Pauli Blocking Effects Research Articles

All-optical light manipulation based on graphene-embedded side-polished fiber.

We present a study of all-optical light manipulation arising in a graphene-embedded side-polished fiber (SPF) with a Norland Optical Adhesives (NOA)-coated structure. With the help of the Pauli blocking effect, such an all-fiber device serves to manage the loss of transverse-electric-polarized light when the control light and the signal light are polarized along the direction parallel to the graphene surface. The insertion loss of this device can be effectively reduced with the NOA coating. An enhanced interaction between the graphene and the propagated light can be achieved via the strong evanescent field of the SPF and longer interaction length. This results in effective all-optical manipulation of light with a modulation depth of 10.4 dB (or modulation efficiency of ∼91%) and a modulation slope of ∼1.3, where the required control power is only about 14 dBm. The device has broadband operation wavelength. The insertion loss for both the signal light and the control light are only about 0.6 dB. The experimental results are well-fitting with the simulation study. Such an all-fiber device has the potential for all-optical signal processing.

Many-body Green's function approaches to the doped Fröhlich solid: Exact solutions and anomalous mass enhancement

In polar semiconductors and insulators, the Fr\"ohlich interaction between electrons and long-wavelength longitudinal optical phonons induces a many-body renormalization of the carrier effective masses and the appearence of characteristic phonon sidebands in the spectral function, commonly dubbed 'polaron satellites'. The simplest model that captures these effects is the Fr\"ohlich model, whereby electrons in a parabolic band interact with a dispersionless longitudinal optical phonon. The Fr\"ohlich model has been employed in a number of seminal papers, from early perturbation-theory approaches to modern diagrammatic Monte Carlo calculations. One limitation of this model is that it focuses on undoped systems, thus ignoring carrier screening and Pauli blocking effects that are present in real experiments on doped samples. To overcome this limitation, we here extend the Fr\"ohlich model to the case of doped systems, and we provide exact solutions for the electron spectral function, mass enhancement, and polaron satellites. We perform the analysis using two approaches, namely Dyson's equation with the Fan-Migdal self-energy, and the second-order cumulant expansion. We find that these two approaches provide qualitatively different results. In particular, the Dyson's approach yields better quasiparticle masses and worse satellites, while the cumulant approach provides better satellite structures, at the price of worse quasiparticle masses. Both approaches yield an anomalous enhancement of the electron effective mass at finite doping levels, which in turn leads to a breakdown of the quasiparticle picture in a significant portion of the phase diagram.

β-decay half-lives of neutron-rich N=82,81 isotones by shell-model calculations

We perform large-scale shell-model calculations and successfully describe the low-lying spectra and half-lives of neutron-rich N = 82 and N = 81 isotones with Z = 42 − 49 in a unified way. Shell-model study shows that their Gamow-Teller strength distribution has a peak in the low-excitation energies, which significantly contributes to the half-lives. This peak is dominated by the ν0g7/2 → π0g9/2 transition and enhanced on the proton deficient side of these isotones due to the Pauli blocking effect and the change of the effective single-particle energy of the ν0g7/2 orbit.

Pauli blocking potential applied to heavy-ion fusion reactions * *Supported by the National Natural Science Foundation of China (12105080, 11822503, 11975091) and the Program for Innovative Research Team (in Science and Technology) in University of Henan Province (21IRTSTHN011), China

In this study, the Pauli blocking potential between two colliding nuclei in the density overlapping region is applied to describe the heavy nuclei fusion process. Inspired by the Pauli blocking effect in the -decay of heavy nuclei, the Pauli blocking potential of single nucleon from the surrounding matter is obtained. In fusion reactions with strong density overlap, the Pauli blocking potential between the projectile and target can be constructed using a single folding model. By considering this potential, the double folding model with a new parameter set is employed to analyze the fusion processes of 95 systems. A wider Coulomb barrier and shallower potential pocket are formed in the inner part of the potential between the two colliding nuclei, compared to that calculated using the Akyüz-Winther potential. The fusion hindrance phenomena at deep sub-barrier energies are described well for fusion systems O + Pb and Ni + Ni.

Nuclear de-excitation associated with neutrino-carbon interactions

Neutrino interactions in low energy regions below 30 MeV, where the experimental searches for supernova relic neutrino are conducted, have a large uncertainty due to complicated nuclear effects such as the Pauli blocking effect and de-excitation of a residual nucleus. Understanding the effect of nuclear de-excitation is especially critical since neutrons measured by liquid scintillator detectors can be emitted via de-excitation. We build a systematic method to predict nuclear de-excitation associated with neutrino-carbon interaction using TALYS and Geant4. This prediction is combined with the results of neutrino event generators, and we find a large increase in neutron multiplicity.

Light hyperclusters and hyperons in low-density hot stellar matter

The abundance of light nuclei and hyperons, that are produced in stellar environments such as supernova or binary mergers, is calculated within a relativistic mean-field model with density dependent couplings in low-density matter. Five light nuclei are considered, together with three light hyper-nuclei. We show that the presence of hyperons shifts the dissolution of clusters to larger densities, and increases the amount of clusters. This effect is larger the smaller the charge fraction, and the higher the temperature. The abundance of hyperons is also affected by the cluster formation: neutral and positively charged hyperons suffer a reduction, and the negatively charged ones an increase. We also observe that the dissolution of the less-abundant clusters occurs at larger densities due to smaller Pauli-blocking effects. Overall, hyper-nuclei set in at temperatures above 25 MeV, and depending on the temperature and chemical composition, they may be more abundant than $\alpha$-particles, or even more abundant than other heavier clusters.

Tuning the Optical Band Gap of Two-Dimensional WS2 Integrated with Gold Nanocubes by Introducing Palladium Nanostructures

The two characteristic absorption peaks of semiconducting two-dimensional tungsten disulfide (WS2) are red-shifted after integrating with gold nanocube (AuNC) arrays. The amount of the red shift is reduced when the AuNCs are coated with a high concentration of Pd. A negligible shift was observed in the absorption peaks of WS2 when smaller amounts of Pd are introduced to the surface of AuNCs. Conversely, the photoluminescence (PL) of WS2 is blue-shifted when measured on top of AuNCs and AuNCs coated with different amounts of Pd. AuNC-Pd Janus nanoparticles are prepared by depositing Pd atoms asymmetrically on AuNCs assembled into 2-D arrays on the surface of a glass substrate by the chemical reduction of Pd ions. Due to the large AuNC or AuNC-Pd/WS2 Schottky barrier, the plasmon-induced hot electron transfer (PHET) from AuNCs and AuNCs coated with a high concentration of Pd is responsible for the red shift of the absorption spectrum of WS2. Introducing a lower concentration of Pd to AuNCs increases the Schottky barrier further due to the formation of the Au-Pd equilibrium Fermi level of lower energy, reducing the efficiency of PHET. The effect of Pd on the Fermi level of AuNCs vanishes at high Pd deposition. Pauli blocking and phase-space filling are responsible for the blue shift of PL of WS2 on top of AuNCs and AuNCs coated with Pd. The Pauli blocking effect is directly proportional to the PHET efficiency. This explains the significant blue shift of PL of WS2 after integrating with AuNCs and AuNCs coated with a high concentration of Pd. Additionally, depositing Pd onto AuNCs elongates the lifetime of the hot electrons and enhances the PHET efficiency.

Low-temperature ultrafast optical probing of topological bismuth selenide

We report the optical response and temperature-dependent excited-state carrier dynamics in the flake of Bi2Se3, which is cleaved from its single crystal. The optical properties are explored using the visible-near infrared (VIS-NIR), infrared (IR), and photoluminescence (PL) spectroscopies. The VIS-NIR spectra are then used to find the Ɛ1 and Ɛ2 using Kramer’s Koning relations, confirming OBT of 2 eV and 1.4 eV. The DFT (density functional theory) calculations are also carried out to confirm the experimental optical transitions (OBT). To probe these OBT in the bismuth selenide, we have studied the temperature, fluence, and excitation dependent ultrafast transient reflectance over a wide spectral range from 2.58–0.77 eV (VIS-NIR) with different excitation energies 3.02 eV, 2.61 eV, 1.9 eV, and 1.4 eV to explore several previously unseen transitions that do not appear in PL spectroscopy and room temperature carrier analysis. The temperature-dependent excited-state dynamics are investigated at 5–300 K. This study clearly indicates the existence of Moss-Burstein shift in the visible region and Pauli blocking effect in the NIR region in the Bi2Se3 topological insulator. Moreover, the low-temperature TRUS confirms the transition to the second surface state present in bismuth selenide.

Nature of the polaron-molecule transition in Fermi polarons

In this work, we explore the polaron and molecule physics by utilizing a unified variational ansatz with up to two particle-hole(p-h) excitations(V-2ph). We confirm the existence of a first-order transition in 3D and 2D Fermi polarons, and show that the nature of such transition lies in an energy competition between systems with different momenta ${\mathbf Q}=0$ and $|{\mathbf Q}|=k_F$, here ${\mathbf Q}$ is defined as the momentum of Fermi polaron system with respect to the Fermi sea of majority fermions (with Fermi momentum $k_F$). The literally proposed molecule ansatz is identified as an asymptotic limit of $|{\mathbf Q}|=k_F$ state in strong coupling regime, which implies a huge $SO(3)$(for 3D) or $SO(2)$ (for 2D) ground state degeneracy in this regime. The recognization of such degeneracy is crucially important for evaluating the molecule occupation in realistic systems with finite impurity density and at finite temperature. To compare with recent experiment of 3D Fermi polarons, we have calculated various physical quantities under the V-2ph framework and obtained results that are in good agreements with experimental data in the weak coupling and near resonance regime. Further, to check the validity of our conclusion in 2D, we have adopted a different variational method based on the Gaussian sample of high-order p-h excitations(V-Gph), and found the same conclusion on the nature of polaron-molecule transition therein. For 1D system, the V-2ph method predicts no sharp transition and the ground state is always at ${\mathbf Q}=0$ sector, consistent with exact Bethe ansatz solution. The presence/absence of polaron-molecule transition is analyzed to be closely related to the interplay effect of Pauli-blocking and p-h excitations in different dimensions.

Fast electrochemical activation of the broadband saturable absorption of tungsten oxide nanoporous film

The on-demand modulation of defects in materials for the effective modulation of optical nonlinearity is desirable, while it remains a great challenge. In this work, we demonstrate that electrochemical activation is a facile and convenient approach to modulating the broadband third-order nonlinear absorption of nanoporous tungsten oxide (WO3−x) thin film. The film does not exhibit optical nonlinearity at the initial state, while shows a distinct saturable absorption under an applied voltage of −2.5 V with the excitation of 515, 800, and 1,030 nm laser. The nonlinear absorption coefficient (βeff) is −766.38 ± 6.67 cm·GW−1 for 1,030 nm laser, −624.24 ± 17.15 cm·GW−1 for 800 nm laser, and −120.70 ± 11.49 cm·GW−1 for 515 nm laser, and the performance is competitive among inorganic saturable absorbers. The activation is accomplished in 2 min. The performance enhancement is ascribed to the formation of abundant in-gap defect states because of the reduction of the tungsten atoms, and a Pauli-blocking effect occurs during the excitation of in-gap defect states. The small feature size of WO3−x (∼ 12 nm) enables the effective and fast introduction and removal of the defects in porous film, and accordingly the fast and broadband modulation of optical nonlinearity. Our results suggest a controllable, effective, and convenient approach to tuning the nonlinear absorption of materials.

Analysis of the dynamical mechanism for elliptic flow production in heavy-ion collisions at intermediate energies

Elliptic flow ($v_{2}$) is an essential observable for studying the dynamic process of heavy-ion collisions, and has attracted significant attention in recent years. Based on the ultra-relativistic quantum molecular dynamics model, by tracking the nucleons that are emitted at mid-rapidity ($|y_{0}|<0.1$) in the entire collision process, the time evolution of elliptic flow of these selected nucleons is studied. The contributions of the mean-field potential and collision term to the elliptic flow are disentangled by recording the momenta of nucleons before and after each collision and propagation in the potential. In the semi-peripheral ($b$=5 fm) Au+Au collision at $E_{\\text{beam}}=0.4$ GeV/nucleon, approximately 30% of the $v_{2}$ is attributed to the mean-field potential, while the remaining 70% is attributed to the nucleon-nucleon collisions. $v_{2}$ is further increased (by approximately 10%) if the Pauli blocking effect is excluded.

Gamow–Teller transitions of neutron-rich N = 82,81 nuclei by shell-model calculations

Abstract $\beta$ -decay half-lives of neutron-rich nuclei around $N=82$ are key data to understand the $r$-process nucleosynthesis. We performed large-scale shell-model calculations in this region using a newly constructed shell-model Hamiltonian, and successfully described the low-lying spectra and half-lives of neutron-rich $N=82$ and $N=81$ isotones with $Z=42\text{--}49$ in a unified way. We found that their Gamow–Teller strength distributions have a peak in the low excitation energies, which significantly contributes to the half-lives. This peak, dominated by $\nu 0g_{7/2} \to \pi 0g_{9/2}$ transitions, is enhanced on the proton-deficient side because the Pauli-blocking effect caused by occupying the valence proton $0g_{9/2}$ orbit is weakened.

Theoretical studies on &amp;alpha; decays of even-even nuclei with the improved square-well cluster model

<p indent=0mm>α decay is one of the main decay modes of some unstable nuclei. It provides rich information on nuclear structures and is crucial for the experimental identification of new nuclides and new elements in heavy and superheavy regions. It is important to develop theoretical models for α-decay researches. Gamow, Gurney, and Condon proposed the first theoretical model to explain α decay within the framework of quantum tunneling in 1928, which is the first application of quantum mechanics in the subatomic systems. After that, several new theoretical models are proposed to get a better understanding of α decay. They provide preliminary descriptions of α decays in medium-mass and heavy nuclei. Square-well cluster model is an important model for α decay studies. It has several valuable advantages and gives a good description of the experimental α-decay half-lives of some even-even nuclei. It assumes that the effective potential between α cluster and daughter nucleus is given by the square well + the Coulomb potential at the surface. The Pauli blocking between α cluster and daughter nucleus is simulated by the Wildermuth condition, which prevents the α cluster from occupying the orbits inside the daughter nucleus. The theoretical α-decay half-lives are given by the WKB approximation. One of the shortcomings of the square-well cluster model is that different α-emitters are assumed to have exactly the same potential-well depth, which is disfavored by, e.g., the double-folding model and is an oversimplification of realistic effective potentials. In this work, we improve the square-well cluster model by taking into consideration that the depth of the square well depends on the mass number and the proton number. Such an improvement preserves, at the same time, many important merits of the original square-well cluster model. The Pauli blocking effect is simulated by the Wildermuth condition. The theoretical α-decay half-lives are calculated by the WKB approximation. The free parameters in the improved square-well cluster model are determined by fitting the experimental α-decay half-lives of the medium-mass, heavy, and superheavy even-even nuclei, respectively. We then study systematically α decays of even-even nuclei in different mass regions. The logarithmic hindrance factors and root-mean-square deviations between the experimental and theoretical results are calculated. We find that the theoretical α-decay half-lives given by the improved square-well cluster model are in better agreement with the experimental data than those given by the square-well cluster model. There are more theoretical data points agreeing with the experimental data within a factor of 1.5 in the improved square-well cluster model than the squared-well cluster model. For instance, the theoretical α-decay half-life of ²⁸⁸Fl is about three times the experimental data in the square-well cluster model, but only deviates from the experimental data by 3% in the improved square-well cluster model. This shows the advantages of the improved square-well cluster model by introducing the mass-number and proton-number dependence of the square-well depth. These results could be useful for experimental and theoretical studies of α decays.

Pauli blocking effects in nα -nucleus-induced fusion reactions

The hindrances in the $n\ensuremath{\alpha}$-nucleus-induced fusion reactions at deep subbarrier energies are investigated by using the coupled-channels model. Inspired by the microscopic Pauli-blocking effects of $\ensuremath{\alpha}$-cluster decay in radioactive nuclei, a Pauli blocking potential is constructed in the $n\ensuremath{\alpha}$-nucleus-induced fusion reactions by using a single folding procedure, in which the $n\ensuremath{\alpha}$ nuclei are assumed to be consisted of $\ensuremath{\alpha}$ particles. A shallow pocket is formed in the inner part of the potential between two colliding nuclei as compared to the one obtained from the double-folding potential with standard Michigan-3-Yukawa effective nucleon-nucleon interaction. The experimental fusion cross sections are described well for fusion systems $^{12}\mathrm{C}+^{198}\mathrm{Pt}$, $^{16}\mathrm{O}+^{208}\mathrm{Pb}$, $^{12}\mathrm{C}+^{30}\mathrm{Si}$, $^{24}\mathrm{Mg}+^{30}\mathrm{Si}$, and $^{28}\mathrm{Si}+^{30}\mathrm{Si}$. At deep subbarrier energies, it is found that this shallow pocket potential reduces the partial fusion cross sections and shields the contributions of high-angular-momentum partial waves to fusion cross sections. In addition, a detailed comparison of fusion processes with different projectiles $^{12}\mathrm{C}$, $^{24}\mathrm{Mg}$, and $^{28}\mathrm{Si}$ on the same target $^{30}\mathrm{Si}$ shows the hindrance effect is stronger for heavier projectiles.

Pauli blocking effects in thermalization of relativistic plasma

We investigate the effects of Pauli blocking on thermalization process of relativistic plasma by solving relativistic Uehling-Uhlenbeck equations with QED collision integral for all binary and triple processes. With this purpose we consider nonequilibrium initial state of plasma to be strongly degenerate. We found that when electron-positron annihilation is efficient, initial plasma degeneracy is quickly destroyed. As a result in a wide range of final temperatures ranging from nonrelativistic to mildly relativistic 0.1mec2≤kBT≤10mec2 thermalization is not affected by Pauli blocking. Conversely, when electron-positron annihilation process is inefficient, thermalization process in such degenerate plasma is strongly affected by Pauli blocking. This is possible either in a nonrelativistic plasma, with equilibrium temperature kBT≤0.3mec2, or in photon-electron plasma. In these cases all reaction rates are strongly suppressed by Pauli blocking and thermalization does not occur until electrons can populate energy states above the Fermi energy. Soon after this happens thermalization proceeds suddenly in an avalanche-like process. Such rapid thermalization can be a unique footprint of strongly degenerate plasma.

Chirally Improved Quark Pauli Blocking in Nuclear Matter and Applications to Quark Deconfinement in Neutron Stars

The relativistic mean field (RMF) model of the nuclear matter equation of state was modified by including the effect of Pauli-blocking owing to quark exchange between the baryons. Different schemes of a chiral enhancement of the quark Pauli blocking was suggested according to the adopted density dependence of the dynamical quark mass. The resulting equations of state for the pressure are compared to the RMF model DD2 with excluded volume correction. On the basis of this comparison a density-dependent nucleon volume is extracted which parameterizes the quark Pauli blocking effect in the respective scheme of chiral enhancement. The dependence on the isospin asymmetry is investigated and the corresponding density dependent nuclear symmetry energy is obtained in fair accordance with phenomenological constraints. The deconfinement phase transition is obtained by a Maxwell construction with a quark matter phase described within a higher order NJL model. Solutions for rotating and nonrotating (hybrid) compact star sequences are obtained, which show the effect of high-mass twin compact star solutions for the rotating case.

Light p -shell nuclei with cluster structures ( 4≤A≤16 ) in nuclear matter

The composition of hot and dense nuclear matter is calculated including the $1p$-shell nuclei $4 \le A \le 16$. In-medium shifts, in particular Pauli blocking, are determined by the intrinsic wave function of the nuclei. Results are given within a shell-model approach for the nucleon wave function. Light nuclei are not always well described by the shell model. The 'clustered' nucleus $^8$Be exhibits strong correlation effects because of $\alpha$-like clustering. Intrinsic cluster structures are also significant for the nuclei $^6$Li, $^7$Li, $^7$Be, and $^9$Be. The contribution of the relatively rare elements Li, Be, and B, to the equation of state (EoS) of matter near the saturation density is overestimated in simple approaches such as the nuclear statistical equilibrium (NSE) model. Both, the treatment of continuum correlations and the account of in-medium modifications are considered for the contribution of $^5$He and $^4$H clusters. Compared to the extended NSE including unstable nuclei, the contributions of the corresponding P$_{3/2}$ channel with $A=5, Z=2$ and P$_{2}$ channel with $A=4, Z=1$, respectively, to the EoS are strongly suppressed at high densities owing to Pauli blocking effects. For the shifts of the binding energies of the light $p$-shell nuclei, simple fit formula are given to calculate the composition of hot and dense matter in a wide parameter range.

Effects of Pauli blocking on pion production in central collisions of neutron-rich nuclei

Pauli blocking is carefully investigated for the processes of $NN \rightarrow N \Delta$ and $\Delta \rightarrow N \pi$ in heavy-ion collisions, aiming at a more precise prediction of the $\pi^-/ \pi^+$ ratio which is an important observable to constrain the high-density symmetry energy. We use the AMD+JAM approach, which combines the antisymmetrized molecular dynamics for the time evolution of nucleons and the JAM model to treat processes for $\Delta$ resonances and pions. As is known in general transport-code simulations, it is difficult to treat Pauli blocking very precisely due to unphysical fluctuations and additional smearing of the phase-space distribution function, when Pauli blocking is treated in the standard method of JAM. We propose an improved method in AMD+JAM to use the Wigner function precisely calculated in AMD as the blocking probability. Different Pauli blocking methods are compared in heavy-ion collisions of neutron-rich nuclei, ${}^{132}\mathrm{Sn}+{}^{124}\mathrm{Sn}$, at 270 MeV/nucleon. With the more accurate method, we find that Pauli blocking is stronger, in particular for the neutron in the final state in $NN \rightarrow N \Delta$ and $ \Delta \to N\pi$, compared to the case with a proton in the final state. Consequently, the $\pi^-/\pi^+$ ratio becomes higher when the Pauli blocking is improved, the effect of which is found to be comparable to the sensitivity to the high-density symmetry energy.

High-K multi-particle bands and pairing reduction in 254No * * Supported by the National Natural Science Foundation of China (11775112, 11535004, 11875027, 11761161001) and the Priority Academic Program Development of Jiangsu Higher Education Institutions

The multi-particle states and rotational properties of the two-particle bands in are investigated by the cranked shell model with pairing correlations treated by the particle number conserving method. The rotational bands on top of the two-particle and states and the pairing reduction are studied theoretically in for the first time. The experimental excitation energies and moments of inertia of the multi-particle states are reproduced well by the calculations. Better agreement with the data is achieved by including the high-order deformation , which leads to enlarged and deformed shell gaps. An increase of in these two-particle bands compared with the ground state band is attributed to the pairing reduction due to the Pauli blocking effect.

Gamow-Teller transitions to Zr93 via the Nb93(t,He3+γ ) reaction at 115 MeV/u and its application to the stellar electron-capture rates

Electron-capture reactions play important roles in the late evolution of core-collapse supernovae. The electron-capture rates used in astrophysical simulations rely on theoretical calculations which have to be tested against and guided by experimental data. We report on the measurement of the Gamow-Teller strength distribution of the odd-mass nucleus $^{93}\mathrm{Nb}$ via the ($t,^{3}\mathrm{He}$ + $\ensuremath{\gamma}$) charge-exchange reaction at a beam energy of 115 MeV/u. The Gamow-Teller strength distributions were extracted up to an excitation energy in $^{93}\mathrm{Zr}$ of 10 MeV. The results were compared with shell-model and quasiparticle random-phase approximation (QRPA) calculations. The theoretical calculations fail to describe the details of the strength distribution, but estimate reasonably well the integrated Gamow-Teller transition strength. Electron-capture rates derived from the measured and theoretical strength distributions match reasonably well, especially at the higher stellar densities of importance for deleptonization during the collapse of the stellar core, since the electron-capture $Q$ value is close to zero and the Fermi energy sufficiently high to ensure that the details of the strength distribution do not have a strong impact on the derived rates. At stellar densities in excess of ${10}^{9}$ g/${\mathrm{cm}}^{3}$, the electron-capture rate based on a single-state approximation used in astrophysical simulations is slightly higher than the rates based on the data and the shell-model and QRPA calculations, likely due to the fact that the approximation includes temperature-dependent effects, which increase the rates. However, the difference is much smaller than that observed in recent studies of nuclei with $Zl40$ near $N=50$, suggesting that the single-state approximation does not account for Pauli-blocking effects for nuclei with $Zl40$ that are much stronger than those for $^{93}\mathrm{Nb}$ with $Z=41$.