Strong correlation referes to electron correlation effects inadequately described by DFT and single-reference methods like Coupled-Clusters. Examples for such systems are dissociation fragments (chemical bond breaking)[1] and partially occupied close-degenerate orbitals, for example in transition metals. Accurate treatment is possible by wave function based multi-reference methods, but...
Due to strong spin-orbit coupling and non-centrosymmetric crystal structure, the narrow band-gap semiconductor BiTeI hosts Rashba-split surface and bulk bands. This makes BiTeI a promising material for the generation of spin-polarized currents. It is intrinsically n-doped and exhibits additional strong band-bending at its polar surfaces, leading to partially occupied electron- and hole-like...
Magnetic impurities on a superconductor act as scattering centers for the Cooper pairs of the latter and thereby induce a bound state, called Yu-Shiba-Rusinov state, in their vicinity. The spatial extent of these Yu-Shiba-Rusinov states is of several nanometers which allows for hybridization between them.
Here, we observe the formation of a Kagome lattice after deposition of...
We have studied the laser-induced magnetization dynamics of single-crystalline Gd(0001) thin films with time- and angle-resolved photoemission spectroscopy (tr-ARPES). Our earlier measurements showed a magnetic non-equilibrium in the valence bands [1,2], between the valence band and the 4f systems [3], and in the surface state [4]. All these measurements share a common excitation energy of...
Terahertz spectroscopy is a powerful tool to probe numerous low energy excitations. However, there are still challenges regarding broadband, gap-free and efficient sources of terahertz radiation driven by a compact femtosecond oscillator.
In our experiments, we employ laser pulses (duration 10 fs, center wavelength 800 nm, repetition rate 80 MHz, pulse energy 2.5 nJ) from a laser oscillator...
A small polaron can be modeled by a supercell with a hole or an electron in periodic boundary conditions. In order to correctly cover long-range contribution, very large supercells are often needed, which makes advanced first-principles simulations prohibitively expensive to run. In this work, we propose a corrected model to efficiently describe the lattice distortion due to the long-range...
The difficulty to reveal the atomic structure of bulk amorphous materials can be overcome using a thin film approach. The development of an amorphous 2D silica bilayer has recently allowed deriving the atomic positions by using scanning tunnelling microscopy (STM) [1], atomic force microscopy (AFM) [2] and transmission electron microscopy (TEM) [3].
In order to establish a general...
We rely on hybrid QM:QM methods that combine high-level MP2 on cluster models with low-level DFT+D2 on periodic models to obtain accurate potential energy surfaces (PESs) for even extended and complex periodic systems. The hybrid MP2:(DFT+D2) PESs are counterpoise corrected (CPC) for the basis set superposition error (BSSE) and extrapolated to the complete basis set (CBS) limit. A posteriori,...
Nanoporous gold has emerged as a promising, highly selective catalyst material for a variety of partial oxidation reactions at low temperatures. Structural aspects and admixtures with other metals, for example copper and silver have been investigated to gain insight in the catalytic properties of this material system. Single crystal surfaces, studied under ultra-high vacuum conditions, can...
Surface Phonon Polaritons (SPhP) are recently investigated as an alternative building block for mid-infrared (MIR) nanophotonic applications, promising to possibly solve the intrinsic loss problem of plasmonics [1]. SPhPs arise in polar dielectrics due to IR-active phonon resonances leading to negative permittivity between transverse and longitudinal optical phonon frequencies, a region called...
Scanning Tunneling Microscopy (STM) atomically resolved 2D-silica in both, the amorphous [1] and the crystalline state, leading to a structural comparison of the two phases [2]. Resolving dynamic changes in 2D network structures can give indications for the fundamental processes at the atomic scale occurring during glass-transformation.
With the aim of monitoring dynamic processes during the...
At finite temperature, the silver-cluster catalysts could have transient meta-stable structures with spin states higher than those of zero kelvin stable structures (singlets for an even number of silver atoms). These transient structures could be crucial in activating adsorbed species like O$_2$. In this work, the temperature-dependent relative stability of Ag$_n$ and Ag$_n$O$_2$ ($n=4,8$)...
In search of a replacement for the expensive and scarce indium in indium-tin oxide (ITO), which is mostly used in transparent electrodes nowadays, zinc-tin oxide (ZTO) has proven to be a promising candidate.
In this study we present the effect of aging and oxygen content of the PtO$_\mathrm{x}$ contact on the efficiency of ZTO diodes. It is found that a high oxygen content in the sputter gas...
With the improvement of efficiency and lower cost, thermoelectric devices make their way into more commercial applications. [1] They have been used to improve efficiency of cars [2], steam turbines[3] and to generate electricity in deep space exploration. [4] One of the strategies to improve the efficiency is lowering the thermal conductivity of the thermoelectric device. [5] The cost can be...
Magnetization reversal, spin transfer torque, giant magnetoresistance [1] and the emission of terahertz (THz) radiation [2] are intriguing spintronic applications. They all require controlled generation and manipulation of spin currents. Promising candidates to generate spin currents for high speed spin information processing are the anomalous and spin Hall effects (AHE, SHE), whose inverse...
