^{2}) infrared (IR) pulses. We monitored the system response by looking at the induced change in the absorbance with a 250-as pulse centred around 40 eV. We observed the appearance of oscillating features which modulate at twice the IR frequency, ωIR, and fully recover after the interaction. Simultaneous photoelectron acquisition from a gas nozzle placed in front of the diamond target allowed us to study the phase relation of the oscillating features and the pumping IR field. We found that the timing of the diamond response changes significantly with the probing energy and does not always follow the IR field adiabatically. Ab initio calculations performed by coupling time-dependent density functional theory (TDDFT) in real time with Maxwell’s equations reproduced the experimental observations. Further comparison with a numerical two-band model allowed us to conclude that intra-band motion dominates over inter-band transitions, thus identifying the dynamical Franz- Keldysh effect as the dominant mechanism in this regime. Our analysis constitutes an important step towards a full understanding of the optical properties of dielectrics in the Petahertz regime. [mehr]

_{3}are a rich family of ionic compounds with many technological interesting properties. They can be traditional inorganic, metal per- ovskites or hybrid perovskites with one organic cation. In this talk I want to discuss some results of a special modification of the latter kind, the so-called layered perovskites. This family of structures is currently rediscovered, and we report on the geometrical and electronic structure of one promising candidate ((C

_{6}H

_{5}C

_{2}H

_{4}NH

_{3})

_{2}PbI

_{4}) with phenethylammonium cations on the A-site and compare the differences towards the benchmark case of three-dimensional (3D) hybrid perovskites, CH

_{3}PbI

_{3}. The influence of varying the cation as well as changing the dimensionality from 3D to 2D systems is discussed by comparing bulk and monolayer structures of both systems. In addition, insight into the optical behavior and the observed electron-phonon coupling will be given. [mehr]

_{3}Fe

_{5}O

_{12}(YIG) and find a quenching of magnetic order on a time scale as short as 1 ps. This observation attests to a highly efficient coupling of crystal lattice and electron spins in this material. [mehr]

*g*" is generically the lowest order symmetry-allowed direct coupling of an IR-active phonon coordinate

_{2}n_{el }x^{2}_{IR}*x*to the electronic density

_{IR}*n*in systems with inversion symmetry. In this talk I will present model evidence for light-enhanced electron-phonon coupling and light-induced effective attraction between electrons based on nonlinear electron-phonon coupling [3], the latter of which was already discussed in a similar context in [4]. [1] M. Mitrano et al., Nature 530, 461 (2016) [2] E. Pomarico et al., Phys. Rev. B 95, 024304 (2017) [3] M. A. Sentef, arXiv: 1702.00952 [4] D. M. Kennes et al., Nature Physics (2017) , doi:10.1038/nphys4024, arXiv:1609.03802 [mehr]

_{el}_{2}, it has been found that the spin randomization is characteristically faster than the time scales for inter- and intra-valley scatterings. In this talk, I present our recent study of the ultrafast non-collinear spin dynamics of the electron in a valley of monolayer MoS2 by using real-time propagation time-dependent density functional theory. We found that the spin precession is sharply selectively coupled only with the particular optical phonon that lifts the in-plane mirror symmetry. We suggest that the observed spin randomization can be attributed to this spin-phonon interaction. Further, our results imply that flipping of spins in a spin-orbit-coupled system can be achieved by the control over phonons. In a later part of the talk, I would also describe the feature of the computational package we have developed and have used for the spin-phonon dynamics, which is based on the plane-wave basis set and various types of pseudopotentials. [mehr]

_{2}, and show that its success is the result of error compensation between semi-local and non-local exchange, resulting in a proper derivative discontinuity (reproduction of the band gap) and a total energy which is a linear function of the fractional occupation numbers (removing most of the electron self-interaction). As it is well known, however, HSE06 does not work equally well for all materials. On the example of Ga

_{2}O

_{3}, I will show that tuning both the mixing and the screening parameter of HSE for the given material allows to ensure the same error compensation. Unless the electronic screening is strongly direction- or orbital-dependent (as in ZnO), the optimized HSE hybrid is nearly self-interaction free and provides a band structure on par with GW. Since the total energy can also be calculated, the real equilibrium structure of a defect can be found and the levels are in good agreement with experimental observations. [mehr]

_{2}Se

_{3}/BSCCO [1] and graphene/h-BN [2,3]. Iwill show how the proximity effect (in Bi

_{2}Se

_{3}/BSCCO) and moire superlatticepotential (in graphene/h-BN) tune the electronic properties and further lead tothe realization of many novel quantum phenomena. The variety of 2D materialsgenerates great possibilities in 2D heterostructures which are waiting for moreresearch investigations. [mehr]

See 'more' for link for lecture notes and supportin material.
[mehr]

_{4,5}-edge (~30 eV). In the experiment, a 5 fs VIS-NIR pump pulse excites carriers across the direct band gap and the dynamics are probed with a time-delayed broadband extreme ultraviolet pulse generated by high harmonic generation in xenon spanning ~20-45 eV. The observed transient absorption signal contains the energetic distribution of both carriers, electrons and holes, due to state blocking as well as spectroscopic features induced by bandshifts (e.g. due to band gap renormalization) and broadening (e.g. due to many body effects). By iterative procedures the measured signal can be successfully decoupled into these contributions resolving the carrier and band dynamics with excellent time and energy resolution. Hot carrier relaxation on a 100-fs time scale and carrier recombination on a 1-ps time scale are observed in nanocrystalline Germanium. Going from bulk semiconductor to two-dimensional layers, long-lived core-exciton states are observed at the MoN

_{2,3}edge between 32 and 35 eV in MoS

_{2}. Comparing the XUV absorption spectra of bulk and monolayer MoS

_{2}, a ~4 eV red-shift suggests a tightly bound core-exciton. The lifetime of the core-exciton states can be directly measured in the time domain. Furthermore, transient Stark shifts, coherences, and coherent population transfer between different core-exciton states are observed. [mehr]

*Nat. Nanotechnol.,*6, 695-704 (2011) [2] de Jonge, N., et al.

*Proc. Natl. Acad. Sci.,*106, 2159-2164 (2009) [3] Peckys, D.B., et al.

*Sci. Adv.,*1, e1500165 (2015) [4] Dahmke, I.N., et al.

*ACS Nano,*11, 11108-11117 (2017) [5] Peckys, D.B., et al.

*Mol. Biol. Cell,*28, 3193-3202 (2017) [6] Verch, A., et al.

*Langmuir,*31, 6956–6964 (2015) [mehr]

Lecture notes see 'more'.
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Lecture notes see 'more'.
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Lecture notes see 'more'
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Lecture IV Abstract will follow.
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Lecture V Abstract will follow.
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Lecture VI Abstract will follow.
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_{c}~400mK). When a mm-sized structure is firmly coupled to a mm-sized substrate of different thermal expansion, the microstructure is under significant strain at low temperatures. By precisely controlling its shape, the emergent strain field can be controlled. The key difference to other approaches, such as uniaxial strain, is that complex, yet well-controlled, spatially varying strain fields can be achieved. In collaboration with Katja Nowack (Cornell), we have experimentally mapped out the resulting superconducting landscape in the devices using scanning-SQUID microscopy, and show that this spatial modulation can be well captured by finite element simulations. [1] Second, I will present our ongoing efforts to experimentally identify pseudo-magnetic fields in 3D Dirac semi-metals [2,3]. Owing to their Dirac dispersion, deformation of the crystal structure does not open a gap at the nodes, but shifts the location of the nodes in k-space and hence playing the role of a “pseudo-magnetic field”, B

_{5}. I will show how microstructuring gives us unprecedented control of such a process, and discuss how future. [mehr]