# Lectures

### 24.01.2020, 10:30 am

#### Prof. Stefan Tautz - Forschungszentrum Jülich

*Brainstorming Session in HS P*

Title: The Role of Spectroscopy in the Realization of Topological Quantum Computing

### 17.01.2020, 10:15 am

#### Federico Cilento Elettra - Sincrotrone Trieste S.C.p.A. Italy

*i-RTG Lecture in HS P*

Title: Table-top time-resolved spectroscopies for complex materials

Abstract:

Time-resolved spectroscopies have emerged as fundamental spectroscopic tools for probing complex materials, to both investigate ground-state-related properties and trigger phase transitions among different states with peculiar electronic and lattice structures. In recent years, they have been used to shed light on a large variety of open issues on the physics of complex and strongly-correlated materials. In particular, time-domain measurements have been widely used to disentangle, by their different timescales, the degrees of freedom of a system that at equilibrium are intertwined, thus advancing the comprehension of ground state properties of solid state compounds. Moreover, photoexcitation at high enough fluence makes it possible to trigger phase transitions among different states of a sample, often not attainable under equilibrium conditions, allowing to achieve a true ultrafast control over the functional properties of materials.

Here I will report on a number of science cases where the non-equilibrium approach allowed to advance the comprehension of the materials properties, and show the latest science-driven advancements in the fields of time-resolved optical and photoelectron spectroscopies from table-top ultrafast light sources. Finally, I will discuss how table-top spectroscopies can complement experiments at large-scale facilities, including Synchrotron Radiation Sources and Free Electron Lasers.

### 10.01.2020, 10:15 am

#### Prof. Dr. Wulf Wulfhekel - Physikalisches Institut, KIT, Karlsruhe

*i-RTG Lecture in HS P*

Title: Design principles, challenges and techniques for scanning tunneling microscopy at mK temperatures

Abstract:

Scanning tunneling microscopy (STM) and spectroscopy (STS) at temperatures in the mK regime requires special efforts. These include restricted design rules for cryostats capable to reach these temperatures in combination with low vibrations and long standing times. Often, the designs lead to machines that are difficult to handle. We will discuss, how to circumvent some of the pitfalls of common designs. To reach the necessary quality of electric signals and the thermalization of the electron temperature, special care has to be taken for many of the signal lines. We will introduce some of the techniques based on a 30mK design at KIT and will show, what trade-offs have to be taken and how the signal quality influences the measuring protocols at ultra-low temperatures.

### 13.12.2019, 10:15 am

#### Dr. Georg Rohringer - University of Hamburg

*i-RTG Lecture in HS P*

Title: Two-particle self-consistency and conservation laws in strongly correlated electron systems.

Abstract:

In the lecture, I will discuss in detail the two-particle self-consistency relations and the conservation

laws for the basic model for strongly correlated electron systems, i.e., the Hubbard model. More

specifically, I will present I derivation of the equations of motion which connects the full two-particle

vertex function with the self-energy. Then I will show, how the requirement of charge conservation

leads to a constraint for the one-particle self-energy and the two-particle irreducible vertex. The final

part of the lecture will address the question how in general approximate theories can be constructed

which fulfill either the equation of motion and the Pauli principle[1] or the conservations laws[2].

[1] G. Rohringer et al., Rev. Mod. Phys. 90, 025003 (2018). [2] G. Baym and Leo P. Kadanoff, Phys. Rev. 124, 287 (1961).

### 06.12.2019, 10:15 am

#### Prof. Dr. Carsten Timm - TU Dresden

*i-RTG Lecture in HS P*

Title: Group-theoretical analysis and synthesis of Hamiltonians

Abstract:

The purpose of this lecture is to show how group theory can be used to analyze model Hamiltonians and also to construct such Hamiltonians based on symmetries. It should help to answer questions such as the following: Why did the authors of paper X write down this weird Hamiltonian? Is the model used in paper Y generic for systems of the relevant symmetry or does it contain hidden approximations? How can I construct a model Hamiltonian for some complicated lattice? Which symmetries of superconducting states are possible for a certain system?

### 29.11.2019, 10:15 am

#### Prof. Dr. Claude Monney - University Of Fribourg

*i-RTG Lecture in SE7*

Title: Lecture on RIXS

Abstract:

This lecture will be devoted to the basics of resonant inelastic x-ray scattering (RIXS). RIXS is a powerful and versatile modern x-ray spectroscopy. We will derive together the Kramers-Heisenberg formula describing RIXS using second-order perturbation theory. We will then discuss how a RIXS experiment is planned in practice, taking advantage of the absorption edge of relevant ions in materials to be chemically sensitive and of the scattering geometry to enhance its selectivity.

In the last 10 years, the development of the RIXS technique and its application to correlated materials followed a steady and impressive progress. We will therefore illustrate the lecture with examples from the recent scientific literature and discuss them in details. For that purpose, we will show how RIXS can measure crystal field excitations, magnetic excitations or interband electron-hole excitations.

### 18.10.2019, 10:15 am

#### Prof. Dr. Herbert Pfnür - Leibniz Universität Hannover

*i-RTG Lecture in SE7*

Title: Elastic and inelastic scattering of low energy electrons

Abstract: Due to their strong interaction with condensed matter, low energy electrons (1 to 500 eV) impinging on a solid surface can only penetrate very few layers before they are elastically or inelastically scattered. This fact not only generates high surface sensitivity, but also makes these electrons a very versatile tool for investigating both surface structure and low-energy excitations predominantly at surfaces. In this lecture I will give an overview about the various possibilities, starting with elastic, coherent electron diffraction. While long range order can mostly be dealt with in single scattering approximation, short range (multiple) scattering contains all the information about the local structure, so that diffracted intensities as a function of energy and/or angle can be used to determine atomic positions at surfaces. Inelastic scattering generates characteristic excitations such as local vibrations of adsorbates, phonons, plasmons or electron-hole pairs. The discrimination between the various possibilities is sometimes not easy and requires the assistance of quantitative simulations. I will both discuss a few characteristic examples as well as experimental aspects.

### 12.07.2019, 10:15 am

#### Prof. Dr. CHristoph Tegenkamp - Technische Universität Chemnitz

*i-RTG Lecture in SE7*

Title: Electronic transport on surface structures: advantages, limitations and challenges

### 14.06.2019, 14:15 pm

#### Dr. Christian Tusche - Forschungszentrum Jülich, Peter Grünberg Institut (PGI-6)

*i-RTG Lecture in SE7*

Title: Principles and Applications of Spin-resolved Photoelectron Spectroscopy with the Momentum Microscope

### 29.03.2019, 11:30 am

#### Dr. Flavio de Souza Nogueira, IFW Dresden

*i-RTG Lecture in SE5*

Title: Chiral anomaly and second-quantized Berry phases

### 27.03.2019, 01:00 pm

#### Dr. Flavio de Souza Nogueira, IFW Dresden

*i-RTG Lecture in SE5*

Title: Haldane's topological nonlinear sigma model theory of one-dimensional antiferromagnets

### 26.03.2019, 01:00 pm

#### Dr. Flavio de Souza Nogueira, IFW Dresden

*i-RTG Lecture in SE5*

Title: Nonlinear sigma models and topological action

### 18.01.2019, 10:15 am

#### Prof. Markus Donath, Universität Münster

*i-RTG Lecture in SE2*

Title: Putting a new spin on unoccupied electronic states

### 17.01.2019, 02:00 pm

#### Prof. Su Ning, EPFL, Lausanne, Switzerland

*i-RTG Lecture in SE5*

Title: Numerical conformal bootstrap II

### 16.01.2019, 04:00 pm

#### Prof. Su Ning, EPFL, Lausanne, Switzerland

*i-RTG Lecture in SE5*

Title: Numerical conformal bootstrap I

### 15.01.2019, 04:00 pm

#### Prof. Su Ning, EPFL, Lausanne, Switzerland

*i-RTG Lecture in SE5*

Title: Crash course in conformal field theory.

### 30.11.2018, 10:15 am

#### Thomasz Story, Institute of Physics, Polish Academy of Sciences, Warsaw, Poland

*i-RTG Lecture in SE2*

Title: Thermoelectricity and topological materials

### 18.06.2018, 10:15 am

#### Dr. Moritz Hoesch, DESY, Hamburg,

*i-RTG Lecture in SE2*

Title: Momentum-resolved solid state spectroscopy using synchrotron radiation (IXS, ARPES)

### 15.06.2018, 10:15 am

#### Dr. Giancarlo Panaccione, ELETTRA synchrotron, Trieste, Italy

*i-RTG Lecture in SE2*

Title: From surface to bulk sensitivity via Photoelectron Spectroscopy with Synchrotron Radiation.

### 01.12.2017, 10:15 am

#### Anna Isaeva, TU Dresden

*i-RTG Lecture in SE2*

Title:Growth of bulk inorganic crystals: theory, tips and cheats

### 21.07.2017, 10:15 am

#### Gianni Profeta, l’Aquila, Italien

*i-RTG Lecture in SE2*

Title: Towards room temperature superconductivity

### 12.05.2017, 10:15 am

#### Dr. Silvia Picozzi, CNR-SPIN Chieti, Italien

i-RTG Lecture in SE2

i-RTG Lecture in SE2

Title: Interplay between spin and dipolar degrees of freedom

### 01.07.2016, 10:00 am

#### Prof. Dr. Markus Morgenstern, RWTH Aachen

*i-RTG Lecture in SE2*

Title: What we can learn about TIs from STM measurements

### 22.04.2016, 10:00 am

#### Prof. L. H. Tjeng, Max-Planck-Institute for Chemistry and Physics of Solids, Dresden

*i-RTG Lecture in SE2*

Title: Strongly correlated systems and their excitations: a back-of-the-envelope introduction

### 29.01.2016, 10:00 am

#### Eugene Krasovskii, Universidad del Pais Vasco

*i-RTG Lecture in SE2*

Title: Relativistic band structure and theory of angle- and spin-resolved photoemission