Influence of the Pseudogap on the Inelastic Neutron Scattering Spectra of the Underdoped Lanthanum Cuprate

The influence of pseudogap on the inelastic neutron scattering spectra of the underdoped lanthanum cuprate is studied on the basis of the model which incorporates both the superconducting state and pseudogap state.It is found that the striking effects of the influence of the pseudogap on the incommensurability of the spin excitation spectrum are that in the superconducting state the pseudogap makes the intensity of the incommensurate peak increase,in the normal state the pseudogap not only makes the intensity of the incommensurate peak increase,but also sharpens the incommensurate peak and increases incommensurability.     

Quantum Phase Transition in Quasi-two-dimensional Heisenberg Antiferromagnet with Single-Ion Anisotropy

In the present paper, we investigate the quantum phase transition in a spatially anisotropic antiferrornagnetic Heisenberg model of S =1 with single-ion energy anisotropy. By using the Schwinger boson representation, we calculate the Gaussian correction to the critical value J⊥^c caused by quantum spin fluctuations. We find that, for the positive single-ion energy, a nonzero value of J⊥^c is always needed to stabilize the antiferromagnetic long-range order in this model. It resolves a difference among literature and shows clearly that the effect of quantum fluctuations may qualitatively change a result obtained by the mean-field theories on lower-dimensional systems.     

Exploring J/ψ Production Mechanism at the Future Electron-Ion Collider

We propose to use transverse momentum p_T distribution of J/ψ production at the future Electron Ion Collider(EIC) to explore the production mechanism of heavy quarkonia in high energy collisions.We apply QCD and QED collinear factorization to the production of a cc pair at high p_T,and non-relativistic QCD factorization to the hadronization of the pair to a J/ψ.We evaluate J/ψ p_T-distribution at both leading and next-to-leading order in strong coupling,and show that production rates for various color-spin channels of a cc pair in electronhadron collisions are very different from that in hadron-hadron collisions,which provides a strong discriminative power to determine various transition rates for the pair to become a J/ψ.We predict that the J/ψ produced in electron-hadron collisions is likely unpolarized,and the production is an ideal probe for gluon distribution of colliding hadron(or nucleus).We find that the J/ψ production is dominated by the color-octet channel,providing an excellent probe to explore the gluon medium in large nuclei at the EIC.     

Order Parameter of a Nanometre-Scale S-Wave Superconducting Grain in Quantum Tunnelling Process： Frequency Space Analysis

A nano-scale s-wave superconducting grain, coupled to a normal metallic contact through a tunnelling junction, is placed in an external magnetic field. We suppose that effect of this quantum tunnelling on the Fourier transform of the order parameter is in the form of a small additive correction to the BCS order parameter. At the first order approximation in terms of this correction term and by using an instanton method, the related Green functions （in frequency space） are obtained. By establishing a self-consistent configuration an analytic formula for the order parameter is also found. We also show that a departure from superconductivity can be captured by this formula. This change of state is indeed a manifestation of a quantum transition induced by quantum fluctuations. In this sense, this is an advantage of our simple method which, like other more elaborate methods, can detect a quantum transition in the state of the grain.     

Superconductivity,Pair Density Wave,and Neel Order in Cuprates

We investigate in underdoped cuprates possible coexistence of the superconducting order at zero momentum and pair density wave(PDW)at momentum Q=(Л,Л)in the presence of a Neel order.By symmetry,the d-wave uniform singlet pairing dS0 can coexist with the d-wave triplet PDW dTq,and the p-wave singlet PDW pSq can coexist with the p-wave uniform triplet pT0.At half filling,we find that the novel pSq+pT0 state is energetically more favorable than the dS0+dTQ state.At finite doping,however,the dS0+dTq state is more favorable.In both types of states,the variational triplet parameters cITq and pT0 are of secondary significance.Our results point to a fully symmetric Z2 quantum spin liquid with spinon Fermi surface in proximity to the Neel order at zero doping,which may not be adiabatically connected to the d-wave singlet superconductivity at finite doping with intertwining d-wave triplet PDW fluctuations and spin moment fluctuations.The results are obtained by variational quantum Monte Carlo simulations.     

Superconductivity,Pair Density Wave,and Néel Order in Cuprates

We investigate in underdoped cuprates possible coexistence of the superconducting order at zero momentum and pair density wave(PDW) at momentum Q=(π,π) in the presence of a Neel order.By symmetry,the d-wave uniform singlet pairing dS_0 can coexist with the d-wave triplet PDW dT_Q,and the p-wave singlet PDW pS_Q can coexist with the p-wave uniform triplet pT_0.At half filling,we find that the novel pS_Q+pT_0 state is energeticall.y more favorable than the dS_0+dT_Q state.At finite doping,however,the dS_0+dT_Q state is more favorable.In both types of states,the variational triplet parameters dT_Q and pTo are of secondary significance.Our results point to a fully symmetric Z_2 quantum spin liquid with spinon Fermi surface in proximity to the Neel order at zero doping,which may not be adiabatically connected to the d-wave singlet superconductivity at Bnite doping with intertwining d-wave triplet PDW fluctuations and spin moment fluctuations.The results are obtained by variational quantum Monte Carlo simulations.     

Screening of Local Magnetic Moment by Electrons of Disordered Graphene

Based on the Anderson impurity model and self-consistent approach, we investigate the condition for the screening of a local magnetic moment by electrons in graphene and the influence of the moment on electronic properties of the system. The results of numerical calculations carried out on a finite sheet of graphene show that when the Fermi energy is above the single occupancy energy and below the double occupancy energy of the local impurity, a magnetic state is possible. A phase diagram in a parameter space spanned by the Coulomb energy U and the Fermi energy is obtained to distinguish the parameter regions for the magnetic and nonmagnetic states of the impurity. We find that the combined effect of the impurity and finite size effect results in a large charge density near the edges of the finite graphene sheet. The density of states exhibits a peak at the Dirac point which is caused by the appearance of the edge states localized at the zigzag edges of the sheet.     

Quantum Effects of a Dissipative Mesoscopic Circuit with Mutual Inductance

We study the quantum fluctuations of the charge and current of two L-C dissipative mesoscopic circuit with the mutual inductance in the vacuum state.Our results show that the system state will evolve to a squeezed coherent state under the effect of external source.We find that the squeezing amplitude parameter is relative to the parameters of circuit and the mutual-inductance coefficient in the existence of dissipation.When the circuit has no dissipation or there is complete coupling between two meshes,the squeezing amplitude parameter only depends on the capacitance‘s ratio.     

NMR and NQR studies on transition-metal arsenide superconductors LaRu_2As_2,KCa_2Fe_4As_4F_2,and A_2Cr_3As_3

We report ~(75)As-nuclear magnetic resonance(NMR) and nuclear quadrupole resonance(NQR) measurements on transition-metal arsenides LaRu_2As_2, KCa_2Fe_4As_4F_2, and A_2Cr_3As_3. In the superconducting state of La Ru_2As_2, a Hebel–Slichter coherence peak is found in the temperature dependence of the spin-lattice relaxation rate 1/T1 just below Tc, which indicates that LaRu_2As_2 is a full-gap superperconducor. For KCa_2Fe_4As_4F_2, antiferromagnetic spin fluctuations are observed in the normal state. We further find that the anisotropy rate RAF= Tc1/Tab1 is small and temperature independent,implying that the low energy spin fluctuations are isotropic in spin space. Our results indicate that KCa_2Fe_4As_4F_2 is a moderately overdoped iron-arsenide high-temperature superconductor with a stoichiometric composition. For A_2Cr_3As_3(A = Na, K, Rb, Cs), we calculate the electric field gradient by first-principle method and assign the ~(75)As-NQR peaks to two crystallographically different As sites, paving the way for further NMR investigation.     

Introduction and Applications of a Generalized Intermediate Entangled State Representation

We introduce a generalized intermediate entangled state representation ｜β〉Λ to study the energy spectrum of an electron in a uniform magnetic field and a harmonic potential through algebraic calculatiOn. We find that the degeneracy of the energy levels is disappeared due to the existence of the additional potential. We make it clear that the eigenfunction is just the expression of eigenvector, defined in n Fock space, in ｜β〉Λ representation.     

Unified treatment of the bound states of the Schioberg and the Eckart potentials using Feynman path integral approach

We obtain analytical expressions for the energy eigenvalues of both the Schioberg and Eckart potentials using an approximation of the centrifugal term.In order to determine the e-states solutions,we use the Feynman path integral approach to quantum mechanics.We show that by performing nonlinear space-time transformations in the radial path integral,we can derive a transformation formula that relates the original path integral to the Green function of a new quantum solvable system.The explicit expression of bound state energy is obtained and the associated eigenfunctions are given in terms of hypergeometric functions.We show that the Eckart potential can be derived from the Schioberg potential.The obtained results are compared to those produced by other methods and are found to be consistent.     

Coexisting Condensates of Weakly Interacting Bose Gas in a Harmonic Trap

We study particles in a vortex state driven to a core state with lower energy and zero angular momentum by the trap potential asymmetries. We find that at T=0 when the role of the thermal gas can be ignored, there will be coexisting condensates. We also calculate the fluctuation of the number difference and argue that in certa/n range of the parameters the state of the whole system is the macroscopic quantum serf-trapping in the Josephson tunnelling regime.     

Dynamical instability of the dark state in the conversion of Bose-Fermi mixtures into stable molecules

In this paper,we investigate the dynamical instability of the dark state in the conversion of Bose-Fermi mixtures into stable molecules through a stimulated Raman adiabatic passage aided by Feshbach resonance.We analytically obtain the regions where the dynamical instability appears and find that such instability in the Bose-Fermi mixture system is caused not only by bosonic interparticle interactions but also by Pauli blocking terms,which is different from the scenario of a pure bosonic system where instability is induced by nonlinear interparticle collisions.Taking a 40 K-87 Rb mixture as an example,we give the unstable regions numerically.     

Study of Pseudogap in Underdoped Cuprate

A mean-field spin-density wave (SDW) analysis of pseudogap in the underdoped cuprates is proposed on the dependence of the energy gap which mimics the pseudogap near (π, 0) point at least. It implies that the pseudogap structure near (π, 0) is not sensitive to the long-range order and will survive leading to the pseudogap phenomenon in the underdoped metallic phase. On the other hand, in the long-range ordering antiferromagnetic region, the mean-field SDW theory holds and the pseudogap structure predicated by the theory should be observable experimentallyv. Then one prediction is that the pseudogap would smoothly extrapolate between itinerant antiferromagnetic phase and underdoped metallic phase.     

Pseudoscalar meson and baryon octet interaction with strangeness zero in the unitary coupled-channel approximation

The interaction of the pseudoscalar meson and the baryon octet is investigated by solving the Bethe-Salpeter equation in the unitary coupled-channel approximation. In addition to the Weinberg-Tomozawa term, the contribution of the s-and u-channel potentials in the-wave approximation are taken into account. In the sector of isospin I=1/2 and strangeness S =0, a pole is detected in a reasonable region of the complex energy plane of ■ in the center-of-mass frame by analyzing the behavior of the scattering amplitude, which is higher than the ηN threshold and lies on the third Riemann sheet. Thus, it can be regarded as a resonance state and might correspond to the N(1535) particle of the Particle Data Group(PDG) review. The coupling constants of this resonance state to the πN,ηN,KΛ and KΣ channels are calculated, and it is found that this resonance state couples strongly to the hidden strange channels. Apparently, the hidden strange channels play an important role in the generation of resonance states with strangeness zero. The interaction of the pseudoscalar meson and the baryon octet is repulsive in the sector of isospin I = 3/2 and strangeness S = 0, so that no resonance state can be generated dynamically.     

Radiative Energy Shifts of an Atom Coupled to the Derivative of a Scalar Field near a Reflecting Boundary

We study the radiative energy level shifts of a two-level atom in dipole coupling to the derivative of a massless scalar quantum field in a spacetime with a perfectly reflecting boundary, and calculate the contributions of vacuum fluctuations and radiation reaction to the level shift. It is found that the energy level shift of the excited state is an oscillating function of the atom＇s distance from the boundary and it can either be positive or negative, while that of the ground state is always positive. The most remarkable feature is that the energy level shift of the ground state behaves like 1/z^4 when the atom＇s distance from the boundary, z, is very large as compared to the transition wavelength of the atom, while it behaves like 1/z^3 when z is very small     

Models of vacuum energy interacting with cold dark matter:Constraints and comparison

In this paper, we investigate the observational constraints on the scenario of vacuum energy interacting with cold dark matter.We consider eight typical interaction forms in such an interacting vacuum energy scenario. The observational data used in this work to constrain these models include the JLA sample of type Ia supernovae observation, the Planck 2015 distance priors data of cosmic microwave background anisotropies observation, the baryon acoustic oscillations data, and the Hubble constant direct measurement. We find that the current observational data almost equally favor these interacting vacuum energy models. We also find that for all these models of vacuum energy interacting with cold dark matter the case of no interaction is actually well consistent with the current observational data within 1σ range.     

Phase transition in finite density and temperature lattice QCD

We investigate the behavior of the chiral condensate in lattice QCD at finite temperature and finite chemical potential. The study was done using two flavors of light quarks and with a series of β and ma at the lattice size 24×12²×6. The calculation was done in the Taylor expansion formalism. We are able to calculate the first and second order derivatives of <ψψ> in both isoscalar and isovector channels. With the first derivatives being small, we find that the second derivatives are sizable close to the phase transition and that the magnitude of ψψ decreases under the influence of finite chemical potential in both channels.     

A Direct Calculation of First-Order Wave Function of Helium

We develop a simple analytic calculation for the first order wave function of helium in a model in which nuclear charge screening is caused by repulsive coulomb interaction. The perturbation term, first-order correlation energy, and first-order wave function are divided into two components, one component associated with the repulsive coulomb interaction and the other proportional to magnetic shielding. The resulting first-order wave functions are applied to calculate second-order energies within the model. We find that the second-order energies are independent of the nuclear charge screening constant in the unperturbed Hamiltonian with a central coulomb potential.     

Effects of Crossed Electric and Magnetic Fields on Shallow Donor Impurity Binding Energy in a Parabolic Quantum Well

We have calculated variationally the ground state binding energy of a hydrogenic donor impurity in a parabolic quantum well in the presence of crossed electric and magnetic fields. These homogeneous crossed fields are such that the magnetic field is parallel to the heterostructure layers and the electric field is applied perpendicular to the magnetic field. The dependence of the donor impurity binding energy to the well width and the strength of the electric and magnetic fields are discussed. We hope that the obtained results will provide important improvements in device applications, especially for a suitable choice of both fields in the narrow well widths.