
A1  - Sperlich, Andreas
A1  - Dyakonov, Vladimir
T1  - Analysis of Triplet Exciton Loss Pathways in PTB7:PC\(_{71}\)BM Bulk Heterojunction Solar Cells
JF  - Scientific Reports
N2  - A strategy for increasing the conversion efficiency of organic photovoltaics has been to increase the VOC by tuning the energy levels of donor and acceptor components. However, this opens up a new loss pathway from an interfacial charge transfer state to a triplet exciton (TE) state called electron back transfer (EBT), which is detrimental to device performance. To test this hypothesis, we study triplet formation in the high performing PTB7:PC\(_{71}\)BM blend system and determine the impact of the morphology-optimizing additive 1,8-diiodoctane (DIO). Using photoluminescence and spin-sensitive optically detected magnetic resonance (ODMR) measurements at low temperature, we find that TEs form on PC\(_{71}\)BM via intersystem crossing from singlet excitons and on PTB7 via EBT mechanism. For DIO blends with smaller fullerene domains, an increased density of PTB7 TEs is observed. The EBT process is found to be significant only at very low temperature. At 300 K, no triplets are detected via ODMR, and electrically detected magnetic resonance on optimized solar cells indicates that TEs are only present on the fullerenes. We conclude that in PTB7:PC\(_{71}\)BM devices, TE formation via EBT is impacted by fullerene domain size at low temperature, but at room temperature, EBT does not represent a dominant loss pathway.
KW  - solar cells
KW  - electronic properties and materials
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-147413
VL  - 6
IS  - 29158
ER  -