ROOM TEMPERATURE LIGHT-THERMO-DETECTOR MADE OF HIGH-Tc SUPERCONDUCTOR

Based on the anisotropic Seebeck tensor coefficients, a light-thermo-radiation detector made of high-T_c superconductor (YBa₂Cu₃O_7-δ) was fabricated, which can function at room temperature. The induced voltaic signals at various modulation frequencies for radiation from He-Ne laser and from a 500 K black body were measured. The noise ratio for detecting He-Ne laser radiation and the D^* for black body were evaluated. Compared with bolometer made of high-T_c superconductor which functions at liquid nitrogen, and with pyroelectric detector, it was found that the advantages of this new device are that the device can work at room temperature with very low noise and very fast response. Although having a lower D^* value than that of bolometer for the present device construction, we point out the possibility and the direction for improving the D^* value, hence the promising prospect of this kind of device.     

X_0(2900) and its heavy quark spin partners in molecular picture

The X₀(2900),recently observed by the LHCb Collaboration in the D-K+invariant mass of the B+→D+D-K+process,is the first exotic candidate with four different flavors,beginning a new era for the hadron community.Under the assumption that the Xo(2900)is a I(J^P)=0(0+)D*K* hadronic molecule,we extracted the whole heavy-quark symmetry multiplet formed by the(D,D*)doublet and the K*meson.For the bound state case,there would be two additional I(J^P)=0(1+)hadronic molecules associated with the DK*and D*K*channels,as well as one additional I(J^P)=0(2+)D*K*molecule.In the light quark limit,they are 36.66 MeV and 34.22 MeV below the DK*and D*K*thresholds,respectively,which are unambiguously fixed by the mass position of the Xo(2900).For the virtual state case,there would be one additional I(J^P)=0(1+)hadronic molecule,strongly coupled to the DK*channel,and one additional I(J^P)=0(2+)D*K*molecule.Searching for these heavy quark spin partners will help shed light on the nature of the X₀(2900).     

Spontaneous U（1） symmetry breaking and Bose-Einstein condensation

Based on Bogoliubov's truncated Hamiltonian H_B for a weakly interacting Bose system, and adding a U(1) symmetry breaking term $\sqrt{V}(\lambda a₀+\lambda^*a₀⁺) to H_B, we show by using the coherent state theory and the mean-field approximation rather than the c-number approximations, that the Bose--Einstein condensation(BEC) occurs if and only if the U(1) symmetry of the system is spontaneously broken. The real ground state energy and the justification of the Bogoliubov c-number substitution are given by solving the Schr\"{o}dinger eigenvalue equation and using the self-consistent condition.     

Exploring hidden-charm and hidden-strange hexaquark states from lattice QCD

Based on five different ensembles of newly generated (2+1)-flavor configurations with pion mass of approximately m_π■(140-310) MeV, we present a lattice analysis of hidden-charm and hidden-strange hexaquarks with the quark content ■. The correlation matrices of two types of operators with J^PC=0⁺⁺, 0^-+, 1⁺⁺ and 1^-- are simulated to extract the masses of the hexaquark candidates, which are subsequently extrapolated to the physical pi...     

Weak decays of doubly heavy baryons:Bcc→BD*

The discovery of Ξ_cc⁺⁺has inspired new interest in studying doubly heavy baryons.In this study,the weak decays of a doubly charmed baryon B_ccto a light baryon B and a charm meson D^*(either a pseudoscalar or a vector one)are calculated.Following our previous work,we calculate the short distance contributions under the factorization hypothesis,whereas the long distance contributions are modeled as the final state interactions,which are calculated with the one particle exchange model.We find that the B_cc→BD^*decays'branching ratios are obviously larger,as they receive contributions of more polarization states.Among the decays that we investigate,the following have the largest branching fractions:BR(Ξ_cc⁺⁺→∑⁺D^*+)∈[0.46%,3.33%]estimated with τΞ_cc⁺⁺=256 fs;BR(Ξ_cc⁺→AD^*+)∈[0.38%,2.63%]and BR(Ξ_cc⁺→∑⁰D^*+)∈[0.45%,3.16%]with τΞ_cc⁺⁺=45 fs;and BR(Ω_cc⁺→Ξ⁰D⁺)∈[0.27%,1.03%),BR(Ω_cc⁺→∑⁰D^*+)∈[0.07%,0.44%],and BR(Ω_cc⁺→∑⁰D^*+)∈[0.06%,0.45%] with τ_(Ω_cc)⁺=75 fs.By comparing the decay widths of pure color commensurate channels with those of pure bow-tie ones we find that the bow-tie mechanism plays an important role in charm decays.     

Double-heavy tetraquark states with heavy diquark-antiquark symmetry

We calculate the masses of the QQqq(Q=c,b:q=u,d,s)tetraquark states with the aid of heavy diquark-antiquark symmetry(HDAS)and the chromomagnetic interaction(CMI)model.The masses of the highestspin(J=2)tetraquarks that have only the(QQ)(3):(qq)₃.color structure are related with those of conventional hadrons using HDAS.Thereafter,the masses of their partner states are determined with the mass splittings in the CMI model.Our numerical results reveal that(i)the lightest ccnn(n=u,d)is an I(J^P)=0(1⁺)state around 3929 MeV(53 MeV above the DD^* threshold),and none of the double-charm tetraquarks are stable;(ii)the stable double-bottom tetraquarks are the lowest 0(1⁺)bbin around 10488 MeV(≈116 MeV below the BB^*threshold)and the lowest 1/2(1⁺)bbns around 10671 MeV(≈20 MeV below the BB_s^*/B_sB^*threshold);and(iii)the two lowest bcnn tetraquarks,namely the lowest 0(0⁺)around 7167 MeV and the lowest 0(1)around 7223 MeV,are in the nearthreshold states.Moreover,we discuss the constraints on the masses of double-heavy hadrons.Specifically,for the lowest nonstrange tetraquarks,we obtain T_cc<3965 MeV,T_bb<10627 MeV,and T_bc<7199 MeV.     

Semileptonic decays B/Bs→(D?,D?s)lνl in the PQCD approach with the lattice QCD input

We study the semileptonic B/Bs→(D^?,D^?s)lνl decays in the framework of the Standard Model(SM),by employing the perturbative QCD(PQCD)factorization formalism combined with the lattice QCD input for the relevant transition form factors.We calculate the branching ratios B(B(s)→D^?(s)lνl)with l=(e,μ,τ),the ratios of the branching fractions R(D^?)and R(D^?s),and the physical observables Pτ(D^?(s)),FL(D?(s))and AFB(τ).The“PQCD+Lattice”predictions for B(B→D^?lνl)and R(D^?)agree with the available experimental measurements within errors.For the ratios R(Ds)and R(D^?s),the"PQCD+Lattice"predictions agree with the other predictions.For Pτ(D^?)and FL(D^?),our theoretical predictions agree with the measured values within errors.Our theoretical predictions of the semileptonic B/Bs decays considered could be tested in the near future by the LHCb and Belle II experiments.     

Diagonal reflection symmetries and universal four-zero texture

In this paper,we consider a set of new symmetries in the SM:diagonal reflection symmetries Rm_u,v^*,R=m_u,v,m_d,e^*=mde with R=diag(-1,1,1).These generalized CP symmetries predict the Majorana phases to beα_2.3/2-0π/2.Realization of diagonal reflection symmetries implies a broken chiral U(1)po symmetry only for the first generation.The axion scale is suggested to be(θ_u,d)~△GuT√m_{u,dm_(c,s})/v-10¹²[GeV].By combining the symmetries with the four-zero texture,the mass eigenvalues and mixing matrices of quarks and leptons are reproduced well.This scheme predicts the normal hierarchy,the Dirac phase ocp≈203°,and|ml|≈2.5 or 6.2[meV].In this scheme,the type-I seesaw mechanism and a given neutrino Yukawa matrix Y_ycompletely determine the structure of the right-handed neutrino mass M_R.A u-y unification predicts the mass eigenvalues to be(M_RI,M_R2,M_R3)=(O(10⁵).O(10⁹),O(10¹⁴)[Gev].     

A density-wave-like transition in the polycrystalline V3Sb2 sample with bilayer kagome lattice

Recently,transition-metal-based kagome metals have aroused much research interest as a novel platform to explore exotic topological quantum phenomena.Here we report on the synthesis,structure,and physical properties of a bilayer kagome lattice compound V₃Sb₂.The polycrystalline V₃Sb₂ samples were synthesized by conventional solid-state-reaction method in a sealed quartz tube at temperatures below 850℃.Measurements of magnetic susceptibility and resistivity revealed consistently a density-wave-like transition at Tdw≈160 K with a large thermal hysteresis,even though some sample-dependent behaviors were observed presumably due to the different preparation conditions.Upon cooling through Tdw,no strong anomaly in lattice parameters and no indication of symmetry lowering were detected in powder x-ray diffraction measurements.This transition can be suppressed completely by applying hydrostatic pressures of about 1.8 GPa,around which no sign of superconductivity was observed down to 1.5 K.Specific-heat measurements revealed a relatively large Sommerfeld coefficientγ=18.5 mJ·mol^-1·K^-2,confirming the metallic ground state with moderate electronic correlations.Density functional theory calculations indicate that V₃Sb₂ shows a non-trivial topological crystalline property.Thus,our study makes V₃Sb₂ a new candidate of metallic kagome compound to study the interplay between density-wave-order,nontrivial band topology,and possible superconductivity.     

GINZBURG-LANDAU THEORY AND VORTEX LATTICE OF HIGH-TEMPERATURE SUPERCONDUCTORS

The thermodynamics of the vortex lattice of high-temperature superconductors has been studied by solving the generalized Ginzburg-Landau equations derived microscopically. Our numerical simulation indicates that the structure of the vortex lattice is oblique at the temperature far away from the transition temperature T_c, where the mixed s-d_x²-y² state is expected to have the lowest energy. Whereas, very close to T_c, the d_x²-y² wave is slightly lower energetically, and a triangular vortex lattice recovers. The coexistence and the coupling between the s and d waves would account for the unusual dynamic behaviours such as the upward curvature of the upper critical field curve H_C2(T), as observed in dc magnetization measurements on single-crystal YBa₂Cu₃O₇ samples.     

EFFECTIVE POTENTIAL OF λφ41+3 AT ZERO AND FINITE TEMPERATURES

The effective potential of $\lambda$$\varphi$⁴₁₊₃ model with both signs of parameter m² is evaluated at T=0 by means of a simple but effective method for regularization and renormalization. Then at T≠0, the effective potential is evaluated in imaginary time Green function approach, using the Plana formula. A critical temperature for restoration of symmetry breaking in the standard model of particle physics is estimated to be T_c≌510 GeV.     

RAMAN STUDY ON $X_i^-$(Pb) CENTERS IN SINGLE CRYSTALS OF ALKALI HALIDES DOPED WITH LEAD

Low frequency modes were observed in a series of alkali halides doped with lead after X-irradiation at 77K. The peak positions of the Raman signals are at 34cm^-1 for NaCl:Pb²⁺, 30cm^-1 for KCl:Pb²⁺,28cm^-1 for RbCl:Pb²⁺ and 22cm^-1 for KBr:Pb²⁺. They are assigned to the inelastic light scattering caused by the local vibration of X^-_i (Pb⁺) center, which consists of an interstitial halogen ion stabilized by a substitutional ion Pb⁺ . Polarized Raman measurements and Behavior Typer(BT) analysis show that the symmetry of the X^-_i (Pb⁺) center belongs to the point group C_3v A structure model of the X^-_i (Pb⁺) center is proposed based on the Raman data and the result of BT analysis.     

Isospin-conserving hadronic decay of the Ds1(2460) into Dsπ+π-

The internal structure of the charm-strange mesons D_s0^*(2317) and D_s1(2460) are the subject of intensive studies.Their widths are small because they decay dominantly through isospinbreaking hadronic channels D_s0^*(2317)⁺→D_s⁺π⁰ and D_s1(2460)⁺→D_s^*+π⁰.The D_s1(2460) can also decay into the hadronic final states D_s⁺ππ...     

Filamentation-assisted fourth-order nonlinear process in KTP crystal

We present an experimental investigation of a filamentation-assisted fourth-order nonlinear optical process in KTP crystals pumped by intense 1.53~eV (807~nm) femtosecond laser pulses. Femtosecond light pulses at 2.58~eV (480~nm) are generated by the fourth-order nonlinear polarization (P⁴(ω ₂ ) = χ ⁴(ω ₂ ,ω ,ω ,ω ,- ω ₁ )E³(ω )E^* (ω ₁ ), where E(ω ) corresponds to the pump frequency and E(ω ₁ ) to the supercontinuum generated through filamentation). If the system is seeded by a laser beam at ω ₁ or ω ₂ and there are spatial and temporal overlaps with the pump beam, E(ω ₁ ) and E(ω ₂ ) are simultaneously amplified. When the intensity of the seed laser beam exceeds a certain intensity threshold, the contribution of P⁴(ω ) = χ ⁴(ω ,ω ₁ ,ω ₂ ,-ω, - ω )E(ω ₁ )E(ω ₂ )(E^* (ω))² becomes non-negligible, and the amplification weakens. The conversion efficiency from the pump to the signal at 2.58~eV (480~nm) attains to 0.1%.     

Observational constraints on the accelerating universe in the framework of a 5D bounce cosmological model

In the framework of a five-dimensional (5D) bounce cosmological model, a useful function f(z) is obtained by giving a concrete expression of deceleration parameter q(z)=q₁+{q₂}/{1+ln (1+ z)}. Then using the obtained Hubble parameter H(z) according to the function f(z), we constrain the accelerating universe from recent cosmic observations: the 192 ESSENCE SNe Ia and the 9 observational H(z) data. The best fitting values of transition redshift z_T and current deceleration parameter q₀ are given as z_T= 0.65_-0.12^0.25 and q₀ = - 0.76_-0.15^+0.15 (1σ). Furthermore, in the 5D bounce model it can be seen that the evolution of equation of state (EOS) for dark energy w_de can cross over -1 at about z=0.23 and the current value w_0de= - 1.15<- 1. On the other hand, by giving a concrete expression of model-independent EOS of dark energy w_de, in the 5D bounce model we obtain the best fitting values z_T= 0.66_0.08^+0.11 and q₀ = - 0.69_0.10^+0.10 (1σ) from the recently observed data: the 192 ESSENCE SNe Ia, the observational H(z) data, the 3-year Wilkinson Microwave Anisotropy Probe (WMAP), the Sloan Digital Sky Survey (SDSS) baryon acoustic peak and the x-ray gas mass fraction in clusters.     

Neutrino mixing matrix and masses from a particular two-zero texture based on A4 symmetry

The current study aims to investigate the particular case of two zeros in a Majorana neutrino mass matrix based on A₄ symmetry,where charged lepton mass matrix is diagonal.The texture is ■ with(μ,μ) and(τ,τ) vanishing element of the neutrino mass matrix.The texture ■ has magic and μ-τ symmetry,with a tribimaximal form of the mixing matrix,which leads to θ₁₃=0 that it is not consistent with experimental data and at first,does not seem to be allowed.Since θ₁₃ a sma...     

Self-organized criticality in multi-pulse gamma-ray bursts

The variability in multi-pulse gamma-ray bursts(GRBs)may help to reveal the mechanism of underlying processes from the central engine.To investigate whether the self-organized criticality(SOC)phenomena exist in the prompt phase of GRBs,we statistically study the proper ties of GRBs with more than 3 pulses in each burst by fitting the distributions of several observed physical variables with a Markov Chain Monte Carlo approach,including the isotropic energy E_iso,the duration time T,and the peak count rate P of each pulse.Our sample consists of 454 pulses in 93 GRBs observed by the CGRO/BATSE satellite.The best-fitting values and uncertainties for these power-law indices of the differential frequency distributions are:α_E^d=1.54±0.09,α_T^d=1.82_-0.15^+0.14andα_P^d=2.09_-0.19^0.18,while the power-law indices in the cumulative frequency distributions are:α_E^c=1.44_-0.10^+0.08,α_T^c=1.75_-0.13^0.11andα_P^c=1.99_-0.19^+0.16.We find that these distributions are roughly consistent with the physical framework of a Fractal-Diffusive,Self^Organized Criticality(FD-SOC)system with the spatial dimension S=3 and the classical diffusionβ=1.Our results support that the jet responsible for the GRBs should be magnetically dominated and magnetic instabilities(e.g.,kink model,or tearing-model instability)lead the GRB emission region into the SOC state.     

Superconducting Properties and Absence of Time Reversal Symmetry Breaking in the Noncentrosymmetric Superconducting Compounds TaxRe1-x(0.1≤x≤0.25)

Unconventional superconductivity,in particular,in noncentrosymmetric systems,has been a long-sought topic in condensed matter physics.Recently,Re-based superconductors have attracted great attention owing to the potential time-reversal symmetry breaking in their superconducting states.We report the superconducting properties of noncentrosymmetric compounds Ta_xRe_1-x with 0.1 ≤x≤0.25,and find that the superconducting transition temperature reaches a maximum of ~8 K at the optimal level x=0.15.Nevertheless,muon-spin rotation and relaxation measurements reveal no time-reversal symmetry breaking existing in its superconducting state,which is in sharp contrast to both centrosymmetric Re metal and many other noncentrosymmetric Re-based superconductors.     

Evidence for a High-Pressure Isostructural Transition in Nitrogen

We observed an isostructural phase transition in the solid nitrogen λ-N₂ at approximately 50 GPa accompanied by anomalies in lattice parameters, atomic volume and Raman vibron modes. The anomalies are ascribed to a slight reorientation of the nitrogen molecules, which does not seem to affect the monoclinic symmetry(space group p2_1/c). Our ab initio calculations further confirm the phenomena, and suggest an optimized structure for the λ-N₂ phase. In addition, a ne...     

Magnetic and electric properties of transition-metal doped wurtzite CdSe from first-principles calculations

The geometrical structures of Cd_0.75TM_0.25Se (TM = Ti, V, Cr and Mn) are optimized, and then their electric and magnetic properties are investigated by performing first-principles calculations within the generalized gradient approximation for the exchange--correlation function based on density functional theory. Cd_0.75TM_0.25Se (TM = Ti and V) are found to have high spin-polarization near 100% at the Fermi level. Cd_0.75TM_0.25Se (TM = Cr and Mn) are half-metallic ferromagnets whose spin-polarization at the Fermi level is absolutely +100%. The supercell magnetic moments of Cd_0.75Cr_0.25Se and Cd_0.75Mn_0.25Se are 4.00 and 5.00~μ_B, which arise mainly from Cr-ions and Mn-ions, respectively. The half-metallicity of Cd_0.75Cr_0.25Se is more stable than that of Cd_0.75Mn_0.25Se. The electronic structures of Cr-ions and Mn-ions are Cr e_g²↑ t_2g²↑ and Mn e_g²↑ t_2g³↑, respectively.