Search results for "Solid-state physics"
showing 10 items of 112 documents
Spinovo rozlisena time-of-flight k-reozlisena fotoemissia Ir-- Kompletny fotoemissny experiment.
2017
Ultramicroscopy 183, 19 - 29 (2017). doi:10.1016/j.ultramic.2017.06.025
Pressure dependence of the exciton absorption and the electronic subband structure of aGa0.47In0.53As/Al0.48In0.52As multiple-quantum-well system
1992
We have measured the optical absorption of a ${\mathrm{Ga}}_{0.47}$${\mathrm{In}}_{0.53}$As/${\mathrm{Al}}_{0.48}$${\mathrm{In}}_{0.52}$As multiple quantum well at 10 K for pressures up to 7 GPa. The energies of optical transitions between heavy- and light-hole subbands and electron levels of the wells show a blueshift with pressure similar to the bulk lowest direct band gap. We observe a decrease with pressure of the energy splitting between heavy- and light-hole subbands with the same quantum number n. From the analysis of the absorption line shape, we have obtained the pressure dependences of exciton binding energies, oscillator strengths, and linewidths. These results are interpreted in…
The Lineshape of Inelastic Neutron Scattering in Relaxor Ferroelectrics
2005
We show that a microscopic reason for the steep drop of the optical phonon branch into an acoustic one (the so-called waterfall effect) in relaxor ferroelectrics may be the coupling of phonons with defects and impurities of different kinds, which is always present in relaxors. Namely, we do not specify the type of impurities but rather represent them as an ensemble of so-called two-level systems (TLS). This approach makes it possible to trace the evolution of the “waterfall” with temperature and the TLS concentration. To facilitate the planning of experiments on inelastic neutron scattering, we present a modification of the so-called Latin hypercube sampling method, which, based on some sig…
Magnetism and Hund's Rule in an Optical Lattice with Cold Fermions
2007
Artificially confined, small quantum systems show a high potential for employing quantum physics in technology. Ultra-cold atom gases have opened an exciting laboratory in which to explore many-particle systems that are not accessible in conventional atomic or solid state physics. It appears promising that optical trapping of cold bosonic or fermionic atoms will make construction of devices with unprecedented precision possible in the future, thereby allowing experimenters to make their samples much more "clean", and hence more coherent. Trapped atomic quantum gases may thus provide an interesting alternative to the quantum dot nanostructures produced today. Optical lattices created by stan…
Emulating Solid-State Physics with a Hybrid System of Ultracold Ions and Atoms
2013
We propose and theoretically investigate a hybrid system composed of a crystal of trapped ions coupled to a cloud of ultracold fermions. The ions form a periodic lattice and induce a band structure in the atoms. This system combines the advantages of scalability and tunability of ultracold atomic systems with the high fidelity operations and detection offered by trapped ion systems. It also features close analogies to natural solid-state systems, as the atomic degrees of freedom couple to phonons of the ion lattice, thereby emulating a solid-state system. Starting from the microscopic many-body Hamiltonian, we derive the low energy Hamiltonian including the atomic band structure and give an…
Dynamics of heavy fermions: Drude response in and
2006
While the effective mass of heavy fermions governs their thermodynamics, the optical properties are dominated by the characteristic relaxation rate which is expected to scale inversely with the effective mass. At the relaxation rate clear features, the so-called Drude response occur in the real and imaginary parts of the complex conductivity. Conventional optical spectroscopy can only indirectly probe the Drude response; thus we use novel broadband microwave spectroscopy to directly measure the frequency-dependent conductivity of UPd2Al3 and UNi2Al3 in the relevant frequency range and unambiguously observe the full low-energy electrodynamics of the heavy fermions including the Drude respons…
High Antiferromagnetic Domain Wall Velocity Induced by Néel Spin-Orbit Torques.
2016
We demonstrate the possibility to drive an antiferromagnetic domain wall at high velocities by fieldlike Neel spin-orbit torques. Such torques arise from current-induced local fields that alternate their orientation on each sublattice of the antiferromagnet and whose orientation depends primarily on the current direction, giving them their fieldlike character. The domain wall velocities that can be achieved by this mechanism are 2 orders of magnitude greater than the ones in ferromagnets. This arises from the efficiency of the staggered spin-orbit fields to couple to the order parameter and from the exchange-enhanced phenomena in antiferromagnetic texture dynamics, which leads to a low doma…
Quantum chemical modelling of "green" luminescence in ABO $ \mathsf {_3}$ perovskites
2002
The origin of the intrinsic excitonic (“green”) luminescence in ABO3 perovskites remains a hot topic over the last quarter of a century. We suggest as a theoretical interpretation for the “green” luminescence in these crystals, the recombination of electron and hole polarons forming a charge transfer vibronic exciton. In order to check quantitatively the proposed model, we performed quantum chemical calculations using the Intermediate Neglect of Differential Overlap (INDO) method combined with the periodic defect model. The luminescence energies calculated for four perovskite crystals are found to be in good agreement with experimental data.
Universal behavior of two-dimensional 3He at low temperatures.
2008
On the example of two-dimensional (2D) 3He we demonstrate that the main universal features of its experimental temperature T - density x phase diagram [see M. Neumann, J. Ny\'{e}ki, J. Saunders, Science 317, 1356 (2007)] look like those in the heavy-fermion metals. Our comprehensive theoretical analysis of experimental situation in 2D 3He allows us to propose a simple expression for effective mass M^*(T,x), describing all diverse experimental facts in 2D 3He in unified manner and demonstrating that the universal behavior of M^*(T,x) coincides with that observed in HF metals.
Dipole surface plasmon in large K N + clusters
1993
The dipole surface plasmon forK N + clusters is analyzed using the RPA sum-rule technique within a semiclassical Density Functional Theory and the spherical jellium model. The theoretical frequencies are blue shifted as compared to the experimental ones. The discrepancies between theory and experiment are reduced when considering non-local energy contributions in the density functional and phenomenologically including atomic lattice effects by means of an electron effective mass and a static dielectric constant.