Symmetry Breaking Research Articles

Discrete anisotropy model of heterogeneous cardiac tissue predicting the occurrence of symmetry breaking of reentrant activity

Discrete anisotropy model of heterogeneous cardiac tissue predicting the occurrence of symmetry breaking of reentrant activity

Gravitational waves from patterns of electroweak symmetry breaking: an effective perspective

Abstract The future space-borne gravitational wave (GW) detectors would provide a promising probe for the new physics beyond the standard model that admits the first-order phase transitions. The predictions for the GW background vary sensitively among different concrete particle physics models but also share a large degeneracy in the model buildings, which motivates an effective model description on the phase transition based on different patterns of the electroweak symmetry breaking (EWSB). 
In this paper, using the scalar $N$-plet model as a demonstration, we propose an effective classification for three different patterns of EWSB: (1) radiative symmetry breaking with classical scale invariance, (2) Higgs mechanism in generic scalar extension, and (3) higher dimensional operators.
We conclude that a strong first-order phase transition could be realized for (1) and (2) with a small quartic coupling and a small isospin of an additional $N$-plet field for the light scalar field model with and without the classical scale invariance, and (3) with a large mixing coupling between scalar fields and a large isospin of the $N$-plet field for the heavy scalar field model.

Symmetry breaking and intensity switching of counterpropagating Raman waves in a microresonator

Symmetry breaking and intensity switching of counterpropagating Raman waves in a microresonator

Tunable Directional Radiation and Reception Based on Magneto-Optical Photonic Crystal Waveguides

Abstract We have proposed a magneto-optical photonic crystal (MOPC) waveguide that can not only realize highly directional radiation but also work as an electromagnetic (EM) wave receiver. This waveguide consists of a square MOPC and a covering layer of Al2O3 PC tilted at 45° that allows for the penetration of EM waves. Due to the broken time-reversal symmetry caused by an external magnetic field, there exists a unidirectional leaky topological edge state within the photonic bandgap. Such the leaky edge state transmits unidirectionally and radiates into the air simultaneously, leading to a broadside radiation beam with a low half-power beam width of less than 4°. More importantly, the radiation direction of the beam can be tuned over a wide angular range by adjusting the operation frequency or the magnetic field strength. Besides, this designed waveguide can also act as a tunable receiver for capturing incident EM waves effectively. These results have potential for various practical applications, such as antennas and sensors.

Collective mode across the BCS-BEC crossover in Holstein model

We investigate the emergence of the collective mode in the phonon spectra of the superconducting state within the Holstein model by varying the electron-phonon coupling. Using dynamical mean field theory combined with the numerical renormalization group technique, we calculate the phonon spectra. In the superconducting state with a pairing gap (ΔP), the peak position of the collective mode (ωcol) evolves from the Bardeen-Cooper-Schrieffer (BCS) regime, manifesting near 2ΔP and increasing with coupling, to the Bose-Einstein condensation (BEC) regime, where ωcol decreases with increasing coupling. The decrease of ωcol matches well with the reduction of superfluid stiffness, which originates from the increasing phase fluctuations of local pairs with coupling strength. In the crossover regime with intermediate coupling, ωcol aligns with the soft phonon mode (ωs) of the normal state and decreases with increasing coupling when ωs<2ΔP. Additionally, comparing the collective mode weight to ΔP suggests that the collective mode predominantly stems from U(1) gauge symmetry breaking across all coupling strengths. Published by the American Physical Society 2024

Leptogenesis from a phase transition in a dynamical vacuum

We show that a phase transition may take place in the early Universe at a temperature T* resulting a temperature dependent mass for right-handed neutrinos (RHN) which finally relaxes to a constant value after electroweak symmetry breaking (EWSB). As a result, a requisite amount of lepton asymmetry can be produced near T* satisfying the observed baryon asymmetry of the Universe via the sphaleron process even when zero temperature masses of the RHNs fall below the electroweak scale enhancing the detection possibility of RHNs. Interestingly, the framework is also capable of predicting a primordial lepton asymmetry (generated after EWSB) as hinted by helium abundance measurements, indicating a correlation with the early phase of leptogenesis. Published by the American Physical Society 2024

Engineering the band structure of type-II MoSe2/WSe2 van der Waals heterostructure by electric field and twist angle: a first principles perspective

Type-II heterostructures composed of transition-metal dichalcogenides have attracted enormous attention due to their facilitation in efficient electron-hole separation. In this work, we performed density-functional theory calculations to systematically investigate the atomic and electronic structures of MoSe2/WSe2van der Waals heterostructure. Its six high-symmetry configurations with different interlayer coupling under external electric field and twist angle were addressed. Our results reveal that all the configurations exhibit type-II band alignment and their band gaps can be effectively modulated by the electric field. Notably, the direct to indirect band gap transition only occurs in the configurations with strong interlayer coupling. Moreover, twist-induced symmetry breaking weakens the interlayer interactions, thus decreasing interlayer charge transfer. Owing to large interlayer distance and weak interlayer coupling, the band structure of the heterostructure remained unchanged for the twist angles ranging from 13.2° to 46.8°. These findings demonstrate the great potential of the MoSe2/WSe2heterostructure for applications in optoelectronic and nanoelectronic devices.

Replica symmetry breaking in spin glasses in the replica-free Keldysh formalism

We show that the algebra of Parisi ultrametric matrices is recovered by the real-time, replica-free, Dyson-Keldysh equations of infinite-range quantum spin glasses in the late time glassy limit. This connects to earlier results on classical and quantum systems showing how ultrametricity emerges from the persistent slow aging dynamics of the glass phase. The stationary spin glass state thereby spontaneously breaks thermal symmetry, or the Kubo-Martin-Schwinger relation of a state in global thermal equilibrium. We describe the Keldysh path integral of the infinite-range Ising model in transverse and longitudinal fields, and in the context of the Landau expansion of the action functional, show how the long-time limit connects to the full replica symmetry breaking obtained in the equilibrium formalism. We also illustrate our formalism by applying it to the spherical quantum pp-spin model, which only exhibits one-step replica symmetry breaking.

Control of diffusion and transition phenomena in a periodic system with temporal symmetry breaking

Control of diffusion and transition phenomena in a periodic system with temporal symmetry breaking

Entropic Order Parameters for Categorical Symmetries in 2D-CFT

In this work, we propose an information theoretic order parameter able to characterize the presence and breaking of categorical symmetries in (1+1)-d rational conformal field theories (RCFTs). Specifically, we compute the quantum relative entropy between the ground states of RCFTs representing the critical point of phase transitions between different symmetry-broken phases of theories with categorical symmetries, and their symmetrized versions. We find that, at leading order in the high temperature limit, this relative entropy only depends on the expectation values of the quantum dimensions of the topological operators implementing the categorical symmetry. This dependence suggests that our proposal can be used to characterize the different broken phases of (1+1)-d theories with categorical symmetries.

Inverse Size-Scaling Ferroelectricity in Centrosymmetric Insulating Perovskite Oxide DyScO3.

The breaking of inversion symmetry dictates the emergence of electric polarization, whose topological states in superlattices and bulks have received tremendous attention for their intriguing physics brought for novel device design. However, as for substrate oxides such as LaAlO3, KTaO3, RScO3 (R = rare earth element), their centrosymmetric trivial attributes make their functionality poorly explored. Here, the discovery of nanoscale thickness gradient-induced nonpolar-to-polar phase transition in band insulator DyScO3 is reported by using atomic resolution transmission electron microscopy. As the free-standing specimen reduces to a critical thickness ≈5 nm, its inversion symmetry is spontaneously broken by surface charge transfer, which gives rise to asymmetric Dy atomic displacements and ferrodistortive octahedral order, as substantiated by the first-principles calculations. Apart from the observation of migratable polar vortex structures, the switchable electric polarization by applied electric field is demonstrated by the piezoresponse force microscopy experiments. Given the decisive role of critical size in generating ferroelectricity, a concept of "inverse size-scaling ferroelectric" is proposed to define a class of such materials. Distinct from the proper and improper ferroelectrics, the findings offer a new platform to explore novel low-dimensional ferroelectrics and device applications in the future.

Refined cyclic renormalization group in Russian doll model

Focusing on Bethe-Ansatz integrable models, robust to both time-reversal symmetry breaking and disorder, we consider the Russian Doll Model (RDM) for finite system sizes and energy levels. Suggested as a time-reversal-symmetry breaking deformation of Richardson’s model, the well-known and simplest model of superconductivity, RDM revealed an unusual cyclic renormalization group (RG) over the system size NN, where the energy levels repeat themselves, shifted by one after a finite period in \ln NlnN, supplemented by a hierarchy of superconducting condensates, with the superconducting gaps following the so-called Efimov (exponential) scaling. The equidistant single-particle spectrum of RDM made the above Efimov scaling and cyclic RG to be asymptotically exact in the wideband limit of the diagonal potential. Here, we generalize this observation in various respects. We find that, beyond the wideband limit, when the entire spectrum is considered, the periodicity of the spectrum is not constant, but appears to be energy-dependent. Moreover, we resolve the apparent paradox of shift in the spectrum by a single level after the RG period, despite the disappearance of a finite fraction of energy levels. We also analyze the effects of disorder in the diagonal potential on the above periodicity and show that it survives only for high energies beyond the energy interval of the disorder amplitude. Our analytic analysis is supported with exact diagonalization.

Dynamical Lorentz symmetry breaking in a scale-free theory of gravity

This paper explores the renormalization of scale-free quadratic gravity coupled to the bumblebee field and its potential for dynamically breaking Lorentz symmetry. We conduct one-loop renormalization of the model and calculate the associated renormalization group functions. Furthermore, we compute the one-loop effective potential for the bumblebee field, demonstrating that it acquires a nontrivial vacuum expectation value (VEV) through radiative corrections—a phenomenon known as the Coleman-Weinberg mechanism. This spontaneous breaking of scale invariance, driven by the nonzero VEV of the bumblebee field, leads to Lorentz symmetry violation. As a result, the nonminimal coupling between the bumblebee and gravitational fields induces a spontaneous generation of an Einstein-Hilbert term via radiative corrections, suggesting a possible link between the Planck scale and Lorentz violation phenomena. Published by the American Physical Society 2024

NLO friction in symmetry restoring phase transitions

Interactions between bubbles/domain walls and the surrounding medium are a topic of active research, particularly as they apply to friction effects on accelerated expansion during first-order phase transitions. In this paper, we analyse for the first time friction pressure on relativistic walls in phase transitions where gauge symmetry is restored, particularly motivated by the observation that this pressure can, in principle, be negative at leading order, since some particles lose mass by definition as they cross into the new phase. We find, however, that at NLO, the soft emission of vectors from a charged current leads to positive pressure scaling as the wall’s Lorentz boost factor γw, similar to the case of gauge symmetry breaking. Contrary to the latter case, we find that the dominant contribution in single emission is safe from IR divergences and exhibits a much stronger dependence on the wall shape. Finally, we argue that in any phase transition, no multi-particle process on the wall can impart negative pressure greater than the leading order result, in the asymptotic limit of large γw.

Holographic drag force with translational symmetry breaking

In order to investigate how the drag force is affected by translational symmetry breaking (TSB), we utilize a holographic model in which the background metric remains translational symmetric while a graviton mass or other fields in the theory break this symmetry. We calculate analytically the drag force, considering an asymptotic AdS5 in which parameter α arises from TSB. This parameter can be intuitively understood as a measure of TSB strength and we anticipate that non-zero values of it will affect the drag force. In this asymptotic AdS5 background, we will demonstrate that a decrease in α results in a reduction of the drag force. Moreover, we study the diffusion constant, which falls with increasing α. It will eventually be shown that at lower values of α or μ (chemical potential), the transverse diffusion coefficient is larger than the longitudinal one, and the speed of the heavy quark has minimal impact on the ratio.

Chiral Symmetry Breaking in Nanocrystal Superlattices Enabled by Shear and Nanowires.

The self-assembly of colloidal nanocrystals typically leads to the formation of highly symmetric superlattices, while chiral symmetry breaking within these structures remains rare. Here, we present a universal approach for achieving chiral symmetry breaking within self-assembled nanocrystal superlattices through the incorporation of nanowires and shear force. The networked film, composed of highly flexible nanowires that are only a few nanometers in diameter and bound by weak van der Waals interactions, can be manipulated to stretch and rotate, resulting in a controlled chiral pattern with a specified handedness. When combined with nanocrystal superlattices, the nanowires convey mechanical torque to the nanocrystals, inducing chiral symmetry breaking in the solid materials. This method is versatile and can be applied to various nanocrystal solids irrespective of their size, shape, or composition. Overall, this study enhances the repertoire of fabrication techniques for chiral nanomaterials, circumventing the need for chiral molecules.

Covalent Organic Frameworks for Boosting H2O2 Photosynthesis via the Synergy of Multiple Charge Transfer Channels and Polarized Field

AbstractCovalent organic frameworks (COFs) serve as one of the most promising candidates for hydrogen peroxide (H2O2) photosynthesis, while attaining high‐performance COFs remains a formidable challenge due to the insufficient separation of photogenerated charges. Here, through the rational design of bicarbazole‐based COFs (Cz‐COFs), we showcase the first achievement in piezo‐photocatalytic synthesis of H2O2 using COFs. Noteworthily, the ethenyl group‐modified Cz‐COFs (COF‐DH‐Eth) demonstrates a record‐high yield of H2O2 (9212 μmol g−1 h−1) from air and pure water through piezo‐photocatalysis, which is ca. 2.5 times higher than that of pristine Cz‐COFs without ethenyl groups (COF‐DH‐H) under identical condition and COF‐DH‐Eth without ultrasonic treatment. The H2O2 production rate originates from the synergistic effect between an ultrasonication‐induced polarized electric field and the spatially separated multiple charge transfer channels, which significantly promote the utilization of photogenerated electrons by directional transfer from bicarbazole groups to the ethenyl group‐modified benzene rings. Several Cz‐COFs and bifluorenylidene‐based COFs (COF‐BFTB‐H) with similar twisted monomers exhibit obvious piezoelectric performance for promoting H2O2 generation, signifying that organic ligands with a twistable structure play a crucial role in creating broken symmetry structures, thereby establishing piezoelectric properties in COFs.

Symmetry and Asymmetry in Mutations and Memory Retention during the Evolutionary Growth of Carbon Nanotubes.

Symmetry is a motif featured in almost all areas of science, and understanding the mechanism of symmetry breaking is challenging. Similar to mutations that disrupt symmetry in evolution, defects in materials offer insight into symmetry breaking. Here, we investigate symmetry in intragenerational mutations and symmetry breaking in transgenerational mutations in the evolutionary growth system of carbon nanotubes (CNTs). Mutations caused by pentagon-heptagon (5-7) pairs in different conformations shorten the lifespans of single-walled carbon nanotubes (SWNTs) by acting as time markers during growth. Symmetric distributions are observed for intragenerational mutations from (n, m) to (n + i, m-i) (where i ∈ caslon Z) with different appearance orders of pentagon and heptagon. Such symmetry breaks occur in transgenerational mutations. Intragenerational mutations occur multiple times on a SWNT, oscillating regularly between i and - i until termination occurs. These types and effects are retained in the form of memory to encode SWNTs during subsequent growth, resulting in a length reduction after each mutation. Our results provide a profound understanding of symmetry breaking and memory retention and offer guidance for the controlled synthesis of materials.

Observation of perovskite topological valley exciton-polaritons at room temperature

Topological exciton-polaritons are a burgeoning class of topological photonic systems distinguished by their hybrid nature as part-light, part-matter quasiparticles. Their further control over novel valley degree of freedom (DOF) has offered considerable potential for developing active topological optical devices towards information processing. Here, employing a two-dimensional (2D) valley-Hall perovskite lattice, we report the experimental observation of valley-polarized topological exciton-polaritons and their valley-dependent propagations at room temperature. The 2D valley-Hall perovskite lattice consists of two mutually inverted honeycomb lattices with broken inversion symmetry. By measuring their band structure with angle-resolved photoluminescence spectra, we experimentally verify the existence of valley-polarized polaritonic topological kink states with a large gap opening of ~ 9 meV in the bearded interface at room temperature. Moreover, these valley-polarized states exhibit counter-propagating behaviors under a resonant excitation at room temperature. Our results not only expand the landscape of realizing topological exciton-polaritons, but also pave the way for the development of topological valleytronic devices employing exciton-polaritons with valley DOF at room temperature.

Simultaneous Development of Antiferromagnetism and Local Symmetry Breaking in a Kagome Magnet (Co0.45Fe0.55)Sn.

CoSn and FeSn, two kagome-lattice metals, have recently attracted significant attention as hosts of electronic flat bands and emergent physical properties. However, current understandings of their physical properties are limited to knowledge of the average crystal structure. Here, we report the Fe-doping induced coemergence of the antiferromagentic (AFM) order and local symmetry breaking in (Co0.45Fe0.55)Sn. Rietveld analysis on the neutron and synchrotron X-ray diffraction data indicates A-type antiferromagnetic order with the moment pointing perpendicular to the kagome layers, associated with the anomaly in the MSn(1)2Sn(2)4 (M = Co/Fe) octahedral distortion and the lattice constant c. Reverse Monte Carlo (RMC) modeling of the synchrotron X-ray total scattering results captured the subtle local orthorhombic distortion involving off-axis displacements of Sn(2). Our results indicate that the stable hexagonal lattice above TN becomes unstable once the A-type AFM order is formed below TN. We argue that the local symmetry breaking has a magnetic origin, since the spatially varied M-Sn(2) bond lengths arise from out-of-plane magnetic exchange coupling Jc via the exchange pathway M-Sn(2)-M. Our study provides comprehensive information on the crystal structure in both long-range scale and local scale, unveiling unique coupling between AFM order, octahedral distortion, and hidden local symmetry breaking.