The phase diagrams of quasi two-dimensional organic superconductors display a plethora of fundamental phenomena associated with strong electron correlations, such as unconventional superconductivity, metal-insulator transitions, frustrated magnetism and spin liquid behavior. We analyze a minimal model for these compounds, the Hubbard model on an anisotropic triangular lattice, using cutting-edge quantum embedding methods respecting the lattice symmetry. We demonstrate the existence of unconventional superconductivity by directly entering the symmetry-broken phase. We show that the crossover from the Fermi liquid metal to the Mott insulator is associated with the formation of a pseudogap. The predicted momentum-selective destruction of the Fermi surface into hot and cold regions provides motivation for further spectroscopic studies. Our results are in remarkable agreement with experimental phase diagrams of $\kappa$-BEDT organics.

The recently proposed center-focused post-processing procedure [Phys. Rev. Res. 2, 033476 (2020)] of cellular dynamical mean-field theory suggests that central sites of large impurity clusters are closer to the exact solution of the Hubbard model than the edge sites. In this paper, we systematically investigate results in the spirit of this center-focused scheme for several cluster sizes up to 8×8 in and out of particle-hole symmetry. First we analyze the metal-insulator crossovers and transitions of the half-filled Hubbard model on a simple square lattice. We find that the critical interaction of the crossover is reduced with increasing cluster sizes and the critical temperature abruptly drops for the 4×4 cluster. Second, for this cluster size, we apply the center-focused scheme to a system with more realistic tight-binding parameters, investigating its pseudogap regime as a function of temperature and doping, where we find doping dependent metal-insulator crossovers, Lifshitz transitions and a strongly renormalized Fermi-liquid regime. Additionally to diagnosing the real space origin of the suppressed antinodal spectral weight in the pseudogap regime, we can infer hints towards underlying charge ordering tendencies.

We study the magnetic and spectral properties of a single-band Hubbard model for the infinite-layer nickelate compound LaNiO 2 . As spatial correlations turn out to be the key ingredient for understanding its physics, we use two complementary extensions of the dynamical mean-field theory to take them into account: the cellular dynamical mean-field theory and the dynamical vertex approximation. Additionally to the systematic analysis of the doping dependence of the non-Curie-Weiss behavior of the uniform magnetic susceptibility, we provide insight into its relation to the formation of a pseudogap regime by the calculation of the one-particle spectral function and the magnetic correlation length. The latter is of the order of a few lattice spacings when the pseudogap opens, indicating a strong-coupling pseudogap formation in analogy to cuprates.

We report a comprehensive study of magnetic correlations in LaNiO_2, a parent compound of the recently discovered family of infinite-layer (IL) nickelate superconductors, using multiple experimental and theoretical methods. Our specific heat, muon-spin rotation (μSR), and magnetic susceptibility measurements on polycrystalline LaNiO_2 show that long-range magnetic order remains absent down to 2 K. Nevertheless, we detect residual entropy in the low-temperature specific heat, which is compatible with a model fit that includes paramagnon excitations. The μSR and low-field static and dynamic magnetic susceptibility measurements indicate the presence of short-range magnetic correlations and glassy spin dynamics, which we attribute to local oxygen non-stoichiometry in the average infinite-layer crystal structure. This glassy behavior can be suppressed in strong external fields, allowing us to extract the intrinsic paramagnetic susceptibility. Remarkably, we find that the intrinsic susceptibility shows non-Curie-Weiss behavior at high temperatures, in analogy to doped cuprates that possess robust non-local spin fluctuations. The distinct temperature dependence of the intrinsic susceptibility of LaNiO_2 can be theoretically understood by a multi-method study of the single-band Hubbard model in which we apply complementary cutting-edge quantum many-body techniques (dynamical mean-field theory, cellular dynamical mean-field theory and the dynamical vertex approximation) to investigate the influence of both short- and long-ranged correlations. Our results suggest a profound analogy between the magnetic correlations in parent (undoped) IL nickelates and doped cuprates.

While calculations and measurements of single-particle spectral properties often offer the most direct route to study correlated electron systems, the underlying physics may remain quite elusive, if information at higher particle levels is not explicitly included. Here, we present a comprehensive overview of the different approaches which have been recently developed and applied to identify the dominant two-particle scattering processes controlling the shape of the one-particle spectral functions and, in some cases, of the physical response of the system. In particular, we will discuss the underlying general idea, the common threads and the specific peculiarities of all the proposed approaches. While all of them rely on a selective analysis of the Schwinger-Dyson (or the Bethe-Salpeter) equation, the methodological differences originate from the specific two-particle vertex functions to be computed and decomposed. Finally, we illustrate the potential strength of these methodologies by means of their applications the two-dimensional Hubbard model, and we provide an outlook over the future perspective and developments of this route for understanding the physics of correlated electrons.

Besides the chemical constituents, it is the lattice geometry that controls the most important material properties. In many interesting compounds, the arrangement of elements leads to pronounced anisotropies, which reflect into a varying degree of quasi-two-dimensionality of their low-energy excitations. Here we start by classifying important families of correlated materials according to a simple measure for the tetragonal anisotropy of their ab initio electronic (band) structure. Second, we investigate the impact of a progressively larger anisotropy in driving the nonlocality of many-body effects. To this end, we tune the Hubbard model from isotropic cubic in three dimensions to the two-dimensional limit and analyze it using the dynamical vertex approximation. For sufficiently isotropic hoppings, we find the low-energy self-energy to be well separable into a static nonlocal and a dynamical local contribution. While the latter could potentially be obtained from dynamical mean-field approaches, we find the former to be nonnegligible in all cases. Further, by increasing the model's anisotropy, we quantify the degree of quasi-two-dimensionality which causes this ``space-time separation'' to break down. Our systematic analysis improves the general understanding of electronic correlations in anisotropic or layered materials and heterostructures and provides useful guidance for future realistic studies.

To fathom the mechanism of high-temperature ($T_{rm c}$) superconductivity, the dynamical vertex approximation (D$Gamma$A) is evoked for the two-dimensional repulsive Hubbard model. After showing that our results well reproduce the cuprate phase diagram with a reasonable $T_{rm c}$ and dome structure, we keep track of the scattering processes that primarily affect $T_{rm c}$. We find that local particle-particle diagrams significantly screen the bare interaction, which in turn suppress the pairing interaction. Hence we identify such vertex corrections as one of the main oppressors of $T_{rm c}$. This may provide a hint for boosting the pairing strength, and hence toward higher $T_{rm c}$.

Recently, diagrammatic extensions of dynamical mean field theory (DMFT) have been proposed for including short- and long-range correlations beyond DMFT on an equal footing. We employ one of these, the dynamical vertex approximation (DΓA), and study the two-dimensional Hubbard model on a square lattice. We define two transition lines in the phase diagram which correspond, respectively, to the opening of the gap in the nodal direction and throughout the Fermi surface. Our self-energy data show that the evolution between the two regimes occurs in a gradual way (crossover) and also that at low enough temperatures the whole Fermi surface is always gapped. Furthermore, we present a comparison of our DΓA calculations at a parameter set where data obtained by other techniques are available.

Mesoporous silica nanoparticles have proved to be efficient stimuli‐responsive controlled release systems for drug delivery when functionalized with nanovalves. Nucleic acid aptamers have recently been adapted to function as novel nanovalves, so‐called “aptavalves,” with molecular‐recognition capabilities and target concentration‐dependent actuation in nanopore‐controlled drug delivery and membrane separation systems. The working mechanism of aptavales relies on their structural rearrangement triggered by a specific target molecule. As a consequence, a controlled and concentration‐dependent release of payload occurs rendering this system particularly appealing for therapeutic applications. However, straightforward monitoring techniques are necessary in order to elucidate the function of aptavalves in situ and varying experimental conditions. Here, the structure‐switching mechanical movements of an ATP‐responsive aptavalve on the surface of mesoporous silica are characterized in real‐time and in situ using circular dichroism (CD). The experimental data obtained on the aptavalve actuation are in excellent agreement with the payload release kinetics determined by fluorescence measurements. It is shown that CD serves as a reliable real‐time analysis of the function of aptalvalves, and that the results obtained obey furthermore standard controlled release models. This allows in principle to pre‐determine the release rate of the modified silica particles according to particular application requirements.

This paper ties to Fuon Theory, where functional icons are suggested to phrase standardized functional units. Having functional unit parameters at hand, products that can be described by these parameters can be put into one family. This further helps to compare the environmental performances of products that fall into the same family.In this paper, a fuon for digital storage devices is developed and tested. The fuon can be used to phrase the functional units of a variety of products such as magnetic hard-discs, USB flash drives, SD cards or SSD drives. The functional unit parameters are derives for the fuon and its applicability is tested through different statistic tests.

In 2010 a new designer drug 4-methylamphetamine was detected in an amphetamine mixture. The structure was elucidated by GC-MS after electron ionization (EI) and chemical ionization (CI) with methane as reagent gas, product ion spectrometry (EI-MS/MS with argon as collision gas under normalized conditions) of the immonium ion, and by NMR spectroscopy. Additionally, the acetyl, the trifluoroacetyl, the heptafluorobutyryl, and the formyl derivatives of 4-methylamphetamine have been prepared and measured on GC-MS.