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Systems which rapidly evolve through symmetry-breaking transitions on timescales comparable to the fluctuation timescale of the single-particle excitations may behave very differently than under controlled near-ergodic conditions. A real-time investigation with high temporal resolution may reveal new insights into the ordering through the transition that are not available in static experiments. We present an investigation of the system trajectory through a normal-to-superconductor transition in a prototype high-temperature superconducting cuprate in which such a situation occurs. Using a multiple pulse femtosecond spectroscopy technique we measure the system trajectory and time-evolution of the single-particle excitations through the transition in La1.9Sr0.1CuO4 and compare the data to a simulation based on time-dependent Ginzburg-Landau theory, using laser excitation fluence as an adjustable parameter controlling the quench conditions in both experiment and theory. The comparison reveals the presence of significant superconducting fluctuations which precede the transition on short timescales. By including superconducting fluctuations as a seed for the growth of superconducting order we can obtain a satisfactory agreement of the theory with the experiment. Remarkably, the pseudogap excitations apparently play no role in this process.The study of the time evolution of complex systems through symmetry breaking transitions (SBT) is of great fundamental interest in different areas of physics [1][2][3]. An SBT of particular general interest is the normal-tosuperconducting (N → S) state transition in which a Lorentz non-invariant system breaks gauge invariance. [4] By studying the N → S transition in time-evolving systems, rather than by slowly varying the temperature through the transition, one can in principle gain new information on the dynamical behavior of elementary excitations which lead to the formation of a superconducting condensate and the collective ordering behavior, leading to new insights into non-ergodic phenomena of collectively ordered systems as well as the mechanism of superconductivity. Particularly, ergodicity breaking in rapidly evolving systems leads to the appearance of topological defects (vortices).The description of the dynamical behavior of the gauge non-invariant systems is given in the timedependent Ginzburg-Landau theory (TDGL theory). It has been first applied to the problem of non-equilibrium phase transitions by Kibble and Zurek who considered the appearance of topological defects throughout the transition.[5, 6] The Kibble-Zurek description has been indirectly confirmed to be correct by static experiments in which trapped vortices were studied. [7,8] In this paper, beyond previous static studies, we study realtime evolution of the superconducting order in the nonequilibrium phase transition. We investigate the applicability of TDGL theory to the phase transition problem and provide a minimal formulation sufficient to describe the data.The paper is organized in the following way: we ...

The current-voltage characteristics of long and narrow superconducting channels are investigated using the time-dependent Ginzburg-Landau equations for complex order parameter. We found out that the steps in the current voltage characteristic can be associated with bifurcations of either steady state or oscillatory solution. We revealed typical instabilities which induced the singularities in current-voltage characteristics, and analytically estimated period of oscillations and average voltage in the vicinity of the critical currents. Our results show that these bifurcations can substantially complicate dynamics of the order parameter and eventually lead to appearance of such phenomena as multistability and chaos. The discussed bifurcation phenomena sheds a light on some recent experimental findings.

α-Ureidoalkylation of N-carbamoyl-α-amino acids (II) and (VI) with imidazolidinones (I) and (V) affords a new type of glycolurils which contain N-alkyl, phenyl and (S)-α-carboxyalkyl groups in various combinations. The yields and diastereoselectivity in the syntheses of glycolurils are affected by both the amount of HCl added as well as the structures of the educts. Increasing the amount of HCl increases the diastereoselectivity but decreases the yield of the glycolurils, due to an increase of the yield of hydantoin by-products. Attempts to separate the mixtures of diastereomers are unsuccessful. - (BARANOV, V. V.; KRAVCHENKO*, A. N.; BELYAKOV, P. A.; MAKHOVA, N. N.; Mendeleev Commun. 18 (2008) 2, 96-98; Zelinsky Inst. Org. Chem., Russ. Acad. Sci., Moscow 117913, Russia; Eng.) -H. Hoennerscheid 38-116

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