400 research outputs found
Electron pairing: from metastable electron pair to bipolaron
Starting from the shell structure in atoms and the significant correlation
within electron pairs, we distinguish the exchange-correlation effects between
two electrons of opposite spins occupying the same orbital from the average
correlation among many electrons in a crystal. In the periodic potential of the
crystal with lattice constant larger than the effective Bohr radius of the
valence electrons, these correlated electron pairs can form a metastable energy
band above the corresponding single-electron band separated by an energy gap.
In order to determine if these metastable electron pairs can be stabilized, we
calculate the many-electron exchange-correlation renormalization and the
polaron correction to the two-band system with single electrons and electron
pairs. We find that the electron-phonon interaction is essential to
counterbalance the Coulomb repulsion and to stabilize the electron pairs. The
interplay of the electron-electron and electron-phonon interactions, manifested
in the exchange-correlation energies, polaron effects, and screening, is
responsible for the formation of electron pairs (bipolarons) that are located
on the Fermi surface of the single-electron band.Comment: 17 pages, 6 figures, Journal of Physics Communications 201
Fidelity susceptibility, scaling, and universality in quantum critical phenomena
We study fidelity susceptibility in one-dimensional asymmetric Hubbard model,
and show that the fidelity susceptibility can be used to identify the
universality class of the quantum phase transitions in this model. The critical
exponents are found to be 0 and 2 for cases of half-filling and away from
half-filling respectively.Comment: 4 pages, 4 figure
Quantum criticality of the Lipkin-Meshkov-Glick Model in terms of fidelity susceptibility
We study the critical properties of the Lipkin-Meshkov-Glick Model in terms
of the fidelity susceptibility. By using the Holstein-Primakoff transformation,
we obtain explicitly the critical exponent of the fidelity susceptibility
around the second-order quantum phase transition point. Our results provide a
rare analytical case for the fidelity susceptibility in describing the
universality class in quantum critical behavior. The different critical
exponents in two phases are non-trivial results, indicating the fidelity
susceptibility is not always extensive.Comment: 3 figure
Preparation of Bioactive Glasses with Controllable Degradation Behavior and Their Bioactive Characterization
Bioactive glasses and ceramics have been widely investigated for bone repair because of their excel-lent bioactive characteristics. However, these biomaterials undergo incomplete conversion into a bone-like material, which severely limits their biomedical application. In this paper, borosilicate bioac-tive glasses were prepared by traditional melting process. The results showed that borosilicate glasses possessed high biocompatibility and bioactivity. In addition, when immersed in a 0.02 mol/L K2HPO4 solution, particles of a borate glass were fully converted to HA. The desirable conversion rate to HA may be achieved through the adjustment of the B2O3/SiO2 ratio. The results of XRD and FTIR analysis indicated that the degradation product was carbonate-substituted hydroxyapatite, which was similar to the inorganic component of bone
Two types of generalized integrable decompositions and new solitary-wave solutions for the modified Kadomtsev-Petviashvili equation with symbolic computation
The modified Kadomtsev-Petviashvili (mKP) equation is shown in this paper to
be decomposable into the first two soliton equations of the 2N-coupled
Chen-Lee-Liu and Kaup-Newell hierarchies by respectively nonlinearizing two
sets of symmetry Lax pairs. In these two cases, the decomposed
(1+1)-dimensional nonlinear systems both have a couple of different Lax
representations, which means that there are two linear systems associated with
the mKP equation under the same constraint between the potential and
eigenfunctions. For each Lax representation of the decomposed (1+1)-dimensional
nonlinear systems, the corresponding Darboux transformation is further
constructed such that a series of explicit solutions of the mKP equation can be
recursively generated with the assistance of symbolic computation. In
illustration, four new families of solitary-wave solutions are presented and
the relevant stability is analyzed.Comment: 23 page
Quasiparticle Scattering Interference in High Temperature Superconductors
We propose that the energy-dependent spatial modulation of the local density
of states seen by Hoffman, et al [hoff2] is due to the scattering interference
of quasiparticles. In this paper we present the general theoretical basis for
such an interpretation and lay out the underlying assumptions. As an example,
we perform exact T-matrix calculation for the scattering due to a single
impurity. The results of this calculation is used to check the assumptions, and
demonstrate that quasiparticle scattering interference can indeed produce
patterns similar to those observed in Ref. [hoff2].Comment: RevTex4 twocolumn, 4 pages, 3 figures. Figs.2-3 virtually embedded
(bacause of too big size) while jpg files available in the postscript/source
package. Further polishe
Interpretation of cone penetration test data in layered soils using cavity expansion analysis
Cavity expansion theory plays an important role in many geotechnical engineering problems, including the cone penetration test (CPT). One of the challenges of interpreting CPT data is the delineation of interfaces between soil layers and the identification of distinct thin layers, a process which relies on an in-depth understanding of the relationship between penetrometer readings and soil properties. In this paper, analytical cavity expansion solutions in two concentric regions of soil are applied to the interpretation of CPT data, with a specific focus on the layered effects during penetration. The solutions provide a large-strain analysis of cavity expansion in two concentric regions for dilatant elastic-perfectly plastic material. The analysis of CPT data in two-layered soils highlights the effect of respective soil properties (strength, stiffness) on CPT measurements within the influence zones around the two-soil interface. Results show good comparisons with numerical results and elastic solutions. A simple superposition method of the two-layered analytical approach is applied to the analysis of penetration in multilayered soils. A good comparison with field data and numerical results is obtained. It is illustrated that the proposed parameters effectively capture the influence of respective soil properties in the thin-layer analysis. It is also shown that results based on this analysis have better agreement with numerical results compared with elastic solutions
Enhanced low-energy magnetic excitations via suppression of the itinerancy in Fe0.98-zCuzTe0.5Se0.5
We have performed resistivity and inelastic neutron scattering measurements
on three samples of Fe0.98-zCuzTe0.5Se0.5 with z = 0, 0.02, and 0.1. It is
found that with increasing Cu doping the sample's resistivity deviates
progressively from that of a metal. However, in contrast to expectations that
replacing Fe with Cu would suppress the magnetic correlations, the low-energy
(no larger than 12 meV) magnetic scattering is enhanced in strength, with
greater spectral weight and longer dynamical spin-spin correlation lengths.
Such enhancements can be a consequence of either enlarged local moments or a
slowing down of the spin fluctuations. In either case, the localization of the
conduction states induced by the Cu doping should play a critical role. Our
results are not applicable to models that treat 3d transition metal dopants
simply as effective electron donors.Comment: 5 pages, 5 figures. To appear in PR
Staggered Currents in the Vortex Core
We study the electronic structure of the vortex core in the cuprates using
the U(1) slave-boson mean-field wavefunctions and their Gutzwiller projection.
We conclude that there exists local orbital antiferromagnetic order in the core
near optimal doping. We compare the results with that of BCS theory and analyze
the spatial dependence of the local tunneling density of states.Comment: 4 pages, 3 figure
Spin-dependent thermoelectric transport through double quantum dots
We study thermoelectric transport through double quantum dots system with
spin-dependent interdot coupling and ferromagnetic electrodes by means of the
non-equilibrium Green function in the linear response regime. It is found that
the thermoelectric coefficients are strongly dependent on the splitting of
interdot coupling, the relative magnetic configurations and the spin
polarization of leads. In particular, the thermoelectric efficiency can achieve
considerable value in parallel configuration when the effective interdot
coupling and tunnel coupling between QDs and the leads for spin-down electrons
are small. Moreover, the thermoelectric efficiency increases with the intradot
Coulomb interactions increasing and can reach very high value at an appropriate
temperature. In the presence of the magnetic field, the spin accumulation in
leads strongly suppresses the thermoelectric efficiency and a pure spin
thermopower can be obtained.Comment: 5 figure
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