Archiv 2017

Raum: Seminar Room III, EG.080

Franco Bonafé - Time-dependent electron-nuclear dynamics in DFTB+: theory and applications

MPSD Seminar
This seminar will be focused on an implementation of electron-nuclear real-time dynamics within the Density Functional Tight-Binding (DFTB) formalism in the DFTB+ package[1], as a result of a collaboration between the Quantum Dynamics Group (University of Córdoba) and the BCCMS (University of Bremen). Some theory details will be presented as well as its application to explain the launching of mechanical oscillations in metal nanoparticles under plasmon-resonant laser illumination[2]. [mehr]

Shaul Mukamel - Ultrafast Multidimensional Spectroscopy of Molecules with x-ray pulses and Quantum Light in Microcavities

MPSD ARD Seminar
Multidimensional spectroscopy uses sequences of optical pulses to study dynamical processes in complex molecules through correlation plots involving several time delay periods. Extensions of these techniques to the x-ray regime will be discussed. Ultrafast nonlinear x-ray spectroscopy is made possible by newly developed free electron laser and high harmonic generation sources. The attosecond duration of X-ray pulses and the atomic selectivity of core X-ray excitations offer a uniquely high spatial and temporal resolution. Stimulated Raman detection of an X-ray probe may be used to monitor the phase and dynamics of nonequilibrium valence electronic state wavepackets created by e.g. photoexcitation, photoionization and Auger processes. Novel ultrafast X ray probes for strongly coupled electron-nuclear dynamics , techniques based on a coherent stimulated Raman process that employs a composite femtosecond/attosecond X-ray pulse to directly detect the electronic coherences (rather than populations) , and new imaging techniques based on x-ray diffraction from electronic coherence will be presented. Nonlinear optical signals induced by quantized light fields and entangled photon pairs are presented. Conventional nonlinear spectroscopy uses classical light to detect matter properties through the variation of its response with frequencies or time delays. Quantum light opens up new avenues for spectroscopy by utilizing parameters of the quantum state of light as novel control knobs and through the variation of photon statistics by coupling to matter. Entangled-photon pairs are not subjected to the classical Fourier limitations on the joint temporal and spectral resolution. Strong coupling of molecules to the vacuum field of micro cavities can modify the potential energy surfaces thereby manipulating the photophysical and photochemical reaction pathways. Crossings of electronic potential surfaces in nuclear configuration space, known as conical intersections, determine the rates and outcomes of virtually all photochemical molecular processes. Strong coupling of molecules to the quantum vacuum field of micro cavities that can be used to manipulate their photophysical and photochemical reaction pathways and polariton relaxation in photosynthetic antennae are demonstrated. [mehr]

Binghai Yan - Nonlinear optical responses of Weyl semimetal materials

MPSD Seminar
In the band structure of a Weyl semimetal (WSM), the conduction and valence bands cross each linearly through Weyl points that are usually treated as “monopoles” of the Berry curvature. As a second-order response, WSMs were very recently demonstrated to show strong nonlinear optical effects including an exotic nonlinear Hall effect. This is caused by the non-equilibrium distribution of the Berry curvature, described as the “dipole” of the Berry curvature. In this talk, I will talk about our recent computational results on nonlinear response for representative WSM materials TaAs and MoTe2. [mehr]

Lipeng Chen - Theory meets spectroscopy: ensemble and single-molecule spectroscopic studies of ultrafast energy transfer processes in light harvesting systems

MPSD ARD Seminar
To a large extent, our knowledge of the photoinduced dynamics of molecular systems at the atomic level is shaped by nonlinear femtosecond spectroscopy. Traditionally, nonlinear femtosecond spectroscopy is an ensemble spectroscopy, performed on ensembles of identical chromophores in the gas phase or in the liquid phase. Modern femtosecond spectroscopy comprises a set of various third-order or higher-order technique including, for example, fluorescence up conversion, transient absorption, and photon echo spectroscopy. Very recently, the portfolio of femtosecond techniques has been extended towards singlemolecule detection by the development of fluorescence-detected double-pump singlemolecule spectroscopy. With this technique, a temporal resolution of about ten femtoseconds has been achieved. The technique permits the real-time monitoring of not only electronic populations, but also of electronic and vibrational coherence for individual molecules. [mehr]

Ryan Requist - Reduced formula for the macroscopic polarization including quantum Fluctuations

MPSD Seminar
The macroscopic polarization of a solid is an fundamental quantity from which permittivity and piezoelectric tensors can be derived. The Berry phase formula of King-Smith and Vanderbilt expresses the macroscopic polarization in terms of the Bloch states of a mean-field band structure, almost invariably taken from density functional theory. Although this procedure has been successful for many materials, quantum fluctuations cause it to break down in strongly correlated systems. [mehr]

Good scientific practice

IMPRS-UFAST skills course
Want to learn more about good scientific practice? This course wants to support doctoral students to develop a responsible professional conduct as researchers. You will gain a general understanding of good scientific practice and scientific misconduct. [mehr]

Dr. Heloise Therien-Aubin - Engineering the interface of nanocolloids with polymers

MPSD Seminar
In the design of nanocolloids for targeted applications, whether the nanoparticles are used as drug delivery vehicles or as filler in nanocomposites, it is crucial to control the stability, the miscibility and/or the self-assembly of the nanocolloids. In order to gain such control, the surface of the nanocolloid is frequently functionalized by tethering a corona of either small molecules or polymer chains. The nature and the composition of the corona formed by the tethered molecules dictate the interactions between the nanocolloids and their environment and thus the final behavior of the material. Nanoparticles functionalized with a corona of polymer brush were used in the design of hierarchically structured materials and displayed new collective properties. By varying the degree of polymerization, the grafting density and the chemical composition of the polymer chains, a variety of structures were obtained. We now want to establish a correlation between the mesoscopic properties observed in these nanoparticle-based systems with the properties, structure and dynamic of the polymer brush layer. [mehr]

Tong Zhou - Quantum Spin-quantum Anomalous Hall Effect with Tunable Edge States in Sb Monolayer-based Materials

MPSD Seminar
The quantum anomalous Hall (QAH) effect, quantum spin Hall (QSH) effect and (quantum) valley Hall ((Q)VH) effect have attracted considerable attention in condensed matter physics and material science. Generally, only one of the QAH, QSH, and QVH effects can be realized in a specific system. It would be very interesting if these three effects can be achieved in one single system. In this talk, I shall represent this interesting imagination may be realized in Sb monolayer-based materials, where the QAH state occurs at one valley and the QSH state occurs at the other valley, called quantum spin-quantum anomalous Hall (QSQAH) effect. [mehr]
Many-Body Perturbation Theory (MBPT) is a methodology routinely employed in computational spectroscopy to calculate photoemission and absorption spectra. However, usually these computational experiments are only possible for real nanostructures, solids, etc. by resorting to simple approximations in which, e.g., self-consistency is neglected. [mehr]

Getting tasks done

IMPRS-UFAST skills course
A PhD is a marathon not a sprint. The sheer number of different tasks that need to be done can sometimes be overwhelming. Being able to set goals, prioritise tasks and remain motivated are skills essential for the progression and achievement of your PhD. [mehr]
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