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[Springer Tracts in Modern Physics] Parity-time Symmetry and Its Applications Volume 280 || Construction of Non- P T $$\mathbb {PT}$$ -Symmetric Complex Potentials with All-Real Spectra
摘要： We review recent work on the generalization of PT symmetry. We show that, in addition to PT -symmetric complex potentials, there are also large classes of non-PT -symmetric complex potentials which also feature all-real spectra. In addition, some classes of these non-PT -symmetric potentials allow phase transitions which do or do not go through exceptional points. These non-PT -symmetric potentials are constructed by a variety of methods, such as the symmetry and supersymmetry methods and the soliton theory. A generalization of PT symmetry in multi-dimensions is also reviewed.
关键词： all-real spectra,exceptional points,soliton theory,symmetry methods,supersymmetry methods,non-PT -symmetric potentials,PT symmetry,phase transitions
更新于2025-09-10 09:29:36
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[Springer Tracts in Modern Physics] Parity-time Symmetry and Its Applications Volume 280 || Nonlinear Beam Propagation in a Class of Complex Non- P T $$\mathcal {PT}$$ -Symmetric Potentials
摘要： The subject of PT -symmetry and its areas of application have been blossoming over the past decade. Here, we consider a nonlinear Schr?dinger model with a complex potential that can be tuned controllably away from being PT -symmetric, as it might be the case in realistic applications. We utilize two parameters: the ?rst one breaks PT -symmetry but retains a proportionality between the imaginary and the derivative of the real part of the potential; the second one, detunes from this latter proportionality. It is shown that the departure of the potential from the PT -symmetric form does not allow for the numerical identi?cation of exact stationary solutions. Nevertheless, it is of crucial importance to consider the dynamical evolution of initial beam pro?les. In that light, we de?ne a suitable notion of optimization and ?nd that even for non PT -symmetric cases, the beam dynamics, both in 1D and 2D – although prone to weak growth or decay– suggests that the optimized pro?les do not change signi?cantly under propagation for speci?c parameter regimes.
关键词： Solitons,PT -symmetry,Unbalanced gain and loss,Stability,Nonlinear Schr?dinger equation,Symmetry breaking
更新于2025-09-10 09:29:36
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Fabry-Perot interferometry in Weyl semi-metals
摘要： We show that the electrical transport across a minimal model for a time-reversal symmetry(TRS) breaking Weyl semi-metal (WSM) involving two Weyl nodes can be interpreted as an interferometer in momentum space. The interference phase depends on the distance between the Weyl nodes ( (cid:126)δk) and is anisotropic. It is further shown that a minimal inversion symmetry broken model for a WSM with four Weyl nodes effectively mimics a situation corresponding to having two copies of the interferometer due to the presence of an orbital pseudo-spin domain wall in momentum space. We point out that the value of the δk and consequently the interference phase can be tuned by driving the WSMs resulting in oscillations in the two terminal conductance measured in the direction of splitting of the Weyl nodes.
关键词： Weyl semi-metals,Fabry-Perot interferometry,inversion symmetry breaking,orbital pseudo-spin,time-reversal symmetry breaking
更新于2025-09-10 09:29:36
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[IEEE 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz2018) - Nagoya, Japan (2018.9.9-2018.9.14)] 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Ultrafast Control of Even-Order Harmonic Generation from Solids by an Intense Terahertz Field
摘要： Nonperturbative even-order harmonics, physically forbidden in centrosymmetric crystals, are observed from both insulator (diamond) and semiconductor (silicon) samples driven by IR pulses, when in addition an intense THz electric field is applied to the solid. The time-resolved study of the high-harmonic spectra with the temporal profile of the THz electric field suggests a transient THz-field-induced symmetry reduction. We also investigate the harmonics’ yields depending on the angles of the linear IR and THz polarizations with respect to the crystal axes. This work might pave the way for THz-based symmetry control in solids with important ramifications for petahertz electronics.
关键词： symmetry reduction,petahertz electronics,Nonperturbative even-order harmonics,THz electric field,centrosymmetric crystals
更新于2025-09-10 09:29:36
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Matrix-induced Linear Stark Effect of Single Dibenzoterrylene Molecules in 2,3-Dibromonaphthalene Crystal
摘要： Absorption and fluorescence from single molecules can be tuned by applying an external electric field – a phenomenon known as the Stark effect. A linear Stark effect is associated to a lack of centrosymmetry of the guest in the host matrix. Centrosymmetric guests can display a linear Stark effect in disordered matrixes, but the response of individual guest molecules is often relatively weak and non-uniform, with a broad distribution of the Stark coefficients. Here we introduce a novel single-molecule host-guest system, dibenzoterrylene (DBT) in 2,3-dibromonaphthalene (DBN) crystal. Fluorescent DBT molecules show excellent spectral stability with a large linear Stark effect, of the order of 1.5 GHz/(kVcm -1), corresponding to an electric dipole moment change of around 2 D. Remarkably, when the electric field is aligned with the a crystal axis, nearly all DBT molecules show either positive or negative Stark shifts with similar absolute values. These results are consistent with quantum chemistry calculations. Those indicate that DBT substitutes three DBN molecules along the a axis, giving rise to eight equivalent embedding sites, related by the three glide planes of the orthorhombic crystal. The static dipole moment of DBT molecules is created by host-induced breaking of the inversion symmetry. This new host-guest system is promising for applications that require a high sensitivity of fluorescent emitters to electric fields, for example to probe weak electric fields.
关键词： 2,3-dibromonaphthalene,linear Stark effect,single-molecule spectroscopy,symmetry breaking,DFT,dibenzoterrylene,insertion sites,induced dipole moment
更新于2025-09-10 09:29:36
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Symmetry-Breaking as a Paradigm to Design Highly-Sensitive Sensor Systems
摘要： A large class of dynamic sensors have nonlinear input-output characteristics, often corresponding to a bistable potential energy function that controls the evolution of the sensor dynamics. These sensors include magnetic field sensors, e.g., the simple fluxgate magnetometer and the superconducting quantum interference device (SQUID), ferroelectric sensors and mechanical sensors, e.g., acoustic transducers, made with piezoelectric materials. Recently, the possibilities offered by new technologies and materials in realizing miniaturized devices with improved performance have led to renewed interest in a new generation of inexpensive, compact and low-power fluxgate magnetometers and electric-field sensors. In this article, we review the analysis of an alternative approach: a symmetry-based design for highly-sensitive sensor systems. The design incorporates a network architecture that produces collective oscillations induced by the coupling topology, i.e., which sensors are coupled to each other. Under certain symmetry groups, the oscillations in the network they exhibit a very large emerge via an infinite-period bifurcation, so that at birth, period of oscillation. This characteristic renders the oscillatory wave highly sensitive to symmetry-breaking effects, thus leading to a new detection mechanism. Model equations and bifurcation analysis are discussed in great detail. Results from experimental works on networks of fluxgate magnetometers are also included.
关键词： sensors,heteroclinic cycles,symmetry breaking
更新于2025-09-10 09:29:36
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[IEEE 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Espoo, Finland (2018.8.27-2018.9.1)] 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Acoustic Metamaterials Crystal for Passive Parity-Time-Symmetric Modulation
摘要： The exploration of parity-time (PT) symmetry with classical wave systems has enabled many counter-intuitive ways of wave manipulation and innovative applications, yet is still a great challenge for sound waves as acoustic gain medium is not readily accessible. Here we report the realization of an acoustic metamaterials crystal that respects passive PT symmetry, by interleaving groove- and holey-structured metamaterials to offer intrinsic PT-symmetric potential without any active element. At the exceptional point where a transition from the unbroken to broken PT symmetry phase happens, unidirectional sound reflectionless effect is numerically achieved. Our demonstration provides a feasible path to the investigation of PT symmetry in acoustic wave system with practical structures free of gain medium.
关键词： unidirectional reflectionless effect,passive modulation,acoustic metamaterials,PT symmetry
更新于2025-09-10 09:29:36
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Exceptional points in a time-periodic parity-time-symmetric Rabi model
摘要： We investigate the effect of a periodic modulation on parity-time symmetry in a non-Hermitian Rabi model with balanced gain or loss. It is shown that under the multiple-photon resonance conditions, this Rabi model supports exact Floquet solutions for certain special parameter conditions which allow us to find exact analytical results for the position of certain exceptional points (EPs). It is also found numerically that there exists a universal relation between the number of the EPs and the gain or loss strength.
关键词： non-Hermitian Rabi model,exceptional points,Floquet solutions,parity-time symmetry,periodic modulation
更新于2025-09-10 09:29:36
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Symmetry Modulation and Enhanced Multiferroic Characteristics in Bi <sub/>1-</sub><i> <sub/>x</sub></i> Nd <i> <sub/>x</sub></i> FeO <sub/>3</sub> Ceramics
摘要： BiFeO3 is recognized as the most important room temperature single phase multiferroic material. However, the weak magnetoelectric (ME) coupling remains as a key issue, which obstructs its applications. Since the magnetoelectric coupling in BiFeO3 is essentially hindered by the cycloidal spin structure, here efforts to improve the magnetoelectric coupling by destroying the cycloidal state and switching to the weak ferromagnetic state through symmetry modulation are reported. The structure is tuned from polar R3c to polar Pna2 1, and finally to nonpolar Pbnm by forming Bi1-xNdxFeO3 solid solutions, where two morphotropic phase boundaries (MPBs) are detected. Greatly enhanced ferroelectric polarization is obtained together with the desired weak ferromagnetic characteristics in Bi1-xNdxFeO3 ceramics at the compositions near MPBs. The change of magnetic state from antiferromagnetic (cycloidal state) to ferromagnetic (canted antiferromagnetic) is confirmed by the observation of magnetic domains using magnetic force microscopy. More interestingly, combining experiments and first-principles-based simulations, an electric field-induced structural and magnetic transition from Pna21 back to R3c is demonstrated, providing a great opportunity for electric field-controlled magnetism, and this transition is shown to be reversible with additional thermal treatment.
关键词： multiferroics,symmetry modulation,electric field-controlled magnetism,BiFeO3
更新于2025-09-10 09:29:36
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[Springer Tracts in Modern Physics] Parity-time Symmetry and Its Applications Volume 280 || Higher Order Exceptional Points in Discrete Photonics Platforms
摘要： The introduction of parity-time (PT) symmetry in optics and photonics has initiated intense activities exploring the exotic properties of these structures, eventually leading to the more general notion of non-Hermitian photonics. Efforts to understand the behavior of these systems have revealed a host of distinct features originating from the unusual character of their eigenspectra and eigenstates. These include for example, spontaneous symmetry breaking, bandgap merging, laser self-termination, unidirectional invisibility, and ultra-sensitivity to external perturbations. A central notion pertinent to all these effects is the concept of exceptional points (EPs). Also known as branch points, EPs are non-Hermitian spectral singularities that arise when two (or more) eigenvalues and their corresponding eigenstates become identical. While exceptional points of order two have been studied thoroughly at both the theoretical and experimental level, higher order EPs are attracting attention only recently. Here we discuss a systematic approach based on a recursive bosonic quantization scheme for generating discrete photonic networks that exhibit exceptional points of any arbitrary order. We also discuss the spectral properties and the extreme dynamics near these singularities as well as their physical implementation in various photonic platforms.
关键词： non-Hermitian photonics,parity-time symmetry,photonic networks,recursive bosonic quantization,exceptional points
更新于2025-09-10 09:29:36