53 research outputs found
Two-Dimensional Dirac Fermions Protected by Space-Time Inversion Symmetry in Black Phosphorus
We report the realization of novel symmetry-protected Dirac fermions in a
surface-doped two-dimensional (2D) semiconductor, black phosphorus. The widely
tunable band gap of black phosphorus by the surface Stark effect is employed to
achieve a surprisingly large band inversion up to ~0.6 eV. High-resolution
angle-resolved photoemission spectra directly reveal the pair creation of Dirac
points and their moving along the axis of the glide-mirror symmetry. Unlike
graphene, the Dirac point of black phosphorus is stable, as protected by
spacetime inversion symmetry, even in the presence of spin-orbit coupling. Our
results establish black phosphorus in the inverted regime as a simple model
system of 2D symmetry-protected (topological) Dirac semimetals, offering an
unprecedented opportunity for the discovery of 2D Weyl semimetals
magnetoARPES: Angle Resolved Photoemission Spectroscopy with Magnetic Field Control
Angle-Resolved Photoemission Spectroscopy (ARPES) is a premier technique for
understanding the electronic excitations in conductive, crystalline matter, in
which the induced photocurrent is collected and dispersed in energy and angle
of emission to reveal the energy- and momentum-dependent single particle
spectral function . So far, ARPES in a magnetic field has
been precluded due to the need to preserve the electron paths between the
sample and detector. In this paper we report progress towards "magnetoARPES", a
variant of ARPES that can be conducted in a magnetic field. It is achieved by
applying a microscopic probe beam ( 10 m ) to a thinned sample
mounted upon a special sample holder that generates magnetic field confined to
a thin layer near the sample surface. In this geometry we could produce ARPES
in magnetic fields up to around 100 mT. The magnetic fields can be varied
from purely in-plane to nearly purely out-of-plane, by scanning the probe beam
across different parts of the device. We present experimental and simulated
data for graphene to explore the aberrations induced by the magnetic field.
These results demonstrate the viability of the magnetoARPES technique for
exploring symmetry breaking effects in weak magnetic fields.Comment: 21 pages, 6 figure
SIRT6 Depletion Suppresses Tumor Growth by Promoting Cellular Senescence Induced by DNA Damage in HCC
The role of Sirtuin 6 (SIRT6) as a tumor suppressor or oncogene in liver cancer remains controversial. Thus, we identified the specific role of SIRT6 in the progression of hepatocellular carcinoma (HCC). SIRT6 expression was significantly higher in HCC cell lines and HCC tissues from 138 patients than in an immortalized hepatocyte cell line, THLE-2 and non-tumor tissues, respectively. SIRT6 knockdown by shRNA suppressed the growth of HCC cells and inhibited HCC tumor growth in vivo. In addition, SIRT6 silencing significantly prevented the growth of HCC cell lines by inducing cellular senescence in the p16/Rb- and p53/p21-pathway independent manners. Microarray analysis revealed that the expression of genes involved in nucleosome assembly was apparently altered in SIRT6-depleted Hep3B cells. SIRT6 knockdown promoted G2/M phase arrest and downregulation of genes encoding histone variants associated with nucleosome assembly, which could be attributed to DNA damage. Taken together, our findings suggest that SIRT6 acts as a tumor promoter by preventing DNA damage and cellular senescence, indicating that SIRT6 represents a potential therapeutic target for the treatment of HCC.11137Ysciescopu
Mathematical Distinction in Action Potential between Primo-Vessels and Smooth Muscle
We studied the action potential of Primo-vessels in rats to determine the electrophysiological characteristics of these structures. We introduced a mathematical analysis method, a normalized Fourier transform that displays the sine and cosine components separately, to compare the action potentials of Primo-vessels with those for the smooth muscle. We found that Primo-vessels generated two types of action potential pulses that differed from those of smooth muscle: (1) Type I pulse had rapid depolarizing and repolarizing phases, and (2) Type II pulse had a rapid depolarizing phase and a gradually slowing repolarizing phase
Universal Mechanism of Band-Gap Engineering in Transition-Metal Dichalcogenides
Two-dimensional (2D) van-der-Waals semiconductors have emerged as a class of
materials with promising device characteristics owing to the intrinsic bandgap.
For realistic applications, the ideal is to modify the bandgap in a controlled
manner by a mechanism that can be generally applied to this class of materials.
Here, we report the observation of a universally tunable bandgap in the family
of bulk 2H transition metal dichalcogenides (TMDs) by in situ surface doping of
Rb atoms. A series of angle-resolved photoemission spectra unexceptionally
shows that the bandgap of TMDs at the zone corners is modulated in the range of
0.8 ~ 2.0 eV, which covers a wide spectral range from visible to near infrared,
with a tendency from indirect to direct bandgap. A key clue to understand the
mechanism of this bandgap engineering is provided by the spectroscopic
signature of symmetry breaking and resultant spin splitting, which can be
explained by the formation of 2D electric dipole layers within the surface
bilayer of TMDs. Our results establish the surface Stark effect as a universal
mechanism of bandgap engineering based on the strong 2D nature of van-der-Waals
semiconductors
Reduction of Functionally Graded Material Layers for Si 3 N 4 -Al 2 O 3 System Using Three-Dimensional Finite Element Modeling
Numerical analysis method was used to reduce the number of functionally graded material (FGM) layers for joining Si 3 N 4 -Al 2 O 3 using polytypoid interlayer by estimating the position of crack. In the past, hot press sintering of multi-layered FGMs with 20 layers of thickness 500 mm each have been fabricated successfully. In this paper, thermal residual stresses were calculated using finite element method (FEM) to find the optimized number of layers and its thicknesses of FGM joint. The number of layers for FGM was reduced to 15 layers from 20 layers. Thicknesses were varied to minimize residual stresses within the layers while reducing the number of FGM layers. The damage caused by thermal residual stress was estimated using maximum principal stress theory and maximum tensile stress theory. The calculated maximum stress was found to be axial stress of 430 MPa around 90% 12H/10% Al 2 O 3 area. For each case, calculated strength of each FGM layer by linear rule of mixture was compared with computed thermal residual stresses. Thermal analysis results correctly predicted the position of crack, and this position agreed well with fabricated joints. Therefore, this numerical analysis method can be applied to reduced FGM layers of crack free joint. Finally, new composition profile of crack free joint was proposed using FGM method
Comparative Electronic Structures of the Chiral Helimagnets Cr1/3NbS2 and Cr1/3TaS2
Magnetic materials with noncollinear spin textures are promising for
spintronic applications. To realize practical devices, control over the length
and energy scales of such spin textures is imperative. The chiral helimagnets
Cr1/3NbS2 and Cr1/3TaS2 exhibit analogous magnetic phase diagrams with
different real-space periodicities and field dependence, positioning them as
model systems for studying the relative strengths of the microscopic mechanisms
giving rise to exotic spin textures. Here, we carry out a comparative study of
the electronic structures of Cr1/3NbS2 and Cr1/3TaS2 using angle-resolved
photoemission spectroscopy and density functional theory. We show that bands in
Cr1/3TaS2 are more dispersive than their counterparts in Cr1/3NbS2 and connect
this result to bonding and orbital overlap in these materials. We also
unambiguously distinguish exchange splitting from surface termination effects
by studying the dependence of their photoemission spectra on polarization,
temperature, and beam size. We find strong evidence that hybridization between
intercalant and host lattice electronic states mediates the magnetic exchange
interactions in these materials, suggesting that band engineering is a route
toward tuning their spin textures. Overall, these results underscore how the
modular nature of intercalated transition metal dichalcogenides translates
variation in composition and electronic structure to complex magnetism.Comment: 46 pages, 18 figures, 5 table
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