Influence of Spin-Orbit Couplings to Nuclear Spin-Lattice Relaxation Rates in Sr-Doped La2CuO4

The electronic structure of Sr-doped La₂CuO₄ has been investigated by means of cluster calculations. The results indicate changes in the energies of the molecular orbitals when a copper atom is in the neighborhood of a Sr; in particular, the spin-orbit coupling is altered. It is shown that the Cu nuclear spin-lattice relaxation time depends crucially on this coupling when measured along the direction perpendicular to the CuO₂ planes. It is argued that the results presented here are compatible with recent experimental observations.     

Shape-Resonant Superconductivity in Nanofilms: from Weak to Strong Coupling

Ultrathin superconductors of different materials are becoming a powerful platform to find mechanisms for enhancement of superconductivity, exploiting shape resonances in different superconducting properties. Here, we evaluate the superconducting gap and its spatial profile, the multiple gap components, and the chemical potential, of generic superconducting nanofilms, considering the pairing attraction and its energy scale as tunable parameters, from weak to strong coupling, at fixed electron density. Superconducting properties are evaluated at mean field level as a function of the thickness of the nanofilm, in order to characterize the shape resonances in the superconducting gap. We find that the most pronounced shape resonances are generated for weakly coupled superconductors, while approaching the strong coupling regime the shape resonances are rounded by a mixing of the subbands due to the large energy gaps extending over large energy scales. Finally, we find that the spatial profile, transverse to the nanofilm, of the superconducting gap acquires a flat behavior in the shape resonance region, indicating that a robust and uniform multigap superconducting state can arise at resonance.     

Crossover from Cooper Pairing to Bose Condensation in van Hove Superconductors with Localized States

We showed that in a two-dimensional superconductor with logarithmic density of states (van Hove superconductor) the crossover between weak and strong coupling is possible. The influence of localized states induced by impurities on this transition has been studied at T=0.     

A Unified and Asymptotically Exact Theory of Superconductivity from Weak to Strong Coupling in an Electron–Phonon Model

Since the discovery of MgB₂, fundamental studies of the electronphonon mechanism have received intense interest. In this paper, starting from an electron–phonon model Hamiltonian, the third formalism of quantum statistics, and a diagonalization theorem, a unified and asymptotically exact theory of superconductivity is developed. The results are compared with those of McMillan, Allen and Dynes and experimental data. It is shown that the new results are in very good agreement with the experimental data. The unified theory has no extra assumptions and also supplies an exactly soluble example of the third formalism of quantum statistics. The T_c of MgB₂ is at a unified T_c line, the reason for the vacuum fluctuation mechanism are also discussed.     

An Effective Interaction Approach to Anisotropic Superconductors Beyond the Weak Coupling Theory—An Origin of the d-wave Symmetry in High-T c Cuprate

We propose an effective interaction approach to superconducting systems which is adapted to periodic systems and intermediate net coupling between charge carriers by phonon mediated and Coulomb repulsive interactions. A coupling function of effective interaction is given for homogeneous field beyond the weak coupling approximation by using a generalized intermediate coupling method. Adequate kernel for the periodic systems is also reduced to that coupling function in homogeneous field and the Fourier coefficients relevant to the Bloch function. Within the present approach we discuss the symmetry of the superconducting gap in cuprate under the assumption that a nonbonding band filled by 2p_σ electrons exists in an undoped system and that doped holes occupy orbitals in this band. Those orbitals are represented by linear combinations of p _x and p _y functions. It is argued, in the tetragonal limit, that the symmetry of the gap function is d-wave-like on account of the products of orbital functions in combination of singlet spin-pair in the kernel.     

Modeling Relaxation Processes for Fluids in Porous Materials Using Dynamic Mean Field Theory: An Application to Partial Wetting

We review a recently developed dynamic mean field theory for fluids confined in porous materials and apply it to a case where the solid-fluid interactions lead to partial wetting on a planar surface. The theory describes the evolution of the density distribution for a fluid in a pore that has contact with the bulk during a quench in the bulk chemical potential. In this way the dynamics of adsorption and desorption can be studied. By focusing on partial wetting situation we can investigate influence of a weaker surface field on the mechanisms of capillary condensation and desorption. We have studied the dynamics of pore filling in a quench of the chemical potential between two states either side of the pore filling step, tracking the density distributions during the process. The pore filling process features an asymmetric density distribution where a liquid droplet appears on one of the walls. The droplet spreads and grows in size and this is followed by the appearance of a liquid bridge between the pore walls (for longer pores two liquid bridges are seen). The density distributions obtained in the dynamics resemble those obtained from static mean field theory in the canonical ensemble for an infinite pore without contact with the bulk.     

Observation of Crossover from Ballistic to Diffusion Regime for Excimer Molecules in Superfluid 4He

We have measured the temperature dependence of the time of flight of helium excimer molecules $\mathrm {He}_{2}^{*}(a^{3}\Sigma ^{+}_{u})$  in superfluid ⁴He and find that the molecules behave ballistically below ～100 mK and exhibit Brownian motion above ～200 mK. In the intermediate temperature range the transport cannot be described by either of the models.     

Evidence for s+d Wave Pairing in Copper Oxide Superconductors from an Analysis of NMR and NQR Data

Knight shift and spin-lattice relaxation rate data of high temperature copper oxide superconductors are analyzed within a two-band model for superconductivity with coupled s+d wave superconducting gaps. The two-gap approach leads to substantial modifications of the coherence factors, which reflects itself in the Knight shift and the relaxation rate 1/T ₁ T. From the analysis it is concluded that the data are consistent with 40% s-wave and 60% d-wave gap admixtures, in agreement with earlier penetration depth data.     

Crossover from meta-magnetic state to spin-glass behaviour upon Ti-substitution for Mn in CuMn2O4

Journal of Materials Science: Materials in Electronics - Tetragonal distorted spinel of CuMn2?xTixO4 (x?=?0, 0.25 and 0.50) was prepared by solid state reaction method followed by...     

Charge dynamics in (La,Sr)2CuO4: from underdoping to overdoping

The normal state transport properties (resistivity, Hall effect) of La_2–xSr_xCuO⁴ have been studied over wide ranges of Sr doping and temperature. The familiar T-linear resistivity and the strongly T dependent Hall effect R_H(T) are found only near the optimal hole concentration (x 0.15–0.18). The charge dynamics changes significantly in the non-superconducting overdoped range with R_H(T) becoming constant above a characteristic temperature T*, and p(T) Tⁿ (n > 1; n 1.5±0.1). The temperature scale T*, decreasing with increasing hole concentration, provides a link between transport and magnetic properties.     

Erratum to: Charge transfer in graphene/polymer interfaces for CO2 detection

Nano Research - The order of the authors in the original version of this article was unfortunately incorrect on the first page and the first page of the ESM. Instead of Myungwoo Son1, Yusin Pak1,...     

A Unified Theory for the Cuprates, Iron-Based and Similar Superconducting Systems: Application for Spin and Charge Excitations in the Hole-Doped Cuprates

A unified theory for the cuprates and the iron-based superconductors is derived on the basis of common features in their electronic structures, including quasi-two-dimensionality, and the large-U nature of the electron orbitals close to E_FE_{_{\textrm{F}}} (smaller-U hybridized orbitals reside at bonding and antibonding states away from E_FE_{_{\textrm{F}}} ). Consequently, low-energy excitations are described in terms of auxiliary particles, representing combinations of atomic-like electron configurations, rather than electron-like quasiparticles. The introduction of a Lagrange–Bose field is necessary to enable the treatments of these auxiliary particles as bosons or fermions. The condensation of the bosons results in static or dynamical inhomogeneities, and consequently in a commensurate or an incommensurate resonance mode. The dynamics of the fermions determines the charge transport, and their strong coupling to the Lagrange-field bosons results in pairing and superconductivity. The calculated resonance mode in hole-doped cuprates agrees with the experimental results, and is shown to be correlated with the pairing gap on the Fermi arcs.     

回归自然:人造岩石固化核素的思考与进展

核工业生产、核能开发、核武器研制等不可避免会产生放射性废物,高放废物是现存放射性废物中最难处理的废物之一。随着我国"积极发展核电"战略的实施,放射性废物的安全有效处理处置成为关系到我国核能可持续发展的关键问题。人造岩石固化体(SYNROC)弥补了玻璃固化体低化学耐久性和亚稳态性能的缺点。本文在综述人造岩石固化的概念、候选矿物固化体分类的基础上,重点介绍了SYNROC固化体快速合成方法、固核机理和长期稳定性评价等方面的最新研究进展。"道阻且长,行则将至"。最后,指出了SYNROC固化存在的不足,并针对今后应重点关注的研究方向与发展趋势提出了建议。     

Study of Extraction of Palladium from Nitric Acid Solutions with Nitrogen-Containing Compounds,as Applied to Recovery of Fission Palladium from Spent Nuclear Fuel of Nuclear Power Plants: 3. Optimization of Extraction Process for Palladium Recovery and Refining

An extraction process for recovery of fission Pd is proposed. The process parameters are optimized with simulated high-level liquid radioactive waste from nuclear power plants using tri-n-octylamine (TOA) and tricaprylmethylammonium nitrate (Aliquat 336 nitrate) as extractants. The degree of Pd decontamination from fission and corrosion products is estimated and the major interfering components are determined.