2,765 research outputs found
First-principles study on the effective masses of zinc-blend-derived Cu_2Zn-IV-VI_4 (IV = Sn, Ge, Si and VI = S, Se)
The electron and hole effective masses of kesterite (KS) and stannite (ST)
structured Cu_2Zn-IV-VI_4 (IV = Sn, Ge, Si and VI = S, Se) semiconductors are
systematically studied using first-principles calculations. We find that the
electron effective masses are almost isotropic, while strong anisotropy is
observed for the hole effective mass. The electron effective masses are
typically much smaller than the hole effective masses for all studied
compounds. The ordering of the topmost three valence bands and the
corresponding hole effective masses of the KS and ST structures are different
due to the different sign of the crystal-field splitting. The electron and hole
effective masses of Se-based compounds are significantly smaller compared to
the corresponding S-based compounds. They also decrease as the atomic number of
the group IV elements (Si, Ge, Sn) increases, but the decrease is less notable
than that caused by the substitution of S by Se.Comment: 14 pages, 6 figures, 2 table
Reply to "Comment on 'Fano resonance for Anderson Impurity Systems' "
In a recent Comment, Kolf et al. (cond-mat/0503669) state that our analysis
of the Fano resonance for Anderson impurity systems [Luo et al., Phys. Rev.
Lett 92, 256602 (2004)] is incorrect. Here we want to point out that their
comments are not based on firm physical results and their criticisms are
unjustified and invalid.Comment: 1 page, 1 figure, to appear in PR
The Fano resonance for Anderson impurity systems
We present a general theory for the Fano resonance in Anderson impurity
systems. It is shown that the broadening of the impurity level leads to an
additional and important contribution to the Fano resonance around the Fermi
surface, especially in the mixed valence regime. This contribution results from
the interference between the Kondo resonance and the broadened impurity level.
Being applied to the scanning tunnelling microscopic experiments, we find that
our theory gives a consistent and quantitative account for the Fano resonance
lineshapes for both Co and Ti impurities on Au or Ag surfaces. The Ti systems
are found to be in the mixed valence regime.Comment: 4 pages, 5 figures, published versio
Alloy Stabilized Wurtzite Ground State Structures of Zinc-Blende Semiconducting Compounds
The ground state structures of the ABC wurtzite (WZ) alloys with
0.25, 0.5, and 0.75 are revealed by a ground state search using the
valence-force field model and density-functional theory total energy
calculations. It is shown that the ground state WZ alloy always has a lower
strain energy and formation enthalpy than the corresponding zinc-blende (ZB)
alloy. Therefore, we propose that the WZ phase can be stabilized through
alloying. This novel idea is supported by the fact that the WZ
AlPSb, AlPSb, ZnSTe, and
ZnSTe alloys in the lowest energy structures are more stable
than the corresponding ZB alloys. To our best knowledge, this is the first
example where the alloy adopts a structure distinct from both parent phases
Strong Dzyaloshinskii-Moriya Interaction and Origin of Ferroelectricity in Cu2OSeO3
By performing density functional calculations, we investigate the origin of
the skyrmion state and ferroelectricity in Cu2OSeO3. We find that the
Dzyaloshinskii-Moriya interactions between the two different kinds of Cu ions
are extremely strong and induce the helical ground state and the skyrmion state
in the absence and presence of magnetic field, respectively. On the basis of
the general model for the spin-order induced polarization, we propose that the
ferroelectric polarization of Cu2OSeO3 in the collinear ferrimagnetic state
arises from an unusual mechanism, i.e., the single-spin-site contribution due
to the spin-orbit coupling
Thermodynamics of the bilinear-biquadratic spin one Heisenberg chain
The magnetic susceptibility and specific heat of the one-dimensional S=1
bilinear-biquadratic Heisenberg model are calculated using the transfer matrix
renormalization group. By comparing the results with the experimental data of
measured by Millet et al. (Phys. Rev. Lett. {\bf 83}, 4176
(1999)), we find that the susceptibility data of this material, after
subtracting the impurity contribution, can be quantitatively explained with
this model. The biquadratic exchange interaction in this material is found to
be ferromagnetic, i.e. with a positive coupling constant.Comment: 4 pages, 4 postscript figure
First-principles study of defect properties of zinc blende MgTe
We studied the general chemical trends of defect formation in MgTe using first-principles band structure methods. The formation energies and transition energy levels of intrinsic defects and extrinsic impurities and some defect complexes in zinc blende MgTe were calculated systematically using a new hybrid scheme. The limiting factors for p-and n-type doping in MgTe were investigated. Possible solutions to overcome the doping limitation of MgTe are proposed. The best p-type dopant is suggested to be N with nonequilibrium growth process and the best n-type dopant is suggested to be I with its doping complex V Mg + 4I Te
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