First-order Line Research Articles

Regions of different critical behavior of the two-flavor Nambu–Jona-Lasinio model

We study the chiral phase diagram in the $T$-$\ensuremath{\mu}$-${m}_{0}$ space of the two-flavor Nambu-Jona-Lasinio model with the approach of the Landau theory of phase transitions. The tricritical point (TCP) is an endpoint of a line of triple points as well as a crosspoint of three $\ensuremath{\lambda}$-transition lines. These double characters bring the connective and consistent problem of a critical phenomenon at the TCP. There is a crossover region from normal critical to tricritical behavior near the TCP, no matter whether the current quark mass is zero or not. The critical exponents need to be renormalized when one approaches the TCP along the first-order phase-transition line.

Suppression of pump-to-Stokes relative intensity noise transfer in Raman fiber laser by injection of modulated signal

A feasible approach is theoretically demonstrated that suppresses the relative intensity noise (RIN) transfer from pump sources to the proposed Raman fiber laser (RFL) output at the first-order Stokes line. The technique is accomplished by injecting a modulated signal at second-order Stokes shift from the pump wavelength according to the monitored RFL output, which indirectly consumes the pump power fluctuations and results in suppression of the RIN transfer to the RFL output. With the RFL used as a pump source for co-pumped Raman fiber amplifiers, further calculation results show that the Q-factor penalty due to RIN transfer can be dramatically reduced.

First-Order Wetting Transition and Line Tension of Hexadecane Lens at Air/Water Interface Assisted by Surfactant Adsorption

Abstract A first-order transition from partial wetting to pseudo-partial wetting of hexadecane droplets on aqueous solutions of surfactant, hexadecyltrimethylammonium bromide, has been investigated by using interfacial tensiometry and ellipsometry. A regular solution model was applied to calculate the surface free energy of the wetting film as a function of thickness and then the connection between calculated surface free energy profiles and line tension measured at the wetting transition was discussed based on the interface displacement model. The reversal of the sign of the line tension associated with the wetting transition was confirmed from both the experiment and the interface displacement model.

Phase transitions in confined water nanofilms

Phase transitions in water are normally classified as first or second order. But in confined quasi-one-dimensional films of water, simulations show that the solid–liquid transition can take place by means of a first-order transition or a continuous one without a distinction between solid and liquid. Bulk water has three phases: solid, liquid and vapour. In addition to undergoing a phase transition (of the first order) between them, liquid and vapour can deform continuously into each other without crossing a transition line—in other words, there is no intrinsic distinction between the two phases. Hence, the first-order line of the liquid–vapour phase transition should terminate at a critical point. In contrast, the first-order transition line between solid and liquid is believed to persist indefinitely without terminating at a critical point1. In recent years, however, it was reported that inside carbon nanotubes, freezing of water may occur continuously as well as discontinuously through a first-order phase transition2. Here we present simulation results for water in a quasi-two-dimensional hydrophobic nanopore slit, which are consistent with the idea that water may freeze by means of both first-order and continuous phase transitions. Our results lead us to hypothesize the existence of a connection point at which first-order and continuous transition lines meet3,4.

High-field metamagnetism in the antiferromagnetCeRh2Si2

A study of the antiferromagnet CeRh$_2$Si$_2$ by torque, magnetostriction, and transport in pulsed magnetic fields up to 50 Tesla and by thermal expansion in static fields up to 13 Tesla is presented. The magnetic field-temperature phase diagram of CeRh$_2$Si$_2$, where the magnetic field is applied along the easy axis $\mathbf{c}$, is deduced from these measurements. The second-order phase transition temperature $T_{N}$ and the first-order phase transition temperature $T_{1,2}$ (=~36 K and 26 K at zero-field, respectively) decrease with increasing field. The field-induced antiferromagnetic-to-paramagnetic borderline $H_c$, which equals 26 T at 1.5 K, goes from first-order at low temperature to second-order at high temperature. The magnetic field-temperature phase diagram is found to be composed of (at least) three different antiferromagnetic phases. These are separated by the first-order lines $H_{1,2}$, corresponding to $T_{1,2}$ at H=0, and $H_{2,3}$, which equals 25.5 T at 1.5 K. A maximum of the $T^2$-coefficient $A$ of the resistivity is observed at the onset of the high-field polarized regime, which is interpreted as the signature of an enhanced effective mass at the field-induced quantum instability. The magnetic field dependence of the $A$ coefficient in CeRh$_2$Si$_2$ is compared with its pressure dependence, and also with the field dependence of $A$ in the prototypal heavy-fermion system CeRu$_2$Si$_2$.

Phase diagram and thermodynamics of the Polyakov linear sigma model with three quark flavors

The phase diagram at finite temperature and density is investigated in the framework of the Polyakov linear sigma model (PLSM) with three light quark flavors in the mean field approximation. It is found that in the PLSM, the three phase transitions, i.e. the chiral restoration of u, d quarks, the chiral restoration of s quark and the deconfinement phase transition, are independent. There exists a two-flavor quarkyonic phase at low-density and a three-flavor quarkyonic phase at high density. The critical end point (CEP) which separates the crossover from the first-order line in the PLSM model is located at (TE, μE) = (188 MeV, 139.5 MeV). In the transition region, the thermodynamic properties and the bulk viscosity over entropy density ratio ζ/s are also discussed in the PLSM.

Photoluminescence study of the annihilation process of donor-bound excitons in ZnO: observation of quantum mechanical interference

We report a photoluminescence observation of the coupling of donor-bound excitons and longitudinal optical phonons in high-quality ZnO crystals at 5 K. The first-order phonon Stockes line of donor-bound excitons exhibits a distinct asymmetric line shape with a clear dip at its higher energy side, suggesting that quantum mechanical interference occurs during the annihilation of donor-bound excitons. The donor binding energy is determined to be 49.3 meV from spectral featural.

High-efficiency continuous-wave Raman conversion with a BaWO_4 Raman crystal

We report a high-efficiency cw Raman conversion with a BaWO(4) Raman crystal in a diode-end-pumped Nd:YVO(4) laser. The Raman threshold is as low as 3.6 W of diode power at 808 nm. The highest output power obtained at the 1,180 nm first-order Stokes line is 3.36 W under the diode power of 25.5 W, corresponding to a slope efficiency of 15.3% and a diode-to-Stokes optical conversion efficiency of 13.2%. The intracavity Raman conversion efficiency is 21.5% with respect to the available output of the 1,064 nm fundamental.

Renormalizedϕ6model for quantum phase transitions in systems of itinerant fermions

We study the impact of quantum and thermal fluctuations on properties of quantum phase transitions occurring in systems of itinerant fermions with main focus on the order of these transitions. Our approach is based on a set of flow equations derived within the functional renormalization-group framework, in which the order parameter is retained as the only degree of freedom and where the effective potential is parametrized with a ${\ensuremath{\phi}}^{6}$ form allowing for both first-order and second-order scenarios. We find a tendency to turn the first-order transitions within the bare model into second-order transitions upon accounting for the order-parameter fluctuations. We compute the first-order and second-order phase boundary lines ${T}_{c}$ as a function of a nonthermal control parameter ${a}_{2}$ in the vicinity of a quantum phase transition. We analyze crossovers of the shift exponent $\ensuremath{\psi}$ governing the shape of the ${T}_{c}$ line when the system is tuned close to a quantum tricritical scenario, where a second-order phase-transition line terminates at a quantum tricritical point.

Low-energy effective theory of the toric code model in a parallel magnetic field

We determine analytically the phase diagram of the toric code model in a parallel magnetic field which displays three distinct regions. Our study relies on two high-order perturbative expansions in the strong- and weak-field limits, as well as a large-spin analysis. Calculations in the topological phase establish a quasiparticle picture for the anyonic excitations. We obtain two second-order transition lines that merge with a first-order line, giving rise to a multicritical point as recently suggested by numerical simulations. We compute the values of the corresponding critical fields and exponents that drive the closure of the gap. We also give the one-particle dispersions of the anyonic quasiparticles inside the topological phase.

Phase diagram of vortices in high-Tcsuperconductors with a melting line in the deepHc2region

We use a simple elastic Hamiltonian for the vortex lattice in a weak impurity background which includes defects in the form of integer-valued fields to calculate the free energy of a vortex lattice in the deep H_{c2} region. The phase diagram in this regime is obtained by applying the variational approach of M{\'e}zard and Parisi developed for random manifolds. We find a first-order line between the Bragg-glass and vortex-glass phase as a continuation of the melting line. In the liquid phase, we obtain an almost vertical third-order glass transition line near the critical temperature in the H-T plane. Furthermore, we find an almost vertical second-order phase transition line in the Bragg-glass as well as the vortex-glass phases which crosses the first-order Bragg-glass, vortex-glass transition line. We calculate the jump of the temperature derivate of the induction field across this second-order line as well as the entropy and magnetic field jumps across the first-order line.

Phase dependence of the spectral properties of the X-ray binary 4U0115+63: Observations with the Beppo-Sax satellite

The phase dependence of the spectral properties of the X-ray source 4U0115+63 is analzed based on X-ray observations obtained with the Beppo-Sax observatory. The spectrum contains a feature that is interpreted as a cyclotron absorption line. Deep lines of the first three orders were always observed, while the fourth-order line was detected only at certain phases. The parameters of the cyclotron feature depend strongly on the phase, while the remaining spectrum varies only relatively weakly with phase. The cyclotron lines of various orders are appreciably non-equidistant, and the second-order line is nearly always deeper than the first-order line. Possible physical conditions in the active region of the source that could give rise to the observed spectrum are discussed.

Extraction of mixed-order multicomponent ship target signals from broadened sea clutter in bistatic shipborne surface wave radar

A dynamic geometry model was built to describe the Doppler-broadening characteristics of the first-order Bragg lines for bistatic shipborne surface wave radar. They are time-varying because the Doppler frequency shifts of sea echoes are simultaneously modulated by the velocity components projected from the unavoidably different motions of both platforms, which is more complex than its counterpart in the monostatic mode. The geometrical relation is used to obtain the received signal model: strong first-order sea clutter interferences and submerged ship targets with constant and non-constant speeds are considered as mixed-order multicomponent polynomial-phase signals (mc-PPSs) and both second-order sea clutter continuum and atmospheric noise as additive noise. Then, a scheme based on the product high-order ambiguity function is proposed to extract the targets; it is a recursive procedure in which the first-order sea clutter is removed by an existing time–space cascaded filtering method. Monte Carlo simulations show the validity and efficiency of the proposed scheme.

Liquid polyamorphism: Possible relation to the anomalous behaviour of water

We present evidence from experiments and computer simulations supporting the hypothesis that water displays polyamorphism, i.e., water sepa- rates into two distinct liquid phases. This concept of a new liquid-liquid phase transition is finding application to other liquids as well as water, such as silicon and silica. Specifically, we investigate, the relation between changes in dynamic and thermodynamic anomalies arising from the presence of the liquid-liquid critical point in (i) Two models of water, TIP5P and ST2, which display a first order liquid-liquid phase transition at low temperatures; (ii) the Jagla model, a spherically symmetric two-scale potential known to possess a liquid-liquid critical point, in which the competition between two liquid structures is generated by repulsive and attractive ramp interactions; and (iii) A Hamiltonian model of water where the idea of two length/energy scales is built in. This model also displays a first order liquid-liquid phase transition at low temperatures besides the first order liquid-gas phase transition at high temperatures. We find a correlation between the dynamic fragility crossover and the locus of specific heat maxima C max ("Widom line") emanating from the critical point. Our findings are consistent with a possible relation between the previously hypothesised liquid-liquid phase transition and the transition in the dynamics recently observed in neutron scattering experiments on confined water. More generally, we argue that this connection between C max P and the dynamic crossover is not limited to the case of water, a hydrogen bonded network liquid, but is a more general feature of crossing the Widom line, an extension of the first-order coexistence line in the supercritical region. Dedicated to Armin Bunde on the occasion of his 60th birthday.

Stability conditions for hydrogen-antihydrogen–like quasimolecules

We present a detailed study of the stability conditions of hydrogen-antihydrogen--like quasimolecules using both variational and finite-size scaling calculations. The stability diagram of the nuclear charge $Z$ as a function of the internuclear distance $R$ shows bound and unbound regions separated by a first-order critical line. Calculations of the leptonic annihilation rate show a peculiar behavior for nuclear charges $Z\ensuremath{\ge}2$, which was not observed for the hydrogen-antihydrogen quasimolecule; it goes through a maximum before it decays exponentially for large interhadronic distances. This might have a practical impact on the study of stability of matter-antimatter systems.

Distortion in optical pulse equalization through phase modulation and dispersive transmission

By combining phase modulation and dispersive transmission we propose an adjustable optical device to compress a time-varying input signal for producing ultrashort light pulses of high optical power. The relationship between the required properties of the input signal and the device parameters to get well-conformed sharp pulses with large energy concentration was established. High-order aberrations effects of the electro-optical modulator acting as the time lens of the employed setup are also considered. We found a mathematical analogy between the output signal of the analyzed device and the signal which would be obtained by using an equivalent first-order dispersive line. Some numerical simulations are shown which illustrate the feasibility of the method.

The influence of nitrogen plasma treatment on the lattice vibrational properties of hydrothermally grown ZnO nanorods

In this study, the authors have investigated the optical properties of hydrothermally grown ZnO nanorods subjected to the combination of thermal annealing and nitrogen plasma treatments. In particular, ultraviolet-visible micro-Raman scattering has been used to study the influence of nitrogen incorporation in ZnO nanorods grown on GaN/sapphire templates. The band-edge photoluminescence spectra show significant changes due to nitrogen plasma treatment. In addition, visible Raman spectra show intensity enhancement of the disorder-activated vibrational modes from plasma-treated ZnO nanorods. Multiple longitudinal optical (LO) phonons are observed under ultraviolet resonant Raman excitation from these nanorods. The first-order resonant LO phonon line shape fitting is correlated to the nitrogen-induced lattice disorder.

The first-order vortex transition line in three-dimensional anisotropic superconductors intilted magnetic fields

The vortex lattice in high-temperature superconductors is affected by thermal fluctuationsand quenched disorder, leading to disordered phases, such as vortex liquid and glass,through a first-order phase transition. We use a transformation proposed by Calero, inorder to obtain the angular generalization of the first-order melting line of the vortexlattice in a three-dimensional anisotropic superconductor, such as YBaCuO, under anexternal magnetic field with arbitrary direction with respect to the anisotropy axis. Thecalculations are performed in the framework of the Ginzburg–Landau theory in the lowestLandau level approximation. The competition between thermal fluctuations and disorder isdescribed following the same method as that developed by Li and Rosenstein.

Phase diagram of generalized fully frustratedXYmodel in two dimensions

It is shown that the phase diagram of the two-dimensional generalized fully frustrated $XY$ model on a square lattice contains a crossing of the chirality transition and the Kosterlitz-Thouless (KT) transition, as well as a stable phase characterized by a finite helicity modulus $\ensuremath{\Upsilon}$ and an unbroken chirality symmetry. The crossing point itself is consistent with a critical point without any jump in $\ensuremath{\Upsilon}$, with the size $(L)$ scaling $\ensuremath{\Upsilon}\ensuremath{\sim}{L}^{\ensuremath{-}0.63}$ and the critical index $\ensuremath{\nu}\ensuremath{\approx}0.77$. The KT transition line remains continuous beyond the crossing but eventually turns into a first-order line. The results are established using Monte Carlo simulations of the staggered magnetization, helicity modulus, and the fourth-order helicity modulus.

An investigation of Fe XVI emission lines in solar and stellar extreme-ultraviolet and soft X-ray spectra

New fully relativistic calculations of radiative rates and electron impact excitation cross-sections for Fe XVΙ are used to determine theoretical emission-line ratios applicable to the 251-361 and 32-77 A portions of the extreme-ultraviolet (EUV) and soft X-ray spectral regions, respectively. A comparison of the EUV results with observations from the Solar Extreme-Ultraviolet Research Telescope and Spectrograph (SERTS) reveals excellent agreement between theory and experiment. However, for emission lines in the 32A 9 A portion of the soft X-ray spectral region, there are large discrepancies between theory and measurement for both a solar flare spectrum obtained with the X-Ray Spectrometer/Spectrograph Telescope (XSST) and for observations of Capella from the Low-Energy Transmission Grating Spectrometer (LETGS) on the Chandra X-ray Observatory. These are probably due to blending in the solar flare and Capella data from both first-order lines and from shorter wavelength transitions detected in second and third order. By contrast, there is very good agreement between our theoretical results and the XSST and LETGS observations in the 50-77 A wavelength range, contrary to previous results. In particular, there is no evidence that the Fe XVI emission from the XSST flare arises from plasma at a much higher temperature than that expected for Fe xvi in ionization equilibrium, as suggested by earlier work.