arXiv subjects

Niklas Dittmann

Publications and source records attributed to Niklas Dittmann.

5 recordsLinked to original sources

arXiv2018

Dynamics of the Anderson impurity model: benchmarking a non-adiabatic exchange-correlation potential in time-dependent density functional theory

In this comparative study we benchmark a recently developed non-adiabatic exchange-correlation potential within time-dependent density functional theory (TDDFT) (Phys.\ Rev.\ Lett.\ {\bf 120}, 157701 (2018)) by (a) validating the transient dynamics using a numerically exact density matrix renormalization group approach as well as by (b) comparing the $RC$-time, a typical linear response quantity, to upto second order perturbation theory results. As a testbed we use the dynamics of the single impurity Anderson model. These benchmarks show that the non-adiabatic functional yields quantitatively accurate results for the transient dynamics for temperatures of the order of the hybridization strength while the TDDFT $RC$-times quantitatively agree with those from second-order perturbation theory for temperatures which are large compared to the hybridization strength. Both results are particularly intriguing given the relatively low numerical cost of a TDDFT calculation (at least compared to exact approaches).

cond-mat.stat-mech↗

arXiv2018

Finite-frequency noise of interacting single-electron emitters: spectroscopy with higher noise harmonics

We derive the symmetrized current-noise spectrum of a quantum dot, which is weakly tunnel-coupled to an electron reservoir and driven by a slow time-dependent gate voltage. This setup can be operated as an on-demand emitter of single electrons into a mesoscopic conductor. By extending a real-time diagrammatic technique which is perturbative in the tunnel coupling, we obtain the time-resolved finite-frequency noise as well as its decomposition into noise harmonics in the presence of both strong Coulomb interaction and slow time-dependent driving. We investigate the noise over a large range of frequencies and point out where the interplay of Coulomb interaction and driving leads to unique signatures in finite-frequency noise spectra, in particular in the first harmonic. Besides that, we employ the first noise harmonic as a spectroscopic tool to access individual fluctuation processes. We discuss how the inverse noise frequency sets a time scale for fluctuations, which competes with time scales of the quantum-dot relaxation dynamics as well as the driving.

cond-mat.mes-hall↗

arXiv2018

Equilibrium finite-frequency noise of an interacting mesoscopic capacitor studied in time-dependent density functional theory

We calculate the frequency-dependent equilibrium noise of a mesoscopic capacitor in time-dependent density functional theory (TDDFT). The capacitor is modeled as a single-level quantum dot with on-site Coulomb interaction and tunnel coupling to a nearby reservoir. The noise spectra are derived from linear-response conductances via the fluctuation-dissipation theorem. Thereby, we analyze the performance of a recently derived exchange-correlation potential with time-nonlocal density dependence in the finite-frequency linear-response regime. We compare our TDDFT noise spectra with real-time perturbation theory and find excellent agreement for noise frequencies below the reservoir temperature.

cond-mat.mes-hall↗

arXiv2017

Non-Adiabatic Dynamics in Single-Electron Tunneling Devices with Time-Dependent Density Functional Theory

We simulate the dynamics of a single-electron source, modeled as a quantum dot with on-site Coulomb interaction and tunnel coupling to an adjacent lead, in time-dependent density functional theory. Based on this system, we develop a time-nonlocal exchange-correlation potential by exploiting analogies with quantum-transport theory. The time non-locality manifests itself in a dynamical potential step. We explicitly link the time evolution of the dynamical step to physical relaxation time scales of the electron dynamics. Finally, we discuss prospects for simulations of larger mesoscopic systems.

cond-mat.mes-hall↗

arXiv2016

Clocked single-spin source based on a spin-split superconductor

We propose an accurate clocked single-spin source for ac-spintronic applications. Our device consists of a superconducting island covered by a ferromagnetic insulator layer through which it is coupled to superconducting leads. Single-particle transfer relies on the energy gaps and the island's charging energy, and is enabled by a bias and a time-periodic gate voltage. Accurate spin transfer is achieved by the ferromagnetic insulator layer which polarizes the island, provides spin-selective tunneling barriers and improves the precision by suppressing Andreev reflection. We analyze realistic material combinations and experimental requirements which allow for a clocked spin current in the MHz regime.

cond-mat.mes-hall↗