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

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

Investigation of drug distribution in tablets using surface enhanced Raman chemical imaging

This paper reports the first application of surface enhanced Raman chemical imaging on pharmaceutical tablets containing the active ingredient (API) in very low concentrations.Taking advantage of the extremely intensive Raman signals in the presence of silver colloids,image aquisition time was radically decreased. Moreover, the investigation of drug distribution below the detection limit of regular micro-Raman spectrometry was made feasible. The characteristics of different manufacturing technologies could be revealed at very low API concentrations by using chemometric methods for processing and evaluating the large number of varying spectra provided with this imaging method

Remarkable impact of PAHs and TPHs on the richness and diversity of bacterial species in surface soils exposed to long-term hydrocarbon pollution

Nowadays, because of substantial use of petroleum-derived fuels the number and extension of hydrocarbon polluted terrestrial ecosystems is in growth worldwide. In remediation of aforementioned sites bioremediation still tends to be an innovative, environmentally attractive technology. Although huge amount of information is available concerning the hydrocarbon degradation potential of cultivable hydrocarbonoclastic bacteria little is known about the in situ long-term effects of petroleum derived compounds on the structure of soil microbiota. Therefore, in this study our aim was to determine the longterm impact of total petroleum hydrocarbons (TPHs), volatile petroleum hydrocarbons (VPHs), total alkyl benzenes (TABs) as well as of polycyclic aromatic hydrocarbons (PAHs) on the structure of bacterial communities of four different contaminated soil samples. Our results indicated that a very high amount of TPH affected positively the diversity of hydrocarbonoclastic bacteria. This finding was supported by the occurrence of representatives of the a-, b-, c-Proteobacteria, Actinobacteria, Flavobacteriia and Bacilli classes. High concentration of VPHs and TABs contributed to the predominance of actinobacterial isolates. In PAH impacted samples the concentration of PAHs negatively correlated with the diversity of bacterial species. Heavily PAH polluted soil samples were mainly inhabited by the representatives of the b-, c- Proteobacteria (overwhelming dominance of Pseudomonas sp.) and Actinobacteria

Distribution of bacterial single cell parameters and their estimation from turbidity detection times

The stochastic growth of homogeneous bacterial populations in the wells of a microtiter plate was studied as a function of the random initial cell number and their random individual lag times. These significantly affected the population growth in the well, while the maximum specific growth rate of the population was constant (or its variance was negligible) for each well. We showed the advantages of the mathematical assumption that a transformation of the single cell lag time, called the single cell physiological state (or, more accurately, that of the sub-population generated by the single cell) follow the Beta distribution. Simulations demonstrated what patterns would such assumption generate for the distribution of the detection times observed in the wells. An estimation procedure was developed, based on the beta-assumption, that resulted in an explicit expression for the expected value of the single cell physiological state as a function of measured “time to detection” values using turbidity experiments. The method was illus- trated using laboratory data with Escherichia coli, Salmonella enterica subsp. enterica strains. The results gave a basis to quantify the difference between the studied organisms in terms of their single-cell kinetics

Diverging dc conductivity due to a flat band in disordered pseudospin-1 Dirac-Weyl fermions

Several lattices, such as the dice or the Lieb lattice, possess Dirac cones and a flat band crossing the Dirac point, whose effective model is the pseudospin-1 Dirac-Weyl equation. We investigate the fate of the flat band in the presence of disorder by focusing on the density of states (DOS) and dc conductivity. While the central hub-site does not reveal the presence of the flat band, the sublattice resolved DOS on the non-central sites exhibits a narrow peak with height 1/pg with g the dimensionless disorder variance. Although the group velocity is zero on the flat band, the dc conductivity diverges as ln(1/g) with decreasing disorder due to interband transitions around the band touching point between the propagating and the flat band. Generalizations to higher pseudospin are given