Eigenfunctions of Five-Qubit XX Chain and Ground State Concurrence

Use Jordan-Wigner transformation the eigenstates and eigenenergies of live qubits XX chain including external magnetic field are obtained. The concurrences Co,1 and Co,2 of ground state are obtained. For the ferromagnetic, when [（√5 - 1）/2]｜J｜ 〈 B ≤ ｜J｜, the values of C0,1 and C0,2 are the same. The C0,2 is easily broken by temperature.     

Off-diagonal long-range order in the ground state of the two-dimensional antiferromagnetic Heisenberg model

A two-dimensional Jordan-Wigner transformation, together with a fermion-boson mapping, has been used to transform the two-dimensional antiferromagnetic Heisenberg model (2D AFMHM) into an interacting boson system with a fixed number of particles. We found that the excitation energy depends linearly on the momentum for small energy, and it is 1.80J for (π,π). Our results suggest that the ground state of the 2D AFMHM is a quantum liquid, and the order is off-diagonal long-range order associated with the Bose-Einstein condensation.     

具有长程相互作用S-1/2 XY链的研究

采用平均场Jordan - Wigner 变换分析方法,研究了外场中且具有Z方向均匀长程相互作用自旋－1/2 XY链的热力学性质,得到了系统格点的亥姆赫兹自由能、内能、比热、磁化强度、磁化率等热力学量的解析表达式及其数值解,讨论了系统的一级和两级相变,数值结果在退化条件下与其他文献的结果符合很好. 关键词： XY链')" href="#">XY链 平均场Jordan-Wigner变换 长程相互作用     

Deexcitation Energy of Superdeformed Secondary Minima as a Probe to Density Dependence of Symmetry Energy

Deexcitation energies of superdeformed secondary minima of odd-odd A u and T1 isotopes are investigated with the relativistic mean field （RMF） model where the isoscalar-isovector coupling is included to change the symmetry energy. It is verified by the theoretical analysis and numerical results that the deexcitation energies of superdeformed secondary minima relative to the ground states in these heavy nuclei are sensitive to differences in the symmetry energy. In particular, the linear correlation between the deexeitation energies of odd-odd Au and T1 isotopes and the neutron skin thickness in 208Pb is established. Moreover, explorations are extended to superdeformed candidates of other mass regions. It is found that the linear correlation can even be established between the deexcitation energies and the symmetry pressure at subsaturation density. These indicate that deexcitation energies can serve as a probe to the density dependence of the symmetry energy.     

Study of Pseudogap in Underdoped Cuprate

A mean-field spin-density wave (SDW) analysis of pseudogap in the underdoped cuprates is proposed on the basis of the t-t^ˊ-U Hubbard model. It is surprised to find that a simple t^ˊ term will do the trick to introduce the momentum 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 experimentally. Then one prediction is that the pseudogap would smoothly extrapolate between itinerant antiferromagnetic phase and underdoped metallic phase.     

Physics picture from neutron scattering study on Fe-based superconductors

Neutron scattering, with its ability to measure the crystal structure, the magnetic order, and the structural and magnetic excitations, plays an active role in investigating various families of Fe-based high-T c superconductors. Three different types of antiferromagnetic orders have been discovered in the Fe plane, but two of them cannot be explained by the spin-density-wave (SDW) mechanism of nesting Fermi surfaces. Noticing the close relation between antiferromagnetic order and lattice distortion in orbital ordering from previous studies on manganites and other oxides, we have advocated orbital ordering as the underlying common mechanism for the structural and antiferromagnetic transitions in the 1111, 122, and 11 parent compounds. We observe the coexistence of antiferromagnetic order and superconductivity in the (Ba,K)Fe 2 As 2 system, when its phase separation is generally accepted. Optimal T c is proposed to be controlled by the local FeAs 4 tetrahedron from our investigation on the 1111 materials. The Bloch phase coherence of the Fermi liquid is found crucial to the occurrence of bulk superconductivity in iron chalcogenides of both the 11 and the 245 families. Iron chalcogenides carry a larger staggered magnetic moment ( 2 μ B /Fe) than that in iron pnictides ( 1 μ B /Fe) in the antiferromagnetic order. Normal state magnetic excitations in the 11 superconductor are of the itinerant nature while in the 245 superconductor the spin-waves of localized moments. The observation of superconducting resonance peak provides a crucial piece of information in current deliberation of the pairing symmetry in Fe-based superconductors.     

From self-assembly to quantum guiding: A review of magnetic atomic structures on noble metal surfaces

Recent advances in the study of magnetic atomic structures on noble metal surfaces are reviewed. These include one- dimensional strings, two-dimensional hexagonal superlattices, and novel structures stabilized by quantum guiding. The combined techniques of low-temperature scanning tunneling microscopy, kinetic Monte Carlo simulations, and ab initio calculations reveal that surface-state-mediated adatom-step and adatom-adatom interactions are the driving forces for self- assembly of these structures. The formation conditions are further discussed by comparing various experimental systems and the kinetic Monte Carlo simulations. Using scanning tunneling spectroscopy and tight-binding calculations together, we reveal that the spectra of these well-ordered structures have characteristic peaks induced by electronic scattering processes of the atoms within the local environment. Moreover, it is demonstrated that quantum confinement by means of nano-size corrals has significant influence on adatom diffusion and self-assembly, leading to a quantum-guided self-assembly.     

Quantum phase transitions in matrix product states of one-dimensional spin-1 chains

We present a new model of quantum phase transitions in matrix product systems of one-dimensional spin-1 chains and study the phases coexistence phenomenon. We find that in the thermodynamic limit the proposed system has three different quantum phases and by adjusting the control parameters we are able to realize any phase, any two phases equal coexistence and the three phases equM coexistence. At every critical point the physical quantities including the entanglement are not discontinuous and the matrix product system has long-range correlation and N-spin maximal entanglement. We believe that our work is helpful for having a comprehensive understanding of quantum phase transitions in matrix product states of one-dimensional spin chains and of certain directive significance to the preparation and control of one-dimensional spin lattice models with stable coherence and N-spin maximal entanglement.     

Microscopic Superconductivity and Room Temperature Electronics of High-Tc Cuprates

Abstract This paper points out that the Landau criterion for macroscopic superfluidity of He H is only a criterion for microscopic superfluidity of ^4He, extends the Landau criterion to microscopic superconductivity in fermions （electron and hole） system and system with Cooper pairs without long-range phase coherence. This paper gives another three non-superconductive systems that are of microscopic superconductivity. This paper demonstrates that one application of microscopic superconductivity is to establish room temperature electronics of the high-To cuprates.     

Octupole deformation for Ba isotopes in a reflection-asymmetric relativistic mean-field approach

The potential energy surfaces of even-even 142-156Ba are investigated in the constrained reflectionasymmetric relativistic mean-field approach with parameter set PK1. It is shown that for the ground states, 142Ba is near spherical,156Ba well quadrupole-deformed, and in between 144-154Ba octupole deformed. In particular, the nuclei 148,150Ba with N=92, 94 have the largest octupole deformations. By including the octupole degree of freedom, energy gaps N = 88, N = 94 and Z = 56 near Fermi surfaces for the singleparticle levels in 148Ba with β2 ～ 0.26 and β3 ～ 0.17 are found. Furthermore, the performance of the octupole deformation driving pairs （ν2f7/2, ν1i13/2） and （π2d5/2, π1h11/2） is demonstrated by analyzing the singleparticle levels near Fermi surfaces in 148Ba.     

Quantum phase transitions in matrix product states of one-dimensional spin-1/2 chains

For the matrix product system of a one-dimensional spin-1/2 chain, we present a new model of quantum2 phase transitions and find that in the thermodynamic limit, both sides of the critical point are respectively described by phases ｜Ψa 〉=｜1··· 1 representing all particles spin up and ｜Ψb 〉=｜0··· 0 representing all particles spin down, while the phase transition point is an isolated intermediate-coupling point where√ the two phases coexist equally, which is2 described by the so-called N-qubit maximally entangled GHZ state ｜Ψpt =√2/2（｜1··· 1 ＋｜0··· 0）. At the critical point,2the physical quantities including the entanglement are not discontinuous and the matrix product system has longrange correlation and N-qubit maximal entanglement. We believe that our work is helpful for having a comprehensive understanding of quantum phase transitions in matrix product states of one-dimensional spin chains and of potential directive significance to the preparation and control of one-dimensional spin lattice models with stable coherence and N-qubit maximal entanglement.     

Disordered ground state and magnetic field-induced long-range order in an S=3/2 antiferromagnetic honeycomb lattice compound Bi3Mn4O12(NO3)

Bi3Mn4O12(NO3), in which the Mn4+ ions carry S=3/2, is the first honeycomb lattice system that shows no long-range magnetic order. Using neutron scattering, we have determined that short-range antiferromagnetic correlations develop at low temperatures. Applied magnetic fields induce a magnetic transition, in which the short-range order abruptly expands into a long-range order.     

Jordan-Wigner approach to the frustrated spin one-half XXZ chain

The Jordan-Wigner transformation is applied to study the ground state properties and dimerization transition in the J₁-J₂ XXZ chain. We consider different solutions of the mean-field approximation for the transformed Hamiltonian. Ground state energy and the static structure factor are compared with complementary exact diagonalization and good agreement is found near the limit of the Majumdar-Ghosh model. Furthermore, the ground state phase diagram is discussed within the mean-field theory. In particular, we show that an incommensurate ground state is absent for large J₂ in a fully self-consistent mean-field analysis.     

Absence of spontaneous magnetic order at nonzero temperature in one- and two-dimensional Heisenberg and XY systems with long-range interactions

The Mermin-Wagner theorem is strengthened so as to rule out magnetic long-range order at T > 0 in one- or two-dimensional Heisenberg and XY systems with long-range interactions decreasing as R(-alpha) with a sufficiently large exponent alpha. For oscillatory interactions, ferromagnetic long-range order at T > 0 is ruled out if alpha > or = 1(D = 1) or alpha > 5/2(D = 2). For systems with monotonically decreasing interactions, ferro- or antiferromagnetic long-range order at T > 0 is ruled out if alpha > or = 2D.     

磁场对一维Heisenberg链低能行为的影响

用Jordan-Wigner变换和玻色化方法研究了一维1/2自旋Heisenberg链.在外加磁场作用下,模型的Fermi速度与Fermi动量均被改变,从而玻色化过程也受到影响.对一维Heisenberg链的反铁磁相(AFM)与顺磁相(PM)分别做了讨论,得出了模型基态能及磁化与外加磁场的关系并给出了公度-非公度阈值磁场h′_cl及上阈值磁场h_c2. 关键词： Heisenberg链 磁场 强关联     

Coexistence of antiferromagnetic and spin cluster glass order in the magnetoelectric relaxor multiferroic PbFe 0.5 Nb 0.5 O3

The coexistence of cluster glass with long-range antiferromagnetic order in the relaxor ferroelectric PbFe 0.5 Nb 0.5 O3 is elucidated. While the transition at T(N) = 153 K on the infinite antiferromagnetic cluster induces 3m symmetry with large EH2 magnetoelectric response, the disconnected subspace of isolated Fe3+ ions and finite clusters accommodates the cluster glass below T(g) = 10.6 K with field-induced m' symmetry and EH-type magnetoelectric response. Critical slowing-down, memory and rejuvenation after aging, occurrence of a de Almeida-Thouless phase line, and stretched exponential relaxation of remanence corroborate the glass nature.     

Approaching the ground state of the kagomé antiferromagnet

Y0.5Ca0.5BaCo4O7 contains kagomé layers of Co ions, whose spins are strongly coupled, with a Curie-Weiss temperature of -2200 K. At low temperature, T=1.2 K, our diffuse neutron scattering study with polarization analysis reveals characteristic spin correlations close to a predicted two-dimensional coplanar ground state with staggered chirality. The absence of three-dimensional long-range antiferromagnetic order indicates negligible coupling between the kagomé layers. The scattering intensities are consistent with high spin S=3/2 states of Co2+ in the kagomé layers and low spin S=0 states for Co3+ ions on interlayer sites. Our observations agree with previous Monte Carlo simulations indicating a ground state of effectively short range, staggered chiral spin order.     

Structural and magnetic characterization of the complete delafossite solid solution (CuAlO?)?-x(CuCrO?)x

We have prepared the complete delafossite solid solution series between diamagnetic CuAlO(2) and the t(2g)(3)frustrated antiferromagnet CuCrO(2). The evolution with composition x in CuAl(1-x)Cr(x)O(2) of the crystal structure and magnetic properties has been studied and is reported here. The room-temperature unit cell parameters follow the Végard law and increase with x as expected. The μ(eff) is equal to the Cr(3+) spin-only S = 3/2 value throughout the entire solid solution. Θ(CW) is negative, indicating that the dominant interactions are antiferromagnetic, and its magnitude increases with Cr substitution. For dilute Cr compositions, the nearest-neighbor exchange coupling constant J(BB) was estimated by mean-field theory to be 3.0 meV. Despite the sizable Θ(CW), long-range antiferromagnetic order does not develop until x is almost 1, and is preceded by glassy behavior. The data presented here, and those on dilute Al substitution from Okuda et al, suggest that the reduction in magnetic frustration due to the presence of non-magnetic Al does not have as dominant an effect on magnetism as chemical disorder and dilution of the magnetic exchange. For all samples, the 5 K isothermal magnetization does not saturate in fields up to 5 T and minimal hysteresis is observed. The presence of antiferromagnetic interactions is clearly evident in the sub-Brillouin behavior with a reduced magnetization per Cr atom. An inspection of the scaled Curie plot reveals that significant short-range antiferromagnetic interactions occur in CuCrO(2) above its Néel temperature, consistent with its magnetic frustration. Uncompensated short-range behavior is present in the Al-substituted samples and is likely a result of chemical disorder.     

Physical properties of quaternary compounds Gd2CoAl4T2 (T= Si,Ge) single crystals

We have synthesized and investigated physical properties of two new quaternary compounds Gd₂CoAl₄T₂ (T= Si, Ge) single crystals, which are isostructural to Tb₂NiAl₄Ge₂ and Er₂CoAl₄Ge₂. The most important structural feature of these materials is the anti-CaF₂-type CoAl₄T₂ slabs. These materials show metallic behavior below 300 K and there is a long-range antiferromagnetic (AFM) transition appearing at 20 and 27 K for Gd₂CoAl₄Ge₂ and Gd₂CoAl₄Si₂, respectively. Resistivity and heat capacity measurements also confirm these bulk AFM transitions. Further analysis indicates that this long-range antiferromagnetism should result from the magnetic interaction between local moments of Gd³⁺ ions.