Excitation Energy Spectrum Research Articles

Laser spectroscopic probing of coexisting superfluid and insulating states of an atomic Bose-Hubbard system.

A system of ultracold atoms in an optical lattice has been regarded as an ideal quantum simulator for a Hubbard model with extremely high controllability of the system parameters. While making use of the controllability, a comprehensive measurement across the weakly to strongly interacting regimes in the Hubbard model to discuss the quantum many-body state is still limited. Here we observe a great change in the excitation energy spectra across the two regimes in an atomic Bose–Hubbard system by using a spectroscopic technique, which can resolve the site occupancy in the lattice. By quantitatively comparing the observed spectra and numerical simulations based on sum rule relations and a binary fluid treatment under a finite temperature Gutzwiller approximation, we show that the spectra reflect the coexistence of a delocalized superfluid state and a localized insulating state across the two regimes.

Second0+state of unboundO12: Scaling of mirror asymmetry

The unbound O12 nucleus was studied via the two-neutron transfer (p,t) reaction in inverse kinematics using a radioactive O14 beam at 51 MeV/u. Excitation energy spectra and differential cross sections were deduced by the missing mass method using MUST2 telescopes. We achieved much higher statistics compared to the previous experiments of O12, which allowed accurate determination of resonance energy and unambiguous spin and parity assignment. The O12 resonance previously reported using the same reaction was confirmed at an excitation energy of 1.62±0.03(stat.)±0.10(syst.). MeV and assigned spin and parity of 0+ from a distorted-wave Born approximation analysis of the differential cross sections. Mirror symmetry of O12 with respect to its neutron-rich partner Be12 is discussed from the energy difference of the second 0+ states. In addition, from systematics of known 0+ states, a distinct correlation is revealed between the mirror energy difference and the binding energy after carrying out a scaling with the mass and the charge. We show that the mirror energy difference of the observed 0+ state of O12 is highly deviated from the systematic trend of deeply bound nuclei and in line with the scaling relation found for weakly bound nuclei with a substantial 2s1/2 component. The importance of the scaling of mirror asymmetry is discussed in the context of ab initio calculations near the drip lines and universality of few-body quantum systems.

Functional integrals and 1/h expansion in the boson–fermion model

The effective action of boson–fermion model is derived by means of the functional integrals method and Popov–Faddeev canonical transformations. The energy gap equation and excitation spectrum equation are obtained from first order and second order perturbation expansions of functional determinant. In the long wave approximation, some analytical expressions of excitation spectrum are calculated by using the 1/h expansion technique, the results showed that analytical calculation is in good agreement with the numerical calculation. Moreover, the Nambu sum rules of Higgs bosons are analyzed and discussed.

Extracting the cross section angular distributions for15C high-energy resonance excited via the (18O,16O) two-neutron transfer reaction

The 13 C( 18 O, 16 O) 15 C reaction has been studied at 84 MeV incident energy. The ejectiles have been momentum analized by the MAGNEX spectrometer and 15 C excitation energy spectra have been obtained up to about 20 MeV. In the region above the two-neutron separation energy, a bump has been observed at 13.7 MeV. The extracted cross section angular distribution for this structure, obtained by using different models for background, displays a clear oscillating pattern, typical of resonant state of the residual nucleus.

Preliminary study of the10Li nucleus via one-neutron transfer

The structure of the 10 Li unbound nucleus is a subject of large interest and its description is nowadays a matter of debate. We have investigated this system using the d( 9 Li,p) 10 Li one-neutron transfer reaction at 100 MeV in inverse kinematics. The experiment was performed at the ISACII facility at TRIUMF laboratory. The excitation energy spectrum has been reconstructed by measuring the emitted protons at backward angles and the 9 Li at forward angles.

Study of Gamow-Teller transitions from132Sn via the (p,n) reaction at 220 MeV/u in inverse kinematics

The charge-exchange (p ,n ) reaction at 220 MeV has been measured to extract the strength distribution of Gamow-Teller transitions from the doubly magic unstable nucleus 132 Sn. A recently developed experimental technique of measuring the (p ,n ) reaction in inverse kinematics has been applied to the study of unstable nuclei in the mass region around A ∼100 for the first time. We have combined the low-energy neutron detector WINDS and the SAMURAI spectrometer at the RIKEN radioactive isotope beam factory (RIBF). The particle identification plot for the reaction residues obtained by the spectrometer provides the clear separation of the CE reaction channel from other background events, enabling us to identify kinematic curves corresponding the (p , n ) reaction. Further analysis to reconstruct the excitation energy spectrum is ongoing.

Search forη′ mesic nuclei by missing-mass spectroscopy of the12C(p,d) reaction

We performed a missing-mass spectroscopy experiment of the 12C(p, d) reaction at 2.5 GeV proton energy in order to search for η′ mesic nuclei. An excitation-energy spectrum of 11C was obtained around the η′ production threshold. As no significant peak structure was observed in the spectrum, upper limits of the formation cross section of η′ mesic nuclei have been determined. Preliminary results of the experiment as well as future prospects are given.

Evolution of single-particle strength in neutron-rich 71Cu

The strength functions of the πf5/2, πp3/2 and πf7/2 orbitals in neutron-rich 71Cu were obtained in a 72Zn(d,3He)71Cu proton pick-up reaction in inverse kinematics using a radioactive beam of 72Zn at 38 MeV/u. A dedicated set-up was developed to overcome the experimental challenges posed by the low cross section of the reaction and the low energy of the outgoing 3He particles. The excitation-energy spectrum was reconstructed and spectroscopic factors were obtained after analysis of the angular distributions with the finite-range Distorted-Wave Born Approximation (DWBA). The results show that unlike for the πf5/2 orbital and contrary to earlier interpretation, the πf7/2 single-particle strength distribution is not appreciably affected by the addition of neutrons beyond N=40.

Raman spectra of hydrocarbons formed in carbon nanotubes - a theoretical study

Recent experimental results based on Raman spectroscopy and mass spectroscopy showed that an appropriate heat treatment of small diameter carbon nanotubes filled with ferrocene molecules results in the formation of hydrocarbon molecules. However, the exact nature of these molecules is still unknown. In order to find possible candidates, we performed density functional theory calculations of the structure, electronic transition energies, and Raman spectrum for a large set of hydrocarbon molecules, including oligoenes and polyaromatic hydrocarbons. To follow the effect of deuteration in the Raman spectra we varied the mass of hydrogen atom from 1 to 2 by 0.1 steps. With increasing mass, the position of the lines red shifted as expected. However, in some rare occasions, the intensity of the red shifted line dramatically decreased and at the same time, an originally weak line gained large intensity at a nearby higher frequency. This can be interpreted in an experiment as an apparent blue shift. From a comparison of the calculations with experiments, based on molecular weight, excitation energy, and Raman spectrum (for both hydrogenated and deuterated forms) either quaterrylene (dimer of perylene) or the dimer of the 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) is the most likely product of the heat treatment.

The collective-excitation spectrum in superfluid helium

On the basis of the Landau quasiparticle concept and the exact relation for the “density–density” response function, an explicit expression for the energy spectrum of collective excitations in superfluid helium is obtained with the strong-interaction effects taken into account.

Gamow-Teller transitions toCa45via theSc45(t,He3+γ)reaction at115 MeV/uand its application to stellar electron-capture rates

Background: Stellar electron-capture reactions on medium-heavy nuclei are important for many astrophysical phenomena, including core-collapse and thermonuclear supernov\ae{} and neutron stars. Estimates of electron-capture rates rely on accurate estimates of Gamow-Teller strength distributions, which can be extracted from charge-exchange reactions at intermediate beam energies. Measured Gamow-Teller transition strength distributions for stable pf-shell nuclei are reasonably well reproduced by theoretical calculations in the shell model, except for lower mass nuclei where admixtures from the sd shell can become important.Purpose: This paper presents a ${\ensuremath{\beta}}^{+}$ charge-exchange experiment on $^{45}\mathrm{Sc}$, one of the lightest pf-shell nuclei. The focus was on Gamow-Teller transitions to final states at low excitation energies, which are particularly important for accurate estimations of electron-capture rates at relatively low stellar densities. The experimental results are compared with various theoretical models.Method: The double-differential cross section for the $^{45}\mathrm{Sc}(t,^{3}\mathrm{He}+\ensuremath{\gamma})$ reaction was measured using the NSCL Coupled-Cyclotron Facility at $115\phantom{\rule{4pt}{0ex}}\mathrm{MeV}/u$. Gamow-Teller contributions to the excitation-energy spectra were extracted by means of a multipole-decomposition analysis. $\ensuremath{\gamma}$ rays emitted due to the deexcitation of $^{45}\mathrm{Ca}$ were measured using GRETINA to allow for the extraction of Gamow-Teller strengths from very weak transitions at low excitation energies.Results: Gamow-Teller transition strengths to $^{45}\mathrm{Ca}$ were extracted up to an excitation energy of 20 MeV, and that to the first excited state in $^{45}\mathrm{Ca}$ at 174 keV was extracted from the $\ensuremath{\gamma}$-ray measurement, which, even though weak, is important for the astrophysical applications and dominates under certain stellar conditions. Shell-model calculations performed in the pf shell-model space with the GXPF1A, KB3G, and FPD6 interactions did not reproduce the experimental Gamow-Teller strength distribution, and a calculation using the quasiparticle random phase approximation that is often used in astrophysical simulations also could not reproduce the experimental strength distribution.Conclusions: Theoretical models aimed at describing Gamow-Teller transition strengths from nuclei in the lower pf shell for the purpose of estimating electron-capture rates for astrophysical simulations require further development. The likely cause for the relatively poor performance of the shell-model theory is the influence of intruder configurations from the sd shell. The combination of charge-exchange experiments at intermediate beam energy and high-resolution $\ensuremath{\gamma}$-ray detection provides a powerful technique to identify weak transitions to low-lying final states that are nearly impossible to identify without the coincidences. Identification of these weak low-lying transitions is important for providing accurate electron-capture rates for astrophysical simulations.

Consequences of critical interchain couplings and anisotropy on a Haldane chain

Effects of interchain couplings and anisotropy on a Haldane chain have been investigated by single crystal inelastic neutron scattering and density functional theory (DFT) calculations on the model compound SrNi$_2$V$_2$O$_8$. Significant effects on low energy excitation spectra are found where the Haldane gap ($\Delta_0 \approx 0.41J$; where $J$ is the intrachain exchange interaction) is replaced by three energy minima at different antiferromagnetic zone centers due to the complex interchain couplings. Further, the triplet states are split into two branches by single-ion anisotropy. Quantitative information on the intrachain and interchain interactions as well as on the single-ion anisotropy are obtained from the analyses of the neutron scattering spectra by the random phase approximation (RPA) method. The presence of multiple competing interchain interactions is found from the analysis of the experimental spectra and is also confirmed by the DFT calculations. The interchain interactions are two orders of magnitude weaker than the nearest-neighbour intrachain interaction $J$ = 8.7~meV. The DFT calculations reveal that the dominant intrachain nearest-neighbor interaction occurs via nontrivial extended superexchange pathways Ni--O--V--O--Ni involving the empty $d$ orbital of V ions. The present single crystal study also allows us to correctly position SrNi$_2$V$_2$O$_8$ in the theoretical $D$-$J_{\perp}$ phase diagram [T. Sakai and M. Takahashi, Phys. Rev. B 42, 4537 (1990)] showing where it lies within the spin-liquid phase.

Exploring the 12C(18O,16O)14C two-neutron transfer reaction at energies far above the Coulomb barrier

The 12C(18O,16O)14C two-neutron transfer reaction has been studied at an incident energy of 275 MeV and the ejectiles have been momentum analysed at forward angles by the MAGNEX spectrometer. The identification of the 16O ejectiles was obtained by combining a standard ΔE-E technique with the simultaneous measurement of the angle and the position at the focal plane. The 14C excitation energy spectra have been obtained and several known bound and resonant states of the residual nuclei have been identified. The results have been compared to a previous measurement of the same reaction at 84 MeV incident energy.

Single-particle strength in neutron-rich 71Cu from the (d,3He) proton pick-up reaction

We have measured the 72Zn(d,3He)71Cu proton pick-up reaction in inverse kinematics at 38 MeV/u. A dedicated set-up was developed to overcome the experimental challenges posed by the low cross section of the reaction and the low energy of the outgoing 3He particles. The excitation-energy spectrum was reconstructed and spectroscopic factors were obtained after analysis of the angular distributions in the finite-range Distorted-Wave Born Approximation (DWBA). The results show that unlike for the πf5/2 orbital, the πf7/2 singleparticle strength is not appreciably affected by the addition of neutrons beyond N = 40.

Shell model description of 0 and 1 ℏω states in neutron-rich N = 18 and 19 nuclei with Z = 14 to 19

The low excitation energy spectra of N = 18 and 19 sd-shell isotones are investigated. A detailed comparison experiment versus theory using the PSDPF interaction of the energy spectra for 32Si and 33Si, 33P and 34P, 34S and 35S, 35Cl and 36Cl, 36Ar and 37Ar, 37K and 38K will be presented. Based on this comparison, important predictions will be proposed and the general evolution of the main structure properties in these isotones will be discussed.

First application of then−Be9optical potential to the study of theBe10continuum via the(O18,O17)neutron-transfer reaction

The $^{9}\mathrm{Be}(^{18}\mathrm{O},^{17}\mathrm{O})^{10}\mathrm{Be}$ reaction has been studied at an incident energy of 84 MeV, and the ejectiles have been detected at forward angles. The $^{10}\mathrm{Be}$ excitation energy spectrum has been obtained up to about 18 MeV, and several known bound and resonant states of $^{10}\mathrm{Be}$ have been identified. Calculations that describe the interaction of the neutron removed from the $^{18}\mathrm{O}$ projectile with the $^{9}\mathrm{Be}$ target by means of an optical potential with a semiclassical approximation for the relative motion account for a significant part of the $^{10}\mathrm{Be}$ continuum. Two parametrizations of the optical-model potential for the system $n\text{\ensuremath{-}}^{9}\mathrm{Be}$ have been used and compared.

Diabatic-ramping spectroscopy of many-body excited states

Due to the experimental time constraints of state of the art quantum simulations, the direct preparation of the ground state by adiabatically ramping the field of a transverse-field Ising model becomes more and more difficult as the number of particles increase. We propose a spectroscopy protocol that intentionally creates excitations through diabatic ramping and measures a low-noise observable as a function of time for a constant Hamiltonian to reveal the structure of the coherent dynamics of the resulting many-body states. To simulate experimental data, noise from counting statistics and decoherence error are added. Compressive sensing is then applied to Fourier transform the simulated data into the frequency domain and extract the low-lying energy excitation spectrum. By using compressive sensing, the amount of data in time needed to extract this energy spectrum is sharply reduced, making such experiments feasible with current technology in, for example, ion trap quantum simulators.

Role of tensor force in light nuclei with tensor-optimized shell model

We investigate the structures of light nuclei focusing on the role of the tensor force. We describe the tensor and short-range correlations with the tensor optimized shell model (TOSM) and the unitary correlation operator method (UCOM), respectively. In the TOSM, the 2p2h states are fully optimized to describe the large tensor contribution that brings high momentum components explicitly in the wave function. We use a bare nucleon-nucleon interaction AV8' and discuss the structures of the He and Li isotopes, such as the excitation energy spectra and the radii. We also investigate the structures of 8Be from the ground-band states to the highly excited states. These states of 8Be are indicated to have different structures of the 2α clustering states and the shell-model like states.

Bond operator theory of Heisenberg ferrimagnetic spin chain

Abstract The bond operator theory is applied to study Heisenberg ferrimagnetic spin chain. We observe four branches of excited spectrum, the gap of excited spectrum and energy spectrum at T = 0 K . The energy gap is 1.64, which agrees quite well with the established numerical results. At finite temperature, the energy gaps, uniform susceptibility, internal energy and specific heat are calculated respectively. These results qualitatively agree with numerical results by other methods quite well.

PbMoO4:Eu3+ red phosphor material for potential applications in white light emitting diodes

Monophasic PbMoO4 possessing tetragonal symmetry with varied Eu3+ concentrations is synthesized by solid state reaction method. The samples are characterized by X-ray diffraction, scanning election microscope, energy dispersive spectra, excitation spectra, emission spectra and decay curves. Single cubic phase of PbMoO4 crystal is confirmed by X-ray diffraction analysis. Analysis of the photoluminescence spectra indicates that the phosphor can be excited by UV light of 386 nm, thus emitting intense red light. The ratio of red emission (5D0 → 7F2) to orange emission (5D0 → 7F1) is very high in present phosphor. This may be due to a lower symmetry of crystal field around Eu3+ ions. The color coordinates are calculated for PbMoO4:Eu3+ phosphor located in International Commission on Illumination chromaticity diagram.