Disentangling dynamical phase transitions from equilibrium phase transitions

Dynamical phase transitions (DPT) occur after quenching some global parameters in quantum systems and are signalled by the non-analytical time evolution of the dynamical free energy, which is calculated from the Loschmidt overlap between the initial and time evolved states. In a recent letter (M. Heyl et al., Phys. Rev. Lett. \textbf{110}, 135704 (2013)), it was suggested that DPTs are closely related to equilibrium phase transitions (EPT) for the transverse field Ising model. By studying a minimal model, the XY chain in transverse magnetic field, we show analytically that this connection does not hold generally. We present examples where DPT occurs without crossing any equilibrium critical lines by the quench, and a nontrivial example with no DPT but crossing a critical line by the quench. Albeit the non-analyticities of the dynamical free energy on the real time axis do not indicate the presence or absence of an EPT, the structure of Fisher-lines for complex times reveal a qualitative difference.Comment: 5+1 pages, 3+1 figures; typos correcte

Topological classification of dynamical phase transitions

Dynamical phase transitions (DPT) are characterized by nonanalytical time evolution of the dynamical free energy. For general 2-band systems in one and two dimensions (eg. SSH model, Kitaev-chain, Haldane model, p+ip superconductor, etc.), we show that the time evolution of the dynamical free energy is crucially affected by the ground state topology of both the initial and final Hamiltonians, implying DPTs when the topology is changed under the quench. Similarly to edge states in topological insulators, DPTs can be classified as being topologically protected or not. In 1D systems the number of topologically protected non-equilibrium time scales are determined by the difference between the initial and final winding numbers, while in 2D no such relation exists for the Chern numbers. The singularities of dynamical free energy in the 2D case are qualitatively different from those of the 1D case, the cusps appear only in the first time derivative.Comment: 5 pages, 3 figure

Nonequilibrium transport and statistics of Schwinger pair production in Weyl semimetals

The non-equilibrium dynamics beyond linear response of Weyl semimetals is studied after a sudden switching on of a DC electric field. The resulting current is a nonmonotonic function of time, with an initial quick increase of polarization current followed by a power-law decay. Particle-hole creation \`a la Schwinger dominates for long times when the conduction current takes over the leading role, with the total current increasing again. The conductivity estimated from a dynamical calculation within a Drude picture agrees with the one obtained from Kubo's formula. The full distribution function of electron-hole pairs changes from Poissonian for short perturbations to a Gaussian in the long perturbation (Landau-Zener) regime. The vacuum persistence probability of high energy physics manifests itself in a finite probability of no pair creation and no induced current at all times.Comment: 7 pages, 4 figure

Új- és újabban járványos méretekben fellépő, gombák okozta növényi betegségek változó, globalizálódó világunkban = New and newly emerging fungal diseases of plants in the globalizated world

A kutatási program célja a globalizáció és klímaváltozás növényvédelmi következményeinek feltárása, a gazdanövények és kórokozóik földrajzi terjedése, és a változó klíma hatásai egyes eseteinek bemutatása. Kutatómunkánk eredménye mintegy 20 új növényi betegség és kórokozóik, új gazda - kórokozó kapcsolatok, újonnan fellépő betegségek, valamint kórokozó introdukció eseteinek feltárása. A kórokozók azonosítása morfológiai és molekuláris módszerekkel történt. Új megállapításaink között vannak lisztharmatbetegségek: (1) Platanus spp; (2) Pyrus calleryana; (3) Carpinus betulus; (4) Magnolia soulangiana; (5) Rosmarinus officinalis gazdanövényeken; rozsdabetegségek: (1) Pyrus calleryana; (2) Bellis perennis (fajták); (3) Levisticum officinale gazdanövényeken; peronoszpóra típusú betegségek: (1) Viola wittrockiana; (2) Coleus x hibridus; (3) Impatiens walleriana gazdanövényeken; levélnekrózis típusú betegségek: (1) Prunus tenella; (2) Pyrus calleryana; (3) Hordeum vulgare gazdanövényeken; antraknózisok: (1) Prunus amygdalus; (2) Prunus cerasus gazdanövényeken; talaj eredetű betegségek: (1) Allium sativum; (2) Ribes rubrum gazdanövényeken; komplex leromlás jellegűek: (1) Juglans regia; (2) Celtis spp. (3) Ribes rubrum növényeken. Új megállapításaink angol és magyar nyelven kerültek közlésre, ill. konferencia- és egyetemi előadások formájában kerültek ismertetésre. A program témájában két szemlecikk jellegű dolgozatunk jelent meg magyar nyelven | Main objective of the present project was to reveal phytopathological consequences of globalization and climate changes in Hungary, to demonstrate the consequences of the geographical redistribution of host plants and their pathogens, and changing weather conditions. Our studies have revealed more then 20 new diseases and their pathogens, new hostplant - pathogen connections, re-emerging diseases, and evidences of introduction or importation of new pathogens. Identification of pathogens has been carried out by morphological and molecular methods. Among the new cases were: powdery mildew diseases of (1) Platanus spp; (2) Pyrus calleryana; (3) Carpinus betulus; (4) Magnolia soulangiana; (5) Rosmarinus officinalis; rust diseases of: (1) Pyrus calleryana; (2) Bellis perennis (cultivars!); (3) Levisticum officinale; mildew diseases of (1) Viola wittrockiana; (2) Coleus x hibridus; (3) Impatiens walleriana; leaf spot diseases of: (1) Prunus tenella; (2) Pyrus calleryana; (3) Hordeum vulgare; anthracnose diseases of: (1) Prunus amygdalus; (2) Prunus cerasus; soilborn diseases of: (1) Allium sativum; (2) Ribes rubrum; decline diseases of: (1) Juglans regia; (2) Celtis spp. (3) Ribes rubrum. Most of the new findings have been published in English and Hungarian, and in form of lectures delivered on special conferences and in universities. Two papers concerning phytopathological consequences of globalization and climate changes were published in Hungaria

Floquet topological phases coupled to environments and the induced photocurrent

We consider the fate of a helical edge state of a spin Hall insulator and its topological transition in presence of a circularly polarized light when coupled to various forms of environments. A Lindblad type equation is developed to determine the fermion occupation of the Floquet bands. We find by using analytical and numerical methods that non-secular terms, corresponding to 2-photon transitions, lead to a mixing of the band occupations, hence the light induced photocurrent is in general not perfectly quantized in the presence of finite coupling to the environment, although deviations are small in the adiabatic limit. Sharp crossovers are identified at frequencies $\Omega$ and $\frac{1}{2}\Omega$ ($\Omega$ is the strength of light-matter coupling) with the former resembling to a phase transition.Comment: 7+4 pages, 6+2 figure