The low energy phonons of two different graphite intercalation compounds (GICs) have been measured as a function of temperature using inelastic x-ray scattering (IXS). In the case of the non-superconductor BaC6, the phonons observed are significantly higher (up to 20 %) in energy than those predicted by theory, in contrast to the reasonable agreement found in superconducting CaC6. Additional IXS intensity is observed below 15 meV in both BaC6 and CaC6. It has been previously suggested that this additional inelastic intensity may arise from defect or vacancy modes in these compounds, unpredicted by theory (d'Astuto et al, Phys. Rev. B 81 104519 (2010)). Here it is shown that this additional intensity can arise directly from the large disorder of the available samples. Our results show that future theoretical work is required to understand the relationship between the crystal structure, the phonons and the superconductivity in GICs.
Phonon softening near structural transition in BaFe2As2 observed by inelastic x-ray scattering
在这项工作中，我们提出了一个非弹性X射线散射实验的结果，详细的行为的横向声学[110]声子在BaFe 2 As 2作为温度的函数。当通过结构转变温度冷却时，横向声学声子能量从室温下的值减少，在非弹性动量传递q=0.1附近达到最大位移。这种软化的晶格的结果在一个变化的对称性从四方晶系到斜方晶系在相同的温度下的过渡到长程反铁磁秩序。虽然晶格畸变很小，但磷属元素化物母体化合物的磁交换常数的各向异性很大。我们提出了电子-声子耦合机制来描述晶格软化和磁有序开始之间的相互作用。
Electron-phonon interaction is of central importance for the electrical and heat transport properties of metals, and is directly responsible for charge-density-waves or (conventional) superconducting instabilities. The direct observation of phonon dispersion anomalies across electronic phase transitions can provide insightful information regarding the mechanisms underlying their formation. Here, we review the current status of phonon dispersion studies in superconductors under hydrostatic and uniaxial pressure. Advances in the instrumentation of high resolution inelastic X-ray scattering beaml…
Inelastic X-ray Scattering Study of superconducting SmFeAs(O$_{1-x}$F$_{y}$) Single Crystals: Evidence for Strong Momentum-Dependent Doping-Induced Renormalizations of Optical Phonons
本文报道了SmFeAsO和超导SmFeAsO $_{0.6}$ F $_{0.35}$单晶晶格动力学的非弹性X射线散射实验。特别注意的是沿[100]方向的三个光学模式接近23 meV，偏振的FeAs平面的色散。值得注意的是，这些模式中的两个强烈重整化氟掺杂。这些结果提供了显着的洞察的能量和动量的依赖性的晶格的耦合到电子系统，并强调自旋-声子耦合的重要性，在超导铁磷属元素化物。
Electron-phonon interaction in copper oxide superconductors is still enigmatic. Strong coupling for certain optic phonons is now well established experimentally, but theoretical understanding is challenging. Scattering of electrons near the Fermi surface by the longitudinal acoustic (LA) phonons is expected from basic theory because these phonons modulate electron density. We used inelastic neutron scattering on a large single crystal sample of optimally-doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ to show that low-energy LA phonons could couple to electronic density fluctuations only at small phonon w…
Bulk charge density waves are now reported in nearly all high-temperature superconducting cuprates, with the noticeable exception of one particular family: the copper oxychlorides. Here, we used resonant inelastic X-ray scattering to reveal a bulk charge density waves in these materials. Combining resonant inelastic X-ray scattering with non-resonant inelastic X-ray scattering, we investigate the interplay between the lattice excitations and the charge density wave, and evidence the phonon anomalies of the Cu-O bond-stretching mode at the charge density wave wave-vector. We propose that such e…
The coupling between lattice vibration quanta and valence electrons can induce charge density modulations and decisively influence the transport properties of materials, e.g. leading to conventional superconductivity. In high critical temperature superconductors, where electronic correlation is the main actor, the actual role of electron-phonon coupling (EPC) is being intensely debated theoretically and investigated experimentally. We present an in-depth study of how the EPC strength can be obtained directly from resonant inelastic x-ray scattering (RIXS) data through the theoretical approach …
The coupling between lattice and charge degrees of freedom in condensed matter materials is ubiquitous and can often result in interesting properties and ordered phases, including conventional superconductivity, charge density wave order, and metal-insulator transitions. Angle-resolved photoemission spectroscopy and both neutron and non-resonant x-ray scattering serve as effective probes for determining the behavior of appropriate, individual degrees of freedom -- the electronic structure and lattice excitation, or phonon dispersion, respectively. However, each provides less direct information…
Metamaterial approach is capable of drastically increasing the critical temperature, Tc, of composite metal-dielectric superconductors. Tripling of Tc was observed in bulk Al-Al2O3 core-shell metamaterials. A theoretical model based on the Maxwell-Garnett approximation provides a microscopic explanation of this effect in terms of electron-electron pairing mediated by a hybrid plasmon-phonon excitation. We report the first observation of this excitation in Al-Al2O3 core-shell metamaterials using inelastic neutron scattering. This result provides support for this novel mechanism of superconducti…
We report on a comparative study of the electronic structure, phonon spectra, and superconducting properties for recently discovered superconducting hydrides, H3S and H3P. While the electronic structures of these two materials are similar, there are notable changes in the phonon spectra and electron-phonon coupling. The low-frequency bond-bending modes are softened in H3P and their coupling to the electrons at the Fermi surface is enhanced relative to H3S. Nevertheless, coupling to the high-frequency modes is reduced so the resulting calculated superconducting transition temperature is reduced…
Phonon-assisted electronic tunnelings through a vibrating quantum dot embedded between normal and superconducting leads are studied in the Kondo regime. In such a hybrid device, with the bias applied to the normal lead, we find a series of Kondo sidebands separated by half a phonon energy in the differential conductance, which are distinct from the phonon-assisted sidebands previously observed in the conventional Andreev tunnelings and in systems with only normal leads. These Kondo sidebands originate from the Kondo-Andreev cooperative cotunneling mediated by phonons, which exhibit a novel Kon…
We present a study of the lattice dynamical properties of superconducting SrPt$_3$P ($T_c = 8.4$ K) via high-resolution inelastic x-ray scattering (IXS) and ab initio calculations. Density functional perturbation theory including spin-orbit coupling (SOC) results in enhanced electron-phonon coupling (EPC) for the optic phonon modes originating from the Pt(I) atoms, with energies $\sim 5$ meV, resulting in a large EPC constant $λ\sim 2$. An overall softening of the IXS powder spectra occurs from room to low temperatures, consistent with the predicted strong EPC and with recent specific-heat exp…
Ab initio lattice dynamics simulations and inelastic neutron scattering spectra for studying phonons in BaFe2As2: Effect of structural phase transition, structural relaxation and magnetic ordering
Phonon density of states, anharmonicity, electron-phonon coupling and possible multigap superconductivity in the clathrate superconductors Ba8Si46 and Ba24Si100: Why is Tc different in these two compounds?
Phonon spectra of detwinned {SrFe$_2$As$_2$} crystals, as measured by inelastic x-ray scattering, show clear anisotropy accompanying the magneto-structural transition at 200 K. We model the mode splitting using magnetic DFT calculations, including a phenomenological reduction in force-constant anisotropy that can be attributed to magnetic fluctuations. This serves as a starting point for a general model of phonons in this material applicable to both magnetic and non-magnetic phase. Using this model, the measured splitting in the magnetic phase below $\it T_{N}$, and the measured phonon linewid…
We report an inelastic x-ray scattering investigation of phonons in FeSe superconductor. Comparing the experimental phonon dispersion with density functional theory (DFT) calculations in the non-magnetic state, we found a significant disagreement between them. Improved overall agreement was obtained by allowing for spin-polarization in the DFT calculations, despite the absence of magnetic order in the experiment. This calculation gives a realistic approximation, at DFT level, of the disordered paramagnetic state of FeSe, in which strong spin fluctuations are present.
Lattice Dynamics of LiFeAs studied by Inelastic Neutron Scattering and Density Functional Theory calculations
II. Physikalisches Institut, Universität zu Köln（科隆大学第二物理研究所）；Institut Laue Langevin（朗之万研究所）；Karlsruher Institut für Technologie (KIT)（卡尔斯鲁厄理工学院）；Université Paris-Saclay, CNRS, CEA, Laboratoire Léon Brillouin（巴黎萨克雷大学）；CNRS UMR 7198, Université de Lorraine（洛林大学）；Leibniz-Institut für Festkörper u. Werkstoffforschung (IFW) Dresden（德累斯顿莱布尼茨固体与材料研究所）；Indian Institute of Science Education and Research, Pune（浦那印度科学教育与研究学院）
Nonlinear electrical effects in superconducting S-c-S contacts, including the spectroscopy of electron-phonon interactions (EPI) in these systems, and the recovery of the EPI function from experimental data are discussed. The effect of a magnetic field on the current-voltage characteristics(I-V curves) and their derivatives for ErNi_2B_2C point contacts (PC) with $d\ge ξ$ (where $d$ is the diameter of the PC and $ξ$ is the coherence length) is studied. It is found that in zero magnetic fields and in near-critical fields, when the size of the superconducting gap can be neglected, the position o…
Fine structures in the tunneling spectra of superconductors have been widely used to identify fingerprints of the interaction responsible for Cooper pairing. Here we show that for scanning tunneling microscopy (STM) of Pb, the inclusion of inelastic tunneling processes is crucial for the proper interpretation of these fine structures. For STM the usual McMillan inversion algorithm of tunneling spectra must therefore be modified to include inelastic tunneling events, an insight that is crucial for the identification of the pairing glue in conventional and unconventional superconductors alike.
Emergence of an orbital-selective Mott phase (OSMP) found in multi-band correlated systems leads to a non-perturbative obliteration of the Landau Fermi liquid in favor of a novel metallic state exhibiting anomalous infra-red (branch-cut) continuum features in one- and two-particle responses. We use a combination of $(1)$ dynamical mean-field theory (DMFT) using the continuous-time-quantum Monte-Carlo (CTQMC) solver for a two-band Hubbard model and $(2)$ analytic arguments from an effective bosonized description to investigate strange metal features in inelastic neutron scattering studies for c…
