Archiv 2016

Gastgeber: Martin Eckstein

Dynamical phase transitions in the long-range (powerlaw) interacting transverse-field Ising model

MPSD Seminar
Dynamical phase transitions (DPTs) have gained a lot of interest in the past few years in a variety of quantum many-body systems, where a system in its groundstate is quenched by abruptly changing a control parameter of the Hamiltonian, such as interaction strength or external field. Afterwards, a DPT can be detected in one of at least two forms: a type-I DPT which is detected, after relaxation in time, through the nonanalyticity of an appropriate order parameter as a function of the control parameter through which the quench is effected; and a type-II DPT which is detected as a nonanalyticity of the Loschmidt echo return rate as a function in time, without giving care as to whether or not a stationary state has been reached in the time evolution. [mehr]

Dynamics of the Transverse Field Ising Chain after a Sudden Quench

MPSD Seminar
Due to experimental advances in the preparation and control of ultra-cold atomic gases, there is a widespread interest in the behaviour of quantum systems out of equilibrium. A common way to probe quantum systems for non-equilibrium phenomena is given by sudden quenches. [mehr]

Nonequilibrium dynamics of strongly coupled phonon-mediated superconductors

CFEL Theory Seminar
Recent developments in ultra-fast laser techniques allow experimentalists to reveal intriguing aspects of the dynamics of superconductors such as the Higgs oscillations (amplitude oscillations of the order parameter) and photo-induced superconductivity. These experiments demonstrate the interesting possibility of manipulating superconductivity in nonequilibrium settings. However, the properties of nonequilibrium superconductors are not fully understood, and further theoretical explorations are needed. [mehr]

Transient Dynamics of d-Wave Superconductors after a Sudden Excitation

MPSD Seminar
In this talk I will discuss the transient dynamics of a d-wave BCS model after a quantum quench of the interaction parameter. The motivation comes from recent ultrafast pump-probe experiments on high-temperature superconductors. [mehr]

Disclosing fluctuations of lattice atomic positions in non-equilibrium optical experiments

MPSD Seminar
Fluctuations of the atomic positions are at the core of a large class of unusual material properties ranging from quantum para-electricity and charge density wave to, possibly, high temperature superconductivity. Their measurement in solids is the subject of an intense scientific debate focused on the research of a methodology capable of establishing a direct link between the variance of the ionic displacements and experimentally measurable observables. In this presentation I will introduce our new approach to address quantum and thermal fluctuation in complex materials. By means of non-equilibrium optical experiments performed in shot-noise limited regime we could reveal that the variance of the time dependent atomic positions and momenta is directly mapped into the quantum fluctuations of the photon number of the scattered probing light. A fully quantum description of the non-linear interactions between photonic and phononic fields pave the way for a direct measurement of fluctuation in complex systems. [mehr]

Dynamical Cooper pairing in non-equilibrium electron-phonon systems

MPSD Seminar
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