arXiv subjects

W. T. Geng

Publications and source records attributed to W. T. Geng.

25 records · Page 2Linked to original sources

arXiv2007

Quark Confinement and the Fractional Quantum Hall Effect

Working in the physics of Wilson factor and Aharonov-Bohm effect, we find in the fluxtube-quark system the topology of a baryon consisting three heavy flavor quarks resembles that of the fractional quantum Hall effect (FQHE) in condensed matter. This similarity yields the result that the constituent quarks of baryon have the "filling factor" 1/3, thus the previous conjecture that quark confinement is a correlation effect was confirmed. Moreover, by deriving a Hamiltonian of the system analogous to that of FQHE, we predict an energy gap for the ground state of a heavy three-quark system.

hep-ph↗

arXiv2006

Understanding entangled spins in QED

The stability of two entangled spins dressed by electrons is studied by calculating the scattering phase shifts. The interaction between electrons is interpreted by fully relativistic QED and the screening effect is described phenomenologically in the Debye exponential form $e^{-αr}$. Our results show that if the (Einstein-Podolsky-Rosen-) EPR-type states are kept stable under the interaction of QED, the spatial wave function must be parity-dependent. The spin-singlet state $s=0$ and the polarized state $\frac 1{\sqrt{2}}(\mid +-> -\mid -+>)$ along the z-axis\QTR{bf}{\}give rise to two different kinds of phase shifts\QTR{bf}{.} Interestingly, the interaction between electrons in the spin-singlet pair is found to be attractive. Such an attraction could be very useful when we extract the entangled spins from superconductors. A mechanism to filter the entangled spins is also discussed.

quant-ph↗

arXiv2005

Atomic size effect in impurity indued grain boundary embrittlement

Bismuth segregated to the grain boundary in Cu is known to promote brittle fracture of this material. Recently, Schweinfest et al. reported first-principles quantum mechanical calculations on the electronic and structural properties of a Cu grain boundary with and without segregated Bi and argue that the grain boundary weakening induced by Bi is a simple atomic size effect. But their conclusion is invalid for both Bi and Pb because it fails to distinguish the chemical and mechanical (atomic size) contributions, as obtained with our recently developed first-principles based phenomenological theory.

cond-mat.mtrl-sci↗

arXiv2003

Room-Temperature Ferromagnetism in Co-Doped TiO$_2$ Anatase: Role of Interstitial Co

TiO$_2$ anatase doped with Co has been recently reported to exhibit room-temperature ferromagnetism. $Ab$ $initio$ study on substitutional Co doping, however, yielded much larger magnetic moment for Co than experiment. Our calculations based on density-functional theory show that the substitutional Co ions incorporated into TiO$_2$ anatase tend to cluster and then the neighboring interstitial tetrahedral sites become energetically favorable for Co to reside, yielding a local environment more like Co$_3$O$_4$ than CoTiO$_3$. The interstitial Co destroys the spin-polarization of the surrounding substitutional Co but enhances the stability of the ferromagnetism significantly. In the absence of carriers, this room-temperature ferromagnetism can only be accounted for by superexchange interaction.

cond-mat.mtrl-sci↗

arXiv2003

Structural, electronic, and magnetic properties of a ferromegnetic semiconductor: Co-doped TiO$_2$ rutile

Room-temperature ferromagnetism has been recently discovered in Co-doped TiO$_2$ rutile. Our $ab$ $initio$ density-functional theory investigations show that the substitutional Co ions incorporated into TiO$_2$ rutile tend to cluster and then the neighboring interstitial sites become energetically favorable for Co to reside. This suggests that a Co-doped rutile containing only substitutional Co is not an appropriate reference bulk system in derterming the local environment of Co in polycrystalline (Ti,Co)O$_2$ rutile. We also find that the interstitial Co is in the low spin state and destroys the spin-polarization of the surrounding substitutional Co, hence reduces the average magnetic moment of impurity atoms.

cond-mat.mtrl-sci↗

arXiv2001

Coordination and chemical effects on the structural, electronic and magnetic properties in Mn pnictides

Simple structures of MnX binary compounds, namely hexagonal NiAs and zincblende, are studied as a function of the anion (X = Sb, As, P) by means of the all-electron FLAPW method within local spin density and generalized gradient approximations. An accurate analysis of the structural, electronic and magnetic properties reveals that the cubic structure greatly favours the magnetic alignment in these compounds leading to high magnetic moments and nearly half-metallic behaviour for MnSb and MnAs. The effect of the anion chemical species is related to both its size and the possible hybridization with the Mn $d$ states; both contributions are seen to hinder the magnitude of the magnetic moment for small and light anions. Our results are in very good agreement with experiment - where available - and show that the generalized gradient approximation is essential to correctly recover both the equilibrium volume and magnetic moment.

cond-mat.mtrl-sci↗

arXiv1999

A simple scaling law between the total energy of a free atom and its atomic number

A simple, approximate relation is found between the total energy of a free atom and its atomic number: E ~= -Z^{2.411}. The existence of this index is inherent in the Coulomb and many-body nature of the electron-electron interaction in the atomic system and cannot be fabricated from the existing fundamental physical constants.

physics.chem-ph↗