Coarsening Dynamics in Nematic Liquid Crystals

Manipulation of m = 1 topological disclination line core structure

The precise manipulation of electronic properties through the introduction of foreign atoms—doping—remains the central paradigm of condensed matter physics and the foundational technology of the information age. From the early formulation of rigid-band semiconductor theory to the contemporary exploration of quantum materials, the physics of doping has evolved from a perturbative treatment of impurities to a complex study of thermodynamic self-regulation, symmetry breaking, and topological phase transitions.1While the twentieth century was defined by the mastery of covalent semiconductors like silicon (Si) and gallium arsenide (GaAs), where dopants act as simple hydrogenic centers, the current frontier involves

We study the influence of random anisotropy type quenched disorder on the phase behavior of the system, which exhibits in undistorted case the 2nd order continuous symmetry breaking phase transition. Invoking the central limit theorem we express the free energy of the system in terms of the order parameter η and the characteristic length ξ of the gauge field ϕ. The latter exhibits the Goldstone fluctuation mode and is consequently extremely susceptible to the imposed disorder. In case of negligible distribution width ΔT of the local transition temperatures the disorder converts the 2nd order transition into a discontinuous one for W<WC, where Wrepresents the disorder strength. Above the critical disorder strength WC the transition becomes gradual. However for the finite width ΔT the transition becomes gradual for any W>0. We demonstrate that for large enough values of ΔT the system behavior is dominated by the distribution of temperatures, while the details of the random field interaction term play a secondary role. The influence of distribution of local (quasi) phase transitions is in most theoretical approaches dealing with randomly perturbed systems neglected from the outset.

Understanding and working with liquid crystals requires a multidisciplinary set of skills that brings topics normally associated with physics, chemistry, and condensed matter physics to bear on a single problem. In this book our interest is to emphasize another discipline—that of optics—which, based on what we have discussed so far, has been a driving application for liquid crystals, as they are a primary component of display technologies. The unique properties of liquid crystals revolve around the position and orientation of their molecules, topics closely associated with condensed matter physics. The tools of condensed matter physics, which deals with the physics of the phases of condensed matter and attempts to explain the observed behavior drawing from thermodynamics and statistical mechanics, have evolved over time, in particular, with the acceptance of quantum mechanics. The early studies that led to the acceptance of quantum mechanics often involved studies of crystal structures, and the use of x-ray diffraction led to the understanding of the order structure of crystals being related to the orientation of atoms in a lattice. The positional variations of properties, anisotropies, are modeled to incorporate the uniqueness of each direction using tensor mathematics. Tensor descriptions of systems are not new in the area of condensed matter physics, and, clearly, liquid crystals deal with the more familiar condensed phases of solids and liquids and, in particular, crystals and liquids. The importance of position and orientation in describing the molecules of liquid crystals makes the descriptions common in condensed matter physics useful in modeling the anisotropies of liquid crystals and lead rapidly to the need to delve into the mathematical topic of vectors and tensors for describing liquid crystals.

Journal of Physics G: Nuclear and Particle Physics is committed to bringing its readers timely reviews in topics of interest to the nuclear and particle physics community, and an active programme of Topical Reviews is scheduled for future issues. Appropriate topics and authors are identified by the Editorial Board prior to invitation and commissioning of reviews, but any suggestions of suitable topics or offers of review contributions will be welcomed by the Board.

The observation of genuine quantum effects in systems governed by non-Hermitian Hamiltonians has been an outstanding challenge in the field. Here we simulate the evolution under such Hamiltonians in the quantum regime on a superconducting quantum processor by using a dilation procedure involving an ancillary qubit. We observe the parity–time ({mathcal{PT}})-symmetry breaking phase transition at the exceptional points, obtain the critical exponent, and show that this transition is associated with a loss of state distinguishability. In a two-qubit setting, we show that the entanglement can be modified by local operations.

Fermion interactions in models with strong Wilson-Yukawa couplings

Our understanding of the mechanism by which topological defects are formed in symmetry breaking phase transitions has recently changed. We examine the non-equilibrium dynamics of defect formation for weakly-coupled global O(N) theories possessing vortices (strings) and monopoles. It is seen that, as domains form and grow, defects are swept along on their boundaries at a density of about one defect per coherence area (strings) or per coherence volume (monopoles).

The paper is devoted to the memory of Dmitry Diakonov. We discuss gravity emerging in the fermionic vacuum as suggested by Diakonov 10 years ago in his paper “Towards lattice-regularized Quantum Gravity”. [1] Gravity emerges in the phase transition. The order parameter in this transition is the tetrad field e^a_mu, which appears as the bilinear composite of the fermionic fields. The similar scenario of the symmetry breaking takes place in the B-phase of superfluid ^3He, where the real part of the spin-triplet p-wave order parameter matrix A_{a i} plays the role of the emerging tetrad (triad). In Diakonov theory this symmetry breaking gives 6 Nambu-Goldstone modes; 6 gauge bosons in the spin-connection fields, which absorb 6 NG modes and become massive gauge bosons; and 6 Higgs fields. In ^3He-B, these Higgs collective modes correspond to 6 massive gravitons, while in the emerging general relativity the Higgs collective modes give rise to two massless gravitational waves.

In this paper we present the study of the topology of the equipotential hypersurfaces of configuration space of the mean-field ϕ^{4} model with a Z_{2} symmetry. Our purpose is discovering, if any, the relation between the second-order Z_{2}-symmetry-breaking phase transition and the geometric entities mentioned above. The mean-field interaction allows us to solve analytically either the thermodynamic in the canonical ensemble or the topology by means of Morse theory. We have analyzed the results in the light of two theorems on sufficiency conditions for symmetry-breaking phase transitions recently proven. This study is part of a research line based on the general framework of geometric-topological approach to Hamiltonian chaos and critical phenomena.

Cosmic strings are generic cosmological predictions of many extensions of the standard model of particle physics, such as a $U(1{)}^{\ensuremath{'}}$ symmetry-breaking phase transition in the early Universe or remnants of superstring theory. Unlike other topological defects, cosmic strings can reach a scaling regime that maintains a small fixed fraction of the total energy density of the Universe from a very early epoch until today. If present, they will oscillate and generate gravitational waves with a frequency spectrum that imprints the dominant sources of total cosmic energy density throughout the history of the Universe. We demonstrate that current and future gravitational wave detectors, such as LIGO and LISA, could be capable of measuring the frequency spectrum of gravitational waves from cosmic strings and discerning the energy composition of the Universe at times well before primordial nucleosynthesis and the cosmic microwave background where standard cosmology has yet to be tested. This work establishes a benchmark case that gravitational waves may provide an unprecedented, powerful tool for probing the evolutionary history of the very early Universe.

“In recent years the ideas of decay of a metastable state by quantum tunnelling of a field, and also of tunnelling between degenerate vacua, have played a major role in particle physics. Analogous problems occur also in condensed-matter physics, where they tend to be more tractable quantitatively because the role of the field is mainly to provide dissipation for the “primary” tunnelling variable. While the explicitly field-theoretic aspects of the problem are in this sense rather trivial, many of the techniques popular in quantum field theory have been applied successfully to such condensed-state problems, and I review here some of these applications.”

Reflections on spontaneous symmetry breaking, and the connection between condensed matter physics and particle physics, as given in a talk at a symposium at the University of Illinois in Urbana, celebrating the 50th anniversary of the theory of superconductivity.

Professor Nikolay Kirov Nikolov graduated in Chemistry from Sofia University ‘St. Kliment Ohridski’, Bulgaria, in 1968. He received his Ph.D. degree in 1973, D.Sc. in 1988 and was appointed to the position of Professor of Physics in the Institute of Solid State Physics (ISSP), Bulgarian Academy of Sciences (BAS), in 1989. Prof. Kirov rose to become an international authority in the area of molecular spectroscopy, and in particular in the vibrational spectroscopy of thermotropic liquid crystals.Prof. Kirov was a scientist of high reputation both in Bulgaria and globally. His scientific papers, numbering some 150, focus on the physics of liquid crystals. His systematic investigations of the vibrational spectroscopy of a wide class of thermotropic liquid crystals were collected in the monograph Vibrational spectroscopy of liquid crystals (1984), in which the molecular structure and properties of various liquid crystals, vibrational assignments, orientational order parameters and their calculation by molecular dynamics are presented. A range of liquid crystal materials was categorised and reported in his second book Atlas of vibrational spectra of liquid crystals (1988). Both publications remain a valuable source of information for specialists in the field of molecular spectroscopy. The outstanding contributions and growing reputation of Prof. Kirov led to periods as Visiting Scientist in the Universities of Parma, Calabria and Wroclaw. His abilities as a scientific organizer and leader were also notable, and led to a long and distinguished period of service in the Institute of Solid State Physics, being first appointed in 1980 as Scientific Secretary, and subsequently as Head of the Laboratory of Optics and Spectroscopy (1990-1998) and Director of the Institute (1991-1999). He was Chairman of the Scientific Council of ISSP over this period, and a member of the Specialized Scientific Council on Condensed Matter Physics. Prof. Kirov was a member of the High Testimonial Committee of the Republic of Bulgaria during 1996.Nikolay Kirov was a key figure in the organization, promotion and success of the International School on Condensed Matter Physics (ISCMP), where he was able to use his network of international contacts to excellent effect. He served as Scientific Secretary (1988-1990), Chairman and Editor of the ISCMP Proceedings (1992-1998), and as Chairman Emeritus (2002-2012).Prof. Kirov is an Honorary Member of the Institute of Solid State Physics. He received the Honorary Diploma ‘Nicola Obreshkov’ in 1986 and the “Marin Drinov” Sign of Honour BAS (on a ribbon) in 1998, for achievements in the physical and mathematical sciences. He was also honoured outside his native Bulgaria, receiving a Gold Medal from Wroclaw University, Poland, in recognition of successful scientific collaborations in the area of molecular structure.

The dynamics of stringlike defects and the shrinkage and annihilation processes of individual defect loops in a nematic polymer liquid crystal have been experimentally investigated. In 40<t<500 s, the line density of defects ρ scales as ρ(t)∼t−1, as expected by theory and as found in the experimental studies of some low molecular weight (LMW) liquid crystals. For individual loops, they first change their complex shape into a circle, resulting in a rapid decrease in length, and then the circular loops continuously shrink. Before a complete annihilation, the relation between the radius R(t) of the circular loop and time t0−t, where t0 is the time to annihilation, is described by R2(t)=2Γ(t0−t)(t⩽t0). The kinetic constant Γ determined from this polymer liquid crystal is 0.34∼0.38 μm2/s, much smaller than those (200∼300 μm2/s) obtained in some LMW liquid crystals. The small Γ is ascribed to the high viscosity of this polymer liquid crystal, compared with LMW liquid crystals.