A5009507451- Photonic and Optical Devices
- Physics of Superconductivity and Magnetism
- Magnetic and transport properties of perovskites and related materials
- Advanced Condensed Matter Physics
- Solid State Laser Technologies
- Photorefractive and Nonlinear Optics
- Photonic Crystals and Applications
- Laser Design and Applications
- Semiconductor materials and devices
- Silicon Nanostructures and Photoluminescence
- Semiconductor Lasers and Optical Devices
- Superconductivity in MgB2 and Alloys
- Advanced Chemical Physics Studies
- Laser Material Processing Techniques
- Rare-earth and actinide compounds
- Electronic and Structural Properties of Oxides
- Carbon Nanotubes in Composites
- Advanced Photonic Communication Systems
- Integrated Circuits and Semiconductor Failure Analysis
- Graphene research and applications
- Nanowire Synthesis and Applications
- Advancements in Battery Materials
- Optical Systems and Laser Technology
- Semiconductor Quantum Structures and Devices
- Advanced NMR Techniques and Applications
PNDetector (Germany)
2024
Waseda University
2021-2024
University of Stuttgart
2006-2020
Center for Integrated Quantum Science and Technology
2019-2020
Max Planck Institute for Solid State Research
2005-2019
Universität Innsbruck
2017
Bern University of Applied Sciences
2011
Université de Montpellier
2005-2006
Centre National de la Recherche Scientifique
2006
Forschungszentrum Jülich
2001-2003
The continued development of computational approaches to many-body ground-state problems in physics and chemistry calls for a consistent way assess its overall progress. In this work, we introduce metric variational accuracy, the V-score, obtained from energy variance. We provide an extensive curated dataset calculations quantum systems, identifying cases where state-of-the-art numerical show limited accuracy future algorithms or platforms, such as computing, could improved accuracy. V-score...
High-quality BaTiO3 epitaxial thin films on MgO substrates have been grown by pulsed-laser deposition. Both, c-axis and a-axis orientations were studied. Mach–Zehnder optical waveguide modulators with a fork angle of 1.7° fabricated ion-beam etching. The waveguides are the ridge type, thickness is 1 μm, step 50 nm, width 2 μm. Light was coupled into from fibers. propagation losses 2–3 dB/cm. Electrodes 3 mm length deposited besides waveguides. Electro-optic modulation has demonstrated Vπ=6.3...
GeSn heterojunction photodetectors on Si substrates were grown with Sn concentration up to 4%, fabricated for vertical light incidence, and characterized. The complete layer structure was by means of ultra low temperature (100 °C) molecular beam epitaxy. content shifts the responsivity into infrared, about 310 nm 4% sample. An increase optical wavelengths higher than 1550 can be observed increasing content. At 1600 nm, is increased more a factor 10 diode in comparison Ge reference diode.
GeSn heterojunction p-i-n diodes with a Sn content of 0.5% are grown special low temperature molecular beam epitaxy. The incorporation in Ge is facilitated by very growth step order to suppress surface segregation. Diodes sharp doping transitions realized as double mesa structures diameter from 1.5 up 80 μm. An optical responsivity these 0.1 A/W at wavelength λ=1.55 μm measured. In comparison pure detector the increased factor 3 result caused band gap reduction.
Ablation characteristics of copper and stainless steel with laser pulses from 10 to 100 ps at 1064 nm wavelength were studied. The influence the pulse duration number on threshold fluence penetration depth has been investigated. results show a strong decrease ablation efficiency quality increasing duration.
We analyzed the intrinsic defects and n-type-carrier concentration generated by nitrogen ion implantation in n-type GaN deep-level-transient spectroscopy capacitance–voltage measurements, respectively. The samples were grown on sapphire metalorganic vapor-phase epitaxy. Nitrogen with different doses postimplantation rapid-thermal annealing (RTA) investigated. observed a growing increasing defect doses. After RTA of free carriers deep levels as found as-grown state are restored. also address...
In this letter, a GeSn light-emitting pin diode integrated on Si via Ge buffer is demonstrated and it compared with made from pure, unstrained Si. The layer structures are grown special low-temperature molecular beam epitaxy process. pseudomorphic layers (1.1% Sn content) the compressively strained. Both diodes clearly show direct bandgap electroluminescence emission at room temperature. peak of shifted by 20 meV into infrared region to diode. shift due lower influence strain.
The continued development of computational approaches to many-body ground-state problems in physics and chemistry calls for a consistent way assess its overall progress. In this work, we introduce metric variational accuracy, the V-score, obtained from energy variance. We provide an extensive curated dataset calculations quantum systems, identifying cases where state-of-the-art numerical show limited future algorithms or platforms, such as computing, could improved accuracy. V-score can be...
We derive ab initio low-energy effective Hamiltonians (LEH) for high-temperature superconducting (SC) copper oxides ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CuO}}_{6}$ (Bi2201, ${N}_{\ensuremath{\ell}}=1$, ${T}_{c}^{\mathrm{exp}}\ensuremath{\sim}10\phantom{\rule{0.16em}{0ex}}\mathrm{K}$), ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8}$ (Bi2212, ${N}_{\ensuremath{\ell}}=2$, ${T}_{c}^{\mathrm{exp}}\ensuremath{\sim}84\phantom{\rule{0.16em}{0ex}}\mathrm{K}$),...
A first-principles model accounts for the wide range of critical temperatures (${T}_{c}$'s) four materials and suggests a parameter that determines ${T}_{c}$ in any high-temperature superconductor.
The electric-current stabilized semimetallic state in the quasi-two-dimensional Mott insulator ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ exhibits an exceptionally strong diamagnetism. Through a comprehensive study using neutron and x-ray diffraction, we show that this nonequilibrium phase assumes crystal structure distinct from those of equilibrium metallic phases realized ruthenates by chemical doping, high pressure, epitaxial strain, which turn leads to electronic band structure. Dynamical...
A genuine feature of projective quantum measurements is that they inevitably alter the mean energy observed system if measured quantity does not commute with Hamiltonian. Compared to classical case, Jacobs proved this additional energetic cost leads a stronger bound on work extractable after single measurement from initially in thermal equilibrium (2009 Phys. Rev. 80 012322). Here, we extend large class feedback-driven engines operating periodically and finite time. The thus implies natural...
The optical properties and the Franz-Keldysh effect at direct band gap of GeSn alloys with Sn concentrations up to 4.2% room temperature were investigated. material was embedded in intrinsic region a Ge heterojunction photodetector on Si substrates. layer structure grown by means ultra-low molecular beam epitaxy. absorption coefficient as function photon energy bandgap energies determined. In all investigated samples, can be observed. A maximum ratio 1.5 determined for 2% voltage swing 3 V.
Excitonic magnetism involving superpositions of singlet and triplet states is expected to arise for two holes in strongly correlated spin-orbit coupled $t_{2g}$ orbitals. However, uncontested material examples its realization are rare. Applying the Variational Cluster Approach square lattice, we find conventional spin antiferromagnetism combined with orbital order at weak excitonic strong coupling. We address specific example Ca$_2$RuO$_4$ using ab-initio modeling conclude it realize despite...
Good-quality polycrystalline BaTiO3 thin films are deposited on MgO substrates by pulsed laserdeposition. The deposition parameters optimized to achieve optical-quality with an attenuation coefficient of 4 dB/cm at the 633-nm wavelength. Thin-film electro-optic Mach-Zehnder modulators fabricated standard lithography and ion-beam etching. waveguides patterned ridge type, they ensure single-mode propagation in wavelength range 633-1550 nm. An 22 pm/V is estimated for films.
Vertical germanium on silicon p-i-n photodetectors were grown by molecular beam epitaxy and further processed a quasi-planar mesa process. In this paper the influence of -top contact layer optical responsivity was investigated. The realized as highly antimony-doped heterostructure. With additional heterostructure top (relaxed relaxed germanium), photodetector broadened. visible wavelength cutoff shifted to , whereas long remained at .
Starting from an effective two-dimensional two-band model for infinite-layered nickelates, consisting of bands obtained $d$- and $s$-like orbitals, we investigate to which extent it can be mapped onto a single-band Hubbard model. We identify screening the more itinerant band as important driver. In absence one strongly correlated gives antiferromagnetic ground state. For weak screening, strong correlations push electrons out $s$ so that undoped nickelate remains Mott insulator with...
The results of numerical simulations based on finite-element methods for thermally induced birefringence in Nd:YAG crystal rods are compared with measurements and analytical solutions. A novel solution inhomogeneous pumping is presented. It shown that the behavior very sensitive to pump geometry.
Electronic properties of single-walled carbon nanotubes intercalated with lithium are investigated by NMR. $^{13}\mathrm{C}$ NMR experiments reveal a metallic ground state for all the following stoichiometries ${\mathrm{LiC}}_{x}$ $x=10$, 7, and 6. A continuous increase density states at Fermi level according to Li concentration is observed up $x\ensuremath{\approx}6$. From $^{7}\mathrm{Li}$ NMR, evidence inequivalent sites reported, corresponding preferential intercalation binding between C.
We have grown c-axis oriented epitaxial thin films of the bilayered perovskite ${\mathrm{La}}_{2\ensuremath{-}2x}{\mathrm{Sr}}_{1+2x}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ $(x=0.3,0.4)$ by laser molecular beam epitaxy on ${\mathrm{NdGaO}}_{3}$ and ${\mathrm{SrTiO}}_{3}$ substrates. X-ray diffraction high-resolution transmission electron microscopy (TEM) revealed excellent quality phase purity films. However, a high density stacking faults could also be detected TEM. A comparison magnetotransport...
Ge on Si p-i-n photodetectors were grown by molecular beam epitaxy minimizing tensile strain. The slope of the absorption curve changes a factor 2 under varying voltages due to clearly observable Franz-Keldysh-Effect.