Weak Field Research Articles

Electrostrictive Structural Transitions and Tensorial Electro-Optics in Mesomorphic Blue Phase Crystals.

Electrostriction is present in all dielectrics, but the electrostriction itself is generally minuscule and is even insignificant in low-dielectric-constant materials. Herein, extraordinary electrostriction is found in mesomorphic blue phase (BP) crystals, which are fluidic "giant" crystals with a lattice constant of several hundred nanometers and contain 107-108 molecules in each unit cell. In situ optical observations revealed that the BP crystals exhibit -19.5% to 15.7% electrostrictive actuation at weak field strengths (<3 V/μm), during which a transient monoclinic phase is found. The monoclinic phase occurs in the form of twinning and single crystals successively, which acts as an intermediate state to dominate the pathway of electrostrictive structural transition. Furthermore, we experimentally confirmed that a tensorial crystal-optic effect is induced in BPs by electrostriction, which updates our conventional understanding about liquid crystalline materials that the electro-optics has always been considered as a scalar effect. This work reveals the structural polymorphism in electrostrictive soft crystals, which, in the meantime, provides additional degrees-of-freedom for their advanced applications in nano or micro actuators, flexible electronics, and photonics of next generation, by precisely manipulating the soft crystalline structures and their crystal-optic characteristics.

Little strokes fell big oaks: The use of weak magnetic fields and reactive oxygen species to fight cancer.

The increase in early-stage cancers, particularly gastrointestinal, breast and kidney cancers, has been linked to lifestyle changes such as consumption of processed foods and physical inactivity, which contribute to obesity and diabetes - major cancer risk factors. Conventional treatments such as chemotherapy and radiation often lead to severe long-term side effects, including secondary cancers and tissue damage, highlighting the need for new, safer and more effective therapies, especially for young patients. Weak electromagnetic fields (WEMF) offer a promising non-invasive approach to cancer treatment. While WEMF have been used therapeutically for musculoskeletal disorders for decades, their role in oncology is still emerging. WEMFs affect multiple cellular processes through mechanisms such as the radical pair mechanism (RPM), which alters reactive oxygen species (ROS) levels, mitochondrial function, and glycolysis, among others. This review explores the potential of WEMF in conjunction with reactive oxygen species as a cancer therapy, highlighting WEMFs selective targeting of cancer cells and its non-ionizing nature, which could reduce collateral damage compared to conventional treatments. In addition, synchronization of WEMF with circadian rhythms may further enhance its therapeutic efficacy, as has been demonstrated in other cancer therapies.

Test particles in Kaluza–Klein models

Abstract Geodesics in general relativity describe the behaviour of test particles in a gravitational field. In 5D Kaluza–Klein, geodesics reproduce the Lorentz force motion of particles in an electromagnetic field. This paper studies geodesic motion on a higher-dimensional M 4 × K with background metrics encoding general 4D gauge fields and Higgs-like scalars. It shows that the classical mass and charge of a test particle become variable quantities when the geodesic traverses regions of spacetime with massive gauge fields, such as the weak force field, or with non-constant Higgs scalars. This agrees with the physical fact that interactions mediated by massive bosons can change the mass and charge of particles. The variation rates of mass and charge along a geodesic are given by natural geometric formulae. In regions where mass is preserved, there are additional constants of motion, one for every abelian or simple summand in the Killing algebra of K. The last part of the paper discusses traditional difficulties of Kaluza–Klein models, such as the low q / m ratios in the 5D model. It suggests possible ways to circumvent them. It also remarks the naturalness of a model in which elementary particles always travel at the speed of light in higher dimensions.

Gravitational helicity flux density from two-body systems

Abstract The helicity flux density is a novel quantity which characterizes the angle-dependence of the helicity of radiative gravitons and it may be tested by gravitational wave experiments in the future. We derive a quadrupole formula for the helicity flux density due to gravitational radiation in the slow motion and the weak field limit. We apply the formula to the bound and unbound orbits in two-body systems and find that the total radiative helicity fluxes are always zero. However, the radiative helicity flux density, which is O ( G 3 ) in the Newtonian limit, still has non-trivial dependence on the angle. Furthermore, we also find a formula for the total helicity flux by including all contributions of the higher multipoles.

Noncollinear phase of the antiferromagnetic sawtooth chain

The antiferromagnetic sawtooth chain is a prototypical example of a frustrated spin system with vertex-sharing triangles, giving rise to complex quantum states. Depending on the interaction parameters, this system has three phases, of which the gapless noncollinear phase (for strongly coupled basal spins and loosely attached apical spins) has received little theoretical attention so far. In this work, we comprehensively investigate the properties of the noncollinear phase using large-scale tensor network computations which exploit the full SU(2) symmetry of the underlying Heisenberg model. We study the ground state both for finite systems using the density-matrix renormalization group (DMRG) as well as for infinite chains via the variational uniform matrix-product state (VUMPS) formalism. Finite temperatures and correlation functions are tackled via imaginary or real time evolutions, which we implement using the time-dependent variational principle (TDVP). We find that the noncollinear phase is characterized by a low-momentum peak and a diffuse tail for the apex-apex correlations. Deep into the phase, the pattern sharpens into a peak indicating a 90∘ spiral. The apical spins are soft and highly susceptible to external perturbations; they give rise to a large number of gapless magnetic states that are polarized by weak fields and cause a long low-temperature tail in the specific heat. The dynamic spin-structure factor exhibits additive contributions from a two-spinon continuum (excitations of the basal chain) and a gapless peak at k=π/2 (excitations of the apical spins). Small temperatures excite the gapless states and smear the spectral weight of the k=π/2 peak out into a homogeneous flat-band structure. Our results are relevant, e.g., for the material atacamite Cu2Cl(OH)3 in high magnetic fields. Published by the American Physical Society 2025

On the analytic generalization of particle deflection in the weak field regime and shadow size in light of EHT constraints for Schwarzschild-like black hole solutions

In this paper, an analytic generalization of the weak field deflection angle (WDA) is derived by utilizing the current non-asymptotically flat generalization of the Gauss–Bonnet theorem. The derived formula is valid for any Schwarzschild-like spacetime, which deviates from the classical Schwarzschild case through some constant parameters. This work provided four examples, including Schwarzschild-like solutions in the context of Bumblebee gravity theory and the Kalb–Ramond framework, as well as one example from a black hole surrounded by soliton dark matter. These examples explore distinct mechanisms of Lorentz symmetry breaking, with results that are either new or in agreement with existing literature. The WDA formula provided a simple calculation, where approximations based on some conditions can be done directly on it, skipping the preliminary steps. For the shadow size analysis, it is shown how it depends solely on the parameter associated with the metric coefficient in the time coordinate. A general formula for the constrained parameter is also derived based on the Event Horizon Collaboration (EHT) observational results. Finally, the work realized further possible generalizations on other black hole models, such as RN-like, dS/AdS-like black hole solutions, and even black hole solutions in higher dimensions.

Noise reduction of low-dose electron holograms using the wavelet hidden Markov model.

The precision in electron holography studies on electrostatic and magnetic fields depends on the image quality of an electron hologram. Enhancing the image quality of electron holograms is essential for the comprehensive analysis of weak electromagnetic fields; however, extended electron beam irradiation can lead to undesirable radiation damage and contamination. Recent studies have demonstrated that noise reduction using the wavelet hidden Markov model (WHMM) can improve the precision of phase analysis for limited thin-foiled crystals. In this study, we examine the effects of WHMM-based denoising on the electron holography data of weakly charged nanoparticles collected under low-electron-dose conditions. The results indicate that effective noise reduction with the WHMM allows for a reduction in the magnitude of the electron dose by approximately half relative to data collection without WHMM denoising, while maintaining the same level of the charge determination precision: less than one elementary charge. Notably, at a low electron dose of 0.40 e-/pixel, WHMM denoising enables the clear visualization of a weak stray electric field outside a charged latex sphere. This method offers significant advantages for electron holography studies of electron-beam-sensitive materials requiring minimal time for electron exposure.

Search for high-frequency gravitational waves with Rydberg atoms

We propose high-frequency gravitational wave (GW) detectors with Rydberg atoms. Rydberg atoms are ultra-sensitive detectors of electric fields. By setting up a constant magnetic field, a weak electric field is generated upon the arrival of GWs. The weak electric field signal is then detected by an electromagnetically induced transparency (EIT) in the system of the Rydberg atoms. Recently, the minimum detectable electric field with the Rydberg atoms is further improved by employing superheterodyne detection method. Hence, even the weak signal generated by GWs turns out to be detectable. We calculate the amplitude of Rabi frequency of the Rydberg atoms induced by the GWs and show that the sensitivity of the Rydberg atoms becomes maximum when the size of the Rydberg atoms is close to the wavelength of GWs. We evaluate the minimum detectable amplitude of GWs with Rubidium Rydberg atoms and find that the detector can probe GWs with a frequency f=4.2GHz and an amplitude around 10-20.

Selecting the Optimal DFT Functionals for Reproducing the UV‐Vis Properties of Transition‐Metal Photocatalysts

AbstractWe have applied our practice‐oriented TDDFT benchmark strategy to assess the performance of pure, hybrid, range‐separated hybrid and double‐hybrid functionals for reproducing the electronic spectra of a set of 137 transition‐metal complexes. Our results enable simple pre‐screening of new transition‐metal based photocatalysts. The reference data is based on recently published measurements, from which we have established a new database. The database is named TMPHOTCAT‐137 to reflect the number of complexes (with Cu, Ru, Ir, Fe, Au, Mo and W centres) included and the fact that all of them are either proven or potential photocatalysts. We have found that the M06 functional is the best performer both in terms of practical accuracy and consistency for all metals except Fe. While B3LYP is similarly accurate for Ru and Ir complexes, for the rest of the metals significant wavelength scaling is necessary. Compared to our previous benchmark for organic photocatalysts, double‐hybrid functionals exhibit considerably poorer results while the range separated hybrids CAM−B3LYP and ωB97X−D offer the most consistent performance for both datasets. Among the metals, iron proved to be most difficult for TDDFT: even M06 predicts singlet‐singlet absorption spectra and quintet ground states erroneously, especially for weak ligand fields (i. e., only Fe−N bonds). The functionals that do not exhibit this behaviour are the pure (GGA, meta‐GGA) functionals, but the role of HF exchange in the spectral prediction is equivocal; while functionals with high amounts of HF exchange perform insufficiently, smaller amount of exact exchange yields overall better performance (M06, B3LYP). We have also shown that inclusion of spin‐orbit coupling for the heavier metals does not improve the results. The updated spectrum optimizer code, the TMPHOTCAT‐137 database and the Jupyter Notebook used for analysis are available at github.com/PeterF1234/spectrum_optimizer.

Strong Interfacial Interaction in Polarized Ferroelectric Heterostructured Nanosheets for Highly Efficient and Selective Photocatalytic CO2 Reduction.

Heterojunctions are sustainable solutions for the photocatalytic CO2 reduction reaction (CO2RR) by regulating charge separation behavior at the interface. However, their efficiency and product selectivity are severely hindered by the inflexible and weak built-in electric field and the electronic structure of the two phases. Herein, ferroelectric-based heterojunctions between polarized bismuth ferrite (BFO(P)) and CdS are constructed to enhance the interfacial interactions and catalytic activity. The intrinsic polarization field depending on the ferroelectric state causes significant electrostatic potential difference and energy-band bending. This helps overcome the unsatisfactory redox potential that differs from the classical catalytic mechanism, and synergy from the heterostructure facilitates effective separation and transfer of photogenerated charges with an extended lifetime (>20ns) and significantly enhanced photovoltage (1002 times that of BFO). The optimized charge carrier dynamics allow the heterojunction to achieve a much higher CO yield compared to state-of-the-art ferroelectric-based photocatalysts, and 85.46 and 23.47 times higher than those of pristine CdS and BFO, respectively. Moreover, it maintains an impressive 100% product selectivity together with excellent repeatability and cycling. This work not only sheds light on how a strong inherent polarity promotes the performance of heterojunction photocatalysts but also provides new insights for designing efficient photocatalytic CO2RR.

THE SYNERGIC ELECTROWEAK SYNCHROTRON RADIATION

The power spectral formula is derived for radiation of neutral electroweak bosons from an electron in a weak external homogeneous electromagnetic field. The calculation method is based on the source theory formulation of quantum field theory introduced by Schwinger. For ultra-relativistic electrons, it is derived that the Z0 emission rate is suppressed relative to photon emission. This implies that the decay of electron into W-boson and neutrino is also exponentially small under similar conditions. The article is written in the form of mathematical simplicity and the Schwinger pedagogical clarity.

Electromagnetically induced transparency and second-order sideband Effects in a Laguerre-Gaussian cavity optorotational system with Kerr medium

Abstract In this paper, we investigate the phenomena of electromagnetically induced transparency (EIT) and the generation of second-order sideband in a Laguerre-Gaussian (LG) cavity optorotational sys tem with a Kerr nonlinear medium. Using the perturbation method, we analyze the first- and second order sideband generations in the output field from the system under the actions of a strong control&amp;#xD;field and a weak probe field. Numerical simulations show that the Kerr nonlinearity can lead to the occurrence of the asymmetric line shape in the transmission of the probe field and the efficiency of second-order sideband generation, and the Kerr nonlinearity can enhance the efficiency of the second order sideband generation. Comparing with traditional scheme for generating the second-order sideband, our spectral shape of the second-order sideband is amplified and becomes asymmetric, which has potential applications in precision measurement, high-sensitivity devices, and frequency conversion.

Reality of inverse cascading in neutron star crusts

The braking torque that dictates the timing properties of magnetars is closely tied to the large-scale dipolar magnetic field on their surface. The formation of this field has been a topic of ongoing debate. One proposed mechanism, based on macroscopic principles, involves an inverse cascade within the neutron star's crust. However, this phenomenon has not been observed in realistic simulations. In this study, we provide compelling evidence supporting the feasibility of the inverse cascading process in the presence of an initial helical magnetic field within realistic neutron star crusts and discuss its contribution to the amplification of the large-scale magnetic field. Our findings, derived from a systematic investigation that considers various coordinate systems, peak wavenumber positions, crustal thicknesses, magnetic boundary conditions, and magnetic Lundquist numbers, reveal that the specific geometry of the crustal domain—with its extreme aspect ratio—requires an initial peak wavenumber from small-scale structures for the inverse cascade to occur. However, this same aspect ratio confines the cascade to structures on the scale of the crust, making the formation of a large-scale dipolar surface field unlikely. Despite these limitations, the inverse cascade remains a significant factor in the magnetic field evolution within the crust and may help explain highly magnetized objects with weak surface dipolar fields, such as low-field magnetars and central compact objects.

Double cavity induced transparency in a Y-type atomic system based on cavity QED photons

We show that a fully quantum-mechanical model consisting of a four-level atom with Y-type atomic structure inside a three-mode cavity can exhibit double cavity induced transparency (CIT). In this model, it is cavity photons that induce the transparency, and there is no need to use external classical fields. As this double-CIT model involves several atomic levels, we adapt the wavefunction approach as a quantum-jump description of dissipation to derive an analytical expression for the steady-state linear susceptibility of a weak cavity field. We then use this analytical expression to investigate the dependence of the CIT transparency windows on the detuning of the coupling fields, intensities of the cavity fields and the cavity linewidths. We also have tested the analytical results by numerically integrating the full set of optical Bloch equations for the atomic density-matrix elements.

Experimental study on the translation behavior of an in-situ bubble pair in the ultrasonic field.

The dynamics of acoustic cavitation bubbles hold significant importance in ultrasonic cleaning, biomedicine, and chemistry. Utilizing an in-situ normal pressure bubble generation and observation system that was developed, this study examined the translational behavior of micrometer-scale normal pressure bubble pairs with initial radius ratio of 1:1 and 2:1 under ultrasonic field excitation. A velocity-distance curve was proposed to quantify the secondary Bjerknes forces during various interaction stages of the bubbles. The findings revealed that equal-sized bubbles underwent an acceleration phase, a deceleration phase, and a velocity jump phase during attraction in both strong and weak acoustic fields. In contrast, bubbles of unequal sizes, due to different oscillation frequencies, experienced multiple acceleration and deceleration phases, presenting asynchronous behaviors. The study further explored the effects of the initial bubble radius, shape oscillation, and volume oscillations on the attraction speed. Results showed that the velocity of the bubble's centroid decreased with an increase in the initial radius, while intensified volume oscillations increased the secondary Bjerknes force, thereby increasing the centroid's velocity. Moreover, strong acoustic fields were more likely to induce severe volume and shape oscillations in bubbles than weak fields. The irregular shape oscillations in twin bubbles resulted in shortened durations of acceleration and deceleration phases, reduced peak velocities of acceleration phase, and diminished acceleration during the velocity jump phase. The research provided some mechanical explanations for acoustic cavitation dynamics and its applications.

Spintronic devices and applications using noncollinear chiral antiferromagnets.

Antiferromagnetic materials have several unique properties, such as a vanishingly small net magnetization, which generates weak dipolar fields and makes them robust against perturbation from external magnetic fields and rapid magnetization dynamics, as dictated by the geometric mean of their exchange and anisotropy energies. However, experimental and theoretical techniques to detect and manipulate the antiferromagnetic order in a fully electrical manner must be developed to enable advanced spintronic devices with antiferromagnets as their active spin-dependent elements. Among the various antiferromagnetic materials, conducting antiferromagnets offer high electrical and thermal conductivities and strong electron-spin-phonon interactions. Noncollinear metallic antiferromagnets with negative chirality, including Mn3Sn, Mn3Ge, and Mn3GaN, offer rich physics of spin momentum locking, topologically protected surface states, large spin Hall conductivity, and a magnetic spin Hall effect that arises from their topology. In this review article, we introduce the crystal structure and the physical phenomena, including the anomalous Hall and Nernst effects, spin Hall effect, and magneto-optic Kerr effect, observed in negative chirality antiferromagnets. Experimental advances related to spin-orbit torque-induced dynamics and the impact of the torque on the microscopic spin structure of Mn3Sn are also discussed. Recent experimental demonstrations of a finite room-temperature tunneling magnetoresistance in tunnel junctions with chiral antiferromagnets opens the prospect of developing spintronic devices with fully electrical readout. Applications of chiral antiferromagnets, including non-volatile memory, high-frequency signal generators/detectors, neuro-synaptic emulators, probabilistic bits, thermoelectric devices, and Josephson junctions, are highlighted. We also present analytic models that relate the performance characteristics of the device with its design parameters, thus enabling a rapid technology-device assessment. Effects of Joule heating and thermal noise on the device characteristics are briefly discussed. We close the paper by summarizing the status of research and present our outlook in this rapidly evolving research field.

Magnetosensitivity of tightly bound radical pairs in cryptochrome is enabled by the quantum Zeno effect

AbstractThe radical pair mechanism accounts for the magnetic field sensitivity of a large class of chemical reactions and is hypothesised to underpin numerous magnetosensitive traits in biology, including the avian compass. Traditionally, magnetic field sensitivity in this mechanism is attributed to radical pairs with weakly interacting, well-separated electrons; closely bound pairs were considered unresponsive to weak fields due to arrested spin dynamics. In this study, we challenge this view by examining the FAD-superoxide radical pair within cryptochrome, a protein hypothesised to function as a biological magnetosensor. Contrary to expectations, we find that this tightly bound radical pair can respond to Earth-strength magnetic fields, provided that the recombination reaction is strongly asymmetric—a scenario invoking the quantum Zeno effect. These findings present a plausible mechanism for weak magnetic field effects in biology, suggesting that even closely associated radical pairs, like those involving superoxide, may play a role in magnetic sensing.

Chess and the Cultivation of Attention

Games as media cultivate attention by demanding us to think, perceive, and feel according to them. In my phenomenological approach inspired by Merleau-Ponty, attention consists of two intertwined acts, intuitive perception and more rational acts of deliberation. Chess serves as a good case study because it tasks its players to become familiar with an insurmountable magnitude of complexity. Chess players learn how to become attentive by training their perceptual and rational capacities so that they understand the problems of a position intuitively, as a state of positional imbalance created through the uneven distribution of pieces on the board. Following the Latin etymology of the word ‘medium’ as ‘in-between’ phenomenon, I assert that games, as processes of play, exist in the very intermediary relation between players and playthings, expressed by this field of strengths and weaknesses, and thus come to shape the thinking, perceiving, and feeling of the player.

Piezoelectric hysteresis and relaxation processes in ferroelectric ceramics in weak electric fields

The processes of piezoelectric relaxation and hysteresis in ferroelectric piezoelectric ceramics based on the lead zirconate-titanate system are studied in the region of weak electric fields. An analysis of the field and time dependences of the complex piezoelectric modulus |d31| obtained by processing sequentially measured piezoresonance spectra of the radial vibration mode of thin piezoceramic disks using the piezoresonance spectrum analysis method and program (PRAP) was carried out. A physical interpretation of the results obtained is proposed.

Effects of dendritic Ca2+ spike on the modulation of spike timing with transcranial direct current stimulation in cortical pyramidal neurons.

Transcranial direct current stimulation (tDCS) generates a weak electric field (EF) within the brain, which induces opposite polarization in the soma and distal dendrite of cortical pyramidal neurons. The somatic polarization directly affects the spike timing, and dendritic polarization modulates the synaptically evoked dendritic activities. Ca2+ spike, the most dramatic dendritic activity, is crucial for synaptic integration and top-down signal transmission, thereby indirectly influencing the output spikes of pyramidal cells. Nevertheless, the role of dendritic Ca2+ spike in the modulation of neural spike timing with tDCS remains largely unclear. In this study, we use morphologically and biophysically realistic models of layer 5 pyramidal cells (L5 PCs) to simulate the dendritic Ca2+ spike and somatic Na+ spike in response to distal dendritic synaptic inputs under weak EF stimulation. Our results show that weak EFs modulate the spike timing through the modulation of dendritic Ca2+ spike and somatic polarization, and such field effects are dependent on synaptic inputs. At weak synaptic inputs, the spike timing is advanced due to the facilitation of dendritic Ca2+ spike by field-induced dendritic depolarization. Conversely, it is delayed by field-induceddendritic hyperpolarization. In this context, the Ca2+ spike exhibits heightened sensitivity to weak EFs, thereby governing the changes in spike timing. At strong synaptic inputs, somatic polarization dominates the changes in spike timing due to the decreased sensitivity of Ca2+ spike to EFs. Consequently, the spike timing is advanced/delayed by field-induced somatic depolarization/hyperpolarization. Moreover, EFs have significant effects on the changes in the timing of somatic spike and Ca2+ spike when synaptic current injection coincides with the onset of EFs. Field effects on spike timing follow a cosine dependency on the field polar angle, with maximum effects in the field direction parallel to the somato-dendritic axis. Furthermore, our results are robust to morphological and biological diversity. These findings clarify the modulation of spike timing with weak EFs and highlight the crucial role of dendritic Ca2+ spike. These predictions shed light on the neural basis of tDCS and should be considered when understanding the effect of tDCS on population dynamics and cognitive behavior.