Soft mode dispersion and ‘waterfall’ phenomenon in relaxors revisited

Results of recent inelastic neutron scattering studies of lead-based relaxor ferroelectrics by Gvasaliya et al. [J. Phys.: Condens. Matter 17, 4343 (2005); J. Phys.: Condens. Matter 19, 016219 (2007)] have put in question the existence of the “waterfall” anomaly–an apparent vertical dispersion segment joining the TA and TO branches–observed earlier in low-energy [ξ00] phonon dispersion curves of these materials. In the present article, we review the results of earlier experiments and model calculations together with the outcome of our recent measurements on PMN using the same instrumental set-up as Gvasaliya et al. to conclude that the “waterfall” feature is not an experimental artefact. We also give some hints on a possible explanation of the results of Gvasaliya et al., by exploring the fact that the reported dispersion of the underdamped transverse optic branch follows the longitudinal acoustic (LA) branch dispersion surprisingly closely.     

The Depinning Transition in Presence of Disorder: A Toy Model

We introduce a toy model, which represents a simplified version of the problem of the depinning transition in the limit of strong disorder. This toy model can be formulated as a simple renormalization transformation for the probability distribution of a single real variable. For this toy model, the critical line is known exactly in one particular case and it can be calculated perturbatively in the general case. One can also show that, at the transition, there is no fixed distribution accessible by renormalization which corresponds to a disordered fixed point. Instead, both our numerical and analytic approaches indicate a transition of infinite order (of the Berezinskii–Kosterlitz–Thouless type). We give numerical evidence that this infinite order transition persists for the problem of the depinning transition with disorder on the hierarchical lattice.     

Rare transition event with self-consistent theory of large-amplitude collective motion

A numerical simulation method, based on Dang et al.’s self-consistent theory of large-amplitude collective motion, for rare transition events is presented. The method provides a one-dimensional pathway without knowledge of the final configuration, which includes a dynamical effect caused by not only a potential but also kinetic term. Although it is difficult to apply the molecular dynamics simulation to a narrow-gate potential, the method presented is applicable to the case. A toy model with a high-energy barrier and/or the narrow gate shows that while the Dang et al. treatment is unstable for a changing of model parameters, our method stable for it.     

A reduction modeling method to assess the electromagnetic emission of multiconductor transmission lines

This article deals with the extension of the so-called “equivalent cable-bundle method” to assess the electromagnetic emission of a cable-bundle. As in the immunity case, the purpose of the method is to reduce the complexity of a reference cable-bundle by creating a “reduced cable-bundle” composed of a limited number of “equivalent conductors”. The significant reduction of the thereby obtained model makes possible its introduction in 3D models without any real increase of their size. To cite this article: G. Andrieu et al., C. R. Physique 10 (2009).     

Coupled cavity polaritons for switching and slow light applications

We derive the frequency response of a chain of weakly coupled cavities, loaded with three-level quantum systems; one transition of the quantum state is entangled with the cavity mode, and the other one is driven by an external field not related to any cavity mode. In a system composed of photonic crystals and quantum states, we can exploit two quantum optical effects: the first due to a totally destructive interference between an incoming field and the field radiated by a dipole in a cavity in Purcell regime, known as “dipole-induced reflectivity” (DIR) reminiscent of the “dipole-induced transparency” reported by Waks et al. [E. Waks, J. Vuckovic, Dipole induced transparency in Drop-Filter Cavity-Waveguide Systems, Phys. Rev. Lett. 96 (2006) 153601], and the “electromagnetic-induced transparency” (EIT) in a quantum state. We demonstrate that it is possible to design tunable flat response filters using external fields with different Rabi frequency values, and furnish the design guidelines for tunable delay lines with very large bandwidth.     

Perturbative analysis of possible failures in the traditional adiabatic conditions

The breakdown of adiabatic approximation, demonstrated by Marzlin and Sanders [K.-P. Marzlin, B.C. Sanders, Phys. Rev. Lett. 93 (2004) 160408] and Tong et al. [D.M. Tong, et al., Phys. Rev. Lett. 95 (2005) 110407] for time-evolving “inverse” systems, is traced to the appearance of some nonzero terms in a perturbational treatment and is related to two time scales in the “inverse” systems' Hamiltonian. New adiabatic conditions of Ye et al. [M.-Y. Ye, et al., quant-ph/0509083] can restore the theoretical consistency.     

Nosonomy of an upside-down hierarchy model (II)

We study supersymmetry breaking in the spectrum of ordinary-energy particles induced by the inverse hierarchy mechanisms.General techniques for computing non-supersymmetric interaction and mass terms are developed and illustrated on a toy model example. Application of these techniques to the upside-down hierarchy model leads to the conclusion that the so-called “sliding singlet” mechanism does not work.     

Calculation of the planar normal vibrations of phenanthrene

The planar normal vibrations of phenanthrene have been calculated using the “aromatic force field” of Schettino et al. (J. Chem. Phys. 44 (1966)). These new values show a better agreement with the experimental assignment than previous calculations. After force constants refinement the observed band positions are reproduced with an average error of less than 8 cm^?1.     

On quantum solitons and their classical relatives: Bethe Ansatz states in soliton sectors of the sine-Gordon system

Previously we have found that the semiclassical sine-Gordon/Thirring spectrum can be received in the absence of quantum solitons via the spin $\text{1}\text{2}$ approximation of the quantized sine-Gordon system on a lattice. Later on, we have recovered the Hilbert space of quantum soliton states for the sine-Gordon system. In the present paper we present a derivation of the Bethe Ansatz eigenstates for the generalized ice model in this soliton Hilbert space. We demonstrate that via “Wick rotation” of a fundamental parameter of the ice model one arrives at the Bethe Ansatz eigenstates of the quantum sine-Gordon system. The latter is a “local transition matrix” ancestor of the conventional sine-Gordon /Thirring model, as derived by Faddeev et al. within the quantum inverse-scattering method. Our result is essentially based on the N < ∞, Δ = 1, m ? 1 regime. Consequently, the spectrum received, though resembling the semiclassical one, does not coincide with it at all.     

Response comments to the article “some comments on magnetization reversal in uniaxial ferrite magnets”

The previous paper contains no new information but is rather based on some wrong conclusions drawn from a paper entitled “Magnetization reversal in ferrite magnets” by Hadjipanayis et al. published in J. Magn. Magn. Mat. 81 (1989) 318. The authors of the previous paper (Paoluzi and Turilli) missed altogether the objectives of the article by Hadjipanayis et al. which were to explain the differences observed in the temperature dependence of coercivity of bulk and small particle BaFe₁₂O₁₉ magnets and relate them to the magnetization reversal processes. The conclusions were that the bulk sintered magnets behave as “nucleation”-type, the ultrafine particles as “single domain”-type and the aerosol coarser particles show a behavior which is a mixture of the above two. In this paper we dispute in detail the main points made by the authors.     

Comment on the paper “Exafs measurements on Nb3Ge thin films” by G.S. Brown et al.

Brown et al. have reported recently that Nb₃Ge specimens showing superconducting transition temperatures less than the maximum possible value contain a “quasi-amorphous phase”. We discuss the possibility that the lower values of T_c of these specimens may be accounted for by the proximity effect due to these quasi-amorphous regions.     

A quark shell model calculation of nuclear magnetic moments

The “Schmidt lines” for nuclear magnetic moments are calculated in a quark shell model. In the pairing scheme proposed by Petry et al., the single-nucleon magnetic moment is simply related to the single quark value. The isoscalar part is essentially the same as that of the conventional Schmidt moment while the isovector part increases too rapidly as the angular momentum increases. Possibilities of improving the model are briefly discussed.     

Infrared spectrum involving forbidden transitions & coriolis interaction and identification of optically pumped far infrared laser lines in asymmetrically mono-deuterated methanol (Methanol-D1)

In this paper new type of ΔK = 2 and 0 transitions have been identified in the Fourier Transform spectrum of Methanol-D₁ (CH₂DOH). These transitions are normally forbidden but a “Coriolis” type interaction with nearby states is believed to be contributing sufficient transition strength through intensity borrowing effect. This is the first time such forbidden transitions are reported to be identified in the excited states, in this molecule. The present conjecture is supported by observation of a many strong allowed transitions to upper terminating levels which are seen to be highly perturbed. This conclusion has been reached by comparing calculated energy levels using known molecular parameters (Pearson et al., 2012; Coudert et al., 2014; El Hilali et al., 2011; Quade et al., 1998; Richard Quade, 1998, 1999; Mukhopadhyay, 1997) and the actually observed FIR lines. The upper levels are seen to be upshifted from expected position. A closer look at the calculated energy values seems to indicate a possible interaction between the above states and other proximate torsional–rotational states could occur. The possible candidates for the interacting level manifolds are narrowed down through the presence of the forbidden transition. We also take the opportunity to propose alternate rotational quantum numbers for some of the assignments recently reported in the literature (El Hilali et al., 2011). Some ambiguities are pointed out on the data and the reported analysis. There remain too many such irregularities and we propose to gather a large body assigned transitions in a future catalog. Assignments and relevant comments on optically pumped FIR laser radiation are also made.     

Numerical simulations of acoustic cavitation noise with the temporal fluctuation in the number of bubbles

Numerical simulations of cavitation noise have been performed under the experimental conditions reported by Ashokkumar et al. (2007) [26]. The results of numerical simulations have indicated that the temporal fluctuation in the number of bubbles results in the broad-band noise. “Transient” cavitation bubbles, which disintegrate into daughter bubbles mostly in a few acoustic cycles, generate the broad-band noise as their short lifetimes cause the temporal fluctuation in the number of bubbles. Not only active bubbles in light emission (sonoluminescence) and chemical reactions but also inactive bubbles generate the broad-band noise. On the other hand, “stable” cavitation bubbles do not generate the broad-band noise. The weaker broad-band noise from a low-concentration surfactant solution compared to that from pure water observed experimentally by Ashokkumar et al. is caused by the fact that most bubbles are shape stable in a low-concentration surfactant solution due to the smaller ambient radii than those in pure water. For a relatively high number density of bubbles, the bubble–bubble interaction intensifies the broad-band noise. Harmonics in cavitation noise are generated by both “stable” and “transient” cavitation bubbles which pulsate nonlinearly with the period of ultrasound.     

Simulating a topological transition in a superconducting phase qubit by fast adiabatic trajectories

The significance of topological phases has been widely recognized in the community of condensed matter physics. The well controllable quantum systems provide an artificial platform to probe and engineer various topological phases. The adiabatic trajectory of a quantum state describes the change of the bulk Bloch eigenstates with the momentum, and this adiabatic simulation method is however practically limited due to quantum dissipation. Here we apply the “shortcut to adiabaticity” (STA) protocol to realize fast adiabatic evolutions in the system of a superconducting phase qubit. The resulting fast adiabatic trajectories illustrate the change of the bulk Bloch eigenstates in the Su-Schrieffer-Heeger (SSH) model. A sharp transition is experimentally determined for the topological invariant of a winding number. Our experiment helps identify the topological Chern number of a two-dimensional toy model, suggesting the applicability of the fast adiabatic simulation method for topological systems.     

Phase segregation in driven diffusive systems

Driven diffusive models describe an array of atoms in an external periodic potential, when the motion is damped due to energy exchange with the substrate. The systems of this class have wide application in modeling of charge and mass transport in solids. Recently, the driven diffusive models have been used in tribology, where the driving force emerges due to motion of one of two substrates, which are separated by a thin atomic layer. When a dc force is applied to the atoms, the system exhibits the locked-to-sliding transition. During the transition the system may split in domains of two kinds, the running domains where the atoms move with almost maximum velocity, and the immobile domains (“traffic jams”). We discuss a new model for a 1D chain, where the particles have a complex structure treated in a mean-field fashion: particle collisions are inelastic and also each particle is considered as having its own thermostat. This model exhibits a hysteresis and the “traffic jams” state even at high temperatures due to the clustering of atoms with the same velocity.     

Exactly solvable toy model that mimics the mode coupling theory of supercooled liquid and glass transition

A toy model is proposed which incorporates the reversible mode coupling mechanism responsible for ergodic-nonergodic transition of the mode coupling theory (MCT) of structural glass transition with trivial Hamiltonian. The model can be analyzed without relying on uncontrolled approximations inevitable in the current MCT. The strength of hopping processes can be easily tuned and the ideal glass transition is reproduced only in a certain range of the strength. On the basis of the analyses of our model, we discuss about a sharp ergodic-nonergodic transition and its smearing out by "hopping."     

Quantum radiation theory in a diffusion model version

Using the diffusion model associated by the author with the wave equations, a part of current quantum radiation theory is reformulated so that the characteristic divergences in the associated calculations no longer arise. The reformulation does this by stipulating, on purely physical grounds, that a transition involving a “virtual” quantum must include a high frequency “cutoff” factor in its interaction Hamiltonian. For a transition involving a “real” quantum, the stipulation is that the “cutoff” factor is not to be included.     

Comment on “the behavior of maxwell's equations under real superluminal lorentz transformations”

Negi et al. have recently obtained field equations for the superluminal electromagnetic field, in theories based on real superluminal transformations along a “tachyon corridor”. Their results differ from equations obtained some time ago by the present authors. We trace the source of the discrepancy to the failure of Negi et al. to consistently transform all relevant quantities from the old to the new Lorentz frame.