Archiv 2016

Raum: Seminar Room IV, O1.111 Gastgeber: Angel Rubio

Cedric Weber - Many body effects in transition metal molecular systems

MPSD Seminar
Phenomena that are connected to quantum mechanics, such as magnetism, transport, and the effect of impurity atoms and disorder, and their relation to material design and energy needs are important for almost every branch of the industry. Density functional theory (DFT) was successful at making accurate Predictions for many materials, in particular compounds which have a metallic behaviour. DFT combines high accuracy and moderate computational cost, but the computational effort of performing calculations with conventional DFT approaches is still non negligible and scales with the cube of the number of atoms. A recent optimised implementation of DFT was however shown to scale linearly with the number of atoms (ONETEP), and opened the route to large scale DFT calculations for molecules and nano-structures. Nonetheless, one bottleneck of DFT and ONETEP, is that it fails at describing well some of the compounds where strong correlations are present, in particular because the computational scheme has to capture both the band-like character of the uncorrelated part of the compound and the Mott-like features emerging from the local strongly correlated centres. A recent progress has been made in this direction by the dynamical mean-field theory (DMFT), that allows to describe the two limits (metal and insulator) in a remarkable precise way when combined with DFT. The ONETEP+DMFT implementation and strategies to overcome the main bottlenecks of this type of calculations will be discussed, and its applications illustrated by a few case of studies, such as the role of quantum entanglement in Myoglobin and heme systems. [mehr]

TDDFT in solids for electron dynamics induced by ultrashort laser pulses

MPSD Seminar
Since 2000, we have been developing a real-time, real-space computationalmethod based on time-dependent density functional theory to describe electron dynamics in crystalline solids induced by light pulses. In a microscopic scale, we solve the time-dependent Kohn-Sham equation in a unit cell of solid treating the applied electric field is by the vector potential. We further combine the microscopic calculation with the dynamics of light electromagnetic field in a multiscale modeling, as describe in the figure. In my presentation, I first explain our method including some historical aspects. Then I will show some recent and on-going applications such as energy transfer from a femtosecond laser pulse to electrons in quartz and graphite, and ultrafast changes of dielectric properties of diamond by an intense laser pulse. [mehr]

Nonlinear optical spectroscopy with nonclassical light, photon counting detection and extreme wavelengths techniques

CFEL Theory Seminar
The progress in quantum optics utilizes a unique photon state configuration for engineering of the ultimate light-matter interactions with relatively simple material systems. It results in a broad range of photonic applications including radiation sources, quantum communication, information, computing and nanotechnology. The development of the ultrafast multidimensional nonlinear spectroscopy that has been enabled by progress in ultrafast optical technology provides a unique tool for probing complex molecules, semiconductors, nanomaterials by classical light fields. [mehr]

Inflated nodes and surface states of topological superconductors

CFEL Theory Seminar
The new paradigm of topology in condensed matter physics does not only pertain to insulators and semimetals but also to superconductors. Topological superconductors are predicted to show many novel physical properties. [mehr]

Chemistry under Strong Coupling

MPSD Seminar
Light-matter interactions have been extensively studied by physicist in quantum optics and condensed matter physics, [1] but there are only fewer attempts to understand this effect in molecular science. [2, 3] [mehr]

Making Majoranas talk to charge

CFEL Theory Seminar
In this talk, I will first give an introduction to Majorana bound states (MBS), zero-energy modes predicted to appear in exotic spin-polarized p-wave superconductors. MBS satisfy non-Abelian statistics and, in addition, encode quantum information in a topologically protected manner, which makes them highly interesting for quantum computation applications. The required p-wave superconductivity seems to be hard to find in nature, but recent theoretical works have shown that it can instead be artificially engineered, for example in a semiconductor nanowire with strong spin-orbit coupling which is covered by a superconductor and exposed to a magnetic field. I will also discuss the recent experimental progress towards creating and detecting MBS. [mehr]

Nonequilibrium Study of Competing Orders

MPSD Seminar
Competition between ordered phases, and their associated phase transitions, are significant in the study of strongly correlated systems. [mehr]

The role of dynamical screening in correlated materials

CFEL Theory Seminar

Theory of light-induced Floquet topological states

CFEL Theory Seminar

Resonant inelastic x-ray scattering: recent experiments, current theoretical understanding, and future challenges

CFEL Theory Seminar
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