arXiv subjects

A. Östlin

Publications and source records attributed to A. Östlin.

18 recordsLinked to original sources

arXiv2026

Analytical results of Typical Medium Theory for the Bethe lattice with Cauchy disorder

We present a combined numerical and analytically tractable realization of the typical medium theory (TMT) for Anderson localization on the infinite-connectivity Bethe lattice with Cauchy-distributed on-site disorder. Exploiting the special properties of the Cauchy distribution and the Bethe lattice, we derive an analytical expression for the typical density of states (TDOS) and obtain a simplified TMT self-consistency scheme. We show that the TDOS at the band center decreases linearly with disorder strength and vanishes at the critical disorder $W_c=D/2$. The resulting $ω$--$W$ phase diagram reveals the continuous collapse of the mobility edge and the disappearance of extended states.

cond-mat.dis-nn↗

arXiv2026

Correlated electronic states at a ferromagnetic oxide interface

We propose a minimal tight-binding model for the electronic interface layer of the LaAlO$_3$/SrTiO$_3$ heterostructure with oxygen vacancies. In this model, the effective carriers are subject to oxygen vacancy induced magnetic impurities. Both the effects of random on-site potentials and Zeeman-like exchange interactions between correlated carriers and magnetic impurities are taken into account. By applying the combined coherent potential approximation (CPA) and dynamical mean-field theory (DMFT) for a ferromagnetic state, we uncover a disordered Fermi-liquid regime for the majority-spins and a low energy scale which controls the transport of the minority-spin carriers, both induced by the magnetic impurities.

cond-mat.str-el↗

arXiv2025

Suppression of magnetism in Co$_3$Sn$_2$S$_2$ under external pressure

The ability to control the magnetic state provides a powerful means to tune the underlying band topology, enabling transitions between distinct electronic phases and the emergence of novel quantum phenomena. In this work, we address the evolution of ferromagnetic state upon applying external pressures up to 10.8~GPa using a combined experimental and theoretical study. The standard \emph{ab initio} Density Functional Theory computation including ionic relaxations grossly overestimates the unit cell magnetization as a function of pressure. In our theoretical analysis we identify two possible mechanisms to remedy this shortcoming. Matching the experimental observations is achieved by a symmetry-preserving adjustment of the sulfur atoms position within the unit cell. Alternatively, we explore various combinations of the exchange and correlation parts of the effective potential which reproduce the experimental magnetization, the structural parameters and the measured optical conductivity spectra. Thus, the pressure-dependent behavior of magnetization demands a careful theoretical treatment and analysis of theoretical and experimental data.

cond-mat.mtrl-sci↗

arXiv2025

Quasiparticle Fermi surfaces of niobium and niobium-titanium alloys at high pressure

The electronic structure of pure niobium and the niobium-titanium alloy Nb$_{0.44}$Ti$_{0.56}$ in the bcc-phase at pressures up to $250$ GPa is investigated, to reveal possible factors conducing toward the robust superconductivity reported for Ti-doped niobium upon a considerable volume reduction. We model the structural disorder using the coherent potential approximation, and the electronic correlations are taken into account using dynamical mean-field theory. At high pressure, a significant change in the topology of the Fermi surface is observed, while electronic correlations weaken with increasing pressure. Thus, the normal state of Nb$_{0.44}$Ti$_{0.56}$ is found to be a Fermi liquid with a well-defined Fermi surface, and well-defined quasiparticles near it. The systematic study of the impact of disorder upon the Fermi surface at such ultra high pressures allows notable insights into the nature of the electronic states near the Fermi level, i.e., within the energy scale relevant for superconducting pairing. Furthermore, our results clearly indicate the necessity of further experimental Fermi surface explorations.

cond-mat.supr-con↗

arXiv2024

Superconducting transition temperatures of pure vanadium and vanadium-titanium alloys in the presence of dynamical electronic correlations

Ordinary superconductors are widely assumed insensitive to small concentrations of random nonmagnetic impurities, whereas strong disorder suppresses superconductivity, ultimately leading to a superconductor-insulator transition. In between these limiting cases, a most fascinating regime may emerge where disorder enhances superconductivity. This effect is discussed here for the $β$-phase of vanadium-titanium alloys. Disorder is modeled using the coherent potential approximation while local electronic interactions are treated using dynamical mean-field theory. The McMillan formula is employed to estimate the superconducting transition temperature, showing a maximum at a Ti concentration of around $0.33$ for a local Coulomb interaction $U$ in the range of $2$ to $3$ eV. Our calculations quantitatively agree with the experimentally observed concentration dependent increase of $T_c$, and its maximal value of about $20\%$.

cond-mat.supr-con↗

arXiv2021

Electronic correlations and Fermi liquid behavior of intermediate-band states in titanium-doped silicon

We study the nature of the electronic states in the intermediate band formed by interstitial titanium in silicon. Our single-site description combines effects of electronic correlations, captured by dynamical mean-field theory, and disorder, modeled using the coherent potential approximation and the typical medium mean-field theory. For all studied concentrations an extended metallic state with a strongly depleted density of states at the Fermi level is obtained. The self-energy is characteristic to Fermi-liquids and for certain temperatures reveals the existence of coherent quasi-particles.

cond-mat.str-el↗

arXiv2021

Dynamical mean-field theory of the Anderson-Hubbard model with local and non-local disorder in tensor formulation

To explore correlated electrons in the presence of local and non-local disorder, the Blackman-Esterling-Berk method for averaging over off-diagonal disorder is implemented into dynamical mean-field theory using tensor notation. The impurity model combining disorder and correlations is solved using the recently developed fork tensor-product state solver, which allows one to calculate the single particle spectral functions on the real-frequency axis. In the absence of off-diagonal hopping, we establish exact bounds of the spectral function of the non-interacting Bethe lattice with coordination number $Z$. In the presence of interaction, the Mott insulating paramagnetic phase of the one-band Hubbard model is computed at zero temperature in alloys with site- and off-diagonal disorder. When the Hubbard $U$ parameter is increased, transitions from an alloy band-insulator through a correlated metal into a Mott insulating phase are found to take place.

cond-mat.str-el↗

arXiv2020

Ab initio typical medium theory of substitutional disorder

By merging single-site typical medium theory with density functional theory we introduce a self-consistent framework for electronic structure calculations of materials with substitutional disorder which takes into account Anderson localization. The scheme and details of the implementation are presented and applied to the hypothetical alloy Li$_{c}$Be$_{1-c}$, and the results are compared with those obtained with the coherent potential approximation. Furthermore we demonstrate that Anderson localization suppresses ferromagnetic order for a very low concentration of (i) carbon impurities substituting oxygen in MgO$_{1-c}$C$_{c}$, and (ii) manganese impurities substituting magnesium in Mg$_{1-c}$Mn$_c$O for the low-spin magnetic configuration.

cond-mat.dis-nn↗

arXiv2020

Lattice dynamics of palladium in the presence of electronic correlations

We compute the phonon dispersion, density of states, and the Grüneisen parameters of bulk palladium in the combined density functional theory (DFT) and dynamical mean-field theory (DMFT). We find good agreement with experimental results for ground state properties (equilibrium lattice parameter and bulk modulus) and the experimentally measured phonon spectra. We demonstrate that at temperatures $T \lesssim 20~K$ the phonon frequency in the vicinity of the Kohn anomaly, $ω_{T1}({\bf q}_{K})$, strongly decreases. This is in contrast to DFT where this frequency remains essentially constant in the whole temperature range. Apparently correlation effects reduce the restoring force of the ionic displacements at low temperatures, leading to a mode softening.

cond-mat.str-el↗

arXiv2018

Correlated electronic structure with uncorrelated disorder

We introduce a computational scheme for calculating the electronic structure of random alloys that includes electronic correlations within the framework of the combined density functional and dynamical mean-field theory. By making use of the particularly simple parameterization of the electron Green's function within the linearized muffin-tin orbitals method, we show that it is possible to greatly simplify the embedding of the self-energy. This in turn facilitates the implementation of the coherent potential approximation, which is used to model the substitutional disorder. The computational technique is tested on the Cu-Pd binary alloy system, and for disordered Mn-Ni interchange in the half-metallic NiMnSb.

cond-mat.str-el↗

arXiv2018

Density functional theory study of vacancy induced magnetism in Li$_{3}$N

The effect of lithium vacancies in the hexagonal structure of $α-$Li$_3$N, is studied within the framework of density functional theory. Vacancies ($\square$) substituting for lithium in $α-$Li$_2$(Li$_{1-x}\square_x$)N are treated within the coherent potential approximation as alloy components. According to our results long range N($p$)-ferromagnetism ($\sim 1$ $μ_B$) sets in for vacancy substitution within the [Li$_2$N] layers ($x \ge 0.7$) with no significant change in unit cell dimensions. By total energies differences we established that in-plane exchange couplings are dominant. Vacancies substituting inter-plane Li, leads to a considerable structural collapse ($c/a \approx 0.7$) and no magnetic moment formation.

cond-mat.mtrl-sci↗

arXiv2018

Magnetic properties of YCo$_5$ compound at high pressure

The crystal structure and magnetic properties of YCo$_5$ compound have been studied by neutron diffraction, in the pressure range $0 \le p \le 7.2 \ GPa$. The experimental data are analyzed together with results from the combined Density Functional and Dynamical Mean-Field Theory. A good agreement between the experimentally determined and calculated values of cobalt moments is shown. Our scenario for the behavior of YCo$_5$ under pressure, is the combined action of the Lifshitz transition with a strong local electron-electron interaction.

cond-mat.str-el↗

arXiv2018

Positron annihilation spectroscopy for the pure and Niobium doped ZrCo$_2$Sn Heusler compound

We perform spin-polarized two-dimensional angular correlation of annihilation radiation (2D-ACAR) calculations for the recently predicted ZrCo$_2$Sn-Weyl Heusler compound within the density functional theory using the generalized gradient approximation (GGA) and its extension GGA+U. We confirm that within the GGA+U method, a pair of Weyl-points are revealed, and that by doping with Niobium, for the composition Nb$_{0.3}$Zr$_{0.7}$Co$_2$Sn, the Weyl points are reaching the Fermi level. Our 2D-ACAR results indicate the existence of the Weyl points, however, within the present calculation, it is uncertain if the smearing at the Fermi level can be attributed to the positron wave function.

cond-mat.str-el↗

arXiv2017

Spin-polarized ballistic conduction through correlated Au-NiMnSb-Au heterostructures

We examine the ballistic conduction through Au-NiMnSb-Au heterostructures consisting of up to four units of NiMnSb in the scattering region. We investigate the dependence of the transmission function computed within the local spin density approximation (LSDA) of the density functional theory (DFT) on the number of half-metallic units in the scattering region. For a single NiMnSb unit the transmission function displays a spin polarization of around 50 % in a window of 1 eV centered around the Fermi level. By increasing the number of layers an almost complete spin polarization of the transmission is obtained in the same energy window. Supplementing the DFT-LSDA calculations with local electronic interactions, of Hubbard-type on the Mn sites, leads to a hybridization between the interface and many-body states. The significant reduction of the spin polarization seen in the density of states is not apparent in the spin-polarization of the conduction electron transmission, which suggests the localized nature of the hybridized interface and many-body induced states.

cond-mat.str-el↗

arXiv2017

Analytic continuation-free Green's function approach to correlated electronic structure calculations

We present a new charge self-consistent scheme combining Density Functional and Dynamical Mean Field Theory, which uses Green's function of multiple scattering-type. In this implementation the many-body effects are incorporated into the Kohn-Sham iterative scheme without the need for the numerically ill-posed analytic continuation of the Green's function and of the self-energy. This is achieved by producing the Kohn-Sham Hamiltonian in the sub-space of correlated partial waves and allows to formulate the Green's function directly on the Matsubara axis. The spectral moments of the Matsubara Green's function enable us to put together the real space charge density, therefore the charge self-consistency can be achieved. Our results for the spectral functions (density of states) and equation of state curves for transition metal elements, Fe, Ni and FeAl compound agree very well with those of Hamiltonian based LDA+DMFT implementations. The current implementation improves on numerical accuracy, requires a minimal effort besides the multiple scattering formulation and can be generalized in several ways that are interesting for applications to real materials.

cond-mat.str-el↗

arXiv2016

The electronic structure of palladium in the presence of many-body effects

Including on-site electronic interactions described by the multi-orbital Hubbard model we study the correlation effects in the electronic structure of bulk palladium. We use a combined density functional and dynamical mean field theory, LDA+DMFT, based on the fluctuation exchange approximation. The agreement between the experimentally determined and the theoretical lattice constant and bulk modulus is improved when correlation effects are included. It is found that correlations modify the Fermi surface around the neck at the $L$-point while the Fermi surface tube structures show little correlation effects. At the same time we discuss the possibility of satellite formation in the high energy binding region. Spectral functions obtained within the LDA+DMFT and $GW$ methods are compared to discuss non-local correlation effects. For relatively weak interaction strength of the local Coulomb and exchange parameters spectra from LDA+DMFT shows no major difference in comparison to $GW$.

cond-mat.str-el↗

arXiv2015

Transmission through correlated Cu$_n$CoCu$_n$ heterostructures

The effects of local electronic interactions and finite temperatures upon the transmission across the Cu$_4$CoCu$_4$ metallic heterostructure are studied in a combined density functional and dynamical mean field theory. It is shown that, as the electronic correlations are taken into account via a local but dynamic self-energy, the total transmission at the Fermi level gets reduced (predominantly in the minority spin channel), whereby the spin polarization of the transmission increases. The latter is due to a more significant $d$-electrons contribution, as compared to the non-correlated case in which the transport is dominated by $s$ and $p$ electrons.

cond-mat.mtrl-sci↗

arXiv2012

One particle spectral function and analytic continuation for many-body implementation in the EMTO method

We investigate one of the most common analytic continuation techniques in condensed matter physics, namely the Padé approximant. Aspects concerning its implementation in the exact muffin-tin orbitals (EMTO) method are scrutinized with special regard towards making it stable and free of artificial defects. The electronic structure calculations are performed for solid hydrogen, and the performance of the analytical continuation is assessed by monitoring the density of states constructed directly and via the Padé approximation. We discuss the difference between the \textbf{k}-integrated and \textbf{k}-resolved analytical continuations, as well as describing the use of random numbers and pole residues to analyze the approximant. It is found that the analytic properties of the approximant can be controlled by appropriate modifications, making it a robust and reliable tool for electronic structure calculations. At the end, we propose a route to perform analytical continuation for the EMTO + dynamical mean field theory (DMFT) method.

cond-mat.mtrl-sci↗