08 Fakultät Mathematik und Physik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/9
Browse
16 results
Search Results
Item Open Access Bell-state measurement exceeding 50% success probability with linear optics(2023) Bayerbach, Matthias J.; D’Aurelio, Simone E.; Loock, Peter van; Barz, StefanieItem Open Access Photo-excited dynamics in the excitonic insulator Ta2NiSe5(2018) Werdehausen, Daniel; Takayama, Tomohiro; Albrecht, Gelon; Lu, Yangfan; Takagi, Hidenori; Kaiser, StefanThe excitonic insulator is an intriguing correlated electron phase formed of condensed excitons. A promising candidate is the small band gap semiconductor Ta2NiSe5. Here we investigate the quasiparticle and coherent phonon dynamics in Ta2NiSe5 in a time resolved pump probe experiment. Using the models originally developed by Kabanov et al for superconductors (Kabanov et al 1999 Phys. Rev. B 59 1497), we show that the material’s intrinsic gap can be described as almost temperature independent for temperatures up to about 250 K to 275 K. This behavior supports the existence of the excitonic insulator state in Ta2NiSe5. The onset of an additional temperature dependent component to the gap above these temperatures suggests that the material is located in the BEC-BCS crossover regime. Furthermore, we show that this state is very stable against strong photoexcitation, which reveals that the free charge carriers are unable to effectively screen the attractive Coulomb interaction between electrons and holes, likely due to the quasi 1D structure of Ta2NiSe5.Item Open Access Measurements of entropic uncertainty relations in neutron optics(2020) Demirel, Bülent; Sponar, Stephan; Hasegawa, YujiThe emergence of the uncertainty principle has celebrated its 90th anniversary recently. For this occasion, the latest experimental results of uncertainty relations quantified in terms of Shannon entropies are presented, concentrating only on outcomes in neutron optics. The focus is on the type of measurement uncertainties that describe the inability to obtain the respective individual results from joint measurement statistics. For this purpose, the neutron spin of two non-commuting directions is analyzed. Two sub-categories of measurement uncertainty relations are considered: noise-noise and noise-disturbance uncertainty relations. In the first case, it will be shown that the lowest boundary can be obtained and the uncertainty relations be saturated by implementing a simple positive operator-valued measure (POVM). For the second category, an analysis for projective measurements is made and error correction procedures are presented.Item Open Access Character of doped holes in Nd1-xSrxNiO2(2021) Plienbumrung, Tharathep; Schmid, Michael Thobias; Daghofer, Maria; Oleś, Andrzej M.We investigate charge distribution in the recently discovered high-𝑇𝑐 superconductors, layered nickelates. With increasing value of charge-transfer energy, we observe the expected crossover from the cuprate to the local triplet regime upon hole doping. We find that the 𝑑-𝑝 Coulomb interaction 𝑈𝑑𝑝 makes Zhang-Rice singlets less favorable, while the amplitude of local triplets at Ni ions is enhanced. By investigating the effective two-band model with orbitals of 𝑥2-𝑦2 and s symmetries we show that antiferromagnetic interactions dominate for electron doping. The screened interactions for the s band suggest the importance of rare-earth atoms in superconducting nickelates.Item Open Access Single-band versus two-band description of magnetism in infinite-layer nickelates(2023) Plienbumrung, Tharathep; Daghofer, Maria; Morée, Jean-Baptiste; Oleś, Andrzej M.We present a weak-coupling analysis of magnetism in infinite-layer nickelates, where we compare a single-band description with a two-band model. Both models predict that (i) hybridization due to hopping is negligible, and (𝑖𝑖) the magnetic properties are characterized by very similar dynamic structure factors, 𝑆(𝑘⃗ ,𝜔), at the points (𝜋,𝜋,0) and (𝜋,𝜋,𝜋). This gives effectively a two-dimensional description of the magnetic properties.Item Open Access Proximate ferromagnetic state in the Kitaev model material α-RuCl3(2021) Suzuki, H.; Liu, H.; Bertinshaw, J.; Ueda, K.; Kim, H.; Laha, S.; Weber, D.; Yang, Z.; Wang, L.; Takahashi, H.; Fürsich, K.; Minola, M.; Lotsch, B. V.; Kim, B. J.; Yavaş, H.; Daghofer, M.; Chaloupka, J.; Khaliullin, G.; Gretarsson, H.; Keimer, B.α-RuCl3 is a major candidate for the realization of the Kitaev quantum spin liquid, but its zigzag antiferromagnetic order at low temperatures indicates deviations from the Kitaev model. We have quantified the spin Hamiltonian of α-RuCl3 by a resonant inelastic x-ray scattering study at the Ru L3 absorption edge. In the paramagnetic state, the quasi-elastic intensity of magnetic excitations has a broad maximum around the zone center without any local maxima at the zigzag magnetic Bragg wavevectors. This finding implies that the zigzag order is fragile and readily destabilized by competing ferromagnetic correlations. The classical ground state of the experimentally determined Hamiltonian is actually ferromagnetic. The zigzag state is stabilized by quantum fluctuations, leaving ferromagnetism - along with the Kitaev spin liquid - as energetically proximate metastable states. The three closely competing states and their collective excitations hold the key to the theoretical understanding of the unusual properties of α-RuCl3 in magnetic fields.Item Open Access Monoclinic SrIrO3 : a Dirac semimetal produced by non-symmorphic symmetry and spin-orbit coupling(2018) Takayama, Tomohiro; Yaresko, Alexander N.; Takagi, HidenoriSrIrO3 crystallizes in a monoclinic structure of distorted hexagonal perovskite at ambient pressure. The transport measurements show that the monoclinic SrIrO3 is a low-carrier density semimetal, as in the orthorhombic perovskite polymorph. The electronic structure calculation indicates a semimetallic band structure with Dirac bands at two high-symmetry points of Brillouin zone only when spin-orbit coupling is incorporated, suggesting that the semimetallic state is produced by the strong spin-orbit coupling. We argue that the Dirac bands are protected by the non-symmorphic symmetry of lattice.Item Open Access An atomic‐scale vector network analyzer(2024) Baumann, Susanne; McMurtrie, Gregory; Hänze, Max; Betz, Nicolaj; Arnhold, Lukas; Malavolti, Luigi; Loth, SebastianElectronic devices have been ever‐shrinking toward atomic dimensions and have reached operation frequencies in the GHz range, thereby outperforming most conventional test equipment, such as vector network analyzers (VNA). Here the capabilities of a VNA on the atomic scale in a scanning tunneling microscope are implemented. Nonlinearities present in the voltage‐current characteristic of atoms and nanostructures for phase‐resolved microwave spectroscopy with unprecedented spatial resolution at GHz frequencies are exploited. The amplitude and phase response up to 9.3 GHz is determined, which permits accurate de‐embedding of the transmission line and application of distortion‐corrected waveforms in the tunnel junction itself. This enables quantitative characterization of the complex‐valued admittance of individual magnetic iron atoms which show a lowpass response with a magnetic‐field‐tunable cutoff frequency.Item Open Access Correlations for computation and computation for correlations(2021) Demirel, Bülent; Weng, Weikai; Thalacker, Christopher; Hoban, Matty; Barz, StefanieQuantum correlations are central to the foundations of quantum physics and form the basis of quantum technologies. Here, our goal is to connect quantum correlations and computation: using quantum correlations as a resource for computation - and vice versa, using computation to test quantum correlations. We derive Bell-type inequalities that test the capacity of quantum states for computing Boolean functions within a specific model of computation and experimentally investigate them using 4-photon Greenberger-Horne-Zeilinger (GHZ) states. Furthermore, we show how the resource states can be used to specifically compute Boolean functions - which can be used to test and verify the non-classicality of the underlying quantum states. The connection between quantum correlation and computability shown here has applications in quantum technologies, and is important for networked computing being performed by measurements on distributed multipartite quantum states.Item Open Access Atomistic simulation of ultra-short pulsed laser ablation of Al : an extension for non-thermalized electrons and ballistic transport(2022) Eisfeld, Eugen; Förster, Daniel; Klein, Dominic; Roth, JohannesFor our model material aluminum, the influence of laser pulse duration in the range between 0.5 and 16 ps on the ablation depth is investigated in a computational study with a hybrid approach, combining molecular dynamics with the well known two-temperature model. A simple, yet expedient extension is proposed to account for the delayed thermalization as well as ballistic transport of the excited electrons. Comparing the simulated ablation depths to a series of our own experiments, the extension is found to considerably increase the predictive power of the model.