@article{LiShanRupprechtetal.2022, author = {Li, Donghai and Shan, Hangyong and Rupprecht, Christoph and Knopf, Heiko and Watanabe, Kenji and Taniguchi, Takashi and Qin, Ying and Tongay, Sefaattin and Nuß, Matthias and Schr{\"o}der, Sven and Eilenberger, Falk and H{\"o}fling, Sven and Schneider, Christian and Brixner, Tobias}, title = {Hybridized exciton-photon-phonon states in a transition-metal-dichalcogenide van-der-Waals heterostructure microcavity}, series = {Physical Review Letters}, journal = {Physical Review Letters}, edition = {accepted version}, issn = {1079-7114}, doi = {10.1103/PhysRevLett.128.087401}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-351303}, year = {2022}, abstract = {Excitons in atomically thin transition-metal dichalcogenides (TMDs) have been established as an attractive platform to explore polaritonic physics, owing to their enormous binding energies and giant oscillator strength. Basic spectral features of exciton polaritons in TMD microcavities, thus far, were conventionally explained via two-coupled-oscillator models. This ignores, however, the impact of phonons on the polariton energy structure. Here we establish and quantify the threefold coupling between excitons, cavity photons, and phonons. For this purpose, we employ energy-momentum-resolved photoluminescence and spatially resolved coherent two-dimensional spectroscopy to investigate the spectral properties of a high-quality-factor microcavity with an embedded WSe\(_2\) van-der-Waals heterostructure at room temperature. Our approach reveals a rich multi-branch structure which thus far has not been captured in previous experiments. Simulation of the data reveals hybridized exciton-photon-phonon states, providing new physical insight into the exciton polariton system based on layered TMDs.}, language = {en} } @article{GabelPickemScheidereretal.2022, author = {Gabel, Judith and Pickem, Matthias and Scheiderer, Philipp and Dudy, Lenart and Leikert, Berengar and Fuchs, Marius and St{\"u}binger, Martin and Schmitt, Matthias and K{\"u}spert, Julia and Sangiovanni, Giorgio and Tomczak, Jan M. and Held, Karsten and Lee, Tien-Lin and Claessen, Ralph and Sing, Michael}, title = {Toward Functionalized Ultrathin Oxide Films: The Impact of Surface Apical Oxygen}, series = {Advanced Electronic Materials}, volume = {8}, journal = {Advanced Electronic Materials}, number = {4}, issn = {2199-160X}, doi = {10.1002/aelm.202101006}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-318914}, year = {2022}, abstract = {Thin films of transition metal oxides open up a gateway to nanoscale electronic devices beyond silicon characterized by novel electronic functionalities. While such films are commonly prepared in an oxygen atmosphere, they are typically considered to be ideally terminated with the stoichiometric composition. Using the prototypical correlated metal SrVO\(_{3}\) as an example, it is demonstrated that this idealized description overlooks an essential ingredient: oxygen adsorbing at the surface apical sites. The oxygen adatoms, which are present even if the films are kept in an ultrahigh vacuum environment and not explicitly exposed to air, are shown to severely affect the intrinsic electronic structure of a transition metal oxide film. Their presence leads to the formation of an electronically dead surface layer but also alters the band filling and the electron correlations in the thin films. These findings highlight that it is important to take into account surface apical oxygen or—mutatis mutandis—the specific oxygen configuration imposed by a capping layer to predict the behavior of ultrathin films of transition metal oxides near the single unit-cell limit.}, language = {en} } @article{FrankPflaum2022, author = {Frank, Maximilian and Pflaum, Jens}, title = {Tuning Electronic and Ionic Transport by Carbon-Based Additives in Polymer Electrolytes for Thermoelectric Applications}, series = {Advanced Functional Materials}, volume = {32}, journal = {Advanced Functional Materials}, number = {32}, issn = {1616-301X}, doi = {10.1002/adfm.202203277}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-318908}, year = {2022}, abstract = {Thermoelectric materials utilizing ionic transport open-up entirely new possibilities for the recuperation of waste heat. Remarkably, solid state electrolytes which have entered the focus of battery research in recent years turn-out to be promising candidates also for ionic thermoelectrics. Here, the dynamics of ionic transport and thermoelectric properties of a methacrylate based polymer blend in combination with a lithium salt is analyzed. Impedance spectroscopy data indicates the presence of just one transport mechanism irrespective of lithium salt concentration. In contrast, the temperature dependent ionic conductivity increases with salt concentration and can be ascribed to a Vogel-Fulcher-Tammann (VFT) behavior. The obtained Seebeck coefficients of 2 mV K\(^{-1}\) allow for high power outputs while the polymer matrix maintains the temperature gradient by its low thermal conductivity. Adding multi-walled carbon nanotubes to the polymer matrix allows for variation of the Seebeck coefficient as well as the ionic and electronic conductivities. As a result, a transition between a high temperature VFT regime and a low temperature Arrhenius regime appears at a critical temperature, T\(_{c}\), shifting upon addition of salt. The observed polarity change in Seebeck voltage at T\(_{c}\) suggests a new mode of thermoelectric operation, which is demonstrated by a proof-of-concept mixed electronic-ionic-thermoelectric generator.}, language = {en} } @article{WyborskiPodemskiWrońskietal.2022, author = {Wyborski, Paweł and Podemski, Paweł and Wroński, Piotr Andrzej and Jabeen, Fauzia and H{\"o}fling, Sven and Sęk, Grzegorz}, title = {Electronic and optical properties of InAs QDs grown by MBE on InGaAs metamorphic buffer}, series = {Materials}, volume = {15}, journal = {Materials}, number = {3}, issn = {1996-1944}, doi = {10.3390/ma15031071}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-297037}, year = {2022}, abstract = {We present the optical characterization of GaAs-based InAs quantum dots (QDs) grown by molecular beam epitaxy on a digitally alloyed InGaAs metamorphic buffer layer (MBL) with gradual composition ensuring a redshift of the QD emission up to the second telecom window. Based on the photoluminescence (PL) measurements and numerical calculations, we analyzed the factors influencing the energies of optical transitions in QDs, among which the QD height seems to be dominating. In addition, polarization anisotropy of the QD emission was observed, which is a fingerprint of significant valence states mixing enhanced by the QD confinement potential asymmetry, driven by the decreased strain with increasing In content in the MBL. The barrier-related transitions were probed by photoreflectance, which combined with photoluminescence data and the PL temperature dependence, allowed for the determination of the carrier activation energies and the main channels of carrier loss, identified as the carrier escape to the MBL barrier. Eventually, the zero-dimensional character of the emission was confirmed by detecting the photoluminescence from single QDs with identified features of the confined neutral exciton and biexciton complexes via the excitation power and polarization dependences.}, language = {en} } @article{PfenningKruegerJabeenetal.2022, author = {Pfenning, Andreas and Kr{\"u}ger, Sebastian and Jabeen, Fauzia and Worschech, Lukas and Hartmann, Fabian and H{\"o}fling, Sven}, title = {Single-photon counting with semiconductor resonant tunneling devices}, series = {Nanomaterials}, volume = {12}, journal = {Nanomaterials}, number = {14}, issn = {2079-4991}, doi = {10.3390/nano12142358}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-281922}, year = {2022}, abstract = {Optical quantum information science and technologies require the capability to generate, control, and detect single or multiple quanta of light. The need to detect individual photons has motivated the development of a variety of novel and refined single-photon detectors (SPDs) with enhanced detector performance. Superconducting nanowire single-photon detectors (SNSPDs) and single-photon avalanche diodes (SPADs) are the top-performer in this field, but alternative promising and innovative devices are emerging. In this review article, we discuss the current state-of-the-art of one such alternative device capable of single-photon counting: the resonant tunneling diode (RTD) single-photon detector. Due to their peculiar photodetection mechanism and current-voltage characteristic with a region of negative differential conductance, RTD single-photon detectors provide, theoretically, several advantages over conventional SPDs, such as an inherently deadtime-free photon-number resolution at elevated temperatures, while offering low dark counts, a low timing jitter, and multiple photon detection modes. This review article brings together our previous studies and current experimental results. We focus on the current limitations of RTD-SPDs and provide detailed design and parameter variations to be potentially employed in next-generation RTD-SPD to improve the figure of merits of these alternative single-photon counting devices. The single-photon detection capability of RTDs without quantum dots is shown.}, language = {en} } @article{RothmayrGuarinCastroHartmannetal.2022, author = {Rothmayr, Florian and Guarin Castro, Edgar David and Hartmann, Fabian and Knebl, Georg and Schade, Anne and H{\"o}fling, Sven and Koeth, Johannes and Pfenning, Andreas and Worschech, Lukas and Lopez-Richard, Victor}, title = {Resonant tunneling diodes: mid-infrared sensing at room temperature}, series = {Nanomaterials}, volume = {12}, journal = {Nanomaterials}, number = {6}, issn = {2079-4991}, doi = {10.3390/nano12061024}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-267152}, year = {2022}, abstract = {Resonant tunneling diode photodetectors appear to be promising architectures with a simple design for mid-infrared sensing operations at room temperature. We fabricated resonant tunneling devices with GaInAsSb absorbers that allow operation in the 2-4 μm range with significant electrical responsivity of 0.97 A/W at 2004 nm to optical readout. This paper characterizes the photosensor response contrasting different operational regimes and offering a comprehensive theoretical analysis of the main physical ingredients that rule the sensor functionalities and affect its performance. We demonstrate how the drift, accumulation, and escape efficiencies of photogenerated carriers influence the electrostatic modulation of the sensor's electrical response and how they allow controlling the device's sensing abilities.}, language = {en} } @article{HerzStefanescuLohretal.2022, author = {Herz, Stefan and Stefanescu, Maria R. and Lohr, David and Vogel, Patrick and Kosmala, Aleksander and Terekhov, Maxim and Weng, Andreas M. and Grunz, Jan-Peter and Bley, Thorsten A. and Schreiber, Laura M.}, title = {Effects of image homogeneity on stenosis visualization at 7 T in a coronary artery phantom study: With and without B1-shimming and parallel transmission}, series = {PloS One}, volume = {17}, journal = {PloS One}, number = {6}, doi = {10.1371/journal.pone.0270689}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-300129}, year = {2022}, abstract = {Background To investigate the effects of B\(_1\)-shimming and radiofrequency (RF) parallel transmission (pTX) on the visualization and quantification of the degree of stenosis in a coronary artery phantom using 7 Tesla (7 T) magnetic resonance imaging (MRI). Methods Stenosis phantoms with different grades of stenosis (0\%, 20\%, 40\%, 60\%, 80\%, and 100\%; 5 mm inner vessel diameter) were produced using 3D printing (clear resin). Phantoms were imaged with four different concentrations of diluted Gd-DOTA representing established arterial concentrations after intravenous injection in humans. Samples were centrally positioned in a thorax phantom of 30 cm diameter filled with a custom-made liquid featuring dielectric properties of muscle tissue. MRI was performed on a 7 T whole-body system. 2D-gradient-echo sequences were acquired with an 8-channel transmit 16-channel receive (8 Tx / 16 Rx) cardiac array prototype coil with and without pTX mode. Measurements were compared to those obtained with identical scan parameters using a commercially available 1 Tx / 16 Rx single transmit coil (sTX). To assess reproducibility, measurements (n = 15) were repeated at different horizontal angles with respect to the B0-field. Results B\(_1\)-shimming and pTX markedly improved flip angle homogeneity across the thorax phantom yielding a distinctly increased signal-to-noise ratio (SNR) averaged over a whole slice relative to non-manipulated RF fields. Images without B\(_1\)-shimming showed shading artifacts due to local B\(_1\)\(^+\)-field inhomogeneities, which hampered stenosis quantification in severe cases. In contrast, B\(_1\)-shimming and pTX provided superior image homogeneity. Compared with a conventional sTX coil higher grade stenoses (60\% and 80\%) were graded significantly (p<0.01) more precise. Mild to moderate grade stenoses did not show significant differences. Overall, SNR was distinctly higher with B\(_1\)-shimming and pTX than with the conventional sTX coil (inside the stenosis phantoms 14\%, outside the phantoms 32\%). Both full and half concentration (10.2 mM and 5.1 mM) of a conventional Gd-DOTA dose for humans were equally suitable for stenosis evaluation in this phantom study. Conclusions B\(_1\)-shimming and pTX at 7 T can distinctly improve image homogeneity and therefore provide considerably more accurate MR image analysis, which is beneficial for imaging of small vessel structures.}, language = {en} } @article{VogelRueckertFriedrichetal.2022, author = {Vogel, Patrick and R{\"u}ckert, Martin Andreas and Friedrich, Bernhard and Tietze, Rainer and Lyer, Stefan and Kampf, Thomas and Hennig, Thomas and D{\"o}lken, Lars and Alexiou, Christoph and Behr, Volker Christian}, title = {Critical Offset Magnetic PArticle SpectroScopy for rapid and highly sensitive medical point-of-care diagnostics}, series = {Nature Communications}, volume = {13}, journal = {Nature Communications}, doi = {10.1038/s41467-022-34941-y}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-300893}, year = {2022}, abstract = {Magnetic nanoparticles (MNPs) have been adapted for many applications, e.g., bioassays for the detection of biomarkers such as antibodies, by controlled engineering of specific surface properties. Specific measurement of such binding states is of high interest but currently limited to highly sensitive techniques such as ELISA or flow cytometry, which are relatively inflexible, difficult to handle, expensive and time-consuming. Here we report a method named COMPASS (Critical-Offset-Magnetic-Particle-SpectroScopy), which is based on a critical offset magnetic field, enabling sensitive detection to minimal changes in mobility of MNP ensembles, e.g., resulting from SARS-CoV-2 antibodies binding to the S antigen on the surface of functionalized MNPs. With a sensitivity of 0.33 fmole/50 µl (≙7 pM) for SARS-CoV-2-S1 antibodies, measured with a low-cost portable COMPASS device, the proposed technique is competitive with respect to sensitivity while providing flexibility, robustness, and a measurement time of seconds per sample. In addition, initial results with blood serum demonstrate high specificity.}, language = {en} } @article{StuehlerKowalewskiReisetal.2022, author = {St{\"u}hler, R. and Kowalewski, A. and Reis, F. and Jungblut, D. and Dominguez, F. and Scharf, B. and Li, G. and Sch{\"a}fer, J. and Hankiewicz, E. M. and Claessen, R.}, title = {Effective lifting of the topological protection of quantum spin Hall edge states by edge coupling}, series = {Nature Communications}, volume = {13}, journal = {Nature Communications}, doi = {10.1038/s41467-022-30996-z}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-300886}, year = {2022}, abstract = {The scientific interest in two-dimensional topological insulators (2D TIs) is currently shifting from a more fundamental perspective to the exploration and design of novel functionalities. Key concepts for the use of 2D TIs in spintronics are based on the topological protection and spin-momentum locking of their helical edge states. In this study we present experimental evidence that topological protection can be (partially) lifted by pairwise coupling of 2D TI edges in close proximity. Using direct wave function mapping via scanning tunneling microscopy/spectroscopy (STM/STS) we compare isolated and coupled topological edges in the 2D TI bismuthene. The latter situation is realized by natural lattice line defects and reveals distinct quasi-particle interference (QPI) patterns, identified as electronic Fabry-P{\´e}rot resonator modes. In contrast, free edges show no sign of any single-particle backscattering. These results pave the way for novel device concepts based on active control of topological protection through inter-edge hybridization for, e.g., electronic Fabry-P{\´e}rot interferometry.}, language = {en} } @article{NoyaletIlgenBuerkleinetal.2022, author = {Noyalet, Laurent and Ilgen, Lukas and B{\"u}rklein, Miriam and Shehata-Dieler, Wafaa and Taeger, Johannes and Hagen, Rudolf and Neun, Tilmann and Zabler, Simon and Althoff, Daniel and Rak, Kristen}, title = {Vestibular aqueduct morphology and Meniere's disease - development of the vestibular aqueduct score by 3D analysis}, series = {Frontiers in Surgery}, volume = {9}, journal = {Frontiers in Surgery}, issn = {2296-875X}, doi = {10.3389/fsurg.2022.747517}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-312893}, year = {2022}, abstract = {Improved radiological examinations with newly developed 3D models may increase understanding of Meniere's disease (MD). The morphology and course of the vestibular aqueduct (VA) in the temporal bone might be related to the severity of MD. The presented study explored, if the VA of MD and non-MD patients can be grouped relative to its angle to the semicircular canals (SCC) and length using a 3D model. Scans of temporal bone specimens (TBS) were performed using micro-CT and micro flat panel volume computed tomography (mfpVCT). Furthermore, scans were carried out in patients and TBS by computed tomography (CT). The angle between the VA and the three SCC, as well as the length of the VA were measured. From these data, a 3D model was constructed to develop the vestibular aqueduct score (VAS). Using different imaging modalities it was demonstrated that angle measurements of the VA are reliable and can be effectively used for detailed diagnostic investigation. To test the clinical relevance, the VAS was applied on MD and on non-MD patients. Length and angle values from MD patients differed from non-MD patients. In MD patients, significantly higher numbers of VAs could be assigned to a distinct group of the VAS. In addition, it was tested, whether the outcome of a treatment option for MD can be correlated to the VAS.}, language = {en} }