Fermi Interaction Research Articles

Hall response of locally correlated two-dimensional electrons at low density

We study the Hall constant in a homogeneous two-dimensional fluid of correlated electrons immersed in a perpendicular magnetic field, with special focus on the regime of low carrier density. The model consists of a one-band tight-binding model and a momentum-independent causal self-energy, representing interaction-induced correlations effects that are restricted to be local in space. We write general gauge-invariant equations for the conductivity tensor at first order in the magnetic field and solve them numerically—–analytically when possible—in a minimal model of anisotropic square lattice with constant self-energy. Our results show that deviations from the universal behavior of the Hall constant, as observed in the semiclassical regime, appear upon entering the quantum regime, where the Fermi energy and interaction are comparable energy scales. Published by the American Physical Society 2024

A Spectroscopic Description of Asymmetric Isotopologues of CO2.

A polyad-conserving algebraic model applied to vibrational excitations of asymmetric isotopologues of CO2 is presented. First, the problem of vibrational excitations is studied by taking into account only the minimum subspace of states to characterize the Fermi interaction. This analysis allows an estimation of the force constants as well as the feasibility of describing the system in a local mode scheme, in terms of SU(2) operators associated with Morse ladder operators for the stretches. This description together with the algebraic U(3) for the bends establishes the dynamical group SU1(2) × U(3) × SU2(2) for a series of isotopologues. Six isotopologues are considered, namely, 16O12C18O, 16O12C17O, 16O13C18O, 16O13C17O, 17O13C18O, and 17O12C18O in their electronic ground states. For isotopologues 16O12C18O, 16O12C17O, 17O12C18O, and 16O13C18O, the vibrational description was carried out using a Hamiltonian involving 14 parameters. For this series of isotopologues with a number of energy terms 90, 57, 42, and 40, the deviations obtained were rms = 0.15, 0.10, 0.06, and 0.07 cm-1, respectively. For 16O13C17O, with 28 experimental energies and involving 13 parameters, the deviation was rms = 0.05 cm-1, while for 17O13C18O, a different strategy was proposed since only 12 experimental energy levels. In all cases, the polyad scheme P212 = 2(ν1 + ν3) + ν2 was considered. In addition, a new criterion of locality/normality degree is proposed, embracing the case of molecules with normal mode behavior, in particular, the isotopologues of CO2.

Line positions and intensities of the ν1 band of 12CH3I using mid-infrared optical frequency comb Fourier transform spectroscopy

We present a new spectral analysis of the ν1 and ν3+ν1−ν3 bands of 12CH3I around 2971 cm−1 based on a high-resolution spectrum spanning from 2800 cm–1 to 3160 cm–1, measured using an optical frequency comb Fourier transform spectrometer. From this spectrum, we previously assigned the ν4 and ν3+ν4−ν3 bands around 3060 cm–1 using PGOPHER, and the line list was incorporated in the HITRAN database. Here, we treat the two fundamental bands, ν1 and ν4, together with the perturbing states, 2ν2+ν3 and ν2+2ν6±2, as a four-level system connected via Coriolis and Fermi interactions. A similar four-level system is assumed to connect the two ν3+ν1−ν3 and ν3+ν4−ν3 hot bands, which appear due to the population of the low-lying ν3 state at room temperature, with the 2ν2+2ν3 and ν2+ν3+2ν6±2 perturbing states. This spectroscopic treatment provides a good global agreement of the simulated spectra with experiment, and hence accurate line lists and band parameters of the four connected vibrational states in each system. It also allows revisiting the analysis of the ν4 and ν3+ν4−ν3 bands, which were previously treated as separate bands, not connected to their ν1 and ν3+ν1−ν3 counterparts. Overall, we assign 4665 transitions in the fundamental band system, with an average error of 0.00071 cm–1, a factor of two better than earlier work on the ν1 band using conventional Fourier transform infrared spectroscopy. The ν1 band shows hyperfine splitting, resolvable for transitions with J ≤ 2 × K. Finally, the spectral intensities of 65 lines of the ν1 band and 7 lines of the ν3+ν1−ν3 band are reported for the first time using the Voigt line shape as a model in multispectral fitting. The reported line lists and intensities will serve as a reference for high-resolution molecular spectroscopic databases, and as a basis for line selection in future monitoring applications of CH3I.

Magnetic field and nuclear spin influence on the DNA synthesis rate

The rate of a chemical reaction can be sensitive to the isotope composition of the reactants, which provides also for the sensitivity of such “spin-sensitive” reactions to the external magnetic field. Here we demonstrate the effect of the external magnetic field on the enzymatic DNA synthesis together with the effect of the spin-bearing magnesium ions (^{25}Mg). The rate of DNA synthesis monotonously decreased with the external magnetic field induction increasing in presence of zero-spin magnesium ions (^{24}Mg). On the contrary, in the presence of the spin-bearing magnesium ions, the dependence of the reaction rate on the magnetic field induction was non-monotonous and possess a distinct minimum at 80–100 mT. To describe the observed effect, we suggested a chemical scheme and biophysical mechanism considering a competition between Zeeman and Fermi interactions in the external magnetic field.

Vibrational spectra, linear and nonlinear optical investigations on 3‑chloro 4-fluoro aniline and 2-iodo aniline for optical limiting applications

Detailed investigations on the linear and nonlinear optical properties of 3‑chloro 4-fluoro aniline (CFA) and 2-iodo aniline (IA) have been carried out to understand their applicability. Natural Bond Orbital (NBO) analysis reveals the potential nonlinearity of CFA and IA by virtue of their π-conjugations in the carbon-ring systems and the n→σ* and n→π* hyperconjugations. Vibrational spectra of the molecules, investigated using the FT-IR and FT-Raman analyses, manifest the incidence of Fermi interaction and Evans hole in IA. The UV–vis spectral analysis brings out the fine photo response of CFA and IA in the visible region.The optical absorption technique has been employed to analyze the optical band gap of the title crystals, through the investigation of the absorption edge, to assess their effectiveness in optical devices.The z-scan measurement brings to light the remarkable third order nonlinearity in IA, with an extraordinary drop in normalized transmittance down to 39% at high laser fluences, which is a clear sign of its potential use as an optical limiter. A study of the molecular docking postures of CFA and IA ligands binding at the active sites of the target proteins reveal them suitable for use as therapeutic agents having anti-inflammation and anti-cancer activities against target proteins.

Anomaly cancellation condition in an effective nonperturbative electroweak theory

We establish the non-perturbative validity of the gauge anomaly cancellation condition in an effective electroweak theory of massless fermions with finite momentum cut-off and Fermi interaction. The requirement that the current is conserved up to terms smaller than the energy divided by the cut-off scale, which is the natural condition as gauge invariance is only emerging, produces the same constraint on charges as in the Standard Model. The result holds at a non-perturbative level as the functional integrals are expressed by convergent power series expansions and are analytic in a finite domain.

Infrared multiple photon dissociation spectroscopy of anionic copper formate clusters.

We investigate the structure of copper formate and deuterated copper formate clusters using infrared multiple photon dissociation in combination with quantum chemical calculations. Symmetric and asymmetric C-O stretching vibrations along with C-H/C-D stretching vibrations were characterized. Fermi interactions between the C-H stretch and likely a C-O combination band and/or the overtone of a C-H in-plane bending motion have been confirmed by deuteration. The spectra reveal a strong dependence on the monodentate or bidentate binding motif of the formate ligands. Many minima are energetically accessible on the potential energy surface through rotation of the monodentate formate ligands into several almost isoenergetic local minima. While the C-H/C-D stretching vibration is heavily influenced by the charge distribution in the cluster, the C-O vibrations are largely unaffected. The C-H stretch region is not very diagnostic due to a variety of possible Fermi resonances, which also depend on the charge distribution at the formate ligand. Deuteration yields unperturbed spectra in the C-D stretch region and reveals characteristic shifts of the C-D stretching mode for the different binding motifs, with a strong dependence of the band position on the oxidation state of the copper center. The observed bands are compared with formate adsorbed on copper surfaces from the literature.

The torsion-torsion-bending spectrum of S-methyl thioformate

The far infrared spectral region of S-methyl thioformate is explored using a theoretical model of reduced dimensionality depending on three large amplitude vibrations: the torsions of the methyl and the COH groups and the CSC bending mode. A Hamiltonian of reduced dimensionality is solved variationally to determine the low-lying energy levels. To evaluate the effect of the S←O substitution, the spectroscopic properties are compared with those of the O-analog, methyl-formate, an abundant astrophysical molecule. The barrier of methyl internal rotation of S-methyl thioformate is predicted to be three times lower than the one of methyl formate. The A/E splitting of the ground vibrational state has been estimated to be 0.475 cm−1. The A/E components of the fundamental frequencies are predicted at 79.523/68.459 cm−1 (methyl torsion), 251.564/251.717 cm−1 (COH torsion), and 255.056/252.523 cm−1 (CSC bending). Small Fermi interactions between the methyl torsion overtone and the CSC bending mode are observed.

Probing non-standard neutrino interactions with supernova neutrinos at Hyper-K

Non-standard neutrino self interactions (NSSI) could be stronger than Fermi interactions. We investigate the ability to constrain these four-neutrino interactions by their effect on the flux of neutrinos originating from a galactic supernova. In the dense medium of a core collapse supernova, these new self interactions can have a significant impact on neutrino oscillations, leading to changes at the flavor evolution and spectra level. We use simulations of the neutrino flux from a 13 solar mass, core collapse supernova at 10 kpc away, and numerically propagate these neutrinos through the stellar medium taking into account vacuum/MSW oscillations, SM ν − ν scattering as well as ν − ν interactions that arise from NSSI. We pass the resulting neutrino flux to a simulation of the future Hyper-Kamiokande detector to see what constraints on NSSI parameters are possible when the next galactic supernova becomes visible. We find that these constraints depend strongly on the neutrino mass hierarchy and if the NSSI is flavor-violating or preserving. Sensitivity to NSSI in the normal hierarchy (NH) at Hyper-K is limited by the experiment’s ability to efficiently detect νe, but deviations from no NSSI could be seen if the NSSI is particularly strong. In the inverted hierarchy (IH) scenario, Hyper-K can significantly improve constraints on flavor-violating NSSI down to mathcal{O} (10−1)GF.

Collective oscillation modes of a superfluid Bose–Fermi mixture

In this work, we present a theoretical study for the collective oscillation modes, i.e. quadrupole, radial and axial mode, of a mixture of Bose and Fermi superfluids in the crossover from a Bardeen-Cooper-Schrieffer (BCS) superfluid to a molecular Bose–Einstein condensate (BEC) in harmonic trapping potentials with cylindrical symmetry of experimental interest. To this end, we start from the coupled superfluid hydrodynamic equations for the dynamics of Bose–Fermi superfluid mixtures and use the scaling theory that has been developed for a coupled system. The collective oscillation modes of Bose–Fermi superfluid mixtures are found to crucially depend on the overlap integrals of the spatial derivations of density profiles of the Bose and Fermi superfluids at equilibrium. We not only present the explicit expressions for the overlap density integrals, as well as the frequencies of the collective modes provided that the effective Bose–Fermi coupling is weak, but also test the valid regimes of the analytical approximations by numerical calculations in realistic experimental conditions. In the presence of a repulsive Bose–Fermi interaction, we find that the frequencies of the three collective modes of the Bose and Fermi superfluids are all upshifted, and the change speeds of the frequency shifts in the BCS–BEC crossover can characterize the different groundstate phases of the Bose–Fermi superfluid mixtures for different trap geometries.

Weak coupling to unitarity crossover in Bose-Fermi mixtures: Mixing-demixing transition and spontaneous symmetry breaking in trapped systems

The usual treatment of a Bose-Fermi mixture relies on weak-coupling Gross-Pitaevskii (GP) and density-functional (DF) Lagrangians, often including the more realistic {perturbative} Lee-Huang-Yang (LHY) corrections. We suggest analytic {non-perturbative} beyond-mean-field Bose and Fermi Lagrangians valid along the crossover from weak- to strong-coupling limits of intra-species interactions consistent with the LHY corrections and the strong-coupling (unitarity) limit for small and large scattering lengths $|a|$, respectively, and use these to study the Bose-Fermi mixture. We study numerically mixing-demixing and spontaneous symmetry breaking in Bose-Fermi mixtures in spherically-symmetric and quasi-one-dimensional traps while the intra-species Bose and Fermi interactions are varied from weak-coupling to strong-coupling limits.The LHY correction is appropriate for medium to weak atomic interactions and diverges for stronger interactions (large scattering length $|a|$), whereas the present beyond-mean-field Lagrangian is finite in the unitarity limit ($|a|\to \infty$). We illustrate our results using the Bose-Fermi $^7$Li-$^6$Li mixture under a spherically-symmetric and a quasi-one-dimensional trap. The results obtained with the present model for density distribution of the Bose-Fermi mixture along the crossover could be qualitatively different from the usual GP-DF Lagrangian with or without LHY corrections. Specifically, we identified spontaneous symmetry breaking and demixing in the present model not found in the usual model with the same values of the parameters.

The Renner-Teller effect revisited 40 years later

Effects of electronic orbital angular momentum in triatomic molecules are reviewed, known collectively under the name Renner-Teller effect. The focus is on the years between 1960 and 1980, when numerous examples of the Renner-Teller effect became known experimentally. In the same years, Renner’s original theory was refined and extended in various groups in order to account for the new observations. The method developed in A. J. Merer’s research group in Vancouver is discussed in some detail. This effort, based on the theory of Hougen, Bunker, and Johns for large amplitude nuclear bending motion (1970), led to the first quantitative interpretation of the quasilinear bending level structure of the NH2 radical – itself the first known example of the Renner-Teller effect observed by Dressler and Ramsay in 1958. Alternative approaches, refinements, and extensions of the theory implemented after 1980 are also described, the most important extension being the inclusion of the stretching vibrational degrees of freedom, which allows the description of anharmonic Fermi interactions. Finally, the manifestations of the Renner-Teller effect expected in Rydberg states are discussed, and a sketch of the corresponding theory is presented. It is shown that the Renner-Teller effect can also play an important role in continuum processes, such as the recombination of electrons with linear ions.

Loop-induced neutrino non-standard interactions

Non-Standard Interactions (NSI) of neutrinos may originate from models in which new particles interact with neutrinos. In scalar extensions of the SM, the typical approach to obtain NSI requires Fierz transformations and charged Higgses, which suffer from strong constraints from collider searches or charged lepton flavor violation processes. We propose here an alternative approach to generate NSI, namely via loop processes. We show that such loop-induced NSI from secret neutrino interactions can reach sizes of mathcal{O} (0.1 ∼ 1) compared to standard Fermi interaction. This approach can also give rise to neutrino-quark NSI.

The vibrational spectra of carbon dioxide and nitrous oxide: A Lie algebraic study

The infrared vibrational levels of nitrous oxide (N2O) and carbon dioxide (CO2) are studied in the framework of Lie algebra. The aim of this work is to compare the frequency obtained in two algebraic models: “the vibron model” and “the mean field approximation of the vibron model”. To compare the two models we choose two triatomic molecules: CO2of symmetry type D∞hand N2O of symmetry type C∞v. To construct the energy levels in the vibron model, the vibron numbers N for the two molecules are estimated from the harmonic frequency and the anharmonicity constant. After the proper estimation of N, the algebraic interaction parameters for both the molecules are evaluated against a least square fit with the experimental values using MATLAB R2015. Using the algebraic interaction parameters, the vibrational frequencies for the two molecules are calculated. Because CO2is a linear symmetric triatomic molecule, the higher vibrational levels are largely affected by the mode mixing due to accidental degeneracy. The accidental degeneracy is studied introducing the Majorana and Fermi interaction parameters and the rms deviations are observed. The effects of accidental degeneracy for each of the molecules are not equal. In the second part of this report, the harmonic frequencies of CO2and N2O are calculated using the mean field approximation. It is found that the results show good agreement.

Improved analysis for μ−e−→e−e− in muonic atoms by photonic interaction

Studies of the charged lepton flavor violating process of $\mu^-e^-\to e^-e^-$ in muonic atoms by the four Fermi interaction [Y. Uesaka \textit{et al}., Phys. Rev. D {\bf 93}, 076006 (2016)] are extended to include the photonic interaction. The wave functions of a muon and electrons are obtained by solving the Dirac equation with the Coulomb interaction of a finite nuclear charge distribution. We find suppression of the $\mu^-e^-\to e^-e^-$ rate over the initial estimation for the photonic interaction, in contrast to enhancement for the four Fermi interaction. It is due to the Coulomb interaction of scattering states and relativistic lepton wave functions. This finding suggests that the atomic number dependence of the $\mu^-e^-\to e^-e^-$ rate could be used to distinguish between the photonic and the four Fermi interactions.

Research on Carrier Correlation in Ballistic Transport Nano-MOSFETs

Objective and Method: In this paper,the experiment proved that shot noise is suppressed by Fermi and Coulomb interaction correlation. Meanwhile, the establishment of shot noise suppression factor (Fano) in ballistic transport nano-MOSFETs the Coulomb interaction correlation and the combination of the two effects are derived from separately considering the Fermi interaction correlation. And on this basis the variation of Fano with voltage, doping concentration and temperature are investigated. Result: The result we obtained which considered the combination of the two effects is in good agreement with experimental studies in the research papers, thus getting a theoretical explanation for the variation of the suppression factor with the bias voltage. Meanwhile, the suppression factor model is suitable for nano-MOSFET.

Research of shot noise based on realistic nano-MOSFETs

Experimental measurements and simulation results have shown that the dominant noise source of current noise changes from thermal noise to shot noise with scaling of MOSFET, and shot noise were suppressed by Fermi and Coulomb interactions. In this paper, Shot noise test system is established, and experimental results proved that shot noise were suppressed, and the expressions of shot noise in realistic nano-MOSFETs are derived with considering Fermi effect, Coulomb interaction and the combination of the both co-existence, respectively. On this basis, the variation of shot noise with voltage, temperature and source-drain doping were researched. The results we obtained are consistent with those from experiments and the theoretically explanation is given. At the same time, the shot noise test system is suitable for traditional nanoscale electronic components; the shot noise model is suitable for nanoscale MOSFET.

Coherent neutrino-nucleus scattering and new neutrino interactions

We investigate the potential to probe new neutrino physics with future experiments measuring coherent neutrino-nucleus scattering. Experiments with high statistics should become feasible soon and allow to constrain parameters with unprecedented precision. Using a benchmark setup for a future experiment probing reactor neutrinos, we study the sensitivity on neutrino non-standard interactions and new exotic neutral currents (scalar, tensor, etc). Compared to Fermi interaction, percent and permille level strengths of the new interactions can be probed, superseding for some observables the limits from future neutrino oscillation experiments by up to two orders of magnitude.

Landau damping in a dipolar Bose–Fermi mixture in the Bose–Einstein condensation (BEC) limit

By using a mean-field approximation which describes the coupled oscillations of condensate and noncondensate atoms in the collisionless regime, Landau damping in a dilute dipolar Bose–Fermi mixture in the BEC limit where Fermi superfluid is treated as tightly bounded molecules, is investigated. In the case of a uniform quasi-two-dimensional (2D) case, the results for the Landau damping due to the Bose–Fermi interaction are obtained at low and high temperatures. It is shown that at low temperatures, the Landau damping rate is exponentially suppressed. By increasing the strength of dipolar interaction, and the energy of boson quasiparticles, Landau damping is suppressed over a broader temperature range.

First high resolution analysis of the 2ν1, 2ν3, and [formula omitted] + [formula omitted] bands of S18O2

We report the results of a highly accurate, (1–3)×10−4cm−1, ro-vibrational analysis of the S18O2 molecule in the spectral region of 2100–2700cm−1. More than 2910, 2130, and 1390 transitions belonging to the 2ν1, ν1+ν3, and 2ν3 bands were assigned for the first time with the values of quantum numbers Jmax./Kamax. equal to 67/26, 81/25 and 53/16, respectively. The weighted fit of experimentally assigned transitions was made with the Hamiltonian model which takes into account Coriolis resonance interactions between the vibrational states (v1v2v3) and (v1∓1v2v3±1) and Fermi interactions between the states (v1v2v3) and (v1∓1v2±2v3). To make the ro-vibrational analysis physically more suitable, the initial values of main spectroscopic parameters have been estimated theoretically. Finally, the set of 43 spectroscopic parameters obtained from the fit reproduces values of 2384 initial “experimental” ro-vibrational energy levels (more than 6430 transitions assigned in the experimental spectra) with the rms=1.74×10−4cm−1.