Faculty of Physics: Research Data
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- Research DataTheoretical Data: Growth of self-integrated atomic quantum wires and junctions of a Mott semiconductor2024-01-08Continued advances in quantum technologies rely on producing nanometer-scale wires. Although several state-of-the-art nanolithographic technologies and bottom-up synthesis processes have been used to engineer these wires, critical challenges remain in growing uniform atomic-scale crystalline wires and constructing their network structures. Here, we discover a simple method to fabricate atomic-scale wires with various arrangements, including stripes, X-junctions, Y-junctions, and nanorings. Single-crystalline atomic-scale wires of a Mott insulator, whose bandgap is comparable to those of wide-gap semiconductors, are spontaneously grown on graphite substrates by pulsed-laser deposition. These wires are one unit cell thick and have an exact width of two and four unit cells (1.4 and 2.8 nm) and lengths up to a few micrometers. We show that the nonequilibrium reaction-diffusion processes may play an essential role in atomic pattern formation. Our findings offer a previously unknown perspective on the nonequilibrium self-organization phenomena on an atomic scale, paving a unique way for the quantum architecture of nano-network.
31 5 - Research DataPhonon renormalization and Pomeranchuk instability in the Holstein model2024-01-09The Holstein model with dispersionless Einstein phonons is one of the simplest models describing electron-phonon interactions in condensed matter. A naive extrapolation of perturbation theory in powers of the relevant dimensionless electron-phonon coupling λ0 suggests that at zero temperature the model exhibits a Pomeranchuk instability characterized by a divergent uniform compressibility at a critical value of λ0 of order unity. In this work, we re-examine this problem using modern functional renormalization group (RG) methods. For dimensions d>3 we find that the RG flow of the Holstein model indeed exhibits a tricritical fixed point associated with a Pomeranchuk instability. This non-Gaussian fixed point is ultraviolet stable and is closely related to the well-known ultraviolet stable fixed point of ϕ3-theory above six dimensions. To realize the Pomeranchuk critical point in the Holstein model at fixed density both the electron-phonon coupling λ0 and the adiabatic ratio ω0/εF have to be fine-tuned to assume critical values of order unity, where ω0 is the phonon frequency and εF is the Fermi energy. However, for dimensions d≤3 we find that the RG flow of the Holstein model does not have any critical fixed points. This rules out a quantum critical point associated with a Pomeranchuk instability in d≤3.
56 3 - Research DataTheory data for: Tuning superconductivity and spin-vortex instabilities in CaKFe4As4 through in-plane antisymmetric strains CaKFe 4 As 4 through in-plane antisymmetric strains2024-05-13Here we present the data for "Tuning superconductivity and spin-vortex instabilities in CaKFe4As4 through in-plane antisymmetric strains CaKFe 4 As 4 through in-plane antisymmetric strains". Given are the SCF input files, and the first ouput file. To obtain the full data with charge densities one can rerun the calculations. It is split to the magnetic orders: hedgehog, and stripe order. Each order has the subdirectories for ground state and strain. The ground state case was used to get a first preconverged charge densities. All other runs are based on this charge density. The strain directories contain two further subdirectory for the type of strain. One is diagonal the other one along the a axis. For both strain cases four different strain values where calculated.
59 6 - Research DataAb initio study of highly tunable charge transfer in β-RuCl3/graphene heterostructures2024-06-25Heterostructures of graphene in proximity to magnetic insulators open the possibility to investigate exotic states emerging from the interplay of magnetism, strain and charge transfer between the layers. Recent reports on the growth of self-integrated atomic wires of $\beta$-RuCl$_3$ on graphite suggest these materials as versatile candidates to investigate these effects. Here we present detailed first principles calculations on the charge transfer and electronic structure of $\beta$-RuCl$_3$/graphene heterostructures and provide a comparison with the work function analysis of the related honeycomb family members $\alpha$-RuX$_3$ (X = Cl,Br,I). We find that proximity of the two layers leads to a hole-doped graphene and electron-doped RuX$_3$ in all cases, which is sensitively dependent on the distance between the two layers. Furthermore, strain effects due to lattice mismatch control the magnetization which itself has a strong effect on the charge transfer. Charge accumulation in $\beta$-RuCl$_3$ strongly drops away from the chain making such heterostructures suitable candidates for sharp interfacial junctions in graphene-based devices.
16 - Research Data8x8 Patch-Antenna-Coupled TeraFET Detector Array for Terahertz Quantum-Cascade-Laser Applications2024-07-31North, Nicholas K.Horbury, Michael D.Kondawar, SanchitKundu, ImonSalih, MohammedKrysl, AnastasiyaLi, LianheLinfield, Edmund H.Freeman, Joshua R.Valavanis, AlexanderLisauskas, AlvydasRoskos, Hartmut G.Monolithically integrated, antenna-coupled field-effect transistors (TeraFETs) are rapid and sensitive detectors for the terahertz range (0.3-10 THz) that can operate at room temperature. We conducted experimental characterizations of a single patch-antenna coupled TeraFET optimized for 3.4 THz operation and its integration into an 8×8 multi-element detector configuration. In this configuration, the entire TeraFET array operates as a unified detector element, combining the output signals of all detector elements. Both detectors were realized using a mature commercial Si-CMOS 65-nm process node. Our experimental characterization employed single-mode Quantum-Cascade Lasers (QCLs) emitting at 2.85 THz and 3.4 THz. The 8x8 multi-element detector yields two major improvements for sensitive power detection experiments. First, the larger detector area simplifies alignment and enhances signal stability. Second, the reduced detector impedance enabled the implementation of a TeraFET+QCL system capable of providing a -3 dB modulation bandwidth up to 21 MHz, which is currently limited primarily by the chosen readout circuitry. Finally, we validate the system’s performance by providing high resolution gas spectroscopy data for methanol vapor around 3.4 THz, where a detection limit of 1.6e-5 absorbance, or 2.6e11 molecules/cm3 was estimated under optimal coupling conditions.
70 4 - Research DataInterconnected renormalization of Hubbard bands and Green's function zeros in Mott insulators induced by strong magnetic fluctuations2024-10-10We analyze the role of spatial electronic correlations and, in particular, of the magnetic fluctuations in Mott insulators. A half-filled Hubbard model is solved at large strength of the repulsion 𝑈 on a two-dimensional square lattice using an advanced diagrammatic approach capable of going beyond Hartree-Fock and single-site dynamical mean-field theories. We show that at high temperatures, when the magnetic fluctuations are weak, the electronic self-energy of the system is mainly local and is well reproduced by the atomic (Hubbard-I) approximation. Upon lowering the temperature toward the magnetically ordered phase, the nonlocality of the self-energy becomes crucial in determining the momentum dispersion of the Hubbard bands and the Green's function zeros. We therefore establish a precise link between Luttinger surface, nonlocal correlations and spectral properties of the Hubbard bands.
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