General Physical Colloquium
SUMMER term 2023
Thursday, 16 o'clock (c.t.), Location: HS 2, IG 1, Wilhelm-Klemm-Str. 10, 48149 Münster
20.04.2023 CRC 1459 Spring Colloquium
Zeit: 15.00 Uhr Ort: Center for Soft Nanoscience (SoN), Busso-Peus-Str. 10
Abstract Book Crc Spring Colloquium 2023
Helen Tran, University of Toronto Macromolecular Bioelectronics
Emre Neftci, Forschungszentrum Jülich Learning with Brain-Inspired Computers
04.05.2023 Prof. Kirill Bolotin
Straintronics of two-dimensional materialsHow can one stretch an atomically thick membrane, and what happens to it in the process? In this talk, we use controllably strained 2D materials (2DMs, such as graphene or transition metal dichalcogenides) as a new platform to study the static and dynamic response of electrons, excitons, and phonons. In the process, we find that the mechanical properties of 2DMs qualitatively differ from that of their three-dimensional counterparts.First, we find that the inevitable out-of-plane crumpling modifies every mechanical property of 2DMs, making their mechanical response more akin to biological membranes than solid objects. Specifically, the out-of-plane crumpling renders the thermal expansion coefficient negative and substrate-dependent, decreases Young’s modulus, increases the bending rigidity by several orders of magnitude, and changes the sign of the Poison’s ratio. Second, we examine the effect of the mechanical strain on phonons in 2DMs. We use strain engineering to control the bandstructure of 2DM phononic crystals and to realize new nanomechanical spectrometers. Finally, we use mechanical strain to control excitons, Coulomb-bound electron-hole pairs in 2D semiconductors. We identify exciton types, bring different excitons into resonance, and control exciton flows in controllably strained devices.
11.05.2023 Dr. Alexander Weber-Bargioni
Controlling Quasiparticle Excitations in 2D Solids through Atomically Precise HeterostructuresIn this presentation, we investigate how atomically defined heterostructures, such as 2D stacks, 1D boundaries within a 2D material, and 0D vacancies and substitutes in 2D materials, localize new protected states that host quasiparticle excitations. Quasiparticles are emergent excitations in condensed matter systems that behave like particles, but are not elementary particles like electrons or protons. In 2D solids, a wide variety of quasiparticle excitations can be experimentally accessed, including localized electrons, excitons, superconducting states, and polaritons, as well as more exotic systems like Tomonaga Luttinger liquid. Each specific quasiparticle excitation is a result of a specific crystalline symmetry. By inducing atomically defined 0D, 1D, and 2D heterostructures, it is possible to localize, protect, and create novel quasiparticle excitations.We demonstrate how to engineer heterostructures into 2D Transition Metal Dichalcogenides and visualize the resulting electronic structure using Scanning Tunneling Microscopy. We discuss the resulting quasiparticle excitations that we directly capture using Scanning Tunneling Microscopy, as well as Time Resolved optical Spectroscopy. We show how 0D heterostructures or defects in 2D MoSe2 and 2D WS2 carry intrinsic point defects that substantially modify electronic properties. For instance, individual S vacancies create two-level systems within the band gap with extremely high spin-orbit coupling, and can mediate single photon emission via optical or electric stimulation. We also demonstrate how C-H for S or Se substitutes in 2D WS2 and 2D WSe2 form locally charged hydrogen-like states. Upon deprotonation, the localized carbon radical hosts a deep in-gap state with a net spin and electron-phonon coupling that is similar to NV color centers in diamond, but with atomistic control. Furthermore, individual Chalcogen Vacancies can be decorated with a variety of different adatoms, creating new types of 0D heterostructures, such as Co-S substitutes that could become relevant for Quantum Information Science.In 1D heterostructures, such as Mirror Twin Boundaries in MoSe2 or WS2, we discovered atomically thin metallic conductors that undergo a quantum phase transition at low temperature to form a Tomonaga Luttinger Liquid (TTL). TTLs are correlated electron systems, where electrons couple to form a bosonic system, and that can foster partial electron and spin transport.As a 2D heterostructure, we explore WS2/WSE2 stacks, where we study the formation and recombination channels of interlayer excitons formed in WS2/WSE2 stacks, which may relate to the recently reported formation of excitonic Bose-Einstein condensates. Another fascinating area of research is coupling quasiparticles to form new quasiparticles. By stacking 2D WSe on linear plasmonic cavities, we were able to couple excitons to plasmons, creating plexcitons. We use techniques such as photo low-temperature Scanning Tunneling Microscopy, near-field optical microscopy, and low-temperature time-resolved optical spectroscopy to investigate the properties and behavior of these quasiparticle excitations.
25.05.2023 Prof. Claus Lämmerzahl
Tests of General Relativity: Status and PerspectivesThe theoretical concepts as well as the related experimental tests of the foundations of General Relativity are introduced in the context of a constructive axiomatic scheme. The experiments with own participation are discussed in more detail: these are the test of the principle of equivalence with the satellite mission MICROSCOPE, the test of the gravitational redshift with the Galileo satellites, and the test of the equality of active and passive gravitational mass using Lunar Laser Ranging. After a brief overview of all observational consequences of General Relativity, which are also extensively tested, the importance of future experiments with quantum matter is presented.
15.06.2023 Prof. Kathrin Valerius
Hot and cold dark matter – how to probe the invisible Universe in the laboratoryOur understanding of the Universe is shaped by two intricate model systems: The Standard Model of elementary particles which describes the subatomic world, and the Standard Model of cosmology which encompasses the cosmos at large. Even though both models have proven remarkably successful, there are still unanswered questions that suggest missing elements within them. This presentation will focus on two of these questions: Firstly, how can we measure (and explain) the minuscule mass of neutrinos, which goes beyond the Standard Model of particle physics and classifies neutrinos as a form of “hot dark matter”? Secondly, are there new particles to make up the “cold dark matter” that outweighs ordinary matter by a factor of five in the Standard Model of cosmology?I will outline two approaches employed in contemporary astroparticle physics to shed light on these questions: exploring the neutrino mass scale and unraveling the nature of Dark Matter. Furthermore, I will highlight how seemingly distinct experimental lines, namely precision spectroscopy of tritium beta decay with the KATRIN experiment and large-volume xenon-based scintillation detectors such as XENONnT, share common technologies and mutually benefit from research and development advances in the field.
22.06.2023 Prof. Daniel Ahmed
29.06.2023 Verleihung des Lehrpreises / Prof. Metin Tolan
Vortragsankündigung Raumänderung: HS 1
Die STAR TREK Physik
Warum die Enterprise nur 158 Kilo wiegt und andere galaktische ErkenntnisseWie genau nehmen es die Star Trek Macher eigentlich mit der Physik? Erstaunlich genau! Das ist der Inhalt dieses Vortrages. Ob Spock in Windeseile ausrechnet, dass genau 1771551 Tribbles in den Laderaum der Enterprise passen, ob sich die Enterprise wirklich in der Nähe des Sterns Sigma Draconis des Spektraltypus Gamma 9 befinden kann, oder warum man nur mit dem Warp-Antrieb die gigantischen Entfernungen des Universums überbrücken kann – all diese Fakten, die bei Star Trek immer wieder vorkommen, werden erklärt und gezeigt, dass bei Star Trek nichts dem Zufall überlassen bleibt, sondern alle genannten Daten immer auf handfester Physik beruhen.
06.07.2023 Dr. Henri Jaffrès