| letzte Änderung (09:00)

Fachbereichskolloquien

Allgemeines Physikalisches Kolloquium
© WWU

Fachbereichs-Kolloquium im WS 2020/21

Aufgrund der aktuellen Lage findet das Kolloquium online (per ZOOM) statt.

  • 26.11.2020

    Mikhail M. Glazov

    Ioffe institute, st. Petersburg, russia

    Einladender: Dr. Arora  |  PDF  |

    Zugangsdaten:
    https://wwu.zoom.us/j/95528553602
    Passwort: Phys20-21


    Quantum effects in optics and transport of excitons in atomically thin semiconductors

    Two-dimensional (2D) semiconductor systems based on quantum wells have revolutionized modern electronics and optoelectronics. Recently, another class of stable 2D materials starting with graphene and transition metal dichalcogenides (TMDCs) such as MoS2 have revealed novel physics at the fundamental level offering unique functionalities relevant for future applications in ‘valleytronics’ and quantum technologies. Atomically thin TMDCs possess spectacular optical and transport properties. Strong Coulomb interaction binds electrons and holes in excitons: neutral quasi-particles with considerable (up to several hundreds of meV) binding energies [1]. I present a brief overview of the key quantum effects in excitonic transport and optical properties in my talk. Particularly, I will describe the main features of the band structure and excitonic properties of TMDC monolayers and then I will focus on two phenomena including the Valley Hall effect and the charged exciton-polarons. In this talk, I will emphasize the phenomena inherent to the atomically thin semiconductors.

    References:

    [1] Gang Wang, et al. Rev. Mod. Phys. 90, 021001 (2018)
    [2] M. M. Glazov and L. E. Golub, et al. Phys. Rev. Lett. 125, 157403 (2020)
    [3] A. Arora, et al. Phys. Rev. Lett. 123, 167401 (2019)
    [4] K. Wagner, et al. arXiv:2007.05396 (2020)

    Schematics of the VHE for excitons, with the black arrow Fd showing the drag force and arrows denoting the propagation directions of the excitons in the opposite valleys. The figure illustrates the skew scattering where the excitons are separated due to the asymmetric scattering by impurities or phonons.
    © M. Glazov

03.12.2020

Pd dr. Harry Mönig

WWU Münster, Physikalisches Institut

Antrittsvorlesung

Einladender: Dekan des FB Physik  |  PDF  |

Zugangsdaten:
https://wwu.zoom.us/j/95528553602
Passwort: Phys20-21


Nanoscale interface analytics for solar cells and in surface chemistry

In this lecture, I will present experiments from scanning probe microscopy, which allows imaging the topography of a surface with an atomic-scale resolution. Furthermore, the methodology provides spectroscopic information about the local surface electronic structure or about the interatomic force interaction with piconewton sensitivity. As a complementary technique we use photoelectron spectroscopy providing not only information about the surface composition, but also about the global electronic properties and chemical binding states. With these correlating methods, we investigate the defect physics of materials used in thin film solar cells. In particular, we analyse the defect-electronic structure and dipole layer formation with a spatial resolution of a few nanometers. Our results help to develop new strategies for the efficiency optimization of these solar cells.

In a different research field, we focus on the properties of various atomically defined probe tips allowing for ultrahigh resolution in atomic force microscopy. Recently, we demonstrated the outstanding imaging properties of a copper-based tip, which is terminated by a covalently bound single oxygen atom. Based on the high structural stability of this tip, we were able to image single hydrogen bonds in a complex organic network. In our latest work we perform force measurements during the controlled manipulation of single xenon atoms on a laterally anisotropic surface with various atomically defined tip structures. Our results show drastic differences in the force interaction from tip to tip providing fundamental insights in the nano-mechanical properties and chemical reactivity in atomically defined contacts.
A, Schematic representation of a force measurement at an oxide boundary during the lateral displacement of a single atom by an atomically defined tip (here: Xe-tip). B, Topography image of a single Xe atom nucleated next to the oxide domain boundary (upper panel). Vertical force field recorded during the manipulation experiment with a Xe-tip (lower panel). C, Corresponding lateral forces and energy dissipation at various tip heights.
© H. Mönig

10.12.2020

TBA

TBA

Einladende/r:


TBA

17.12.2020

laura fabbietti

TU MÜNCHEN, Physik-Department, Dense and Strange hadronic matter

Einladender: Prof. Andronic


renaissance of nuclear physics at the lhc

07.01.2021

stefan schoenert

TU München, Physik-Department

Einladender: Prof. Weinheimer


TBA

14.01.2021

MARC AẞMANN

TU DORTMUND, fakultät physik, experimentelle physik 2

Einladende: Jun.-Prof. Reiter  |  PDF  |


An Unexpected Twist - Vortex Control in Optically Imprinted Polariton Landscapes

Exciton-polaritons are mixed light-matter quasiparticles arising due to the strong coupling of photons and excitons inside a semiconductor microcavity. As they are composite bosons of low mass, they may form a macroscopically coherent non-equilibrium condensate at elevated temperatures [1], which led to fascinating demonstrations of superfluidity [2] and quantized vortices [3] in the solid state. The photons leaking from the cavity are a part of the polariton wave function. Thus, the properties of the polariton condensate, including its energy, spin, momentum and phase may be investigated by spectroscopic means.

Under non-resonant excitation, polaritons form spontaneously from free carriers and form a condensate that interacts with them. As polaritons are several orders of magnitude lighter than these carriers, the latter effectively form a static repulsive potential for the condensed polaritons. Spatially shaping the excitation beam then enables us to investigate polariton condensates in optically imprinted potential landscapes. We show how to utilize them to control the momentum and direction of flowing polaritons. Further, we discuss the creation of quantized vortices that couple directly to the orbital angular momentum of the emitted light. Finally, we demonstrate how to robustly switch the flow direction of such a vortex using a time-dependent potential and monitor the switching dynamics using a dedicated orbital angular momentum spectroscopy technique with picosecond temporal resolution [4], which opens up new perspectives for polaritonics.

References:

[1] J. Kasprzak et al., Nature 443, 409 (2006).
[2] A. Amo et al., Nat. Phys. 5, 805 (2009).
[3] K.G. Lagoudakis et al., Nat. Phys. 4, 706 (2008).
[4] X. Ma et al., Nat. Comm. 11, 897 (2020).

© M. Aßmann

21.01.2021

TBA

TBA

Einladende/r:


TBA

28.01.2021

tba

tba

Einladende/r:


TBA

04.02.2021

TBA

TBA

Einladende/r:


TBA

11.02.2021

TBA

TBA

Einladende/r:


TBA