Symmetric Phase Research Articles

Ising spin glass on random graphs at zero temperature: Not all spins are glassy in the glassy phase

We investigate the replica symmetry broken (RSB) phase of spin glass (SG) models in a random field defined on Bethe lattices at zero temperature. From the properties of the RSB solution we deduce a closed equation for the extreme values of the cavity fields. This equation turns out not to depend on the parameters defining the RSB, and it predicts that the spontaneous RSB does not take place homogeneously on the whole system. Indeed, there exist spins having the same effective local field in all local ground states, exactly as in the replica symmetric (RS) phase, while the spontaneous RSB manifests only on the remaining spins, whose fraction vanishes at criticality. The characterization in terms of spins having fixed or fluctuating local fields can be extended also to the random field Ising model (RFIM), in which case the fluctuating spins are the only responsible for the spontaneous magnetization in the ferromagnetic phase. Close to criticality we are able to connect the statistics of the local fields acting on the spins in the RSB phase with the correlation functions measured in the paramagnetic phase. Identifying the two types of spins on given instances of SG and RFIM, we show that they participate very differently to avalanches produced by flipping a single spin. From the scaling of the number of spins inducing RSB effects close to the critical point and using the $M$-layer expansion we estimate the upper critical dimension $D_U \geq 8$ for SG.

Planted XY model: Thermodynamics and inference.

In this paper we study a fully connected planted spin glass named the planted XY model. Motivation for studying this system comes both from the spin glass field and the one of statistical inference where it models the angular synchronization problem. We derive the replica symmetric (RS) phase diagram in the temperature, ferromagnetic bias plane using the approximate message passing (AMP) algorithm and its state evolution (SE). While the RS predictions are exact on the Nishimori line (i.e., when the temperature is matched to the ferromagnetic bias), they become inaccurate when the parameters are mismatched, giving rise to a spin glass phase where AMP is not able to converge. To overcome the defects of the RS approximation we carry out a one-step replica symmetry-breaking (1RSB) analysis based on the approximate survey propagation (ASP) algorithm. Exploiting the state evolution of ASP, we count the number of metastable states in the measure, derive the 1RSB free entropy and find the behavior of the Parisi parameter throughout the spin glass phase.

Nonreciprocal charge transport in topological kagome superconductor CsV3Sb5

Nonreciprocal charge transport phenomena are widely studied in two-dimensional superconductors, which demonstrate unidirectional-anisotropy magnetoresistances as a result of symmetry breaking. Here, we report a strong nonreciprocal transport phenomenon in superconducting CsV3Sb5 thin flakes. The second harmonic voltages, mainly originating from the rectification effect of vortex motion, are unambiguously developed with in-plane and out-of-plane magnetic fields, and their magnitudes are comparable to those in noncentrosymmetric superconductors. The second harmonic magnetoresistances split into several peaks and some of them reverse their signs by ramping the magnetic field or the current within the superconducting transition. The nonreciprocity suggests a strong asymmetry in CsV3Sb5. The centrosymmetric structure and symmetric electronic phases in CsV3Sb5 can hardly induce the distinct nonreciprocal transport phenomenon, which could be correlated to a symmetry breaking from an unconventional superconducting order parameter symmetry.

Fractionality and PT symmetry in a square lattice

We study the spectral stability of a 2D discrete Schr\"{o}dinger equation on a square lattice, in the simultaneous presence of a fractional Laplacian and $\cal{PT}$ symmetry. For that purpose, we compute the plane-wave spectrum in closed form, as a function of the gain/loss parameter and the fractional exponent. Examination of the spectrum reveals that an increase of the gain/loss parameter favors the early appearance of complex eigenvalues, thus is, the onset of a broken ${\cal PT}$ symmetry. On the other hand, as the fractional exponent decreases from unity, at a critical value a gap opens up separating the upper and lower bands, and the spectrum becomes real. Further decrease of the exponent increases the width of the gap and the system remains in the $\cal{PT}$-symmetric phase down to a vanishing value of the fractional exponent. Examination of the density of states and the participation ratio reinforce these observations and lead one to conclude that, unlike the standard, non-fractional case where the binary lattice is always in the broken $\cal{PT}$ phase, for the fractional case it is possible to have a symmetric $\cal{P}{\cal T}$ phase in the presence of a finite gain/loss parameter and a small enough fractional exponent.

Hermitian Nonlinear Wave Mixing Controlled by a PT-Symmetric Phase Transition.

While non-Hermitian systems are normally constructed through incoherent coupling to a larger environment, recent works have shown that under certain conditions coherent couplings can be used to similar effect. We show that this new paradigm enables the behavior associated with the PT-symmetric phase of a non-Hermitian subsystem to control the containing Hermitian system through the coherent couplings. This is achieved in parametric nonlinear wave mixing where simultaneous second harmonic generation replaces the role of loss to induce non-Hermitian behavior that persists through a full exchange of power within the Hermitian system. These findings suggest a new approach for the engineering of dynamics where energy recovery and sustainability are of importance that could be of significance for photonics and laser science.

Triangular lattice quantum dimer model with variable dimer density

Quantum dimer models are known to host topological quantum spin liquid phases, and it has recently become possible to simulate such models with Rydberg atoms trapped in arrays of optical tweezers. Here, we present large-scale quantum Monte Carlo simulation results on an extension of the triangular lattice quantum dimer model with terms in the Hamiltonian annihilating and creating single dimers. We find distinct odd and even {{mathbb{Z}}}_{2} spin liquids, along with several phases with no topological order: a staggered crystal, a nematic phase, and a trivial symmetric phase with no obvious broken symmetry. We also present dynamic spectra of the phases, and note implications for experiments on Rydberg atoms.

The energy budget of cosmological first-order phase transitions beyond the bag equation of state

The stochastic gravitational-wave backgrounds (SGWBs) from the cosmological first-order phase transitions (FOPTs) serve as a promising probe for the new physics beyond the standard model of particle physics. When most of the bubble walls collide with each other long after they had reached the terminal wall velocity, the dominated contribution to the SGWBs comes from the sound waves characterized by the efficiency factor of inserting the released vacuum energy into the bulk fluid motions. However, the previous works of estimating this efficiency factor have only considered the simplified case of the constant sound velocities in both symmetric and broken phases, either for the bag model with equal sound velocities or ν-model with different sound velocities in the symmetric and broken phases, which is unrealistic from a viewpoint of particle physics. In this paper, we propose to solve the fluid EoM with an iteration method when taking into account the sound-velocity variation across the bubble wall for a general and realistic equation of state (EoS) beyond the simple bag model and ν-model. We have found a suppression effect for the efficiency factor of bulk fluid motions, though such a suppression effect could be negligible for the strong FOPT, in which case the previous estimation from a bag EoS on the efficiency factor of bulk fluid motions still works as a good approximation.

Critical Dynamics in Stratospheric Potential Energy Variations Prior to Significant (M > 6.7) Earthquakes

Lithosphere–atmosphere–ionosphere coupling (LAIC) is studied through various physical or chemical quantities, obtained from different sources, which are observables of the involved complex processes. LAIC has been proposed to be achieved through three major channels: the chemical, the acoustic, and the electromagnetic. Accumulated evidence supporting the acoustic channel hypothesis has been published, while atmospheric gravity waves (AGWs) play a key role in LAIC as the leading mechanism for the transmission of energy from the lower atmosphere to the stratosphere and mesosphere, associated with atmospheric disturbances observed prior to strong earthquakes (EQs). The seismogenic AGW is the result of temperature disturbances, usually studied through stratospheric potential energy (EP). In this work, we examined 11 cases of significant EQs (M > 6.7) that occurred during the last 10 years at different geographic areas by analyzing the temperature profile at the wider location of each one of the examined EQs. The “Sounding of the Atmosphere using Broadband Emission Radiometry” (SABER) instrument, part of the “Thermosphere Ionosphere Mesosphere Energetics Dynamics” (TIMED) satellite, data were employed to compute the potential energy (EP) of the AGW. Using the temperature profile, we first calculated EP and determined the altitudes’ range for which prominent pre-seismic disturbances were observed. Subsequently, the EP time series at specific altitudes, within the determined “disturbed” range, were for the first time analyzed using the criticality analysis method termed the “natural time” (NT) method in order to find any evidence of an approach to a critical state (during a phase transition from a symmetric phase to a low symmetry phase) prior to the EQ occurrence. Our results show criticality indications in the fluctuation of EP a few days (1 to 15 days) prior to the examined EQs, except from one case. In our study, we also examined all of the temperature-related extreme phenomena that have occurred near the examined geographic areas, in order to take into account any possible non-seismic influence on the obtained results.

A High-Efficiency and High-Power-Density Interleaved Integrated Buck-Boost-LLC Converter and Its Comprehensive Optimal Design Method

Integrated buck-boost- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> (IBBL) dcconverter is a good solution for high efficiency and high power density applications. However, the bridge leg integration causes asymmetrical zero-voltage-switching process and asymmetrical secondary current. The method of high quality factor or symmetric phase shift modulation proposed in the existing research can improve the asymmetrical current issue under heavy load, but is ineffective for light load conditions. This article proposes a novel Interleaved IBBL converter to improve the asymmetry issue for whole load range. Interleaving makes the secondary current be symmetric naturally. In addition, a comprehensive optimal design method for phase-shift angle and choke inductor is proposed to minimize the total power loss of all primary elements. A 600 W/1 MHz prototype verifies that the proposed IIBBL converter achieves symmetric secondary current in whole load range, and it achieves 95.7% efficiency and 180 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> under the proposed comprehensive optimal design method.

Detecting inhomogeneous chiral condensation from the bosonic two-point function in the (1 + 1)-dimensional Gross–Neveu model in the mean-field approximation* *The list of authors is sorted by (former) affiliations and surnames. All authors contributed in equal shares to this work. S Rechenberger initiated this project and produced preliminary results before leaving academia.

The phase diagram of the (1 + 1)-dimensional Gross–Neveu model is reanalyzed for (non-)zero chemical potential and (non-)zero temperature within the mean-field approximation. By investigating the momentum dependence of the bosonic two-point function, the well-known second-order phase transition from the symmetric phase to the so-called inhomogeneous phase is detected. In the latter phase the chiral condensate is periodically varying in space and translational invariance is broken. This work is a proof of concept study that confirms that it is possible to correctly localize second-order phase transition lines between phases without condensation and phases of spatially inhomogeneous condensation via a stability analysis of the homogeneous phase. To complement other works relying on this technique, the stability analysis is explained in detail and its limitations and successes are discussed in context of the Gross–Neveu model. Additionally, we present explicit results for the bosonic wave-function renormalization in the mean-field approximation, which is extracted analytically from the bosonic two-point function. We find regions—a so-called moat regime—where the wave function renormalization is negative accompanying the inhomogeneous phase as expected.

Perturbation influence of a parity-time optical resonator pair

In this article, we study the perturbation influence on a parity-time (PT) optical resonator pair. Critical characteristics of this type of device, including the sensitivity, dynamic range, and robustness, are formulated and discussed systematically. Through the study of three operational phase regimes, the exceptional point (EP), the PT-symmetry, and symmetric broken phases, we find that the optimal range of the PT resonator pair prefers to be at the PT-broken phase regime near the EP state, considering both the robustness and sensitivity factors. Furthermore, we also find that the device’s dynamic range is proportional to the temporal coupling coefficient κ and gain/loss coefficient γ, which means increasing the coupling and gain/loss coefficients will enable a broader dynamic response. Additionally, we further suggest that: (1) to enhance the sensitivity, γ should be no less than 0.94κ; (2) to achieve a large gain factor of a ⩾ 2, γ must satisfy 0.995κ ⩽ γ ⩽ 1.06κ; and (3) to obtain a larger dynamic range, γ needs to be closer to κ. In particular, for γ = κ, i.e., the EP case, the largest dynamic range of ɛ ⩽ 0.24κ is obtained.

Comprehensive Analysis of Asymmetric Modulated Dual-Active-Bridge Converter and Its Hybrid Control Strategy

Dual active bridge (DAB) converter has been widely used in distributed power supply, new energy vehicles, energy storage systems, etc. Their modulation strategy is an important research direction. At present, the research on modulation strategy is basically symmetric phase shift, but it is not enough to generalize modulation strategy comprehensively. In this article, an asymmetric phase-shifting (APS) strategy is proposed to control the power flow by simultaneously adjusting the asymmetric duty cycle and the phase-shifting angle. With this modulation scheme, the current stress and cyclic power loss can be reduced by adjusting the modulation ratio of the inductor current waveform. As a result, the light-load efficiency can be improved compared with the conventional symmetric modulation scheme. The power characteristic, current stress, soft switching characteristic, and backflow power of this modulation strategy are analyzed and calculated comprehensively. Then, based on this asymmetric strategy, a hybrid modulation strategy that can achieve ZVS over the entire power range with low current stress, low return power, and minimum rms current at light load is proposed. Finally, a 100–50 V/300 W prototype is built to verify the analysis.

A Drop-in, Focus-Extending Phase Mask Simplifies Microscopic and Microfluidic Imaging Systems for Cost-Effective Point-of-Care Diagnostics.

Microscopic imaging and imaging flow cytometry have wide potential in point-of-care assays; however, their narrow depth of focus necessitates precise mechanical or fluidic focus control of a sample in order to acquire high-quality images that can be used for downstream analysis, increasing the cost and complexity of the imaging system. This complexity represents a barrier to miniaturization and translation of point-of-care assays based on microscopic imaging or imaging flow cytometry. To address this challenge, we present a simple drop-in phase mask with a physics-informed, circularly symmetric asphere phase profile that extends the depth of focus by >5-fold while largely preserving the image quality compared to other depth extending methods. We show that such a focus-extended system overcomes manufacturing tolerances in low-cost sample chambers, enlarges the useable field-of-view of low-cost objectives, and permits increased throughput and precision in flow imaging systems without the need for complex flow-focusing. As the image quality is preserved without the need for postacquisition image restoration, our solution is also highly appropriate for on-line applications such as cell sorting.

Spontaneous symmetry breaking without classical fields: A functional renormalization group approach

We propose an approach to describe spontaneous symmetry breaking that does not rely on the order parameter dependent free energy (Landau theory). We use the functional renormalization group evolution of the explicitly broken theory, using a truncation scheme that is compatible with the Ward identities. To represent the symmetry breaking, we propose to use the ``Ward ratio'' which is zero in the symmetric phase and unity in the broken phase. In this approach a unified scale evolution of the effective potential is applicable in both phases. It is peculiar that the scale evolution is accelerated in the critical regime.

Harnessing PT -symmetry in non-Hermitian stiffness-modulated waveguides

The recent progress in the context of elastic metamaterials and modulated waveguides with digitally controllable properties has opened new pathways to overcome the limitations dictated by Hermitian Hamiltonians in mechanics. Among the possible implementations, non-Hermitian, $\mathcal{PT}$-symmetric systems with balanced gain and loss have emerged as an elegant mechanism to access novel functionalities by lifting the non-Hermitian degeneracies (exceptional points). Motivated by this, the paper deals with a non-Hermitian and $\mathcal{PT}$-symmetric elastic waveguide with complex stiffness-modulation. The strength of the stiffness-modulations, tailored in the form of a balanced gain/loss, delineates a transition from unbroken to broken $\mathcal{PT}$-symmetric phases, where distinct Bloch-wave modes coalesce into exceptional points. It is shown that, in the unbroken $\mathcal{PT}$-symmetric regime, and due to the interplay between real and imaginary components of the elasticity, the waveguide operates as a phononic filter. When the strength of the gain/loss interactions increases, the frequency gap closes and the bulk bands degenerate into an exceptional point, where the system operates as a waveguide with asymmetric scattering capabilities. The paper provides a connection between the distinct wave modes that populate the non-Hermitian degeneracies and the directional reflection/transmission capabilities. The asymmetric behavior is herein explained by combining the dispersion properties of a $\mathcal{PT}$-symmetric rod, obtained through the plane wave expansion method (PWEM), and the scattering matrix method (SMM) for a modulated slab series-connected to semi-infinite media.

BRST view of spontaneous symmetry breaking

After the phase transition of a Grand Unified Theory (GUT), its single coupling splits into the couplings of the basic interactions. On the other side, the measurement of the Weinberg mixing angle in the eletroweak theory determines that the couplings associated to the SU(2) and U(1) symmetries were already distinct in its symmetric phase, before the electroweak breaking. This picture is consistent as we understand that such couplings evolve independently with the energy scale, meeting a common point together with the strong interaction coupling at the GUT scale. From a BRST symmetry point of view, this implies that each independent coupling should be associated to independent cocycles defined on a cohomological basis. The problem is that, before the GUT symmetry breaking, the BRST operator associated to this symmetric phase predicts a single Yang-Mills coupling. This sets the question of what should be the BRST operator of the asymmetric phase, that would allow for the splitting of this coupling but at the same time remain compatible with the BRST operator of the symmetric phase. In this work we proceed to answer this question.

Structural evolution of epitaxial CeO2-HfO2 thin films using atomic-scale observation: Formation of ferroelectric phase and domain structure

We investigated the structural evolution of 0.1CeO2–0.9HfO2 epitaxial films upon thermal annealing using X-ray diffraction and scanning transmission electron microscopy. The films were deposited via a sputtering method at room temperature onto (001)yttria-stabilized zirconia substrates and subsequently annealed. The crystalline phase of the deposited films changed from amorphous to highly symmetric phase (tetragonal and/or cubic phases) and then to orthorhombic with increasing annealing temperature. Isothermal annealing at 900 °C resulted in a series of transitions from the highly symmetric phase to a mixture of highly symmetric and orthorhombic phases, and finally to the orthorhombic phase as a function of time. Atomic-scale observations revealed the formation of nanosized orthorhombic domains within the dominant tetragonal phase; their number density and size increased with the annealing time. However, in-situ transmission electron microscopy of the crystallized film with the dominant orthorhombic phase revealed that the orthorhombic phase transformed back to the tetragonal phase above 540 °C upon reheating. Therefore, the tetragonal phase is a prerequisite for forming the orthorhombic phase, and the tetragonal-to-orthorhombic phase transition is reversible. Thus, this study offers a strategy to control the formation of tetragonal and orthorhombic phases of Ce-substituted HfO2 ferroelectric films by optimizing the annealing conditions.

High Performance, Stoichiometric ZnSnP2 Anode for Rechargeable Lithium‐Ion Battery with Concomitant Conversion from Chalcopyrite to Sphalerite Phase

AbstractHerein, we report chalcopyrite phase of zinc tin phosphide (ZnSnP2) as an anode for high rate, rechargeable, lithium‐ion battery. In‐situ Raman spectroscopy reveals the conversion of chalcopyrite phase of ZnSnP2 to a symmetric sphalerite phase upon cycling, which helps in achieving stable and reversible capacity at high discharge rates. This is due to the low bandgap and high conductivity of the sphalerite phase. The in‐situ phase conversion is extremely important as it is difficult to synthesize bulk ZnSnP2 sphalerite phase by the known methods till date. After full phase conversion, a reversible capacity of 750 mAh g−1 is obtained towards the end of 1700 cycles at a rate of 5 A g−1. Full cell assembled using LiCoO2 as the cathode material yields a stable performance with a discharge capacity of around 500 mAh g−1 at 0.5 A g−1 and the rate capability studies demonstrate reversible capacities up to 15 A g−1 current.

Structural, impedance, and photoluminescence properties of Ho3+ substituted Na0·5Bi0·5TiO3

Complex impedance and photoluminescence properties have been investigated in Na0.5 Bi(1-x) HoxTiO3 x = 0, 0.5, 1, 2 and 3 mol %. The observation of semicircle in the higher temperature regime from the Nyquist plots confirms the Debye type relaxation. Overlapping of normalized Z″ and M″ peaks suggested the long-range relaxation of charge carriers. The grain resistance (Rg) decreased with temperature. The improved insulating character was found for a small concentration (0.5 mol %) of holmium substituted NBT. Additionally, photoluminescence emission peaks associated with the transitions in Ho3+ ions were observed in the visible range. Quenching in photoluminescence intensities was observed in the higher composition (3 mol % Ho3+ substituted NBT) which we surmise as due to the collective impact of concentration quenching and the emergence of higher symmetric orthorhombic phase (Pbnm) within lower symmetric (R3c + Cc) phase.

Sound velocity effects on the phase transition gravitational wave spectrum in the sound shell model

Cosmological first-order phase transition gravitational wave could provide a novel approach to study the early Universe. In most cases, the acoustic gravitational wave from sound wave mechanism is dominant. Considering different sound velocities in symmetric and broken phases, we study sound velocity effects on the acoustic phase transition gravitational wave spectra in the Sound Shell Model. We demonstrate that different sound velocities could obviously modify the peak frequency and peak amplitude of the gravitational wave power spectra. Therefore, taking more realistic sound velocities might provide more accurate predictions for various gravitational wave experiments.