Revealing the insulating gap in α'-NaV (2)O(5) with resonant inelastic x-ray scattering

We measured the low energy excitation spectrum of α'-NaV (2)O(5) across its charge ordering and crystallographic phase transition with resonant inelastic x-ray scattering (RIXS) at the V L(3) edge. Exploiting the polarization dependence of the RIXS signal and the high resolution of the data, we reveal the excitation across the insulating gap at 1?eV and identify the excitations from occupied 3d(xy) bonding orbitals to unoccupied bonding 3d(xy) and 3d(yz)/3d(xz) orbitals. Furthermore we observe a progressive change of the electronic structure of α'-NaV (2)O(5) induced by soft x-ray irradiation, with the appearance of features characteristic of sodium deficient Na(x)V (2)O(5) (x?相似文献   

Direct observation of melted Mott state evidenced from Raman scattering in 1T-TaS_2 single crystal

The evolution of electron correlation and charge density wave(CDW)in 1T-TaS_2 single crystal has been investigated by temperature-dependent Raman scattering,which undergoes two obvious peaks of A_(1g) modes about 70.8 cm~(-1) and 78.7 cm~(-1) at 80 K,respectively.The former peak at 70.8 cm~(-1) is accordant with the lower Hubbard band,resulting in the electron-correlation-driven Mott transition.Strikingly,the latter peak at 78.7 cm~(-1) shifts toward low energy with increasing the temperature,demonstrating the occurrence of nearly commensurate CDW phase(melted Mott phase).In this case,phonon transmission could be strongly coupled to commensurate CDW lattice via Coulomb interaction,which likely induces appearance of hexagonal domains suspended in an interdomain phase,composing the melted Mott phase characterized by a shallow electron pocket.Combining electronic structure,atomic structure,transport properties with Raman scattering,these findings provide a novel dimension in understanding the relationship between electronic correlation,charge order,and phonon dynamics.     

Dependence of the excitation wavelength on the Raman-active phonons of YBa2Cu3O7 Search for Landau damping in single-domain crystals

In single-domain crystals of YBa₂Cu₃O₇, we examine the dependence of phonon linewidth on wavevector by varying the wavelength of the exciting laser. In three crystals, we find the linewidths of the Raman-active phonons at 120 and 150 cm⁻¹ to be nearly invariant for excitation wavelengths between 647 and 413 nm. That is, we find no broadening of the phonon linewidths with increasing phonon wavevector (decreasing excitation wavelength), and thus no evidence of Landau damping in our crystals. In addition, the correlation between the intensity of the chain-related Raman feature at ≈232 cm⁻¹ and the temperature dependence of the B_1g-like phonon at 340 cm⁻¹ has been investigated. In all three crystals, we find a net sharpening of the 340 cm⁻¹ phonon below T_c and essentially no intensity for the ≈232 cm⁻¹ mode under resonance conditions.     

Zone-folding effects on phonons and excitons in polytypic BiI3 single crystals

Resonant Raman scattering (RRS) of new mode phonons in BiI₃ crystals containing stacking faults is reported. Under excitation with laser light tuned to a characteristic sharp absorption line, new mode Raman lines show the resonance behavior. The new phonon modes and the origin of the sharp absorption line can be interpreted in terms of folding back effects of the Brillouin zone for phonons and excitons in a polytypic structure     

钆镓石榴石单晶的喇曼光谱

测量了助熔剂法和提拉法生长的钆镓石榴石单晶的喇曼光谱。识别了该晶体的喇曼活性声子。和文献[6]相比,本文得到了更完全的结果。我们也比较了两种方法生长的晶体的喇曼谱,声子模式彼此一致。发现一些不同的谱线,这被识别为不同稀土掺杂离子的荧光谱线。 关键词：     

Hydrostatic pressure effect on the electron mobility in a ZnSe/Zn1－xdx Se strained heterojunction

With a memory function approach, this paper investigates the electronic mobility parallel to the interface in a ZnSe/Zn1-xCdxSe strained heterojunction under hydrostatic pressure by considering the intersubband and intrasubband scattering from the optical phonon modes. A triangular potential approximation is adopted to simplify the potential of the conduction band bending in the channel side and the electronic penetrating into the barrier is considered by a finite interface potential in the adopted model. The numerical results with and without strain effect are compared and analysed. Meanwhile, the properties of electronic mobility under pressure versus temperature, Cd concentration and electronic density are also given and discussed, respectively. It shows that the strain effect lowers the mobility of electrons while the hydrostatic pressure effect is more obvious to decrease the mobility. The contribution induced by the longitudinal optical phonons in the channel side is dominant to decide the mobility. Compared with the intrasubband scattering it finds that the effect of intersubband scattering is also important for the studied material.     

Raman scattering from mixed crystals (HgBr2)1−x(HgI2)x

The behavior of long wavelength optic phonons in mixed system HgBr₂-HgI₂ has been investigated in Raman scattering. Different types of behavior, i.e. ‘persistent type’ and ‘amalgamation type’ were observed. Three strong Raman bands were observed for persistent type mode. These correspond to stretching vibration of HgBr₂, HgBrI, HgI₂ molecules. Intensity of these bands showed striking concentration dependence. A model based on nearly free molecular approximation have been proposed to explain the dependence. The analysis indicated that the distribution of anions on the sublattices is essentially random. For amalgamation (one-mode) type behavior, it is suggested that the intramolecular force relevant to the vibration is comparable to the intermolecular force and that the band width of the corresponding phonon branch in the parent crystal is broad enough to be degenerate with impurity mode at the low concentration limit.     

LiNbO3:Fe晶体的光折变对喇曼光谱的影响(Ⅱ)

继文献[1]之后,我们又研究了掺Fe浓度为0.07％的LiNbO₃:Fe晶体的光折变对喇曼光谱的影响。发现在x(zx)z和y(zy)z配置下出现异常。这可以由异常声子的极化电场与光折变在晶体中形成的强空间电荷场的相互作用来解释。 关键词：     

Synthesis and electrical properties of In2O3(ZnO)m superlattice nanobelt

One-dimensional（ID） In₂O₃（ZnO）_m superlattice nanobelts are synthesized by a chemical vapor deposition method.The formation of the In₂O₃（ZnO）_m superlattice is verified by the high-resolution transmission electron microscopy images.The typical zigzag boundaries could be clearly observed.An additional peak at 614 cm^-1 is found in the Raman spectrum,which may correspond to the superlattice structure.The study about the electrical transport properties reveals that the In₂O₃（ZnO）_m nanobelts exhibit peculiar nonlinear I-V characteristics even under the Ohmic contact measurement condition,which are different from the Ohmic behaviors of the In-doped ZnO nanobelts.The photoelectrical measurements show the differences in the photocurrent property between them,and their transport mechanisms are also discussed.     

Second order resonant Raman scattering at the E1 and E1 + Δ1 edges of germanium

The resonance of the 2TO phonon second order Raman band of germanium was investigated in the vicinity of the E₁, E₁ + Δ₁ gaps. The peak reported earlier for 2TO phonons at Γ is interpreted as due to a resonant process of the iterative type, involving two first order electron-phonon vertices. The rest of the 2TO band is interpreted as a process involving a second order electron-two phonon interaction vertex. From these measurements three phonon coupling constants for the electron-two phonon interaction are obtained.     

Raman scattering of NiS2

Raman scattering measurements of NiS₂ is done and five optical phonon peaks are found. These peaks are assigned to A_g, E_g and 3T_g phonons which are all of the Raman active optical phonons in pyrite-type crystal. The results are compared with those of FeS₂ and MnS₂.     

Optical phonons in CuAlS2

The optical phonons at k=0 of CuAlS₂ have been investigated by Raman scattering, infrared reflectivity and absorption measurements from 50 to 1000 cm^-1 at T=300 K. Eleven of the thirteen expected optically active phonons have been observed and identified with respect to their symmetry types. The phonon frequencies appear in a range from 498 to 76 cm^-1 with predominant polar modes at 445 and 266 cm^-1. The dielectric dispersion for E ⊥ c and E ∥ c has been determined by Kramers-Kronig integrations.     

静压下(CdTe)_2(ZnTe)_4-ZnTe多量子阱结构的多声子共振拉曼散射

用加静高压的方法改变光学能隙来实现共振条件。在以(CdTe)_2(ZnTe)_4短周期超晶格为阱层,(ZnTe)_(4)为垒层的多量子阱结构中观察到高达四阶的类 ZnTe 纵光学声子模的多声子共振拉曼散射。通过对拉曼位移随压力变化的分析,发现在与(CdTe)_2(ZnTe)_4短周期超晶格共振时测得的类ZnTe 纵光学声子模的频率比与 ZnTe 势垒层共振时测得的 ZnTe 纵光学声子模的频率低4cm~(-1)。并将它归结为在短周期超品格中纵光学声子模的限制效应。在与短周期超品格严格的2LO 声子出射共振条件下观察到了类 CdTe 的2LO 声子的共振拉曼峰。     

自旋梯状化合物Sr14(Cu1-yFey)24O41的拉曼散射谱研究

利用常规的固相合成法制备了三种Sr₁₄(Cu_1-yFe_y)₂₄O₄₁(y=0,0.03,0.05)多晶样品,其中y=0.03是单纯Fe³⁺掺杂,y=0.05是Fe³⁺和Fe²⁺混合掺杂.在100—1500cm^-1频移范围内测量了这三种样品的偏 关键词： 拉曼散射 电输运性质 自旋梯状化合物     

Raman scattering and optical absorption in S2N2 and partially polymerized S2N2 films

Raman scattering and optical absorption measurements between 0.5 and 5.0 eV on crystalline films of S₂N₂ and partly polymerized S₂N₂ have been made for the first time. The Raman active molecular and librational phonons have been observed and assigned. The Raman spectra of partly polymerized S₂N₂ show the appearance of weak scattering at 635 cm⁻¹ and appreciable broadening of the librational phonon peaks. Optical absorption maxima occur at 4.0 and 4.7 eV in pure S₂N₂ at 14 K, while absorptions at 0.86, 1.1 and 4 eV evolve with increasing polymerization.     

Raman phonon anomalies in Sr(Fe1-xCox)2As2

Phonon anomalies have been reported in iron-pnictide superconductors indicating a diverse interplay between different orders in the materials.Here,we report Raman scattering measurements on Sr(Fe_1-xCo_x)₂As₂(x=0 and x=0.04)single crystals in the B;symmetry with respect to a 1 Fe unit cell.Upon cooling,we observe a larger split(13 cm;)of Eg Raman phonon modes pertaining to in-plane Fe and As displacements as the crystals undergo the tetragonal-toorthorhombic structural phase transition,although a considerable split(9 cm;)has been reported in BaFe_1-xCo_x)₂As₂.Furthermore,the splitting of E;phonon modes is strongly reduced upon doping.We perform an order-parameter analysis revealing a similar doping dependence of E;phonon splitting as reported in other compounds of the 122 family,indicating these phonon anomalies widely exist in 122 iron-based superconductors and might share the same mechanisms.     

First-principles phonon calculations of Fe?? impurity in SrTiO?

The results of hybrid density functional theory calculations on phonons in Sr(Fe(x)Ti(1-x))O(3) solid solution within the formalism of a linear combination of atomic orbitals are presented. The phonon density of states (DOS) calculated for 6.25% Fe(4+) impurities is reported and defect-induced phonon modes are identified. Based on our calculations and group-theoretical analysis, we suggest for the first time an interpretation of experimentally observed Raman- and IR-active modes.     

Phonons in the organic conductor TEA(TCNQ)2 studied by neutron inelastic scattering

The lattice dynamics of the one-dimensional organic conductor TEA(TCNQ)₂ is studied by inelastic neutron scattering at temperatures 77, 175 and 295 K. Special attention is paid to the phonons propagating along c¹ which is approximately along the conducting axis. These phonons show a well defined Kohn anomaly at 2k_F as well as gaps which we attribute to both the tetrametic structure of the crystals and to the electron- phonon coupling. The temperature variation of the phonons along c¹ is found to be typical for a system where electron-phonon coupling dominates.     

Raman scattering in intermediate valent SmB6

We have measured the Raman spectra of intermediate valent (IV) SmB₆ and compared it to LaB₆ and EuB₆. Beside the three high energy Raman active phonons we found additional features in the spectra. Most prominent is a peak at 172 cm^-1 for SmB₆, at 214 cm^-1 for LaB₆ and at ～220 cm^-1 for EuB₆. The spectra are analysed in terms of defect induced phonon excitations yielding a weighted phonon density of states. The softening of the line in IV SmB₆ compared to the other hexaborides is unusual since even in the trivalent MB₆ compounds the Raman active phonon modes normally are at lower frequencies than in semiconducting, divalent samples. This phonon softening is explained in analogy with the phonon anomalies in other IV compounds like Sm_1?xY_xS and TmSe.     

Spin-dependent phonon Raman scattering in CdCr2Se4

Influences of ferromagnetic ordering on the phonon Raman scattering are studied for CdCr₂Se₄ through the intensity measurements of Raman spectra between 25 and 300 K with various wavelengths of excitation light (488.0–676.4 nm). Spin-dependent enhancements of Raman cross section are observed for optical phonon lines D(168 cm^?1) and F(238 cm^?1) with excitation wavelengths of about 630 and 550 nm, respectively. This kind of phenomenon in spinel-type chalcogen chromites seems to originate in spin-dependent intermediate interactions in the excited states of specific electronic transitions with which the incident or scattered light is resonant.