Laser induced collisional energy transfer in Sr—Li system

A four-state model considering the relative velocity distribution function for calculating the cross section of laserinduced collisional energy transfer in a Sr-Li system is presented and profiles of laser-induced collision cross section are obtained.The resulting spectra obtained from different intermediate states are strongly asymmetrical in an opposite asymmetry.Both of the two intermediate states have contributions to the final state,and none of the intermediate states should be neglected.The peak of the laser-induced collisional energy transfer(LICET) profile shifts toward the red and the FWHM becomes narrower obviously with laser field intensity increasing.A cross section of 1.2 × 10-12 cm 2 at a laser field intensity of 2.17 × 10 7 V/m is obtained,which indicates that this collision process can be an effective way to transfer energy selectively from a storage state to a target state.The existence of saturation for cross section with the increase of the laser intensity shows that the high-intensity redistribution of transition probabilities is an important feature of this process,which is not accounted for in a two-state treatment.     

COHERENT POPULATION TRAPPING IN THE SYSTEM OF A Λ-CONFIGURATION MULTILEVEL ATOM DRIVEN BY A TWO-MODE QUANTIZED FIELD

We have studied the atomic coherent population trapping in the system of a two-mode quantized field interacting with a Λ-configuration multilevel atom with one lower discrete state mad two sets of quasicontinuum states, or a set of quasicontinuum states and a set of true continuum states. The influence of the atom's initial preparation and the properties of the atomic upper levels on whether or not atomic coherent population trapping occurs, and the states of the field which trap the atom are analyzed.     

Theoretical Study on the Spectroscopic Parameters and Transition Properties of MgH Radical Including Spin-orbit Coupling

An accurate theoretical study on the MgH radical is reported by adopting the high-level relativistic MRCI+Q method with a quintuple-zeta quality basis set.The reliable potential energy curves of the five AS states of MgH are derived.Then the associated spectroscopic parameters are determined and found to be in good accordance with the available experimental results.The permanent dipole moments(PDMs) and the spin-orbit(SO) matrix elements of A-S states are computed.The results show that the abrupt changes of PDMs and SO matrix elements are attributed to the variations of electronic configurations at the avoided crossing point.The SOC effect leads to the five AS states split into ten Ω states and results in the double potential well of(2)1/2 state.Finally,the transition properties from the(2)1/2,(1)3/2 and(3)1/2 states to the ground state X~2 Σ+1/2 transitions are obtained,including the transition dipole moments,Franck-Condon factors and radiative lifetimes.     

Physical Properties Revealed by Transport Measurements for Superconducting Nd_(0.8)Sr_(0.2)NiO_2 Thin Films

The newly discovered superconductivity in infinite-layer nickelate superconducting films has attracted much attention,largely because their crystalline and electronic structures are similar to those of high-T_c cuprate superconductors.The upper critical field can provide a great deal of information on the subject of superconductivity,but detailed experimental data are still lacking for these films.We present the temperature-and angle-dependence of resistivity,measured under different magnetic fields H in Nd_(0.8)Sr_(0.2)NiO_2 thin films.The onset superconducting transition occurs at about 16.2 K at 0 T.Temperature-dependent upper critical fields,determined using a criterion very close to the onset transition,show a clear negative curvature near the critical transition temperature,which can be explained as a consequence of the paramagnetically limited effect on superconductivity.The temperaturedependent anisotropy of the upper critical field is obtained from resistivity data,which yields a value decreasing from 3 to 1.2 with a reduction in temperature.This can be explained in terms of the variable contribution from the orbital limit effect on the upper critical field.The angle-dependence of resistivity at a fixed temperature,and at different magnetic fields,cannot be scaled to a curve,which deviates from the prediction of the anisotropic Ginzburg-Landau theory.However,at low temperatures,the resistance difference can be scaled via the parameter Hβ| cos θ|(β=6-1),with θ being the angle enclosed between the c-axis and the applied magnetic field.As the first detailed study of the upper critical field of nickelate thin films,our results clearly indicate a small anisotropy,and a paramagnetically limited effect,in terms of superconductivity,in nickelate superconductors.     

About the Morin transition in hematite in relation with particle size and aluminium substitution

The results of a M?ssbauer study of the Morin transition behaviour in three series of hematite and Al-hematite samples are reviewed and discussed. The first two series comprise small-particle hematites and Al-hematites prepared from decomposition of lepidocrocite, whereas in the third series Al-hematites up to the μm range are obtained from co-precipitated oxinates. It is demonstrated that the Morin transition temperature follows quite well the overall properties of the samples such as particle size and Al substitution, while the transition region is rather determined by all kind of distributive effects. A model involving intermediate states is suggested for the Morin transition behaviour in non-ideal hematite. Presented at the International Colloquium “M?ssbauer Spectroscopy in Materials Science”, Velké Losiny, Czech Republic, 3–8 September 2000. Finacial support from the FWO-Flanders (project G.000797) and the Belgian Federal Interuniversity Attraction Pole (PAI/UIAP) on reduced dimensionalities is acknowledged.     

Even-parity states of the Sm atom with stepwise excitation

Two-colour stepwise excitation and photoionization schemes are adopted to study the spectra of high-lying states of the Sm atom. These bound even-parity states are excited with three different excitation paths from the 4f66s6p7DJ (J = 1, 2, 3) intermediate states, respectively. They are probed by photoionization process with an extra photon driving them to the continuum states. In this experiment, 270 states are detected in an energy range from 36160 cm-1 to 42250 cm-1, 109 of which are newly discovered, while the rest of them are confirmed to be the energy levels reported previously. Furthermore, based on the J-momentum selection rules of three excitation paths, a unique assignment of J-momentum for all observed states is determined, eliminating all remaining ambiguities in the literature. Finally, 53 single-colour transitions originating from the scanning laser are also identified. For all the relevant transitions, the information about their relative intensities is also given in the paper.     

Bose–Einstein condensates in an eightfold symmetric optical lattice

We investigate the properties of Bose–Einstein condensates(BECs) in a two-dimensional quasi-periodic optical lattice(OL) with eightfold rotational symmetry by numerically solving the Gross–Pitaevskii equation. In a stationary external harmonic trapping potential, we first analyze the evolution of matter-wave interference pattern from periodic to quasiperiodic as the OL is changed continuously from four-fold periodic to eight-fold quasi-periodic. We also investigate the transport properties during this evolution for different interatomic interaction and lattice depth, and find that the BEC crosses over from ballistic diffusion to localization. Finally, we focus on the case of eightfold symmetric lattice and consider a global rotation imposed by the external trapping potential. The BEC shows vortex pattern with eightfold symmetry for slow rotation, becomes unstable for intermediate rotation, and exhibits annular solitons with approximate axial symmetry for fast rotation. These results can be readily demonstrated in experiments using the same configuration as in Phys. Rev.Lett. 122 110404(2019).     

Quantum transport signatures of non-trivial topological edge states in a ring-shaped Su–Schrieffer–Heeger double-chain system

In the ring-shaped Su–Schrieffer–Heeger(SSH)double-chain,the quantum interference between the two different electron tunneling paths of the upper and lower chains has an important influence on the electron transport properties of non-trivial topological edge states.Here,we have studied the electron transport signatures of non-trivial topological edge states in a ring-shaped SSH double-chain system based on the wave-guide theory and transfer-matrix method.In the ringshaped SSH double-chain with the upper chain being different from the lower one,it is demonstrated that the electron transmission probability displays the four and two resonance peaks associated with the non-trivial topological edge states in the weak and strong coupling regimes,respectively.Whereas in the case of the upper chain being the same as the lower one,the two transmission resonance peaks associated with the non-trivial topological edge states in the weak coupling regime are only found,and that in the strong coupling regime disappear that originated from the destructive interference between the two different electron tunneling paths of the upper and lower chains.Consequently,the variation of the number of transmission resonance peaks associated with the non-trivial topological edge states in the weak and strong coupling regimes suggests that an alternative scheme for detecting non-trivial topological edge states in the ring-shaped SSH doublechain system.     

Tunable charge density wave in TiS_3 nanoribbons

Recently, modifications of charge density wave(CDW) in two-dimensional(2D) show intriguing properties in quasi-2D materials such as layered transition metal dichalcogenides(TMDCs). Optical, electrical transport measurements and scanning tunneling microscopy uncover the enormous difference on the many-body states when the thickness is reduced down to monolayer. However, the CDW in quasi-one-dimensional(1D) materials like transition metal trichalcogenides(TMTCs) is yet to be explored in low dimension whose mechanism is likely distinct from their quasi-2D counterparts.Here, we report a systematic study on the CDW properties of titanium trisulfide(TiS_3). Two phase transition temperatures were observed to decrease from 53 K(103 K) to 46 K(85 K) for the bulk and 15-nm thick nanoribbon, respectively,which arises from the increased fluctuation effect across the chain in the nanoribbon structure, thereby destroying the CDW coherence. It also suggests a strong anisotropy of CDW states in quasi-1D TMTCs which is different from that in TMDCs.Remarkably, by using back gate of-30 V ～ 70 V in 15-nm device, we can tune the second transition temperature from110 K(at-30 V) to 93 K(at 70 V) owing to the altered electron concentration. Finally, the optical approach through the impinging of laser beams on the sample surface is exploited to manipulate the CDW transition, where the melting of the CDW states shows a strong dependence on the excitation energy. Our results demonstrate TiS_3 as a promising quasi-1D CDW material and open up a new window for the study of collective phases in TMTCs.     

孤立条件下布洛芬分子手性转变过程的理论研究

基于密度泛函理论的B3LYP方法,采用6-31+g(d,p)基组,对孤立条件下布洛芬分子的手性转变过程进行研究.通过寻找反应过程中包括过渡态和中间体的各极值点结构,绘制了布洛芬分子手性转变路径反应势能面,分析了各极值点的几何和电子结构特性.结果表明:布洛芬实现从S型到R型手性转变的反应路径有两条.路径1包括三个过渡态和两个中间体,路径2包括四个过渡态和三个中间体.反应路径上最大的能垒是73.54 Kcal/mol,来源于手性碳上的氢向羧基上的氧转移.这一研究为进一步实现一些有重要应用价值的点手性分子手性转变反应调控提供了理论参考.     

Probing configuration mixing in 12Be with Gamow-Teller transition strengths

We present a novel technique for studying the quenching of shell gaps in exotic isotopes. The method is based on extracting Gamow-Teller (ΔL=0, ΔS=1) transition strengths [B(GT)] to low-lying states from charge-exchange reactions at intermediate beam energies. These Gamow-Teller strengths are very sensitive to configuration mixing between cross-shell orbitals, and this technique thus provides an important complement to other tools currently used to study cross-shell mixing. This work focuses on the N=8 shell gap. We populated the ground and 2.24 MeV 0+ states in 12Be using the 12B(1+) (7Li, 7Be) reaction at 80 MeV/u in inverse kinematics. Using the ground-state B(GT) value from β-decay measurements (0.184±0.007) as a calibration, the B(GT) for the transition to the second 0+ state was determined to be 0.214±0.051. Comparing the extracted Gamow-Teller strengths with shell-model calculations, it was determined that the wave functions of the first and second 0+ states in 12Be are composed of 25±5% and 60±5% (0s)4(0p)8 configurations, respectively.     

Manipulating the phase of a single-mode micromaser by polarized three-level atoms

We investigate the phase probability distribution (PPD) of a single-mode micromaser pumped by atoms injected in the most general case, i.e. in the superposition of the upper, intermediate and lower states by the Monte Carlo wave function approach. The phase properties of the cavity mode are greatly influenced by the relative phases and the amplitudes of the polarized atoms, and the detunings between the atom and cavity. The cavity field has a single preferred phase if the cavity is pumped by the atoms in the superposition of the upper and intermediate states or of the intermediate and lower states. However, a double-peak feature appears in the PPD of the cavity field when the cavity is pumped by the atoms in the superposition of the upper and lower states. With appropriate detunings, the double peaks become narrower and more remarkable, which shows the better defined phase of the cavity field, as compared to the resonant case. The PPD displays complicated characteristics when the cavity is pumped by the atoms in the superposition of the upper, intermediate and lower states. The phase distribution changes from a single peak to double peaks and to another single peak when we modulate the phase of the intermediate state, which has been explained in the semi-classical radiation theory.     

Nonperturbative coherent population trapping: an analytic model

Coherent population trapping is shown to occur in a driven symmetric double-well potential in the strong-field regime. The system parameters have been chosen to reproduce the 0(-) <--> 3(+) transition of the inversion mode of the ammonia molecule. For a molecule initially prepared in its lower doublet we find that, under certain circumstances, the 3(+) level remains unpopulated, and this occurs in spite of the fact that the laser field is resonant with the 0(-) <--> 3(+) transition and intense enough so as to strongly mix the 0(+) and 0(-) ground states. This counterintuitive result constitutes a coherent population trapping phenomenon of nonperturbative origin which cannot be accounted for with the usual models.     

Density structures and giant vortex in spin-orbit coupled Bose-Einstein condensates with the harmonic-plus-radial potential

We study the ground-state properties of two-dimensional Bose-Einstein condensate with spin-orbit coupling (SOC) loaded in the harmonic-plus-radial potential. In the immiscible regime, odd-petal-number states can be found. By increasing the effective atom interactions, the odd-petal-number states transform into a phase where petals in the outer annular potential trough are coexisting with inner longitudinal stripes, and finally become the ‘serpentine’ stripe structures. In a rotating system, the giant vortex (GV) can be stabilized and controllable. The favorable conditions for GV are relatively small atom interactions, intermediate rotation frequency and intermediate SOC strength. Further, this type of harmonic-plus-radial trapping with a strong radial part is a suitable choice to create GV state.     

Search for exchange-antisymmetric states for spin-0 particles at the 10(-11) level

We set a new upper limit of 1.7x10(-11) to the probability that two spin-0 16O nuclei are in forbidden exchange-antisymmetric states, testing the validity of fundamental principles of quantum mechanics. A newly designed difference-frequency spectrometer is used to look for the existence of these states. The experimental test was performed by tuning the spectrometer across a molecular transition of 12C 16O (2) belonging to the rovibrational band at 4.25 microm, connecting the forbidden states (00(0)0,J = 25) and (00(0)1,J = 26).     

Renormalization group analysis of the random first-order transition

We consider the approach describing glass formation in liquids as a progressive trapping in an exponentially large number of metastable states. To go beyond the mean-field setting, we provide a real-space renormalization group (RG) analysis of the associated replica free-energy functional. The present approximation yields in finite dimensions an ideal glass transition similar to that found in the mean field. However, we find that along the RG flow the properties associated with metastable glassy states, such as the configurational entropy, are only defined up to a characteristic length scale that diverges as one approaches the ideal glass transition. The critical exponents characterizing the vicinity of the transition are the usual ones associated with a first-order discontinuity fixed point.     

A new interactive thermoluminescence mixed-order glow curve deconvolution function

An interactive mixed-order thermoluminescence (TL) glow curve deconvolution function is presented for the first time in which the retrapping of thermally stimulated charge carriers in deep traps during the heating stage is taken into account. Considering this transition in the set of differential equations by describing the TL process and by solving them, an analytical function for TL intensity was obtained. This equation reduces to the known deconvolution function for the mixed-order model in the limiting case of saturation of deep trapping (DT) states. In intermediate cases, where the DT states are partially occupied, the proposed function acts as a real interactive model which allows the thermally stimulated electrons to be retrapped to deep electron traps. Applicability of the proposed model in a real TL system is also presented and discussed.     

The laser-induced fluorescence spectroscopy of CoF in the ultra violet region

The laser-induced fluorescence (LIF) spectrum of jet-cooled CoF has been obtained in the wavelength region of 260-290 nm for the first time. Seventeen vibronic bands were observed and assigned to three types of transition from the ground state to upper states Ω′ = 3, 4, 5 by rotational analysis. A new vibrational transition with the 0-0 band at 34697.22 cm⁻¹ has been assigned as the [34.7]³Γ₅-X³Φ₄ transition and effective equilibrium molecular constants for the upper state have been determined. In addition, lifetime measurements have been carried out for most of the bands under collision-free conditions. On the basis of the spectroscopic data and lifetime measurements, the electronic structures of these possible high-lying electronic states are discussed.     

Sum rules for radiative quarkonium decays from short-range interactions

Sum rules previously derived for proton decay are extended and applied to treat effects of bound states spectroscopy on radiative quarkonium decays. The transition involves boson (photon or pion) emission followed by quark annihilation. Sum rules for the contributions from different intermediate bound states are derived by using closure and the assumptions (1) that the boson emission is described by a plane wave or multipole operator which satisfies a wave equation, and (2) that the annihilation depends on the bound state wave function or its derivative at the origin.