Pauli Blocking Effects Research Articles

Investigation of the high-spin rotational properties of the proton emitter 113Cs using a particle-number conserving method**Supported by National Natural Science Foundation of China (11275098, 11275248, 11505058) and Fundamental Research Funds for the Central Universities (2015QN21)

The recently observed two high-spin rotational bands in the proton emitter 113Cs are investigated using the cranked shell model with pairing correlations treated by a particle-number conserving method, in which the Pauli blocking effects are taken into account exactly. By using the configuration assignments of band 1 [π3/2+[422](g7/2), α = −1/2] and band 2 [π1/2+[420](d5/2), α = 1/2], the experimental moments of inertia and quasiparticle alignments can be reproduced much better by the present calculations than those using the configuration assginment of π1/2−[550] (h11/2), which in turn may support these configuration assignments. Furthermore, by analyzing the occupation probability nμ of each cranked Nilsson level near the Fermi surface and the contribution of each orbital to the angular momentum alignments, the backbending mechanism of these two bands is also investigated.

Effect of Pauli blocking on coherent states of composite bosons

The quantum nature of elementary bosons can be completely erased by using coherent states known as Glauber states. Here, we consider composite bosons (cobosons) made of two fermions and look for the possibility to erase the bosonic quantum nature of the field and the fermionic quantum nature of its constituents, when the distribution of the coboson Schmidt decomposition is either flat like Frenkel excitons, or localized like Wannier excitons. We show that for Frenkel-like cobosons, complete erasure of the field quantum nature is possible up to a density which corresponds to a sizable fraction of the number of fermion-pair states making the coboson at hand. At higher density, the Pauli exclusion principle between fermionic constituents shows up dramatically. It induces: (i) the decrease of number-operator eigenvalues down to 1 and the increase of the number-state second-order correlation function up to 2; (ii) the disappearance of the usual sharp peak in the coherent-state distribution and the increase of the coherent-state second-order correlation function up to 2. It also is possible to construct number states and coherent states for Wannier-like cobosons, but their forms are far more complex. Finally, we show that Pauli blocking makes the coboson coherent states qualitatively different from the Anderson's ansatz.

Transport Dynamics of Neutral Excitons and Trions in Monolayer WS2.

Understanding the spatial motion of excitons is of both fundamental interest and central importance for optoelectrical applications. Here, we have investigated the temperature (T) dependence of the transport dynamics of neutral excitons and charged excitons (trions) in atomically thin two-dimensional crystals of the transition-metal dichalcogenide WS2. The transport dynamics of neutral excitons can be divided into three temperature ranges, where the diffusion of neutral excitons is governed by thermal activation (≤∼75 K), ionized impurity scattering (∼75 K ≤ T ≤∼200 K), and LO phonon scattering (≥∼200 K). The trions have a diffusion length that is over 20 times longer than that of neutral excitons at very low temperatures (≤∼10 K), which may be related to theoretically predicted Pauli-blocking effects during the excitation process.

Quark-Pauli effects in three octet-baryons

To sustain a neutron star with about two times the solar mass, multi baryons including hyperons are expected to produce repulsive effects in the interior of its high baryon-density region. To examine possible quark-Pauli repulsion among the baryons, we solve the eigenvalue problem of the quark antisymmetrizer for three octet-baryons that are described by most compact spatial configurations. We find that the Pauli blocking effect is weak in the $\Lambda nn$ system, while it is strong in the $\Sigma^-nn$ system. The appearance of the $\Sigma^-$ hyperon is suppressed in the neutron star interior but no quark-Pauli repulsion effectively works for the $\Lambda$ hyperon.

Pauli-blocking effect in two-body collisions dominates the in-medium effects in heavy-ion reactions near Fermi energy

The dissipation phenomenon in the heavy-ion reaction at incident energy near Fermi energy is studied by simulating the reactions 129Xe + 129Sn and 58Ni + 58Ni with isospin-dependent quantum molecular dynamics model (IQMD). The isotropy ratio in terms of transverse and longitudinal energies of the free protons emitted in the final states of these reactions is quantitatively analyzed to explore the in-medium correlation of the binary collisions. Comparison of the calculations with the experimental data recently released by INDRA collaboration exhibits that the ratio is very sensitive to the Pauli blocking effect in two-body collisions and Pauli exclusion principle is indispensable in the theoretical simulations for the heavy-ion reactions near the Fermi energy.

Many-body, Pauli blocking and carrier-impurity interaction effects on the band gap of aluminum doped zinc oxide thin films: A new method to evaluate both hole and electron effective masses of degenerate semiconductors

In this study, the role of many-body interactions, Pauli blocking, and impurity-carrier interactions on the band gap variation were used to analyze the observed blue shift of the Al doped ZnO thin films. The optical constants and the band gap variations of our samples were obtained using spectroscopic ellipsometry method. Tauc-Lorentz model and effective medium approximation were used to model the dielectric function. We demonstrated for the first time that the combination of the Tauc formalism for absorption and the proposed model by Jain et al. for the band gap variation, can be used to determine both electron and hole effective masses. Reasonable results were obtained for carriers effective mass and their dependence on carrier concentration.

Platform for spectrally resolved x-ray scattering from imploding capsules at the National Ignition Facility

We present a new experimental platform to perform spectrally resolved x-ray scattering measurements of ionization, density and temperature in imploding CH or beryllium capsules at the National Ignition Facility. Scattered x-rays at 9 keV from a zinc He-alpha plasma source at a scattering angle of 120 degrees are highly sensitive to K-shell ionization, while at the same time constraining density and temperature. This platform will allow for x-ray scattering studies of dense plasmas with free electron densities up to 1025 cm-3 giving the possibility to investigate effects of pressure ionization and Pauli blocking on the ablator ionization state right before or shortly after stagnation of the implosion.

Maximum modulation of plasmon-guided modes by graphene gating

The potential of graphene in plasmonic electro-optical waveguide modulators has been investigated in detail by finite-element method modelling of various widely used plasmonic waveguiding configurations. We estimated the maximum possible modulation depth values one can achieve with plasmonic devices operating at telecom wavelengths and exploiting the optical Pauli blocking effect in graphene. Conclusions and guidelines for optimization of modulation/intrinsic loss trade-off have been provided and generalized for any graphene-based plasmonic waveguide modulators, which should help in consideration and design of novel active-plasmonic devices.

Third-Order Optical Nonlinearities in Organometallic Methylammonium Lead Iodide Perovskite Thin Films

With solar conversion efficiencies surpassing 20%, organometallic perovskites show tremendous promise for solar cell technology. Their high brightness has also led to demonstrations of lasing and power-efficient electroluminescence. Here we show that thin films of methylammonium lead iodide, prepared by solution processing at temperatures not exceeding 100 °C, exhibit a highly nonlinear intensity-dependent refractive index due to changes in the free-carrier concentration and for femtosecond excitation at higher intensities undergo saturation that can be attributed to the Pauli blocking effect. Nonlinear refractive index and nonlinear absorption coefficients were obtained by the Z-scan technique, performed simultaneously in open- and closed-aperture configurations. Both nanosecond- and femtosecond-pulsed lasers at multiple wavelengths were used in order to distinguish between the mechanisms inducing the nonlinearities. The magnitude and sign of the nonlinear refractive index n2 were determined. For resonan...

Particle-number fluctuation of pairing correlations for Dy isotopes**Supported by Fundamental Research Funds for the Central Universities (JUSRP1035), National Natural Science Foundation of China (11305077)

Within the relativistic mean field (RMF) theory, the ground state properties of dysprosium isotopes are studied using the shell-model-like approach (SLAP), in which pairing correlations are treated with particle-number conservation, and the Pauli blocking effects are taken into account exactly. For comparison, calculations of the Bardeen–Cooper–Schrieffer (BCS) model with the RMF are also performed. It is found that the RMF+SLAP calculation results, as well as the RMF+BCS ones, reproduce the experimental binding energies and one- and two-neutron separation energies quite well. However, the RMF+BCS calculations give larger pairing energies than those obtained by the RMF+SLAP calculations, in particular for nuclei near the proton and neutron drip lines. This deviation is discussed in terms of the BCS particle-number fluctuation, which leads to the sizable deviation of pairing energies between the RMF+BCS and RMF+SLAP models, where the fluctuation of the particle number is eliminated automatically.

THz saturable absorption in turbostratic multilayer graphene on silicon carbide.

We investigated the room-temperature Terahertz (THz) response as saturable absorber of turbostratic multilayer graphene grown on the carbon-face of silicon carbide. By employing an open-aperture z-scan method and a 2.9 THz quantum cascade laser as source, a 10% enhancement of transparency is observed. The saturation intensity is several W/cm2, mostly attributed to the Pauli blocking effect in the intrinsic graphene layers. A visible increase of the modulation depth as a function of the number of graphene sheets was recorded as consequence of the low nonsaturable losses. The latter in turn revealed that crystalline disorder is the main limitation to larger modulations, demonstrating that the THz nonlinear absorption properties of turbostratic graphene can be engineered via a proper control of the crystalline disorder and the layers number.

Steady-state ab initio laser theory for complex gain media.

We derive and test a generalization of the steady-state ab initio laser theory (SALT) to treat complex gain media. The generalized theory (C-SALT) is able to treat atomic and molecular gain media with diffusion and multiple lasing transitions, and semiconductor gain media in the free carrier approximation including fully the effect of Pauli blocking. The key assumption of the theory is stationarity of the level populations, which leads to coupled self-consistent equations for the populations and the lasing modes that fully include the effects of openness and non-linear spatial hole-burning. These equations can be solved efficiently for the steady-state lasing properties by a similar iteration procedure as in SALT, where a static gain medium with a single transition is assumed. The theory is tested by comparison to much less efficient finite difference time domain (FDTD) methods and excellent agreement is found. Using C-SALT to analyze the effects of varying gain diffusion constant we demonstrate a cross-over between the regime of strong spatial hole burning with multimode lasing to a regime of negligible spatial hole burning, leading to gain-clamping, and single mode lasing. The effect of spatially inhomogeneous pumping combined with diffusion is also studied and a relevant length scale for spatial inhomogeneity to persist under these conditions is determined. For the semiconductor gain model, we demonstrate the frequency shift due to Pauli blocking as the pumping strength changes.

Analysis of delocalization of clusters in linear-chainα-cluster states with entanglement entropy

I investigate entanglement entropy of one dimension (1D) cluster states to discuss the delocalization of clusters in linear-chain $3\alpha$- and $4\alpha$-cluster states. In analysis of entanglement entropy of 1D Tohsaki-Horiuchi-Schuck-R\"opke (THSR) and Brink-Bloch cluster wave functions, I show clear differences in the entanglement entropy between localized cluster wave functions and delocalized cluster wave functions. In order to clarify spatial regions where the entanglement entropy is generated by the delocalization of clusters, I analyze the spatial distribution of entanglement entropy. In the linear-chain $3\alpha$ cluster state, the delocalization occurs dominantly in a low-density tail region while it is relatively suppressed in an inner region because of Pauli blocking effect between clusters. In the linear-chain 4$\alpha$ state having a larger system size than the linear-chain $3\alpha$ state, the delocalization occurs in the whole system. The entanglement entropy is found to be a measure of the delocalization of clusters in the 1D cluster systems.

Theoretical study of optical conductivity of graphene with magnetic and nonmagnetic adatoms

We present a theoretical study of the optical conductivity of graphene with magnetic and nonmagnetic adatoms. First, by introducing alternating potential in a pure graphene, we demonstrate a gap formation in the density of states and the corresponding optical conductivity. We highlight the distinction between such a gap formation and the so-called Pauli blocking effect. Next, we apply this idea to graphene with adatoms by introducing magnetic interactions between the carrier spins and the spins of the adatoms. Exploring various possible ground-state spin configurations of the adatoms, we find that antiferromagnetic configuration yields the lowest total electronic energy, and is the only configuration that forms a gap. Furthermore, we analyze four different circumstances leading to similar gaplike structures and propose a means to interpret the magneticity and the possible orderings of the adatoms on graphene solely from the optical conductivity data. We apply this analysis to the recently reported experimental data of oxygenated graphene.

Antistrange meson-baryon interaction in hot and dense nuclear matter

We present a study of in-medium cross sections and (off-shell) transition rates for the most relevant binary reactions for strange pseudoscalar meson production close to threshold in heavy-ion collisions at energies available at the Facility for Antiproton and Ion Research. Our results rely on a chiral unitary approach in coupled channels which incorporates the $s$ and $p$ waves of the kaon-nucleon interaction. The formalism, which is modified in the hot and dense medium to account for Pauli blocking effects, mean-field binding on baryons, and pion and kaon self-energies, has been improved to implement unitarization and self-consistency for both the $s$- and the $p$-wave interactions at finite temperature and density. This gives access to in-medium amplitudes in several elastic and inelastic coupled channels with strangeness content $S=\ensuremath{-}1$. The obtained total cross sections mostly reflect the fate of the $\ensuremath{\Lambda}(1405)$ resonance, which melts in the nuclear environment, whereas the off-shell transition probabilities are also sensitive to the in-medium properties of the hyperons excited in the $p$-wave amplitudes $[\ensuremath{\Lambda},\ensuremath{\Sigma}$, and ${\ensuremath{\Sigma}}^{*}(1385)]$. The single-particle potentials of these hyperons at finite momentum, density, and temperature are also discussed in connection with the pertinent scattering amplitudes. Our results are the basis for future implementations in microscopic transport approaches accounting for off-shell dynamics of strangeness production in nucleus-nucleus collisions.

Non-Markovian dynamics with fermions

Employing the quadratic fermionic Hamiltonians for the collective and internal subsystems with a linear coupling, we studied the role of fermionic statistics on the dynamics of the collective motion. The transport coefficients are discussed as well as the associated fluctuation-dissipation relation. Due to different nature of the particles, the path to equilibrium is slightly affected. However, in the weak coupling regime, the time-scale for approaching equilibrium is found to be globally unchanged. The Pauli-blocking effect can modify the usual picture in open quantum system. In some limits, contrary to boson, this effect can strongly hinder the influence of the bath by blocking the interacting channels.

Rotation and alignment of high-jorbitals in transfermium nuclei

The structure of nuclei with $Z\sim100$ is investigated systematically by the Cranked Shell Model (CSM) with pairing correlations treated by a Particle-Number Conserving (PNC) method. In the PNC method, the particle number is conserved and the Pauli blocking effects are taken into account exactly. By fitting the experimental single-particle spectra in these nuclei, a new set of Nilsson parameters ($\kappa$ and $\mu$) is proposed. The experimental kinematic moments of inertia and the band-head energies are reproduced quite well by the PNC-CSM calculations. The band crossing, the effects of high-$j$ intruder orbitals and deformation are discussed in detail.

Solution of the Bethe-Goldstone equation without partial-wave decomposition

We present a method for solving the nucleon-nucleon scattering equation without the use of a partial wave expansion of the scattering amplitude. After verifying the accuracy of the numerical solutions, we proceed to apply the method to the in-medium scattering equation (the Bethe-Goldstone equation) in three dimensions. A focal point is a study of Pauli blocking effects calculated in the (angle-dependent) three-dimensional formalism as compared to the usual spherical approximation. We discuss our results and their implications.

CHARMING MESONS WITH BARYONS AND NUCLEI

The properties of charmed mesons in nuclear matter and nuclei are reviewed. Different frameworks are discussed paying a special attention to unitarized coupled-channel approaches which incorporate heavy-quark spin symmetry. Several charmed baryon states with negative parity are generated dynamically by the s-wave interaction between pseudoscalar and vector meson multiplets with 1/2+ and 3/2+ baryons. These states are compared to experimental data. Moreover, the properties of open-charm mesons in matter are analyzed. The in-medium solution accounts for Pauli blocking effects, and for the meson self-energies in a self-consistent manner. The behavior in the nuclear medium of the rich spectrum of dynamically-generated baryon states is studied as well as their influence in the self-energy and, hence, the spectral function of open charm. The possible experimental signatures of the in-medium properties of open charm are finally addressed, such as the formation of charmed nuclei, in connection with the future FAIR facility.

ν¯linduced pion production from nuclei at∼1 GeV

We have studied charged current ${\overline{\ensuremath{\nu}}}_{l}$ induced one pion production from $^{12}\mathrm{C}$ and $^{16}\mathrm{O}$ nuclear targets at MiniBooNE and atmospheric antineutrino energies. The calculations have been done for the incoherent pion production process as well as for the pions coming from the hyperons in the quasielastic production of $\ensuremath{\Lambda}$ and $\ensuremath{\Sigma}$. The calculations are done in the local density approximation. For the inelastic processes the calculations have been done in the $\ensuremath{\Delta}$ dominance model, and we take into account the effect of Pauli blocking, Fermi motion of the nucleon, and renormalization of $\ensuremath{\Delta}$ properties in the nuclear medium. The effect of final state interaction (FSI) of pions is also taken into account. For the hyperon production, the nuclear medium effects due to Fermi motion and FSI effects due to hyperon-nucleon scattering have been taken into account. These results may be quite useful in the analysis of SciBooNE, MicroBooNE, $\mathrm{MINER}\ensuremath{\nu}\mathrm{A}$, and ArgoNeuT experiments when the pion analysis is done by using antineutrino beams.