Bachelor’s Thesis in Physics

This thesis project focuses on communication processes between cells in the context of pattern formation from a statistical physics point of view. The class of Ising/Potts models provides a simple framework for studying the interplay of direct contact interactions with an external signal. This class of models originated in the context of magnetism, but its basic assumptions also fit the minimal requirements  for some interactions between biological cells. In this thesis, the Ising/Potts model will be studied numerically on biologically inspired lattices with or without the presence of spatially inhomogeneous external signals. The results of this simulations will then be analysed and interpreted with the help of tools from statistical physics and information theory. Prior knowledge in biophysics and information theory is not required, but a solid background in statistical physics is necessary.

Anforderung

• Ÿ  Abgeschlossenes 5. Fachsemester im Bachelor Studiengang Physik
• Ÿ  Spezialisierung Kondensierte Materie (KM) oder Kern-, Teilchen- und Astrophysik (KTA) sinnvoll

Stand der Wissenschaft und Technik

Lithium-Ionen Akkumulatoren kommen in Handys, Laptops und Akkuwerkzeugen als Energiespeicher zum Einsatz. Die Lebenszeit und Ladegeschwindigkeit dieser modernen Akkus sind allerdings durch physikalische als auch chemische Alterungsprozesse begrenzt, die vor allem an den Elektroden stattfinden.

Aufgaben

Ziel dieser Bachelorarbeit ist es, den Alterungsprozess von Graphit-basierte Elektroden zu untersuchen und die Einlagerung von immobilisiertem Lithium in den Elektroden während des Auf- und Entladens tiefenabhängig nachzuverfolgen, um so die die Alterungsprozesse besser zu verstehen und die Lebenszeit künftiger Lithium-Ionen-Batterien zu verlängern. Im Rahmen der Arbeit werden die Tiefenprofile mit dem N4DP Instrument an der Neutronenleiterhalle des Forschungsreaktors München (FRM II) in Garching vermessen.

Wir bieten

Ein interessantes Arbeitsthema, welches die Materialforschung der Kondensierten Materie mit Grundlagen der Kern- und Teilchenphysik kombiniert.

A fascinating manifestation of spin physics in the solid state are pure spin currents. Their generation and detection is often based on the interconversion of spin and charge currents in ferromagnetic insulator/normal metal heterostructures. The aim of this thesis is the fabrication of high-crystalline thin film heterostructures using reflection high energy diffracton (RHEED) assisted laser molecular beam epitaxy (laser-MBE) as well as electron beam physical vapor deposition. The thin film samples will then be characterized structurally using high-resolution X-ray diffractometry (HR-XRD) as well as magnetically via superconducting quantum interference device (SQUID) magnetometry. By using the best heterostructures, spin Hall magnetoresistance as well as spin Seebeck experiments will then be performed to investigate their spin current properties.
This thesis provides deep insight into thin film technology, laser-MBE, HR-XRD, SQUID magnetometry as well as magnetotransport experiments.  An important aspect hereby will be the fabrication of high-crystalline thin film heterostructures with excellent interface qualities.

Contact: Stephan.Gepraegs@wmi.badw.de, Rudolf.Gross@wmi.badw.de

Our quantum sensor of choice, the nitrogen-vacancy center in diamond, is on its way to become the world's smallest MRI scanner. It could give a 3D image of a single bio molecule while simultaneously resolving the chemical components. One limiting problem on this way is the reliable preparation of nitrogen-vacancy centers with long coherence times. We provide a state-of-the art measurement setup and a handful of ideas how to approach this task. We are looking for an enthusiastic student to try several preparation approaches and to perform quantum measurements on the coherence properties of the resulting single quantum sensors. Favorable personality qualities: interest in quantum information science, fun with handicrafts and no fear of software (python)

Molecular brushes are composed of a polymer backbone grafted densely by polymeric side arms. In solution, factors that can influence the molecular size and shape include the molar masses of the backbone and the side arms, polymer concentration and temperature.

In this bachelor thesis, a series of molecular brushes, differing in the molar mass of the backbone and side arms, will be investigated in solution. The aim is to determine the dependence of the molecular size on the concentration using dynamic light scattering (DLS).

After a literature research, samples will be prepared and measured, and data analysis will be carried out. For more information, please contact Prof. Christine Papadakis, papadakis@tum.de.

Responsive Blockcopolymere mit hydrophoben Endblöcken und hydrophilen Mittelblöcken (Telechele) zeigen großes Potential für die Anwendung in intelligenten Membranen, Gelen und selbstheilenden Materialien. Durch Verwendung von responsiven Blöcken hängen die Eigenschaften des Telechels stark von Parametern wie dem pH-Wert und der Temperatur ab.

In dieser Bachelorarbeit soll ein solches Polymer im dünnen Film untersucht werden. Es soll zunächst ermittelt werden, wie dünne, defektfreie Filme präpariert werden können. Diese sollen mit verschiedenen Methoden charakterisiert werden. Anschließend wird das Quellverhalten der Filme in Wasserdampf durch Messung der spektralen Reflexion bestimmt.

Nach einer Literaturrecherche sollen die Probenpräparation, die Messungen und die Datenanalyse durchgeführt werden. Für weitere Informationen melden Sie sich bitte bei Prof. Christine Papadakis, papadakis@tum.de.

Various astronomical and cosmological observations point towards the existence of a non-luminous matter component in our Universe, dubbed dark matter. The whole body of observations is consistent with the dark matter being constituted by new particles not contained in the Standard Model. This hypothesis could be tested if dark matter particles have sizable interactions with the nucleons. If this is the case, dark matter particles traversing a detector located at Earth could scatter off the nuclei in the target material, producing a potentially detectable signal. Unfortunately, the theoretical interpretation of the experimental results is subject to our ignorance of the microphysics governing the dark matter interactions with the nucleons. Using the fact that dark matter particles in our Galaxy are expected to move non-relativistically, one can write down the most general form of the dark matter-nucleon interaction using the restrictions of Galilean invariance and momentum conservation. The goal of this thesis is to construct the full set of operators describing the non-relativistic dark matter-nucleon interaction, analyze the expected signals at direct detection experiments, and investigate the embedding of these non-relativistic operators into a relativistic framework.

Planar superconducting microwave resonators are key for the ultra-sensitive detection of spin properties using magnetic resonance techniques. In this thesis you will compare the performance of planar microwave resonators fabricated from various superconducting materials regarding their frequency stability and Q-factors when magnetic fields are applied. In particular, their performance close to the transition temperature of the superconducting phase to the normal conducting phase shall be investigated, as this imposes a stringent limit for the application of those microwave resonators.

Your bachelor thesis will bring you in touch with state-of-the art microwave spectroscopy tools like vector network analyzers, as well as cryogenic measurement environments. Moreover, the careful data analysis of the magnetic field dependent datasets will put you in the position to make a meaningful impact on microwave resonator technology.

Contact: Stefan.Weichselbaumer@wmi.badw.de, Hans.Huebl@wmi.badw.de

Angular momentum transport is the fundamental requirement for spintronic devices. By utilizing spin-orbit interaction in heavy metals it is possible to transform a charge current into a pure spin current, i.e. the transport of angular momentum without an accompanying charge current. The goal of this thesis is to utilize magnetotransport measurements for the investigation of this interconversion effect in heterostructures consisting of a heavy metal interfaced with a ferromagnetic insulator. Within this thesis the deposition conditions of the heavy metal are to be optimized with regard to the charge to spin current interconversion. This task requires optical lithography, ultra-high vacuum thin film deposition and electrical transport measurements in a superconducting magnet cryostat.
We are looking for an enthusiastic bachelor student to carry out this versatile optimization experiment. The thesis work is divided into of the fabrication of the thin films using a new UHV sputter deposition system and a laser writer for optical lithography, as well as the experimental study of these samples with standard electrical and magnetic characterization techniques.

Contact: Matthias.Althammer@wmi.badw.de, Rudolf.Gross@wmi.badw.de

The field of magnonics aims to use spin waves for novel computational schemes. Spin waves in low-damping, metallic ferromagnets are of particular interest for this purpose. In this thesis, you will fabricate low-damping metallic ferromagnetic thin films with high saturation magnetization and study spin wave propagation in films with spatially varying properties. To this end, you will use sputter deposition, laser lithography and Brillouin light scattering spectroscopy.
We are looking for a highly motivated candidate with an interest in magnetization dynamics, thin film deposition and optical spectroscopy. Your thesis will be embedded in our core research program and you will closely collaborate with Master and PhD students.

Contact: Mathias.Weiler@wmi.badw.de, Rudolf.Gross@wmi.badw.de

Within this experimental project, topological charge and spin currents shall be explored in atomistic layered crystals with a strong spin orbit interaction.

Phononen sind quantisierte Gitterschwingungen, die an alle Anregungen eines Festkörpers koppeln. Zum Beispiel koppeln in den eisenbasierten Verbindungen einige der mit Lichtstreuung beobachtbaren Phononen an die elektronische Struktur, die wiederum durch die verschiedenen magnetischen Ordnungsphänomene bei tiefen Temperaturen modifiziert wird. Es ist geplant, Untersuchungen an EuFe2As2 durchzuführen, das einen magnetischen Phasenübergang bei etwa 190 K hat. In der magnetischen Phase ist das Kristallgitter orthorhombisch verzerrt und zeigt wegen des geringen Unterschieds zwischen a- und b-Achse eine Domänenstruktur (Verzwillingung). Die Kristalle können mit moderaten Magnetfeldern von etwa 1 T entzwillingt werden und bleiben eindomänig auch nach dem Abschalten des Feldes. Diese Vorgehensweise erlaubt ein „sauberes“ Experiment ohne externes Magnet- oder Kraftfeld, das mithilft, die Frage nach der Triebfeder hinter dem Magnetismus, der Strukturumwandlung und der Supraleitung in den Verbindungen auf Eisenbasis aufzuklären. Es ist geplant, die Phononen an EuFe2As2 (Jannis Maiwald und Philipp Gegenwart, Universität Augsburg) zu untersuchen als Funktion der Temperatur zu untersuchen. Die Arbeit schließt eine fundierte Einführung in die Physik unkonventioneller Supraleiter, in die Spektroskopie, sowie die Tieftemperatur- und Hochfeldtechnologie ein.