Symmetry Breaking Research Articles

Anomalous distribution of magnetization in an Ising spin glass with correlated disorder

The effect of correlations in disorder variables is a largely unexplored topic in spin glass theory. We study this problem through a specific example of correlated disorder introduced in the Ising spin glass model. We prove that the distribution function of the magnetization along the Nishimori line in the present model is identical to the distribution function of the spin glass order parameter in the standard Edwards-Anderson model with symmetrically distributed independent disorder. This result means that if the Edwards-Anderson model exhibits replica symmetry breaking, the magnetization distribution in the correlated model has support on a finite interval, in sharp contrast to the conventional understanding that the magnetization distribution has, at most, two delta peaks. This unusual behavior challenges the traditional argument against replica symmetry breaking on the Nishimori line in the Edwards-Anderson model. In addition, we show that when temperature chaos is present in the Edwards-Anderson model, the ferromagnetic phase is strictly confined to the Nishimori line in the present model. These findings are valid not only for finite-dimensional systems but also for the infinite-range model, and highlight the need for a deeper understanding of disorder correlations in spin glass systems. Published by the American Physical Society 2024

Heterotic strings and quantum entanglement

We construct ℤN orbifolds of the ten-dimensional heterotic string theories appropriate for implementing the stringy replica method for the calculation of quantum entanglement entropy. A novel feature for the heterotic string is that the gauge symmetry must be broken by a Wilson line to ensure modular invariance. We completely classify the patterns of symmetry breaking. We show that the tachyonic contributions in all cases can be analytically continued, with a finite answer in the domain 0 < N ≤ 1, relevant for calculating entanglement entropy across the Rindler horizon. We discuss the physical implications of our results.

Discrete spacetime crystal: Intertwined spacetime symmetry breaking in a driven-dissipative spin system

Discrete spacetime crystal: Intertwined spacetime symmetry breaking in a driven-dissipative spin system

Supergravity spectrum of AdS5 black holes

We embed Kerr-Newman-AdS black holes into N = 8 gauged supergravity and study quadratic fluctuations around the black hole backgrounds of all fields in the larger theory. The equations of motion of the perturbations are partially diagonalized by the group theory of broken symmetry. Nearly all fields in theory have non-minimal couplings, so their equations of motion are not merely massive Klein-Gordon equations with minimal coupling to background gauge fields, and their analogues for fields with spin. In the special case of extremal black holes we identify specific modes of instability, some of which touch supersymmetric locus. For example, we identify scalar fields in supergravity that condense in the near horizon region and transition the black hole into a superconducting phase. We also identify supergravity modes that are susceptible to superradiant instability.

Probing radiative electroweak symmetry breaking with colliders and gravitational waves

Radiative symmetry breaking provides an appealing explanation for electroweak symmetry breaking and addresses the hierarchy problem. We present a comprehensive phenomenological study of this scenario, focusing on its key feature: the logarithmic-shaped potential. This potential gives rise to a relatively light scalar boson that mixes with the Higgs boson and leads to first-order phase transitions (FOPTs) in the early Universe. Our study includes providing exact and analytical solutions for the vacuum structure and scalar interactions, classifying four patterns of cosmic thermal history, and calculating the supercooled FOPT and gravitational waves (GWs). A detailed treatment of the FOPT dynamics reveals that an ultra-supercooled FOPT does not always imply strong GW signals, due to its short duration. By combining future collider and GW experiments, we can probe the conformal symmetry breaking scales up to 105–108 GeV. Published by the American Physical Society 2024

Functional renormalization group approach for signal detection

This review paper utilizes renormalization group techniques for signal detection in nearly continuous positive spectra. We emphasize the universal aspects of the analogue field-theory approach. The primary objective is to present an extended self-consistent construction of the analogue effective field-theory framework for data, which can be interpreted as a maximum entropy model. In particular, we leverage universality arguments to justify the \mathbb{Z}_2ℤ2 symmetry of the classical action, highlighting the existence of both a large-scale (local) regime and a small-scale (nonlocal) regime. Secondly, in relation to noise models, we observe the universal relationship between phase transitions and symmetry breaking near the detection threshold. Finally, we address the challenge of defining the covariance matrix for tensor-like data. Based on the cutting graph prescription, we note the superiority of definitions that rely on complete graphs of large size for data analysis.

Duality and hidden symmetry breaking in the q-deformed Affleck-Kennedy-Lieb-Tasaki model

We revisit the question of string order and hidden symmetry breaking in the qq-deformed AKLT model, an example of a spin chain that possesses generalized symmetry. We first argue that the non-local Kennedy-Tasaki duality transformation that was previously proposed to relate the string order to a local order parameter leads to a non-local Hamiltonian and thus does not provide a physically adequate description of the symmetry breaking. We then present a modified non-local transformation which is based on a recently developed generalization of Witten’s Conjugation to frustration-free lattice models and capable of resolving this issue.

Possibility of spontaneous symmetry breaking in the Nambu-Jona-Lasinio model with torsion

Possibility of spontaneous symmetry breaking in the Nambu-Jona-Lasinio model with torsion

Room temperature polarization-resolved Raman and photoluminescence in uniaxially strained layered MoS2

Transition metal dichalcogenides (TMDCs) are one of the material systems of choice toward achieving room temperature quantum coherence. Externally applied strain is used as a more common control mechanism to tune electro-optical properties in TMDCs like molybdenum disulfide (MoS2). However, room temperature electron–phonon interactions in the presence of strain in transition metal dichalcogenides are still not fully explored. In this work, we employ uniaxial strain dependent Raman and photoluminescence (PL) studies on monolayer and bilayer MoS2 to explore electron–phonon physics. Helicity-resolved Raman in MoS2 obeys robust selection rules. Our studies reveal clear modification in these helicity-based selection rules in the presence of moderate uniaxial strain (ϵ = 0.4%–1.2%). The selection rules are restored upon clear symmetry breaking of the in-plane vibrational mode (ϵ &amp;gt; 1.2%). We assign these changes to the onset of Fröhlich interaction in this moderate strain regime. The changes in Raman scattering are accompanied by changes in valley selective relaxation observed through non-resonant photoluminescence (PL). The moderate strain regime also exhibits the onset of PL polarization for indirect excitonic emission under non-resonant excitation. Our experimental observations point toward electron–phonon coupling mechanisms affecting both valley-selective electron relaxation during PL emission as well as polarization-selective Raman scattering of two-dimensional semiconductors at room temperature.

Quasi-Nambu-Goldstone modes in many-body scar models

From the quasisymmetry-group perspective [J. Ren , ], we show the universal existence of collective, coherent modes of excitations in many-body scar models in the degenerate limit, where the energy spacing in the scar tower vanishes. The number of these modes, as well as the quantum numbers carried by them, are given, not by the symmetry of the Hamiltonian, but by the quasisymmetry of the scar tower: hence the name quasi-Nambu-Goldstone modes. Based on this, we draw a concrete analogy between the paradigm of spontaneous symmetry breaking and the many-body scar physics in the degenerate limit. Published by the American Physical Society 2024

A cosmological reconstruction of the Higgs vacuum expectation value

We present a simple toy model of cosmic acceleration driven purely by a self-interacting scalar field embedded in theory of grand unification. The scalar self-interaction is Higgs-like and provokes a spontaneous symmetry breaking. The coefficient of the quadratic term in the self-interaction potential has an evolution and it leads to a cosmic variation of proton-to-electron mass ratio, μ. We perform a cosmological reconstruction from the kinematic parameter jerk and discuss a few cosmological consequences of the theory. We also compare the theoretically calculated μ variation with the observations of molecular absorption spectra from Cesium Atomic Clock data.

Symmetry breaking and dynamic characteristics of post-buckling in bilayer van der Waals structures

Symmetry breaking and dynamic characteristics of post-buckling in bilayer van der Waals structures

Optically active persistent luminescence in supramolecular nanoassemblies constructed from entirely achiral building blocks

Optically active persistent luminescent materials have attracted significant attention due to their distinctive luminescent characteristics and ability to exhibit rich circular polarization information. Despite extensive efforts to develop circularly polarized persistent luminescence (CPPL) materials using chiral molecules or polymers, fabricating CPPL materials from achiral units remains a big challenge. In this work, we introduce an efficient co-assembly strategy to create CPPL materials using entirely achiral organic molecules. The optical activities of co-assembled complexes are attributed to structural chirality, which arises from chiral nanohelices formed during symmetry breaking in the self-assembly process of C3-symmetric molecules. Achiral molecules with long-lasting phosphorescence can adhere to these chiral nanostructures via hydrogen bonding, and during the drying phase, form nanocrystals that align along helical fibers, resulting in circularly polarized, long-lasting phosphorescence. Enhanced CPPL efficiency, ranging from blue to yellow with a dissymmetry factor over 1.2 × 10−2 and lifetime of up to 0.6 s at room temperature, is achieved through hydrogen bonding driven co-assembly. Additionally, the CPPL spectra of these co-assemblies are captured using a homemade time-resolved circularly polarized long afterglow detection platform. This study not only presents a new approach for the high-efficiency design of CPPL materials from achiral building blocks but also significantly broadens the research possibilities in real-time CPPL analysis, offering a horizon in the exploration of CPPL materials.

Polarization-rotation-driven modulation of second harmonic generation in van der Waals layered ferroelectric CuInP2S6

Two-dimensional van der Waals (vdW) ferroelectrics, renowned for their spontaneous breaking of inversion symmetry and finite electric polarization, are pivotal in nonlinear optics and low-power nanoelectronics. Prior studies primarily focused on materials exhibiting out-of-plane or in-plane ferroelectric polarization, whose rotational degrees of freedom are commonly overlooked. Herein, we experimentally validate the existence of a weak yet symmetry-allowed in-plane polarization in the low-symmetry vdW ferroelectric CuInP2S6 by rigorous structural analysis and vectorial property characterizations. Remarkably, the magnitude of this in-plane polarization is tunable via an interface-induced electric field, leading to a significant contrast in second harmonic generation between oppositely polarized domains. Based on this unique rotational capability of electric polarization, we demonstrate an electrically tunable second-order optical emission in a fabricated vdW ferroelectric capacitor. Our findings highlight the intricate interplay between crystal symmetry and tensorial physical properties, providing a novel pathway for manipulating nonlinear optical functionalities in vdW layered ferroelectrics.

Schottky Anomaly of the Kalb-Ramond-de Sitter Spacetime

In the theory of gravity, the spontaneous breaking of Lorentz symmetry due to the non-minimal coupling between the Kalb-Ramond field and Einstein gravity results in the existence of exactly static and spherically symmetric black hole solutions related to the Lorentz violating parameter. Based on the consideration of the interaction between the black hole and cosmological horizons, this paper studies the thermodynamic properties of Kalb-Ramond-de Sitter (KR-dS) spacetime. The Smarr relation expressed by equivalent thermodynamic quantities is found, and it is proved that the equivalent thermodynamic quantities of the KR-dS spacetime satisfy the universal Euler's theorem. It is discovered that the heat capacity of the KR-dS spacetime with respect to the ratio of the two horizons and the variation curve of the heat capacity with effective temperature possess the characteristics of Schottky specific heat. Moreover, the black hole and the cosmological horizon in the equivalent thermodynamic system are regarded as two different energy levels, and the heat capacity of the KR-dS spacetime is discussed using the general form given by the ordinary two-level system. It is found that the heat capacity of KR-dS spacetime described by equivalent thermodynamic quantities not only conforms to the characteristics of Schottky specific heat but also is consistent with the heat capacity of the ordinary two-level system. This result reflects that when the cosmological constant and the charged carried in the KR-dS spacetime remain unchanged, the heat capacity of the system can be represented by a universal two-level system. By comparing the maximum value of the heat capacity curves, the number of microscopic particles between the two horizons can be estimated, which reflects the quantum properties of the KR-dS spacetime. These studies will open a new perspective to probe the thermodynamics of black holes.

Magnetically tunable bound states in the continuum with arbitrary polarization and intrinsic chirality

Bound states in the continuum (BICs), which are exotic localized eigenstates embedded in the continuum spectrum and exhibit topological polarization singularities in momentum space, have recently attracted great attention in both fundamental and applied physics. Here, based on a magneto-optical (MO) photonic crystal (PhC) slab placed in external magnetic fields with time-reversal symmetry (TRS) breaking, we theoretically propose magnetically tunable BICs with arbitrary polarization covering the entire Poincaré sphere and efficient off-Γ chiral emission of circularly polarized states (C point). More interestingly, by further breaking the in-plane inversion symmetry of the MO PhC slab to generate a pair of C points spawning from the eliminated BICs and tuning the external magnetic field strength to move one C point to the Γ point, an at-Γ intrinsic chiral BIC exhibits chiral characteristics on both sides of the PhC slab with near-unity circular dichroism exceeding 0.99 and a high-quality factor of 46,000 owing to the preserved out-of-plane mirror symmetry. Moreover, the chirality of the chiral BICs can be inverted by flipping the magnetic bias. Our work opens an unprecedented avenue to explore the unique topological photonics of BICs with broken TRS and promises multiple applications in chiral-optical effects, structured light, and tunable optical devices.

Control of Instabilities in Resonant Converters Using Half‐Period Time Delay Output Feedback

ABSTRACTBifurcation phenomena in power electronic converters lead to undesired instabilities. In this paper, different types of bifurcations are identified, which can occur in a series load resonant converter with the variation of the parameters for example, input voltage, load resistance, and so forth. These instabilities are associated mainly to three different bifurcations: (a) Neimark–Sacker, (b) saddle–node, and (c) symmetry breaking bifurcations. Due to the symmetry property of load resonant converters, a half‐period time delay output feedback control is used to avoid all of these instabilities. The ideal time delay is realized by a first‐order all‐pass‐filter. The stability analysis is performed and the values of the feedback gains are determined to identify the stable domain in the parameter space. By identifying the unstable orbits, the analytical stability analysis helps to understand as well as to control the mechanisms of these instabilities, which extends the stability domain of the system. This study can also be extended to other load resonant converters where the symmetry property naturally exists.

Observation of field-free spin–orbit torque switching in a single crystalline (Ga,Mn)(As,P) ferromagnetic film with perpendicular anisotropy

We report the observation of field-free spin–orbit torque (SOT) magnetization switching in a single layer of (Ga,Mn)(As,P) ferromagnetic film exhibiting perpendicular magnetic anisotropy. The SOT switching phenomenon is characterized by distinct transitions between two Hall resistance (HR) states during current scans. When subjected to an in-plane bias field, the observed switching chirality in the HR hysteresis loop consistently aligns with SOT induced by spin polarization arising from Rashba- and Dresselhaus-type spin–orbit fields within the tensile-strained crystalline structure of the (Ga,Mn)(As,P) film. Remarkably, in the present experiments, we observe SOT switching even in the absence of an external bias field, and with its chirality depending on the direction of initial magnetization. We attribute this field-free switching to symmetry breaking facilitated by an internal coupling field, the orientation of which is determined by the external field experienced as the magnetization is initialized. Further evidence supporting the presence of such a coupling field includes a shift in the field-scan HR hysteresis depending on the direction of initialized magnetization. Structural analysis reveals a surface layer enriched in Mn and O, indicating the presence of oxide-based magnetic structures that are magnetically coupled to the (Ga,Mn)(As,P) film. The temperature dependence of field-free SOT switching corroborates this explanation, as the internal coupling field disappears above 40 K, consistent with the expected magnetic transition of the Mn3O4 structure. Our discovery of field-free SOT magnetization switching in a single-layer film represents a significant advancement, offering a novel pathway for the development of simpler and more energy-efficient spintronic devices.

Microwave Hall measurements using a circularly polarized dielectric cavity.

We have developed a circularly polarized dielectric rutile (TiO2) cavity with a high quality-factor that can generate circularly polarized microwaves from two orthogonal linearly polarized microwaves with a phase difference of ±π/2 using a hybrid coupler. Using this cavity, we have established a new methodology to measure the microwave Hall conductivity of a small single crystal of metal in the skin-depth region. Based on the cavity perturbation technique, we have shown that all components of the surface impedance tensor can be extracted under the application of a magnetic field by comparing the right- and left-handed circularly polarized modes. To verify the validity of the developed method, we performed test measurements on tiny Bi single crystals at low temperatures. As a result, we have successfully obtained the surface impedance tensor components and confirmed that the characteristic field dependence of the ac Hall angle in the microwave region is consistent with the expectation from the dc transport measurements. These results demonstrate a significant improvement in sensitivity compared to previous methods. Thus, our developed technique allows for more accurate microwave Hall measurements, opening the way for new approaches to explore novel topological quantum phenomena, such as time-reversal symmetry breaking in superconductors.

Thick brane in mimetic-like gravity

We analyze a five-dimensional braneworld governed by a mimetic-like gravity, a plausible candidate for explaining dark matter. Within this scenario, we examine Friedmann-Lemaître-Robertson-Walker (FLRW) branes and find that constant curvature and Minkowskian solutions are possible. We then show that the mimetic model leads to kink-like and lump-like thick brane solutions without the need for spontaneous symmetry breaking. Its stability against small perturbations is also verified.