arXiv subjects

Stefan Kurth

Publications and source records attributed to Stefan Kurth.

At least 19 recordsLinked to original sources

arXiv2026

Doping-driven Mott transition from steady-state density functional theory

We describe the doping-driven Mott transition in the Hubbard model within the framework of steady-state density functional theory, or i-DFT. In order to access the many-body spectral function in i-DFT, an approximation to the exchange-correlation (xc) bias at arbitrary density and current is required. By making use of Fermi-liquid theory, we derive conditions on the xc bias of i-DFT in terms of the quasiparticle weight, thus establishing a clear connection between i-DFT and Fermi-liquid theory. The Fermi liquid conditions are then employed to guide the construction of an approximation to the xc bias functional. Numerical results obtained with this functional demonstrate that the doping-driven Mott transition can indeed be captured with i-DFT. More generally, our i-DFT approach to calculate spectral functions establishes an explicit form for the functional relationship between the many-body spectral function and the ground state electronic density.

cond-mat.str-el↗

arXiv2026

Spectral and transmission properties of multiple correlated quantum dots made simple

Steady-state density functional theory, called i-DFT, is employed to compute spectral and transmission properties of general interacting nanoscale regions coupled to electronic reservoirs. Exchange-correlation functionals are constructed for different interactions and coupling geometries. The potential of the method is illustrated by applications to various multiple quantum dots from the Coulomb blockade to the Kondo regime, capturing phenomena such as quantum phase transitions. The results are in excellent agreement with many-body approaches at a fraction of the computational cost.

cond-mat.mes-hall↗

arXiv2026

Fano Resonances in Mismatched C$_3$N Nanoribbon Junctions

Mismatched junctions formed by two C$_3$N zigzag nanoribbons of different widths provide a useful setting for studying quantum interference effects involving edge state transport. A crucial ingredient for this interference to appear is, besides the presence of edge states, the formation of localized interface states at the mismatched interface of the junction. At the level of a tight-binding model it is shown that, by means of an external gate potential, one of the edge state energy bands can selectively be shifted into the energy range of the localized interface states. The resulting coupling between the edge and localized interface states gives rise to pronounced Fano resonances in both the density of states and the transmission spectrum with line shapes well described by the canonical Fano formula. Furthermore, it is found that the geometrical mismatch of the junction not only determines the number of resonances but also the energetic orientation of their asymmetric line shapes. These results identify mismatched C$_3$N nanojunctions as a tunable and robust platform for engineering interference-driven transport.

cond-mat.mes-hall↗

arXiv2025

Analytic approach to thermoelectric transport in double quantum dots

A recently proposed analytical solution for the equations of motion of the one-body Green function of the double quantum dot is extended to the out-of-equilibrium situation. By solving a linear system for the density correlators, not only the local occupations but also charge and heat currents as well as transport coefficients and the figure of merit are analytically derived in terms of system parameters and external driving forces. The emerging regions of stable occupation and finite currents are explained in terms of addition and removal energies, corresponding to the poles of the Green function. The analytical results are validated against the hierarchical equations of motion method, showing excellent agreement.

cond-mat.mes-hall↗

arXiv2024

Fully analytical equation of motion approach for the double quantum dot in the Coulomb blockade regime

A fully analytical approach based on the equation of motion technique to investigate the spectral properties and orbital occupations in an interacting double quantum dot in equilibrium is presented. By solving a linear system for the density correlators analytically, an explicit expression for the one body Green's function in terms of local occupations, intra- and inter-dot Coulomb interactions, and the model parameters is derived. In the uncontacted limit, the results coincide with those obtained from the grand canonical ensemble. The analytical results compare favourably with numerical results obtained with the non-crossing approximation and the hierarchical equation of motion methods accurately reproducing peak positions and spectral weight distributions in the Coulomb blockade regime.

cond-mat.mes-hall↗

arXiv2023

What can lattice DFT teach us about real-space DFT?

In this paper we establish a connection between density functional theory (DFT) for lattice models and common real-space DFT. We consider the lattice DFT description of a two-level model subject to generic interactions in Mermin's DFT formulation in the grand canonical ensemble at finite temperature. The case of only density-density and Hund's rule interaction studied in earlier work is shown to be equivalent to an exact-exchange description of DFT in the real-space picture. In addition, we also include the so-called pair-hopping interaction which can be treated analytically and, crucially, leads to non-integer occupations of the Kohn-Sham levels even in the limit of zero temperature. Treating the hydrogen molecule in a minimal basis is shown to be equivalent to our two-level lattice DFT model. By means of the fractional occupations of the KS orbitals (which, in this case, are identical to the many-body ones) we reproduce the results of full configuration interaction, even in the dissociation limit and without breaking the spin symmetry. Beyond the minimal basis, we embed our HOMO-LUMO model into a standard DFT calculation and, again, obtain results in overall good agreement with exact ones without the need of breaking the spin symmetry.

cond-mat.str-el↗

arXiv2023

Thermoelectric efficiency in multiterminal quantum thermal machines from steady-state density functional theory

The multi-terminal generalization of the steady-state density functional theory for the description of electronic and thermal transport (iq-DFT) is presented. The linear response regime of the framework is developed leading to exact expressions for the many-body transport coefficients and thermoelectric efficiency purely in terms of quantities accessible to the framework. The theory is applied to a multi-terminal interacting quantum dot in the Coulomb blockade regime for which accurate parametrizations of the exchange-correlation kernel matrix are given. The thermoelectric efficiency and output power of the multi-terminal system are studied. Surprisingly, the strong-interaction limit of these quantities can be understood in terms of the non-interacting one.

cond-mat.mes-hall↗

arXiv2022

Level occupation switching with density functional theory

The charge transport properties of zero-temperature multi-orbital quantum dot systems with one dot coupled to leads and the other dots coupled only capacitatively are studied within density functional theory. It is shown that the setup is equivalent to an effective single impurity Anderson model. This allows to understand the level occupation switching effect as transitions between ground states of different integer occupations in the uncoupled dots. Level occupation switching is very sensitive to small energy differences and therefore also to the details of the parametrized exchange-correlation functionals. An existing functional already captures the effect on a qualitative level but we also provide an improved parametrization which is very accurate when compared to reference numerical renormalization group results.

cond-mat.mes-hall↗

arXiv2021

Thermoelectric transport within density functional theory

A new formalism to describe steady-state electronic and thermal transport in the framework of density functional theory is presented. A one-to-one correspondence is proven between the three basic variables of the theory, i.e., the density on as well as the electrical and heat currents through the junction, and the three basic potentials, i.e., the local potential in as well as the DC bias and thermal gradient across the junction. Consequently, the Kohn-Sham system of the theory requires three exchange-correlations potentials. In linear response, the new formalism leads to exact expressions for the many-body transport coefficients (both electrical and thermal conductances and Seebeck coefficient) in terms of both the corresponding Kohn-Sham coefficients and derivatives of the exchange-correlations potentials. The theory is applied to the Single Impurity Anderson Model, and an accurate analytic parametrization for these derivatives in the Coulomb blockade regime is constructed through reverse engineering.

cond-mat.mes-hall↗

arXiv2020

Mott metal-insulator transition from steady-state density functional theory

We present a computationally efficient method to obtain the spectral function of bulk systems in the framework of steady-state density functional theory (i-DFT) using an idealized Scanning Tunneling Microscope (STM) setup. We calculate the current through the STM tip and then extract the spectral function from the finite-bias differential conductance. The fictitious non-interacting system of i-DFT features an exchange-correlation (xc) contribution to the bias which guarantees the same current as in the true interacting system. Exact properties of the xc bias are established using Fermi-liquid theory and subsequently implemented to construct approximations for the Hubbard model. We show for two different lattice structures that the metal-insulator transition is captured by i-DFT.

cond-mat.str-el↗

arXiv2020

Exchange-correlation potentials for multi-orbital quantum dots subject to generic density-density interactions and Hund's rule coupling

By reverse-engineering from exact solutions we obtain Hartree-exchange-correlation (Hxc) potentials for a double quantum dot subject to generic density-density interactions and Hund's rule coupling. We find ubiquitous step structures of the Hxc potentials that can be understood and derived from an analysis of stability diagrams. We further show that a generic Hxc potential can be decomposed into four basic potentials which allows for a straight-forward parametrization and paves the road for the construction of Hxc potentials for interacting multi-orbital systems. Finally we employ our parametrization of the Hxc potential in density functional theory calculations of multi-orbital quantum dots and find excellent agreement with exact many-body calculations.

cond-mat.mes-hall↗

arXiv2019

Steady-state density functional theory for thermoelectric effects

The recently proposed density functional theory for steady-state transport (i-DFT) is extended to include temperature gradients between the leads. Within this framework, a general and exact expression is derived for the linear Seebeck coefficient which can be written as the sum of the Kohn-Sham coefficient and an exchange-correlation contribution. The formalism is applied to the single-impurity Anderson model for which approximate exchange-correlation functionals are suggested for temperatures both above and below the Kondo temperature. A certain structural property of the exchange-correlation potentials in the Coulomb blockade regime allows to recover an earlier result expressing the Seebeck coefficient in terms of quantities of equilibrium density functional theory. The numerical i-DFT results are compared to calculations with the numerical renormalization group over a wide range of temperatures finding a reasonable agreement while i-DFT comes at a much lower computational cost.

cond-mat.str-el↗

arXiv2019

Non-equilibrium spectral functions from multi-terminal steady-state density functional theory

Multi-terminal transport setups allow to realize more complex measurements and functionalities (e.g., transistors) of nanoscale systems than the simple two-terminal arrangement. Here the steady-state density functional formalism (i-DFT) for the description of transport through nanoscale junctions with an arbitrary number of leads is developed. In a three-terminal setup and in the ideal STM limit where one of the electrodes (the `STM tip') is effectively decoupled from the junction, the formalism allows to extract its non-equilibrium spectral function (at arbitrary temperature) while a bias is applied between the other two electrodes. Multi-terminal i-DFT is shown to be capable of describing the splitting of the Kondo resonance in an Anderson impurity in the presence of an applied bias voltage, as predicted by numerically exact many-body approaches.

cond-mat.mes-hall↗

arXiv2018

Exchange-correlation functionals of i-DFT for asymmetrically coupled leads

A recently proposed density functional approach for steady-state transport through nanoscale systems (called i-DFT) is used to investigate junctions which are asymmetrically coupled to the leads and biased with asymmetric voltage drops. In the latter case, the system can simply be transformed to a physically equivalent one with symmetric voltage drop by a total energy shift of the entire system. For the former case, known exchange correlation gate and bias functionals have to be generalized to take into account the asymmetric coupling to the leads. We show how differential conductance spectra of the constant interaction model evolve with increasing asymmetry of both voltage drops and coupling to the leads.

cond-mat.mes-hall↗

arXiv2018

Many-body spectral functions from steady state density functional theory

We propose a scheme to extract the many-body spectral function of an interacting many-electron system from an equilibrium density functional theory (DFT) calculation. To this end we devise an ideal STM-like setup and employ the recently proposed steady-state DFT formalism (i-DFT) which allows to calculate the steady current through a nanoscopic region coupled to two biased electrodes. In our setup one of the electrodes serves as a probe ('STM tip'), which is weakly coupled to the system we want to measure. In the ideal STM limit of vanishing coupling to the tip, the system is restored to quasi-equilibrium and the normalized differential conductance yields the exact equilibrium many-body spectral function. Calculating this quantity from i-DFT, we derive an exact relation expressing the interacting spectral function in terms of the Kohn-Sham one. As illustrative examples we apply our scheme to calculate the spectral functions of two non-trivial model systems, namely the single Anderson impurity model and the Constant Interaction Model.

cond-mat.mes-hall↗

arXiv2015

Density Functional Theory of the Seebeck coefficient in the Coulomb blockade regime

The Seebeck coefficient plays a fundamental role in identifying the efficiency of a thermoelectric device. Its theoretical evaluation for atomistic models is routinely based on Density Functional Theory calculations combined with the Landauer-Büttiker approach to quantum transport. This combination, however, suffers from serious drawbacks for devices in the Coulomb blockade regime. We show how to cure the theory through a simple correction in terms of the {\em temperature derivative} of the exchange correlation potential. Our results compare well with both rate equations and experimental findings on carbon nanotubes.

cond-mat.mes-hall↗

arXiv2014

Time-Dependent Density-Functional Theory of Strong-Field Ionization of Atoms under Soft X-Rays

We demonstrate the capabilities of time-dependent density functional theory (TDDFT) for strong-field, short wavelength (soft X-ray) physics, as compared to a formalism based on rate equations. We find that TDDFT provides a very good description of the total and individual ionization yields for Ne and Ar atoms exposed to strong laser pulses. We assess the reliability of different adiabatic density functionals and conclude that an accurate description of long-range interactions by the exchange and correlation potential is crucial for obtaining the correct ionization yield over a wide range of intensities ($10^{13}$ -- $5 \times 10^{15}$ W/cm$^2$). Our TDDFT calculations disentangle the contribution from each ionization channel based on the Kohn-Sham wavefunctions.

physics.atm-clus↗

arXiv2014

Modelling the effect of nuclear motion on the attosecond time-resolved photoelectron spectra of ethylene

Using time dependent density functional theory (TDDFT) we examine the energy, angular and time-resolved photoelectron spectra (TRPES) of ethylene in a pump-probe setup. To simulate TRPES we expose ethylene to an ultraviolet (UV) femtosecond pump pulse, followed by a time delayed extreme ultraviolet (XUV) probe pulse. Studying the photoemission spectra as a function of this delay provides us direct access to the dynamic evolution of the molecule's electronic levels. Further, by including the nuclei's motion, we provide direct chemical insight into the chemical reactivity of ethylene. These results show how angular and energy resolved TRPES could be used to directly probe electron and nucleus dynamics in molecules.

physics.atm-clus↗