#
Dynamics and Fluctuations in Single-Electron Tunneling Devices
Doktorsavhandling, 2018

In this thesis, we first propose a novel clocked spin-current source, which consists of a superconducting island tunnel coupled to two superconducting contacts via a ferromagnetic insulator layer. We demonstrate that this nanostructure can be operated as an emitter of a precise quantized spin current and we point out its working principle as well as its experimental feasibility.

The second device we analyze is a single-electron source, which is built from an interacting quantum dot with tunnel coupling to a single contact. The single-electron emission is triggered by a slow time-dependent gate-voltage driving, and we present a comprehensive study of the noise spectrum of the emitted current signal. The noise contains information on the system's excitation spectrum and its dynamics, and it also reveals signatures of Coulomb interaction. To derive the noise spectra over a large frequency range, we extend a real-time diagrammatic perturbative method in the tunnel coupling to finite noise frequencies in the presence of the slow time-dependent drive. We then perform a harmonic decomposition of the noise spectra, present an interpretation of the noise in terms of individual fluctuation processes, and point out characteristic signatures for the interplay between Coulomb interaction and the time-dependent driving.

Third, we turn to time-dependent density-functional theory, which is a numerical method, and we transfer insights from the diagrammatic calculations to this theory. This novel combination of methods allows us to develop a nonadiabatic (i.e. time-nonlocal) approximation of this theory's exchange-correlation potential. We relate properties of the exchange-correlation potential to physical time scales of the electron dynamics and we apply it to obtain numerical time evolutions of single and multiple quantum dots coupled to a shared electron reservoir. In addition, we extend this combination of methods to another nanosystem, namely an interacting quantum dot coupled to two contacts and exposed to time-dependent gate and bias voltages. The results presented in this part of the thesis constitute a significant step towards the application of time-dependent density-functional theory for the description of charge dynamics in complex single-electron tunneling devices.

quantum dot

time-dependent density-functional theory

perturbation theory

single-electron source

## Författare

### Niklas Dittmann

Chalmers, Mikroteknologi och nanovetenskap (MC2), Tillämpad kvantfysik

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

New Journal of Physics,; Vol. 18(2016)p. Article Number: 083019 -

**Artikel i vetenskaplig tidskrift**

### Nonadiabatic Dynamics in Single-Electron Tunneling Devices with Time-Dependent Density-Functional Theory

Physical Review Letters,; Vol. 120(2018)

**Artikel i vetenskaplig tidskrift**

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

Journal of Physics: Conference Series,; Vol. 969(2018)

**Paper i proceeding**

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

Physical Review B,; Vol. 98(2018)

**Artikel i vetenskaplig tidskrift**

### Niklas Dittmann, Nicole Helbig, Dante Kennes, Dynamics of the Anderson impurity model: benchmarking a non-adiabatic exchange-correlation potential in TDDFT

### Niklas Dittmann, Nicole Helbig, Nonadiabatic dynamics of a biased quantum dot with time-dependent density-functional theory

### Styrkeområden

Nanovetenskap och nanoteknik (2010-2017)

### Fundament

Grundläggande vetenskaper

### Ämneskategorier

Annan fysik

Den kondenserade materiens fysik

### ISBN

978-91-7597-828-4

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4509

### Utgivare

Chalmers