Path-integral Monte Carlo simulation

2018. 04. 16. 14:15
Building F, Entrance III, Department of Theoretical Physics, Library
Csaba Tőke (BME)

Title: "Path-integral Monte Carlo simulation of time-reversal noninvariant bulk systems with a case study of rotating Yukawa gases"

Abstract: "We elaborate on the methodology to simulate bulk systems in the absence of time-reversal symmetry by the phase-fixed path-integral Monte Carlo method under (possibly twisted) periodic boundary conditions. Such systems include two-dimensional electrons in the quantum Hall regime and rotating ultracold Bose and Fermi gases; time-reversal symmetry is broken by an external magnetic field and the Coriolis force, respectively. We provide closed-form expressions in terms of Jacobi elliptic functions for the thermal density matrix (or the Euclidean propagator) of a single particle on a flat torus under very general conditions. We then modify the multi-slice sampling method in order to sample paths by the magnitude of the complex-valued thermal density matrix. Finally, we demonstrate that these inventions let us study the vortex melting process of a two-dimensional Yukawa gas in terms of the de Boer interaction strength parameter, temperature, and rotation (Coriolis force). The bosonic case is relevant to ultracold Fermi-Fermi mixtures of widely different masses under rotation."

Cold fusion - low-energy nuclear reactions

2018. 06. 01. 09:15
Building F, Entrance III, room F3123
Péter Kálmán

Történeti áttekintés: Elfelejtett kísérletek a kvantummechanika megszületése előttről (1896-1927). A Fleischmann-Pons kísérlet (1989) - ellenérvek - a Coulomb taszítás. A hidegfúzió körüli vihar okairól. Alacsonyenergiás magreakciókon alapuló kutatás-fejlesztés napjainkban. A kvantummechanika perturbációszámításáról.


A hidegfúzió elméleti alapjai: Másodrendű folyamatok. A visszalökődés asszisztált LENR. A visszalökődés szerepe - a magyarázat kulcsa


Következmények: Visszalökődés plazmában. Visszalökődés asszisztált p+d->3He magreakció. Két fragmensű reakciók. A Fleischmann-Pons kísérlet az előzőek fényében.




Kálmán, P. and Keszthelyi, T.: Effect of impurities on nuclear fusion, arXiv 1712.05270v3.
Recoil assisted low energy nuclear reactions, J. Condensed Matter Nucl.Sci. 25 (2017) 142.
(Cooperative internal conversion process, J. Condensed Matter Nucl. Sci. 25 (2017) 129.)

Electric-field poling of improper ferroelectrics

2018. 06. 06. 09:30
Building F, entrance I, 1st floor, Schay room
Stephan Krohns (Augsburg)

Dr. Stephan Krohns
Experimental Physics V, University of Augsburg


Electric-field poling of improper ferroelectrics - step towards domain wall based nano electronics?


Manipulating domains within ferroelectric semiconductors has attracted attention in recent years for potentially allowing domains and domain walls to be used as functional elements in nanoelectronics. One type of multiferroic material, hexagonal manganites, has shown particular potential because of their unusual, improper ferroelectric properties. We report an electric-field poling study of the geometric-driven improper ferroelectric h-ErMnO3. From a detailed dielectric analysis, we deduce the temperature- and frequency-dependent range for which single-crystalline h-ErMnO3 exhibits purely intrinsic dielectric behavior. This provides a comprehensive experimental study addressing the switching dynamics in hexagonal manganites. Controlling the domain walls via electric fields brings us an important step closer to their utilization in resource-efficient domain-wall-based electronics.


[1] C. Helbig, C. Kolotzek, A. Thorenz, A. Reller, A. Tuma, M. Schafnitzel, S. Krohns, Benefits of Resource Strategy for Sustainable Materials Research and Development, Sustainable Materials and Technologies 12, 1–8 (2017).
[2] E. Ruff, S. Krohns, M. Lilienblum, D. Meier, M. Fiebig, P. Lunkenheimer, A. Loidl, Conductivity contrast and tunneling charge transport in the vortex-like ferroelectric domain patterns of multiferroic hexagonal YMnO3, Phys. Rev. Lett. 118, 036803 (2017)
[3] A. Ruff, Z. Li, A. Loidl, J. Schaab, M. Fiebig, A. Cano, Z. Yan, E. Boureet, J. Glaum, D. Meier, S. Krohns, Freqeuncy dependent polarisation switching in h-ErMnO3, Appl. Phys. Lett. 112, 182908 (2018).
[4] T.S. Holstad, D.M. Evans, A. Ruff, D.R. Smabraten, J. Schaab, Ch. Tzschaschel, Z. Yan, E. Bourret, S.M. Selbach, S. Krohns, D. Meier, Electronic bulk and domain wall properties in B-Site doped hexagonal ErMnO3, Phys. Rev. B 97, 085143 (2018).
[5] J. Schaab, S.H. Skjaervo, S. Krohns, X. Dai, M. Holtz, A. Cano, M. Lilienblum, Z. Yan, E. Bourret, D.A. Muller, M. Fiebig, S.M. Selbach, D. Meier, Electrical half-wave rectification at improper ferroelectric domain walls, arXiv:1803.08253