Dynamics of magnetic defects in heavy fermion LiV2O4 from stretched exponential 7Li NMR relaxation

7Li NMR measurements on LiV2O4 from 0.5 to 4.2 K are reported. A small concentration of magnetic defects within the structure drastically changes the nuclear magnetization relaxation versus time from a pure exponential as in pure LiV2O4 to a stretched exponential, indicating glassy behavior of the magnetic defects. The stretched exponential function is described as arising from a distribution of 7Li nuclear spin-lattice relaxation rates and we present a model for the distribution in terms of the dynamics of the magnetic defects. Our results explain the origin of recent puzzling 7Li NMR literature data on LiV2O4 and our model is likely applicable to other glassy systems.     

Heavy-fermion-like state in a transition metal oxide LiV2O4 single crystal: indication of Kondo resonance in the photoemission spectrum

We have performed a vacuum ultraviolet laser excited photoemission spectroscopy on a d-electron heavy-fermion-like material LiV2O4 single crystal. We observed a sharp peak structure in the density of states at approximately 4 meV above the Fermi level (E(F)). The evolution of the peak height corresponds well with the crossover behavior to the heavy-fermion-like state as observed in the thermal and transport properties. The position, shape, and temperature (T) dependence of the peak structure is quite similar to the Kondo resonance observed in conventional f-electron heavy Fermion compounds.     

Spin fluctuations in a magnetically frustrated metal LiV(2)O(4).

Inelastic neutron scattering is used to characterize spin fluctuations in the d-electron heavy fermion spinel LiV(2)O(4). The spin-relaxation rate, gamma(Q), for Q = 0.6 A(-1) is 1.4(2) meV at low temperatures and increases linearly with temperature at a rate of 0.46(8)k(B). There is antiferromagnetic short-range order at low temperatures with a characteristic wave vector Q(c) = 0.64(2) A(-1) and a correlation length of 6(1) A. While warming shifts intensity towards lower Q, the staggered susceptibility peaks at a finite wave vector for T < 80 K. The data are compared with conventional heavy fermion systems, geometrically frustrated insulating magnets, and recent theories for LiV(2)O(4).     

CuO掺杂C3N对C5F10O分解组分吸附性能的第一性原理研究

全氟五碳酮（C5F10O）作为可替代SF6的新型环保绝缘气体已被投入到实际应用中. 在绝缘设备内部不可避免的会发生局部放电等故障,造成C5F10O绝缘气体分解产生弱绝缘性能甚至剧毒的分解组分,为保证绝缘设备的安全运行,在不影响气敏传感器正常检测绝缘设备内部故障的情况下,需对这些分解组分进行有选择地吸附去除. 新型类石墨烯C3N材料在气体吸附领域具有良好的应用前景,文中基于第一性原理计算了CuO分子掺杂C3N对主要分解组分CF4、C2F6及剧毒产物CF2O、HF的吸附过程,计算并分析了各分解组分吸附时的吸附能、态密度、电荷转移量、差分电荷密度以及不同环境温度下的恢复时间. 结果表明,CuO-C3N对HF表现出良好的吸附性,CF2O次之,但其无法吸附CF4与C2F6,因此CuO-C3N可以作为一种高性能的气体吸附剂对C5F10O绝缘设备内的剧毒分解组分HF进行吸附去除.     

Electret properties and chemical modification of cellular polypropylene films

The electret properties of virginal cellular polypropylene (PP) films and chemically modified cellular PP films by extraction from CH₂Cl₂ solution, oxidation in a mixture solution of H₂SO₄, CrO₃ and H₂O and fluorination in a hydrofluoric acid (HF) solution, were systematically studied by measuring the open-circuit thermally stimulated discharge (TSD) current spectra, charge TSD spectra and isothermal charge decay. The results point out that there are more deep traps than shallow traps in the surface region while the contrary case occurs in the bulk region. The thermal stability of charge storage of the chemically modified cellular PP film is significantly improved in comparison with that of the virginal one. Light irradiation or reacting at elevated temperature has remarkable promotion effect on the reaction of HF with the extracted and oxidized film. Moreover, a method for investigating the dynamic changes of mean charge depth relative to its initial value during heating was proposed.     

Doped Mott insulator as the origin of heavy-fermion behavior in LiV2O4

We investigate the electronic structure of LiV2O4, for which heavy-fermion behavior has been observed in various experiments, by the combination of the local density approximation and dynamical mean field theory. To obtain results at zero temperature, we employ the projective quantum Monte Carlo method as an impurity solver. Our results show that the strongly correlated a 1g band is a lightly doped Mott insulator which, at low temperatures, shows a sharp (heavy) quasiparticle peak just above the Fermi level, which is consistent with recent photoemission experiments by Shimoyamada et al. [Phys. Rev. Lett. 96, 026403 (2006)10.1103/PhysRevLett.96.026403].     

LiV2O4: frustration induced heavy fermion metal

We propose a two-stage spin-quenching scenario for the unusual heavy fermion state realized in the mixed valent metal LiV2O4. In this theory, local valence fluctuations are responsible for the formation of partially quenched, spin-1 / 2 moments below room temperature. Frustration of the intersite spin couplings then drives the system to produce the heavy Fermi liquid seen at low temperatures. The anomalous resistivity and the sign change of the Hall constant can be understood naturally within this model, which also predicts a unique symmetry for the heavy quasiparticle bands that may be observed in de Haas-van Alphen experiments.     

Tetramerization of a frustrated spin-1/2 chain

We investigate a model of a frustrated spin-1/2 Heisenberg chain coupled to adiabatic phonons with a general form of magnetoelastic coupling. For large enough frustration and lattice coupling, a new tetramerized phase with three different bond lengths is found. We argue that the zigzag spin-1/2 chain LiV2O5 might be a good candidate to observe such a phase.     

Charge order and the origin of giant magnetocapacitance in LuFe2O4

The nature of the charge order in the charge frustrated compound LuFe(2)O(4) and its effect on magnetocapacitance were examined on the basis of first-principles electronic structure calculations and Monte Carlo simulations of electrostatic energy. Our work shows that two different types of charge order of almost equal stability (i.e., square root of 3 x square root of 3 and chain types) occur in the Fe(2)O(4) layers of LuFe(2)O(4), and that the ground state of LuFe(2)O(4) has a ferrielectric arrangement of the Fe(2)O(4) layers with square root of 3 x square root of 3 charge order. The giant magnetocapacitance effect of LuFe(2)O(4) at room temperature is accounted for in terms of charge fluctuations arising from the interconversion between the two types of charge order, that becomes hindered by an applied magnetic field.     

LiV2O4 spinel as a heavy-mass fermi liquid: anomalous transport and role of geometrical frustration

Transport and specific heat measurements on hydrothermally grown single crystals reveal the formation of a heavy-mass Fermi liquid in the LiV2O4 spinel, below a coherence temperature of T* = 20-30 K. A few observations which illustrate the uniqueness of this spinel are discussed in connection with the origin of the heavy mass, such as the anomalous absence of resistivity saturation above T* and the close proximity to a spin glass phase where the influence of the magnetic frustration is evident.     

Angle-resolved photoemission study of insulating and metallic Cu-O chains in PrBa2Cu3O7 and PrBa2Cu4O8

We compare the angle-resolved photoemission spectra of the hole-doped Cu-O chains in PrBa2Cu3O7 (Pr123) and in PrBa2Cu4O8 (Pr124). While, in Pr123, a dispersive feature from the chain takes a band maximum at k(b) (momentum along the chain) approximately pi/4 and loses its spectral weight around the Fermi level, it reaches the Fermi level at k(b) approximately pi/4 in Pr124. Although the chains in Pr123 and Pr124 are approximately 1/4 filled, they show contrasting behaviors: While the chains in Pr123 have an instability to charge ordering, those in Pr124 avoid it and show an interesting spectral feature of a metallic coupled-chain system.     

ICP-OES测定月季中矿质元素的五种前处理方法比较

采用五种不同的前处理方法(干灰化法、HNO3+ H2 O2微波消解法、HNO3 +H2O2 +HF微波消解法、HNC3+ HClO4微波消解法、HNO3+ HClO4+HF微波消解法),对月季样品进行消解,利用ICP-OES法测定九种常量和微量元素,加标回收结果显示:HN(3 +HClO4微波消解法是最优的处理方法,对...     

Evidence for unconventional strong-coupling superconductivity in PrOs4Sb12: an Sb nuclear quadrupole resonance study

We report Sb-NQR results which evidence a heavy-fermion (HF) behavior and an unconventional superconducting (SC) property in Pr(Os4Sb12 with T(c)=1.85 K. The temperature (T) dependence of nuclear-spin-lattice-relaxation rate, 1/T(1), and NQR frequency unravel a low-lying crystal-electric-field splitting below T0 approximately 10 K, associated with Pr3+(4f(2))-derived ground state. In the SC state, 1/T(1) shows neither a coherence peak just below T(c) K nor a T3-like power-law behavior observed for anisotropic HF superconductors with the line-node gap. The isotropic energy gap with its size Delta/k(B)=4.8 K seems to open up across T(c) below T(*) approximately 2.3 K. It is surprising that Pr(Os4Sb12 looks like an isotropic HF superconductor-it may indeed argue for Cooper pairing via quadrupolar fluctuations.     

Charge-stripe order in the electronic ferroelectric LuFe2O4

The structural features of the charge ordering states in LuFe(2)O(4) are characterized by in situ cooling transmission electron microscopy observations from 300 K down to 20 K. Two distinctive structural modulations, a major q1=(1/3,1/3,2) and a weak q2 = q1/10+(0,0,3/2), have been well determined at the temperature of approximately 20 K. Systematic analysis demonstrates that the charges at low temperatures are well crystallized in a charge-stripe phase, in which the charge-density wave behavior in a nonsinusoidal fashion results in elemental electric dipoles for ferroelectricity. It is also noted that the charge ordering and ferroelectric domains often change markedly with lowering temperatures and yield a rich variety of structural phenomena.     

Ferroelectricity in an ising chain magnet

We report discovery of collinear-magnetism-driven ferroelectricity in the Ising chain magnet Ca3Co2-xMn(x)O6 (x approximately 0.96). Neutron diffraction shows that Co2+ and Mn4+ ions alternating along the chains exhibit an up-up-down-down ( upward arrow upward arrow downward arrow downward arrow) magnetic order. The ferroelectricity results from the inversion symmetry breaking in the upward arrow upward arrow downward arrow downward arrow spin chain with an alternating charge order. Unlike in spiral magnetoelectrics where antisymmetric exchange coupling is active, the symmetry breaking in Ca3(Co,Mn)2O6 occurs through exchange striction associated with symmetric superexchange.     

Connection between charge fluctuations and the coherent temperature in the heavy-fermion system SmOs4Sb12: a {121, 123}Sb NQR study

We report {121, 123}Sb nuclear quadrupole resonance measurements under pressure in a novel heavy fermion (HF) system SmOs4Sb12. The nuclear spin-spin relaxation rate 1/T{2} exhibits a distinct peak near the coherent temperature of the Kondo effect. The isotope effect of 121Sb and 123Sb indicates that the peak in 1/T{2} is electrical in origin. The connection between the peak in 1/T{2} and the development of coherency of the Kondo effect is robust even under pressure. It is conjectured that charge fluctuation plays an important role in forming the HF state in SmOs4Sb12.     

Surface Verwey transition in magnetite

We report density functional studies of the (001) surface of magnetite that account for local Coulomb interactions. Iron cations in the surface layers exhibit charge and t2g orbital ordering that is coupled with the lattice strains. Orbital ordering is present for various surface stoichiometries and causes opening of the band gap Eg approximately 0.3 eV at the surface, such that the (001) surface of Fe3O4 remains insulating also in the high temperature cubic phase. The (radical 2 x radical 2)R45 degrees surface reconstruction is related to orbital ordering.     

RPA calculation of the effective charge in a hartree-fock basis

Using a Hartree-Fock basis the diagrams of the Tamm-Dancoff and random-phase approximations have been summed to calculate the effective charge in the (1s0d) shell. The enhancement of the effective charge found by this summation is much less than in an oscillator basis, in fact in most cases the HF RPA result is smaller than the value obtained from the lowest order core polarization diagram in an oscillator basis. The HF neutron effective charges are thus too small. For protons the enhancement of the bare effective charge in a HF basis must also be taken into account, but for cases involving the 0d_5/2 orbital the final result appears rather small.     

电荷调控下Ti3C2O2和V2CO2吸附CH4的第一性原理计算

本文采用第一性原理计算首先研究了Ti3C2O2和V2CO2与CH4气体分子之间的相互作用,发现Ti3C2O2和V2CO2对CH4的吸附较弱属于物理吸附,不适宜用作探测CH4。在此基础上研究了电荷调控下CH4气体分子与Ti3C2O2和V2CO2之间的相互作用。结果表明：随着体系电荷态的增加,Ti3C2O2和V2CO2对CH4气体分子的吸附作用逐渐增加变为化学吸附。当体系电荷态大于或等于-2时,CH4气体分子在Ti3C2O2和V2CO2表面可以被有效捕获。撤去电荷后,Ti3C2O2、V2CO2与CH4气体分子之间的吸附恢复至物理吸附,CH4气体分子易脱附。因此,通过调控Ti3C2O2和V2CO2的电荷态,可以简单地实现CH4的捕获与释放。Ti3C2O2和V2CO2有望成为CH4探测或捕获材料。