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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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The effect of the geometrical optical phase on the propagation of Hermite-Gaussian beams through transversal and parallel dielectric blocks
摘要： When an optical beam propagates through dielectric blocks, its optical phase is responsible for the path of the beam. In particular, the first order Taylor expansion of the geometrical part reproduces the path predicted by the Snell and reflection laws whereas the first order expansion of the Fresnel phase leads to the Goos-H?nchen shift. In this paper, we analyze the effects of the second order Taylor expansion of the geometrical phase on the shape of the optical beam and show how it affects the transversal symmetry of Hermite-Gaussian beams. From the analytical expression of the transmitted beam, it is possible to determine in which transversal and parallel dielectric blocks configuration the transversal symmetry breaking is maximized or when the symmetry is recovered. We also discuss the axial spreading delay.
关键词： spreading delay,Hermite-Gaussian beams,Optical phase,transversal symmetry breaking
更新于2025-09-09 09:28:46
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True Random Number Generator Realized by Extracting Entropy from a Negative-Inductance Superconducting Quantum Interference Device
摘要： A new type of superconductive true random number generator (TRNG) based on a negative-inductance superconducting quantum interference device (nSQUID) is proposed. The entropy harnessed to generate random numbers comes from the phenomenon of symmetry breaking in the nSQUID. The experimental circuit is fabricated by the Nb-based lift-off process. Low-temperature tests of the circuit verify the basic function of the proposed TRNG. The frequency characteristics of the TRNG have been analyzed by simulation. The generation rate of random numbers is expected to achieve hundreds of megahertz to tens of gigahertz.
关键词： true random number generator,negative-inductance superconducting quantum interference device,Nb-based lift-off process,frequency characteristics,symmetry breaking
更新于2025-09-09 09:28:46
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Transient Glass Formation around a Quadrupolar Photoexcited Dye in a Strongly H-Bonding Liquid Observed by Transient 2D-IR Spectroscopy
摘要： A photoexcited quadrupolar dye is directly observed using transient 2D-IR spectroscopy. Upon solvent-induced symmetry breaking, the H-bond accepting abilities of the two nitrile end-groups change drastically, and in extreme protic (‘superprotic’) solvents, a tight H-bond complex forms at one end. The time evolution of the 2D C≡N lineshape in methanol points to rapid, 2-3 ps, spectral diffusion due to fluctuations of the H-bonding network. Similar behaviour is observed in a superprotic solvent shortly after photoexcitation of the dye. However, at later time, the completely inhomogeneous band does not exhibit spectral diffusion for at least 5 ps, pointing to a glass-like environment around one side of the dye. About half of the excited dyes show this behaviour attributed to the tight H-bond complex, whereas the others are loosely bound. A weak cross peak these excited state sub- indicates partial exchange between populations.
关键词： charge transfer,symmetry breaking,ultrafast spectroscopy,Hydrogen bonds,solvation dynamics
更新于2025-09-09 09:28:46
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CPT and Lorentz Violation in the Photon and Z-Boson Sector
摘要： Violation of CPT and Lorentz symmetry in the photon sector is described within the minimal Standard-Model Extension by a dimension-3 Chern–Simons-like operator parametrized by a four-vector parameter kAF that has been very tightly bounded by astrophysical observations. On the other hand, in the context of the SU(2) × U(1) electroweak gauge sector of the Standard-Model Extension, CPT and Lorentz violation is described similarly, by dimension-3 operators parametrized by four-vector parameters k1 and k2. In this work, we investigate in detail the effects of the resulting CPT and Lorentz violation in the photon and Z-boson sectors upon electroweak-symmetry breaking. In particular, we show that, for the photon sector, the relevant Lorentz-violating effects are described at the lowest order by the kAF term, but that there are higher-order momentum-dependent effects due to photon-Z boson mixing. As bounds on CPT and Lorentz violation in the Z sector are relatively weak, these effects could be important phenomenologically. We investigate these effects in detail in this work.
关键词： Lorentz violation,dispersion relations,electroweak symmetry breaking
更新于2025-09-09 09:28:46
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Nanometer-scale local structural study of the paraelectric cubic phase of KNbO <sub/>3</sub> by convergent-beam electron diffraction
摘要： Nanometer-scale local structures of the paraelectric cubic phase of potassium niobate (KNbO3) are examined by convergent-beam electron diffraction (CBED) using a nanometer-size electron probe. The breaking of the cubic symmetry has been directly observed in the nanometer-scale areas of the cubic phase of KNbO3. This indicates the existence of local polarization clusters in the cubic phase. Symmetry breaking index maps for the fourfold rotation symmetry are given at different temperatures with the combined use of scanning transmission electron microscopy (STEM) and CBED (STEM–CBED). ? 2017 The Japan Society of Applied Physics
关键词： local polarization clusters,CBED,convergent-beam electron diffraction,STEM,KNbO3,symmetry breaking
更新于2025-09-09 09:28:46
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Topological properties of bound states in the continuum in geometries with broken anisotropy symmetry
摘要： Waveguiding structures made of anisotropic media support bound states in the continuum (BICs) that arise when the radiation channel of otherwise semileaky modes is suppressed. Hitherto, only structures with optical axes aligned in symmetric orientations inside the waveguide plane, where BICs appear as lines in the momentum-frequency dispersion diagram, have been considered. Here we address settings where such symmetry is broken and unveil a number of fundamental different features. Weak and strong symmetry-breaking regimes are identified, corresponding to azimuthal and polar optical axes orientation asymmetries, respectively. The azimuthal symmetry breaking is found to still preserve the existence loci of BICs in the momentum-frequency dispersion diagram as lines. However, all possible BICs become interferometric, while the polarization separable states that occur in symmetric settings cease to exist. The polar symmetry breaking has stronger effects and transforms the BICs’ existence loci from lines to points, which correspond to full-vector states that exist at discrete values of the optical axis orientation for a given wavelength. Such transformation results in fundamental changes in the topological properties of the radiated field around the BICs.
关键词： anisotropic media,bound states in the continuum,topological properties,symmetry breaking,waveguiding structures
更新于2025-09-04 15:30:14