Collective Modes Research Articles

Ground-state phases and collective modes of supersolid spin-orbit-coupled Bose-Einstein condensates

Ground-state phases and collective modes of supersolid spin-orbit-coupled Bose-Einstein condensates

Observation of interlayer plasmon polaron in graphene/WS2 heterostructures

Harnessing electronic excitations involving coherent coupling to bosonic modes is essential for the design and control of emergent phenomena in quantum materials. In situations where charge carriers induce a lattice distortion due to the electron-phonon interaction, the conducting states get “dressed", which leads to the formation of polaronic quasiparticles. The exploration of polaronic effects on low-energy excitations is in its infancy in two-dimensional materials. Here, we present the discovery of an interlayer plasmon polaron in heterostructures composed of graphene on top of single-layer WS2. By using micro-focused angle-resolved photoemission spectroscopy during in situ doping of the top graphene layer, we observe a strong quasiparticle peak accompanied by several carrier density-dependent shake-off replicas around the single-layer WS2 conduction band minimum. Our results are explained by an effective many-body model in terms of a coupling between single-layer WS2 conduction electrons and an interlayer plasmon mode. It is important to take into account the presence of such interlayer collective modes, as they have profound consequences for the electronic and optical properties of heterostructures that are routinely explored in many device architectures involving 2D transition metal dichalcogenides.

Photon quantum kinetic equations and collective modes in an axion background

Photon quantum kinetic equations and collective modes in an axion background

Study the structure of the low-lying states of 206Po

Abstract The nucleus $^{206}$Po was studied in the two proton transfer reaction $^{204}$Pb($^{16}$O,$^{14}$C)$^{206}$Po and the lifetime of the first excited $2^+$ state was determined by utilizing the Recoil Distance Doppler Shift method. 
The experimental results are compared with shell-model calculations based on different effective interactions. 
The calculations qualitatively reproduced the experimentally observed $B(E2; 2^+_1 \to 0^+_1)$ value, suggesting that the $2^+_1$ state of $^{206}$Po exhibits a collective nature. However, the employed effective interactions revealed some limitations, particularly in their description of the $4^+_{1,2}$ states. These results emphasize the importance of understanding the properties of low-lying states, especially their evolution from single-particle dynamics to collective modes, in evaluating various effective nuclear interactions.

Intrinsic Information-Theoretic Models

With this follow-up paper, we continue developing a mathematical framework based on information geometry for representing physical objects. The long-term goal is to lay down informational foundations for physics, especially quantum physics. We assume that we can now model information sources as univariate normal probability distributions N (μ, σ0), as before, but with a constant σ0 not necessarily equal to 1. Then, we also relaxed the independence condition when modeling m sources of information. Now, we model m sources with a multivariate normal probability distribution Nm(μ,Σ0) with a constant variance–covariance matrix Σ0 not necessarily diagonal, i.e., with covariance values different to 0, which leads to the concept of modes rather than sources. Invoking Schrödinger’s equation, we can still break the information into m quantum harmonic oscillators, one for each mode, and with energy levels independent of the values of σ0, altogether leading to the concept of “intrinsic”. Similarly, as in our previous work with the estimator’s variance, we found that the expectation of the quadratic Mahalanobis distance to the sample mean equals the energy levels of the quantum harmonic oscillator, being the minimum quadratic Mahalanobis distance at the minimum energy level of the oscillator and reaching the “intrinsic” Cramér–Rao lower bound at the lowest energy level. Also, we demonstrate that the global probability density function of the collective mode of a set of m quantum harmonic oscillators at the lowest energy level still equals the posterior probability distribution calculated using Bayes’ theorem from the sources of information for all data values, taking as a prior the Riemannian volume of the informative metric. While these new assumptions certainly add complexity to the mathematical framework, the results proven are invariant under transformations, leading to the concept of “intrinsic” information-theoretic models, which are essential for developing physics.

Gottesman-Kitaev-Preskill Encoding in Continuous Modal Variables of Single Photons.

GKP states, introduced by Gottesman, Kitaev, and Preskill, are continuous variable logical qubits that can be corrected for errors caused by phase space displacements. Their experimental realization is challenging, in particular, using propagating fields, where quantum information is encoded in the quadratures of the electromagnetic field. However, traveling photons are essential in many applications of GKP codes involving the long-distance transmission of quantum information. We introduce a new method for encoding GKP states in propagating fields using single photons, each occupying a distinct auxiliary mode given by the propagation direction. The GKP states are defined as highly correlated states described by collective continuous modes, as time and frequency. We analyze how the error detection and correction protocol scales with the total photon number and the spectral width. We show that the obtained code can be corrected for displacements in time-frequency phase space, which correspond to dephasing, or rotations, in the quadrature phase space and to photon losses. Most importantly, we show that generating two-photon GKP states is relatively simple, and that such states are currently produced and manipulated in several photonic platforms where frequency and time-bin biphoton entangled states can be engineered.

Localized and extended collective optical phonon modes in regular and random arrays of contacting nanoparticles: Escape from phonon confinement

Localized and extended collective optical phonon modes in regular and random arrays of contacting nanoparticles: Escape from phonon confinement

Detecting Respondent Burden in Online Surveys: How Different Sources of Question Difficulty Influence Cursor Movements

Online surveys are a widely used mode of data collection. However, as no interviewer is present, respondents face any difficulties they encounter alone, which may lead to measurement error and biased or (at worst) invalid conclusions. Detecting response difficulty is therefore vital. Previous research has predominantly focused on response times to detect general response difficulty. However, response difficulty may stem from different sources, such as overly complex wording or similarity between response options. So far, the question of whether indicators can discriminate between these sources has not been addressed. The goal of the present study, therefore, was to evaluate whether specific characteristics of participants’ cursor movements are related to specific properties of survey questions that increase response difficulty. In a preregistered online experiment, we manipulated the length of the question text, the complexity of the question wording, and the difficulty of the response options orthogonally between questions. We hypothesized that these changes would lead to increased response times, hovers (movement pauses), and y-flips (changes in vertical movement direction), respectively. As expected, each manipulation led to an increase in the corresponding measure, although the other dependent variables were affected as well. However, the strengths of the effects did differ as expected between the mouse-tracking indices: Hovers were more sensitive to complex wording than to question difficulty, while the opposite was true for y-flips. These results indicate that differentiating sources of response difficulty might indeed be feasible using mouse-tracking.

An Application of Interacting Boson Fermion-Fermion Model (IBFFM) for <sup>134</sup>Cs Nucleus

This work concerns the calculations of interacting boson fermion-fermion model (IBFFM) for the odd-odd nucleus <sup>134</sup>Cs. The energy levels (positive and negative parity states), electric transition probability B(E2), magnetic transition probability B(M1), quadrupole and magnetic dipole moments have been studied in this work. The IBFFM results are compared with the available experimental data. In the present work, the IBFFM pattern of total and parametric dependent level densities for the odd-odd nucleus <sup>134</sup>Cs is investigated and compared to the pattern found in previous investigations in the framework of combinatorial and spectral distribution approaches. When comparing the theoretical values with the available experimental values, it was found that there is a good match between them. This is due to the values of the Hamiltonian parameters that were found accurately, so this IBFFM model is considered one of the effective models in studying the nuclear structure of odd-odd nuclei. The level density of the odd-odd nucleus <sup>196</sup>Au is investigated in the interacting boson-fermion-fermion model (IBFFM) which accounts for collectivity and complex interaction between quasiparticle and collective modes. The IBFFM spin-dependent level densities show high-spin reduction with respect to Bethe formula. This can be well accounted for by a modified spin-dependent level density formula.

Upgrade of crystallography beamline BL19U1 at the Shanghai Synchrotron Radiation Facility

BL19U1, an energy-tunable protein complex crystallography beamline at the Shanghai Synchrotron Radiation Facility, has emerged as one of the most productive MX beamlines since opening to the public in July 2015. As of October 2023, it has contributed to over 2000 protein structures deposited in the Protein Data Bank (PDB), resulting in the publication of more than 1000 scientific papers. In response to increasing interest in structure-based drug design utilizing X-ray crystallography for fragment library screening, enhancements have been implemented in both hardware and data collection systems on the beamline to optimize efficiency. Hardware upgrades include the transition from MD2 to MD2S for the diffractometer, alongside the installation of a humidity controller featuring a rapid nozzle exchanger. This allows users to opt for either low-temperature or room-temperature data collection modes. The control system has been upgraded from Blu-Ice to MXCuBE3, which supports website-mode data collection, providing enhanced compatibility and easy expansion with new features. An automated data processing pipeline has also been developed to offer users real-time feedback on data quality.

Excess Density of Vibrational States at Terahertz Frequencies in the IR Spectra of Glassy Polymers

The IR spectra of glassy polymers were studied in the terahertz range 0.27 − 6 THz (9–200 cm−1), where absorption appears due to both individual and collective torsional (libration) vibrations preceding the manifestation of relaxation dynamics. It is shown that collective torsional-vibrational modes, caused by the correlation of librational vibrations in a section of the chain commensurate with its thermodynamic segment, are responsible for the excess density of vibrational states at terahertz frequencies in the IR spectra of glassy polymers.

Unravelling the Bi-Functional Electrocatalytic Properties of {Mo72Fe30} Polyoxometalate Nanostructures for Overall Water Splitting Using Scanning Electrochemical Microscope and Electrochemical Gating Methods.

This study reports the use of Keplerate-type {Mo72Fe30} polyoxometalate (POMs) nanostructures as a bi-functional-electrocatalyst for HER and OER in an alkaline medium with a lower overpotential (135mV for HER and 264mV for OER), and excellent electrochemical stability. The bi-functional catalytic properties of {Mo72Fe30} POM are studied using a scanning electrochemical microscope (SECM) via current mapping using substrate generation and tip collection mode. Furthermore, the bipolar nature of the {Mo72Fe30} POM nano-electrocatalysts is studied using the electrochemical gating via simultaneous monitoring of the electrochemical (cell) and electrical ({Mo72Fe30} POM) signals. Next, a prototype water electrolyzer fabricated using {Mo72Fe30} POM electrocatalysts showed they can drive 10mAcm-2 with a low cell voltage of 1.62V in lab-scale test conditions. Notably, the {Mo72Fe30} POM electrolyzers' performance assessment based on recommended conditions for industrial aspects shows that they require a very low overpotential of 1.89V to drive 500mAcm-2, highlighting their promising candidature toward clean-hydrogen production.

Dynamics of strongly correlated quantum systems from an extended Singwi‐Tosi‐Land‐Sjölander closure for the BBGKY hierarchy

AbstractThe BBGKY hierarchy in the Wigner representation is used with an extended Singwi‐Tosi‐Land‐Sjölander (STLS) ansatz for the two‐particle distribution function [H. Kählert, G. J. Kalman, and M. Bonitz, Phys. Rev. E 90, 011101 (2014)] to study the density response function and the dispersion relation of collective modes in a strongly coupled quantum system. It is shown that the local field correction (LFC) and the dispersion relation reduce to the results of the Quasi‐Localized Charge Approximation (QLCA) in the classical limit. In the quantum case, the LFC acquires a frequency‐dependence, similar to the quantum version of the STLS theory. The dispersion relation is governed by a generalization of the QLCA dynamical matrix. The results are expected to be relevant for the analysis of collective modes in quantum liquids with strong correlations.

Quantum phase synchronization via exciton-vibrational energy dissipation sustains long-lived coherence in photosynthetic antennas

The lifetime of electronic coherences found in photosynthetic antennas is known to be too short to match the energy transfer time, rendering the coherent energy transfer mechanism inactive. Exciton-vibrational coherence time in excitonic dimers which consist of two chromophores coupled by excitation transfer interaction, can however be much longer. Uncovering the mechanism for sustained coherences in a noisy biological environment is challenging, requiring the use of simpler model systems as proxies. Here, via two-dimensional electronic spectroscopy experiments, we present compelling evidence for longer exciton-vibrational coherence time in the allophycocyanin trimer, containing excitonic dimers, compared to isolated pigments. This is attributed to the quantum phase synchronization of the resonant vibrational collective modes of the dimer, where the anti-symmetric modes, coupled to excitonic states with fast dephasing, are dissipated. The decoupled symmetric counterparts are subject to slower energy dissipation. The resonant modes have a predicted nearly 50% reduction in the vibrational amplitudes, and almost zero amplitude in the corresponding dynamical Stokes shift spectrum compared to the isolated pigments. Our findings provide insights into the mechanisms for protecting coherences against the noisy environment.

THz spectroscopy on the amino acids L-serine and L-cysteine.

We present a detailed study on the temperature-dependent THz spectra of the polycrystalline amino acids, L-serine and L-cysteine, for wavenumbers from 20 to 120cm-1 and temperatures from 4 to 300K. Even though the structure of these two amino acids is very similar, with a sulfur atom in the side chain of cysteine instead of an oxygen atom in serine, the excitation spectra are drastically different. Obviously, the vibrational dynamics strongly depend on the ability of cysteine to form sulfur-hydrogen bonds. In addition, cysteine undergoes an order-disorder type phase transition close to 80K, documented by additional specific heat experiments, with accompanying anomalies in the THz results. On increasing temperatures, well-defined vibrational excitations exhibit significant shifts in the eigenfrequencies with concomitant line-broadening yielding partly overlapping modes. Interestingly, several modes completely lose all their dipolar strength and are unobservable under ambient conditions. Comparing the recent results to the published work utilizing THz, Raman, and neutron-scattering techniques, as well as with abinitio simulations, we aim at a consistent analysis of the results ascribing certain eigenfrequencies to distinct collective lattice modes. We document that THz spectra can be used to fine-tune the parameters of model calculations and as fingerprint properties of certain amino acids. In addition, we analyzed the low-temperature heat capacity of both the compounds and detected strong excess contributions compared to the canonical Debye behavior of crystalline solids, indicating soft excitations and a strongly enhanced phonon-density of states at low frequencies.

Fano resonance and enhanced sensing in the excitation of the surface phonon polariton

The surface phonon polariton is a collective oscillation mode of phonons and incident electromagnetic waves in polar dielectric materials. Compared with the surface plasmon polariton, it has low loss and can be applied to the mid-infrared band. A surface phonon resonance sensor based on waveguide-coupling is proposed. The sensor structure is a typical Kretschmann configuration consisting of a germanium (Ge) prism, a silicon carbide (SiC) layer, an indium selenide (In2Se3) film, a titanium dioxide (TiO2) film, and the surrounding dielectric. The reflectivity possesses significant asymmetric Fano resonance dips. In sensing applications, the waveguide-coupling structure yields a sensitivity by intensity of 11278RIU−1 and a figure of merit of 10344RIU−1. Our investigation provides an alternative method for refractive index sensing, thus opening up opportunities for the design of various phonon devices based on Fano resonance.

Idealistic Modification of the Materialistic Veda

This article explores the origin and the later developments of the Veda. The objective is to examine the materialist philosophical content of the early Vedas and contrast it with the idealistic readings of the text from later eras. This article discusses the research issues surrounding the historical roots of the Vedic literature and the idealistic changes made to it in later times. The study has used historical materialism as a methodological tool and examined several Vedic verses, relating them to the socioeconomic conditions of the period in which they were composed. The article has analyzed the roots of some terminologies frequently used in the text and their connections to the philosophy of the Veda.  The terms bhagavan, rita, Dānam, Havana, Brahman, yajña and name of some gods are frequently used in the Veda and their meanings are analyzed in a particular historical contexts. The article reveals that the Vedic verses are the simple creations of Vedic Aryans and they are associated with the everyday desires of the Vedic people, such as those for food, cattle, rain, safety, prosperity, health, and progeny. The early creation of the Vedic verses are this-worldly and materialistic in content and they are in no way otherworldly and spiritualistic. The meaning of most of the terminologies found in the text has materialistic origin and in course of time, their meanings are converted into opposite. The philosophy of the Veda has its root in the collective mode of production and with the introduction of private property and classes, the text is made an ideological tool of the minority of governing classes. The Veda's original materialistic meaning is altered, and the book is transformed into a spiritual guidebook—an ideological weapon used by the ruling classes to deceive and repress the vast majority of laboring people.

THE MEDIATING ROLE OF COGNITIVE FLEXIBILITY ON THE RELATIONSHIP BETWEEN EMOTIONAL INTELLIGENCE AND ACADEMIC SELF-REGULATED LEARNING OF SENIOR HIGH SCHOOL STUDENTS

The purpose of this study was to determine the mediating role of cognitive flexibility in the relationship between emotional intelligence and academic self-regulated learning. Utilizing quantitative, non-experimental design via correlational technique, data were obtained from 267 respondents of the study who are learners among public elementary schools in Cateel 1 and 2, Davao Oriental. The researcher utilized a stratified random sampling technique and an online survey mode of data collection. The researcher also utilized the statistical tools mean, Pearson r, and Medgraph using the Sobel z-test. From the results of the study, it was found that there is a very high level of cognitive flexibility, emotional intelligence, and academic self-regulated learning. Also, results revealed that there is a significant relationship between emotional intelligence and academic self-regulated learning, a significant relationship between emotional intelligence and cognitive flexibility, and a significant relationship between cognitive flexibility and academic self-regulated learning. Further, it was revealed that there is a partial mediating effect of cognitive flexibility on the relationship between emotional intelligence and academic self-regulated learning.<p> </p><p><strong> Article visualizations:</strong></p><p><img src="/-counters-/lit/0758/a.php" alt="Hit counter" /></p>

Collective Tunneling Modes in Superconducting Hydrogen Sulfide

Collective Tunneling Modes in Superconducting Hydrogen Sulfide

Strong Coupling of Two-Dimensional Excitons and Plasmonic Photonic Crystals: Microscopic Theory Reveals Triplet Spectra.

Monolayers of transition metal dichalcogenides (TMDCs) are direct-gap semiconductors with strong light-matter interactions featuring tightly bound excitons, while plasmonic crystals (PCs), consisting of metal nanoparticles that act as meta-atoms, exhibit collective plasmon modes and allow one to tailor electric fields on the nanoscale. Recent experiments show that TMDC-PC hybrids can reach the strong-coupling limit between excitons and plasmons, forming new quasiparticles, so-called plexcitons. To describe this coupling theoretically, we develop a self-consistent Maxwell-Bloch theory for TMDC-PC hybrid structures, which allows us to compute the scattered light in the near- and far-fields explicitly and provide guidance for experimental studies. One of the key findings of the developed theory is the necessity to differentiate between bright and originally momentum-dark excitons. Our calculations reveal a spectral splitting signature of strong coupling of more than 100 meV in gold-MoSe2 structures with 30 nm nanoparticles, manifesting in a hybridization of the plasmon mode with momentum-dark excitons into two effective plexcitonic bands. The semianalytical theory allows us to directly infer the characteristic asymmetric line shape of the hybrid spectra in the strong coupling regime from the energy distribution of the momentum-dark excitons. In addition to the hybridized states, we find a remaining excitonic mode with significantly smaller coupling to the plasmonic near-field, emitting directly into the far-field. Thus, hybrid spectra in the strong coupling regime can contain three emission peaks.