Electronic structure and magnetic properties of rare-earth perovskite gallates from first principles

The density functional calculation is performed for centrosymmetric（La–Pm） GaO3 rare earth gallates, using a full potential linear augmented plane wave method with the LSDA and LSDA＋U exchange correlation to treat highly correlated electrons due to the very localized 4f orbitals of rare earth elements, and explore the influence of U = 0.478 Ry on the magnetic phase stability and the densities of states. LSDA＋U calculation shows that the ferromagnetic（FM） state of RGaO3 is energetically more favorable than the anti-ferromagnetic（AFM） one, except for LaGaO3 where the NM state is the lowest in energy. The energy band gaps of RGaO3 are found to be in the range of 3.8–4.0 eV, indicating the semiconductor character with a large gap.

Strongly correlated new state Fermi systems as a of matter

The aim of this review paper is to expose a new state of matter exhibited by strongly correlated Fermi systems represented by various heavy-fermion （HF） metals, two-dimensional liquids like 3He, compounds with quantum spin liquids, quasicrystals, and systems with one-dimensional quantum spin liquid. We name these various systems HF compounds, since they exhibit the behavior typical of HF metals. In HF compounds at zero temperature the unique phase transition, dubbed throughout as the fermion condensation quantum phase transition （FCQPT） can occur; this FCQPT creates flat bands which in turn lead to the specific state, known as the fermion condensate. Unlimited increase of the effective mass of quasiparticles signifies FCQPT; these quasiparticles determine the thermodynamic, transport and relaxation properties of HF compounds. Our discussion of numerous salient experimen- tal data within the framework of FCQPT resolves the mystery of the new state of matter. Thus, FCQPT and the fermion condensation can be considered as the universal reason for the non-Fermi liquid behavior observed in various HF compounds. We show analytically and using arguments based completely on the experimental grounds that these systems exhibit universal scaling behavior of their thermodynamic, transport and relaxation properties. Therefore, the quantum physics of different HF compounds is universal, and emerges regardless of the microscopic structure of the compounds. This uniform behavior allows us to view it as the main characteristic of a new state of matter exhibited by HF compounds.

Strongly correlated intermetallic rare-earth monoaurides(Ln-Au):Ab-initio study

In this paper, we explored the structural, elastic and mechanical properties of the strongly correlated electron systems, intermetallic Ln-Au（Ln = Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu） in cubic structure,using PF-LAPW method within the density functional theory. Structural properties of these intermetallics were investigated by treating the exchange-correlation potential with the GGA-PBE, GGA-PBEsol and GGA ＋ U. The effectiveness of the U for the structural properties as compared to other methods confirms the strong correlated nature of these compounds and the calculated lattice constants endorse the divalency of Yb. The results demonstrate the stable cubic CsCl structure of these compounds. Bulk modulus, Young＇s modulus, shear modulus, B/G ratio, Cauchy pressure, Poisson＇s ratio, anisotropic ratio,Kleinman parameters and Lame＇s coefficients were studied using the PBEsol to evaluate their importance in various types of engineering applications. The most prominent features of these compounds are their ductility, very high melting points, resistance to corrosion, and anisotropic nature.

Na_xCoO_2·yH_2O体系的高分辨电子能量损失谱和电子结构研究

本文通过高分辨电子能量损失谱(EELS)的实验分析与密度泛函计算相结合的方法,研究了NaxCoO2.yH2O系统的电子结构特性和电子关联效应。实验结果表明,金属性Na0.3CoO2材料和电荷有序绝缘体Na0.5CoO2的O-K吸收边存在明显的结构差别,在Na0.5CoO2的EELS中第一个峰发生明显分裂,密度泛函计算证实这种分裂现象和电子关联效应直接相关。通过理论模拟谱线与实验谱线的比较确定了其电子关联强度为U=3.0 eV。在Na0.3CoO2.yH2O(y=0,0.6,1.3)超导体系中,实验发现其能损谱的低能部分随着水含量的增加发生系统的变化,损失峰向低能量方向逐步移动。电子结构计算表明水分子的插入可以引起费米面附近能态原子轨道杂化情况的改变,从而导致EELS的变化。

The Contribution of the Nearest-Neighborhood Interaction to the Persistent Current in a Mesoscopic Ring Studied by a New Model

We propose an effective description of the interaction between the nearest-neighboring particles in a continuum theory. The contributions of the electron-electron interaction to the persistent current in 1D strongly correlating mesoscopic rings with or without impurities are analyzed. It is shown that the nearest-neighborhood int eraction gives significant contributions to the current and correlation functions. The enhance of the theoretical value of current magnitude is observed at finite temperature in the presence of the impurity scattering. The statistical property of the persistent current over random impurity distribution is also discussed. It is found that the exponential law of the persistent current for a non-interacting system will remain in an interacting one, as long as the interactions between nonnearest-neighborhoods are excluded.

Persistent Currents and Edge States in a Quasi-One-Dimensional Mesoscopic Ring with a Screened Interaction

The effect ofthe edge state on the persistent current in quasi-1D mesoscopic rings with a screened interactionwhich exists only between nearest-neighboring particles is studied with the Hartree-Fock approximation. The theoreticalvalue of the current magnitude is greatly enhanced by both the edge state and the Coulomb interaction, and pinningthe electrons into a lattice is good for the enhancement if screening happens. In high dimensional systems the screeningeffect can make the interacting range show anisotropy, and create a tendency of gathering for particles with a repulsivepotential.

The Numerical Study of the S = 1/2 XXZ Chain

We adopt the Lanczos method combined with the quantum conformal field theory to investigate the S = 1/2XXZ chain in detail. The bulk-limit ground state energy, the anomalous scaling dimension of the spin operators, theFermi velocity and the zero-temperature susceptibility are numerically calculated. The results agree to the exact solution well.

Persistent Currents and Edge States in a Quasi－One－Dimensional Mesoscopic Ring with a Screened Interaction

The effect ofthe edge state on the persistent current in quasi-1D mesoscopic rings with a screened interactionwhich exists only between nearest-neighboring particles is studied with the Hartree-Fock approximation. The theoreticalvalue of the current magnitude is greatly enhanced by both the edge state and the Coulomb interaction, and pinningthe electrons into a lattice is good for the enhancement if screening happens. In high dimensional systems the screeningeffect can make the interacting range show anisotropy, and create a tendency of gathering for particles with a repulsivepotential.

Novel Synthesis Method of Nonst0ichiometric Na2-xlrO3 Crystal Structure, Transport and Magnetic Properties

Transition metal oxides with 4d or 5d metals are of great interest due to the competing interactions, of the Coulomb repulsion and the itineracy of the d-electrons, opening a possibility of building new quantum ground states. Particularly the 5d metal oxides containing Iridium have received significant attention within the last years, due to their unexpected physical properties, caused by a strong spin orbit coupling observed in It（IV）. A prominent example is the Mott-insulator Sr2IrO4. Another member of this family, the honeycomb lattice compound Na2IrO3, also being a Mott-insulator having, most probably, a Kitaev spin liquid ground state. By deintercalating sodium from Na2IrO3, the authors were able to synthesize a new honeycomb lattice compound with more than 50% reduced sodium content. The reduction of the sodium content in this layered compound leads to a change of the oxidation state of iridium from ＋ IV to ＋ V/＋ VI and a symmetry change from C2/c to P-3. This goes along with significant changes of the physical properties. Besides the vanishing magnetic ordering at 15 K, also the transport properties changes and instead insulating semiconducting properties are observed.

Influence of C-Axis Inter Unit Cell Resonant Tunneling on the Spectral Function in Bilayer Cuprates

The role of intra unit cell coupling along with inter unit cell resonant tunneling between the copper-oxygen planes on the electronic spectral function in normal state of bilayer high Tc cuprates like Bi2Sr2CaCu2O8+x is investigated. The Hubbard model including terms representing hopping between the planes within the unit cell, and resonant tunneling between the planes in two adjoining cells is used along with the Green’s function equation of motion approach to obtain an expression of spectral function. The spectral function at (&#960,0) point of the Brillouin zone is numerically calculated. It is found that the intra unit cell coupling lead to splitting of spectral peak especially close to (&#960,0) point, while the inter unit cell resonant tunneling lead to a broadening in the spectral function and suppression of bilayer splitting in the normal state. In the presence of finite electron correlations the inter unit cell tunneling induce strong broadening in the spectral features. The electron correlations and inter unit cell tunneling is important in determining the shape of the spectral function in doped bilayer cuprates. These results are viewed in terms of the existing ARPES measurements on bilayer cuprates.

处理强关联量子杂质系统的费米子级联运动方程方法的最新进展

近年来,由于强关联量子杂质系统(QIS)表现出多样化的、有趣新颖的量子现象,因此对它的研究也成为了一个备受关注的课题。级联运动方程方法(HEOM)是描述与环境线性耦合的量子杂质系统的最流行的数值方法之一。这篇综述全面介绍了形式上严格、数值上收敛的HEOM方法,其中包括量子杂质系统的模型化描述和费米子HEOM形式的概述。此外,各种各样的谱分解方案和级联方程的截断方案被提出和发展,显著地提高了HEOM方法的精度和效率,尤其是在低温区域。通过对非平衡量子输运和强关联近藤态的表征的数值模拟,以及对非平衡量子的热力学研究,HEOM方法在处理强关联问题上的实用性和有效性得到了充分地例证。

Scaling behavior of the thermopower of the archetypal heavy-fermion metal YbRh2Si2

We reveal and explain the scaling behavior of the thermopower S/T exhibited by the archetypal heavy-fermion （HF） metal YbRh2Si2 under the application of magnetic field B at temperature T. We show that the same scaling is demonstrated by different HF compounds such as/3-YbA1B4 and the strongly correlated layered cobalt oxide [BiBa0.66K0.3602]CoO2. Using YbRh2Si2 as an example, we demonstrate that the scaling behavior of SIT is violated at the antiferromagnetic phase transition, while both the residual resistivity Po and the density of states, N, experience jumps at the phase transition, causing the thermopower to make two jumps and change its sign. Our elucidation is based on flattening of the single-particle spectrum that profoundly affects Po and N. To depict the main features of the SIT behavior, we construct a T-B schematic phase diagram of YbRh2Si2. Our calculated SIT for the HF compounds are in good agreement with experimental facts and support our observations.