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Electron transport properties in a triple-quantum-dot ring with three terminals are theoretically studied. By introducing local Rashba spin-orbit interaction on an individual quantum dot, we calculate the charge and spin currents in one lead. We find that a pure spin current appears in the absence of a magnetic field. The polarization direction of the spin current can be inverted by altering the bias voltage. In addition, by tuning the magnetic field strength, the charge and spin currents reach their respective peaks alternately.PACS numbers: 73.63. Kv, 71.70.Ej, One of the central issue in spintronics is how to realize the spin accumulation and spin transport in nanodevices. Recently, there has been many theoretical proposals to achieve the pure spin current without an accompanying charge current in mesoscopic systems, such as the use of spin Hall effects, 1,2 optical spin orientation by linearly polarized light, 3,4 adiabatic or nonadiabatic spin pumping in metals and semiconductors,generation in three-terminal spin devices. 7 Among these schemes, spin-orbit(SO) coupling is exploited to influences the electron spin state. In particular, in low-dimensional structures Rashba SO interaction comes into play by introducing an electric potential to destroy the symmetry of space inversion in an arbitrary spatial direction.8,9 Thus, by virtue of the Rashba interaction, electric control and manipulation of the electronic spin state is feasible. 10,11,12,13,14 In this Letter, we introduce Rashba interaction to act locally on one component quantum dot(QD) of a triple-QD ring with three terminals. Our theoretical investigation indicates that it is possible to form the pure spin current in one of the three leads even in the absence of a magnetic field. And the polarization direction of the spin current can be inverted by altering the bias voltage.The structure that we consider is illustrated in Fig.1. The single-particle Hamiltonian for an electron in such a structure can be written as H s = H 0 + H so = P 2 2m * + V (r) + H so where, accompanying the kinetic energy term P 2 2m * , the electron confined potential V (r) defines the structure geometry; And H so = y 2 · [α(σ × p) + (σ × p)α] denotes the local Rashba SO coupling on QD-2 (QD-j represents the QD with a single-particle level ε j shown in Fig.1(a)). We select the basis set {ψ kj χ σ , ψ j χ σ }(j=1,2,3) to second-quantize the Hamiltonian. The wavefunctions ψ j and ψ kj have the physical meaning of the orbital eigenstates of the isolated QD and leads, in the absence of Rashba interaction, where k j indicates the continuum state in lead-j. χ σ with σ =↑, ↓ denotes the eigenstates of Pauli spin operatorσ z .The second-quantized Hamiltonian consists of three parts:where c † kj σ and d † jσ (c kj σ and d jσ ) are the creation (annihilation) operators corresponding to the basis states in lead-j and QD-j. ε kj is the single-particle level in lead-j. V jσ = ψ j χ σ |H s |ψ kj χ σ denotes QDlead hopping amplitude. The interdot hopping amplitude, written as t lσ = t l − iσs...

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Mechanical, acoustic and thermal properties for three common hydrates structures sI, sII, and sH were investigated using first-principles methods. Elastic constants were estimated by fitting strain energy versus Lagrangian strain. Bulk modulus, shear modulus, Young's modulus and Poisson's ratio deduced from elastic constants are in reasonable agreement to experimental values. The longitude and transverse velocity compare reasonably with the experimental results with systematical overestimation. Using the quasi-harmonic approximation and Debye model, some thermal properties including heat capacity, linear thermal expansion, Grüneisen parameter, and Debye temperature for structure sI and sII were estimated and compared with available experiments.

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To develop a better understanding of the mechanism responsible for topochemical microcrystal conversion (TMC) from Aurivillius SrBi4Ti4O15 precursors to perovskite SrTiO3 microplatelets, compositional/structural evolutions, morphological development, and reaction interface evolution of the (001) oriented SrBi4Ti4O15 microplatelets were investigated during the conversion process. The results show that multiple topotactic nucleation events of SrTiO3 occurred directly on the surfaces of SrBi4Ti4O15 above 700 °C, while reacting zones of intermediate phase(s) with less Bi(3+) contents were observed to form in the interior of SrBi4Ti4O15. Extensive exfoliation of the precursors occurred generally parallel to the (001) surfaces above 775 °C. At 950 °C, the original single-crystal SrBi4Ti4O15 platelet was replaced by a polycrystalline aggregate consisting of (001) aligned SrTiO3 crystallites and poorly crystallized intermediate phase(s). With further increasing the temperature or holding time, the SrTiO3 phase formed from related intermediate phase(s), and the aligned crystallites were sintered to form dense SrTiO3 with strong (001) orientation. The obtained SrTiO3 microplatelets preserved the shape of SrBi4Ti4O15 and show high chemical and phase purity. This TMC mechanism has general applicability to a variety of compounds and will be very useful for the design and synthesis of novel anisotropic perovskite crystals with high quality in the future.

For a quantum dot ͑QD͒ in the Kondo regime, we introduce a side QD attached to one of the two leads to mimic an Anderson impurity in the conduction electron reservoir. Then, we study the peculiar Kondo effect in such a double QD structure. We find that the Kondo peak in the local density of states in the QDs exhibits a notable deviation from the Lorentzian line shape. More importantly, the expected Kondo peak in the linear conductance turns into zero when a Kondo level or a single-particle level of the side QD is aligned with the Fermi level. This result indicates that the presence of an Anderson impurity in the leads can quench the electron transport through the central QD. The underlying mechanism to cause this behavior is ascribed to quantum interference, which is clearly described in the language of Feynman paths.