Irreversible dynamics in quantum many-body systems

Irreversibility, despite being a necessary condition for thermalization, still lacks a sound understanding in the context of isolated quantum many-body systems. In this work we approach this question by studying the behavior of generic many-body systems under imperfect effective time reversal, where the imperfection is introduced as a perturbation of the many-body state at the point of time reversal. Based on numerical simulations of the full quantum dynamics we demonstrate that observable echos occurring in this setting decay exponentially with a rate that is independent of the perturbation; hence, the sensitivity to perturbations is intrinsic to the system meaning that the dynamics is effectively irreversible

Effective time reversal and echo dynamics in the transverse field Ising model

The question of thermalisation in closed quantum many-body systems has received a lot of attention in the past few years. An intimately related question is whether a closed quantum system shows irreversible dynamics. However, irreversibility and what we actually mean by this in a quantum many-body system with unitary dynamics has been explored very little. In this work we investigate the dynamics of the Ising model in a transverse magnetic field involving an imperfect effective time reversal. We propose a definition of irreversibility based on the echo peak decay of observables. Inducing the effective time reversal by different protocols we find algebraic decay of the echo peak heights or an ever persisting echo peak indicating that the dynamics in this model is well reversible

Universal nonanalytic behavior of the Hall conductance in a Chern insulator at the topologically driven nonequilibrium phase transition

We study the Hall conductance of a Chern insulator after a global quench of the Hamiltonian. The Hall conductance in the long time limit is obtained by applying the linear response theory to the diagonal ensemble. It is expressed as the integral of the Berry curvature weighted by the occupation number over the Brillouin zone. We identify a topologically driven nonequilibrium phase transition, which is indicated by the nonanalyticity of the Hall conductance as a function of the energy gap m_f in the post-quench Hamiltonian H_f. The topological invariant for the quenched state is the winding number of the Green's function W, which equals the Chern number for the ground state of H_f. In the limit that m_f goes to zero, the derivative of the Hall conductance with respect to m_f is proportional to ln(|m_f|), with the constant of proportionality being the ratio of the change of W at m_f = 0 to the energy gap in the initial state. This nonanalytic behavior is universal in two-band Chern insulators such as the Dirac model, the Haldane model, or the Kitaev honeycomb model in the fermionic basis.Comment: 18 pages, 8 figure

Diffusion based degradation mechanisms in giant magnetoresistive spin valves

Spin valve systems based on the giant magnetoresistive (GMR) effect as used for example in hard disks and automotive applications consist of several functional metallic thin film layers. We have identified by secondary ion mass spectrometry (SIMS) two main degradation mechanisms: One is related to oxygen diffusion through a protective cap layer, and the other one is interdiffusion directly at the functional layers of the GMR stack. By choosing a suitable material as cap layer (TaN), the oxidation effect can be suppressed.Comment: 3 pages, 3 figures. to be published in Appl. Phys. Let

The Dynamics of Reactive Halogen Species at the Dead Sea Valley

Reactive halogen species (RHS) have a significant impact on the chemical composition of the atmosphere. With its high halite abundance and unique topography the Dead Sea Valley (DSV) is predestined for the investigation of RHS. In the frame work of this thesis, two extensive measurement campaigns were carried out at the DSV in May 2012 and November 2014. The comparison of MAX-DOAS and LP-DOAS data with meteorological measurements indicates strong impact of transport process on the observed trace gas dynamics. The strong depletion of NO2 mixing ratios during daytime coincides with increased RHS abundance and suggests the formation of halogenated nitrate compounds. These are assumed to enhance the release of RHS from aerosol surfaces by heterogeneous processes. Elevated, confined layers of BrO of up to 50 pptv suggest the release of reactive bromine compounds from aerosol surfaces. The correlation of IO with surface waves indicates abiotic iodine release as a result of increased gas exchange at the water surface. For the first time, gaseous molecular iodine (up to 70 pptv) was detected at the DSV serving as a precursor for reactive iodine. Further, first direct evidence for reactive chlorine chemistry at the DSV was found by the detection of OClO at mixing ratios of up to 6 pptv