847 research outputs found
Electronic Structure of KFeSe from First Principles Calculations
Electronic structure and magnetic properties for iron-selenide KFeSe
are studied by first-principles calculations. The ground state is stripe-like
antiferromagnetic with calculated 2.26 magnetic moment on Fe atoms; and
the , coupling strengths are calculated to be 0.038 eV and 0.029 eV.
The states around are dominated by the Fe-3d orbitals which hybridize
noticeably to the Se-4p orbitals. While the band structure of KFeSe is
similar to a heavily electron-doped BaFeAs or FeSe system, the Fermi
surface of KFeSe is much closer to \fs11 system since the electron
sheets around is symmetric with respect to - exchange. These
features, as well as the absence of Fermi surface nesting, suggest that the
parental KFeSe could be regarded as an electron over-doped 11 system
with possible local moment magnetism.Comment: accepted by Chinese Physics Letter, to appear as Chinese Physics
Letter, Vol 28, page 057402 (2011
Malat1 as an evolutionarily conserved lncRNA, plays a positive role in regulating proliferation and maintaining undifferentiated status of early-stage hematopoietic cells
Background: The metastasis-associated lung adenocarcinoma transcription 1 (Malat1) is a highly conserved long non-coding RNA (lncRNA) gene. Previous studies showed that Malat1 is abundantly expressed in many tissues and involves in promoting tumor growth and metastasis by modulating gene expression and target protein activities. However, little is known about the biological function and regulation mechanism of Malat1 in normal cell proliferation. Results: In this study we conformed that Malat1 is highly conserved across vast evolutionary distances amongst 20 species of mammals in terms of sequence, and found that mouse Malat1 expresses in tissues of liver, kidney, lung, heart, testis, spleen and brain, but not in skeletal muscle. After treating erythroid myeloid lymphoid (EML) cells with All-trans Retinoic Acid (ATRA), we investigated the expression and regulation of Malat1 during hematopoietic differentiation, the results showed that ATRA significantly down regulates Malat1 expression during the differentiation of EML cells. Mouse LRH (Lin-Rhodamine low Hoechst low ) cells that represent the early-stage progenitor cells show a high level of Malat1 expression, while LRB (Lin − Hoechst Low Rhodamine Bright ) cells that represent the late-stage progenitor cells had no detectable expression of Malat1. Knockdown experiment showed that depletion of Malat1 inhibits the EML cell proliferation. Along with the down regulation of Malat1, the tumor suppressor gene p53 was up regulated during the differentiation. Interestingly, we found two p53 binding motifs with help of bioinformatic tools, and the following chromatin immunoprecipitation (ChIP) test conformed that p53 acts as a transcription repressor that binds to Malat1’s promoter. Furthermore, we testified that p53 over expression in EML cells causes down regulation of Malat1. Conclusions: In summary, this study indicates Malat1 plays a critical role in maintaining the proliferation potential of early-stage hematopoietic cells. In addition to its biological function, the study also uncovers the regulation pattern of Malat1 expression mediated by p53 in hematopoietic differentiation. Our research shed a light on exploring the Malat1 biological role including therapeutic significance to inhibit the proliferation potential of malignant cells
Entanglement and quantum phase transition in quantum mixed spin chains
The ground entanglement and thermal entanglement in quantum mixed spin chains
consisting of two integer spins 1 and two half integer spins 1/2 arrayed as
in a unit cell with antiferromagnetic nearest-neighbor
couplings () between the spins of equal (different) magnitudes, are
investigated by adopting the log-negativity. The ground entanglement transition
found here is closely related with the valence bond state transition, and the
thermal entanglement near the critical point is calculated and shown that two
distinct behaviors exist in the nearest neighbor same kind of spins and
different kind of spins, respectively. The potential application of our results
on the quantum information processing is also discussed.Comment: 5 pages, 4 figures, RevTex4, A minor correction is added into the
figure captio
Single Transverse Spin Asymmetries at Parton Level
Two factorization approaches have been proposed for single transverse spin
asymmetries. One is the collinear factorization, another is the
transverse-momentum-dependent factorization. They have been previously derived
in a formal way by using diagram expansion at hadron level. If the two
factorizations hold or can be proven, they should also hold when we replace
hadrons with parton states. We examine these two factorizations at parton level
with massless partons. It is nontrivial to generate these asymmetries at parton
level with massless partons because the asymmetries require helicity-flip and
nonzero absorptive parts in scattering amplitudes. By constructing suitable
parton states with massless partons we derive the two factorizations for the
asymmetry in Drell-Yan processes. It is found from our results that the
collinear factorization derived at parton level is not the same as that derived
at hadron level. Our results with massless partons confirm those derived with
single massive parton state in our previous works.Comment: shortened version to match published versio
Spontaneous symmetry breaking and bifurcations in ground state fidelity for quantum lattice systems
Spontaneous symmetry breaking occurs in a system when its Hamiltonian
possesses a certain symmetry, whereas the ground state wave functions do not
preserve it. This provides such a scenario that a bifurcation, which breaks the
symmetry, occurs when some control parameter crosses its critical value. It is
unveiled that the ground state fidelity per lattice site exhibits such a
bifurcation for quantum lattice systems undergoing quantum phase transitions.
The significance of this result lies in the fact that the ground state fidelity
per lattice site is \textit{universal}, in the sense that it is
model-independent, in contrast to (model-dependent) order parameters. This
fundamental quantity may be computed by exploiting the newly-developed tensor
network algorithms on infinite-size lattices. We illustrate the scheme in terms
of the quantum Ising model in a transverse magnetic field and the spin 1/2 XYX
model in an external magnetic field on an infinite-size lattice in one spatial
dimension.Comment: 4+pages, 3 figure
Detection of a superconducting phase in a two-atom layer of hexagonal Ga film grown on semiconducting GaN(0001)
The recent observation of superconducting state at atomic scale has motivated
the pursuit of exotic condensed phases in two-dimensional (2D) systems. Here we
report on a superconducting phase in two-monolayer crystalline Ga films
epitaxially grown on wide band-gap semiconductor GaN(0001). This phase exhibits
a hexagonal structure and only 0.552 nm in thickness, nevertheless, brings
about a superconducting transition temperature Tc as high as 5.4 K, confirmed
by in situ scanning tunneling spectroscopy, and ex situ electrical
magneto-transport and magnetization measurements. The anisotropy of critical
magnetic field and Berezinski-Kosterlitz-Thouless-like transition are observed,
typical for the 2D superconductivity. Our results demonstrate a novel platform
for exploring atomic-scale 2D superconductor, with great potential for
understanding of the interface superconductivity
Electronic structure and phase stability of MgTe, ZnTe, CdTe, and their alloys in the B3, B4, and B8 structures
The electronic structure and phase stability of MgTe, ZnTe, and CdTe were examined in the zinc-blende Í‘B3Í’, wurtzite Í‘B4Í’, and NiAs-type Í‘B8Í’ crystal structures using a first-principles method. Both the band-gap and valence-band maximum Í‘VBMÍ’ deformation potentials of MgTe, ZnTe, and CdTe in the B3 structure were analyzed, revealing a less negative band-gap deformation potential from ZnTe to MgTe to CdTe, with a VBM deformation potential increase from CdTe to ZnTe to MgTe. The natural band offsets were calculated taking into account the core-level deformation. Ternary alloy formation was explored through application of the special quasirandom structure method. The B3 structure is found to be stable over all Í‘Zn,CdÍ’Te compositions, as expected from the preferences of ZnTe and CdTe. However, the Í‘Mg,ZnÍ’Te alloy undergoes a B3 to B4 transition above 88% Mg concentration and a B4 to B8 transition above 95% Mg concentration. For Í‘Mg,CdÍ’Te, a B3 to B4 transition is predicted above 80% Mg content and a B4 to B8 transition above 90% Mg concentration. Using the calculated band-gap bowing parameters, the B3 Í‘Mg,ZnÍ’Te Í“Í‘Mg,CdÍ’TeÍ” alloys are predicted to have accessible direct band gaps in the range 2.39Í‘1.48Í’-3.25Í‘3.02Í’ eV, suitable for photovoltaic absorbers
Spin Injection and Inverse Edelstein Effect in the Surface States of Topological Kondo Insulator SmB6
There has been considerable interest in exploiting the spin degrees of
freedom of electrons for potential information storage and computing
technologies. Topological insulators (TI), a class of quantum materials, have
special gapless edge/surface states, where the spin polarization of the Dirac
fermions is locked to the momentum direction. This spin-momentum locking
property gives rise to very interesting spin-dependent physical phenomena such
as the Edelstein and inverse Edelstein effects. However, the spin injection in
pure surface states of TI is very challenging because of the coexistence of the
highly conducting bulk states. Here, we experimentally demonstrate the spin
injection and observe the inverse Edelstein effect in the surface states of a
topological Kondo insulator, SmB6. At low temperatures when only surface
carriers are present, a clear spin signal is observed. Furthermore, the
magnetic field angle dependence of the spin signal is consistent with
spin-momentum locking property of surface states of SmB6.Comment: 15 pages, 5 figures, Accepted to Nature Communications (In Press
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