94 research outputs found
Pseudogap behavior in charge density wave kagome material ScVSn revealed by magnetotransport measurements
Over the last few years, significant attention has been devoted to studying
the kagome materials AVSb (A = K, Rb, Cs) due to their unconventional
superconductivity and charge density wave (CDW) ordering. Recently
ScVSn was found to host a CDW below 90K, and, like
AVSb, it contains a kagome lattice comprised only of V ions. Here we
present a comprehensive magnetotransport study on ScVSn. We discovered
several anomalous transport phenomena above the CDW ordering temperature,
including insulating behavior in interlayer resistivity, a strongly
temperature-dependent Hall coefficient, and violation of Kohler's rule. All
these anomalies can be consistently explained by a progressive decrease in
carrier densities with decreasing temperature, suggesting the formation of a
pseudogap. Our findings suggest that high-temperature CDW fluctuations play a
significant role in determining the normal state electronic properties of
ScVSn
High ambient-contrast-ratio display using tandem reflective liquid crystal display and organic light-emitting device
A high ambient-contrast-ratio (A-CR) and large aperture-ratio display is conceptually demonstrated and experimentally validated by stacking a normally black reflective liquid crystal display (NB-RLCD) and an organic light-emitting device (OLED). Such a tandem device can be switched between the NB-RLCD mode and the OLED mode under bright and dark ambient light, respectively. The normally black characteristic of the RLCD also helps to boost the A-CR under OLED-mode operation. To obtain a better image quality in the RLCD mode, a bumpy and transmissive structure is used to eliminate the specular reflection and to increase the viewing angle performance that results in CR \u3e 2:1 over 55 degrees viewing cone. Besides, such a structure can also increase the external quantum efficiency of the OLED by 49.4%. In our experiments, regardless of the ambient intensity the A-CR is kept higher than 100:1
Improvement in Device Performance and Reliability of Organic Light-Emitting Diodes through Deposition Rate Control
We demonstrated a fabrication technique to reduce the driving voltage, increase the current efficiency, and extend the operating lifetime of an organic light-emitting diode (OLED) by simply controlling the deposition rate of bis(10-hydroxybenzo[h]qinolinato) beryllium (Bebq 2 ) used as the emitting layer and the electron-transport layer. In our optimized device, 55 nm of Bebq 2 was first deposited at a faster deposition rate of 1.3 nm/s, followed by the deposition of a thin Bebq 2 (5 nm) layer at a slower rate of 0.03 nm/s. The Bebq 2 layer with the faster deposition rate exhibited higher photoluminescence efficiency and was suitable for use in light emission. The thin Bebq 2 layer with the slower deposition rate was used to modify the interface between the Bebq 2 and cathode and hence improve the injection efficiency and lower the driving voltage. The operating lifetime of such a two-step deposition OLED was 1.92 and 4.6 times longer than that of devices with a single deposition rate, that is, 1.3 and 0.03 nm/s cases, respectively
Uniaxial ferromagnetism in the kagome metal TbVSn
The synthesis and characterization of the vanadium-based kagome metal
TbVSn is presented. X-ray measurements confirm this material forms
with the same crystal structure type as the recently investigated kagome metals
GdVSn and YVSn, with space group symmetry P6/mmm. A signature
of a phase transition at 4.1K is observed in heat capacity, resistivity, and
magnetic susceptibility measurements, and both resistivity and magnetization
measurements exhibit hysteresis in magnetic field. Furthermore, a strikingly
large anisotropy in the magnetic susceptibility was observed, with the c-axis
susceptibility nearly 100 times the ab plane susceptibility at 2K. This is
highly suggestive of uniaxial ferromagnetism, and the large size of
9.4/f.u. indicates the Tb electronic moments cooperatively
align perpendicular to the V kagome lattice plane. The entropy at the phase
transition is nearly Rln(2), indicating that the CEF ground state of the
Tb ion is a doublet, and therefore the sublattice of electrons in
this material can be shown to map at low temperatures to the Ising model in a
D symmetry environment. Hall measurements at temperatures from 300K to
1.7K can be described by two-band carrier transport at temperatures below
around 150K, with a large increase in both hole and electron mobilities,
similar to YVSn, and an anomalous Hall effect is seen below the
ordering temperature. Angle-resolved photoemission measurements above the
magnetic ordering temperature reveal typical kagome dispersions. Our study
presents TbVSn as an ideal system to study the interplay between
Ising ferromagnetism and non-trivial electronic states emerging from a kagome
lattice
Two-dimensional Dirac fermions in a topological insulator: transport in the quantum limit
Pulsed magnetic fields of up to 55T are used to investigate the transport
properties of the topological insulator Bi_2Se_3 in the extreme quantum limit.
For samples with a bulk carrier density of n = 2.9\times10^16cm^-3, the lowest
Landau level of the bulk 3D Fermi surface is reached by a field of 4T. For
fields well beyond this limit, Shubnikov-de Haas oscillations arising from
quantization of the 2D surface state are observed, with the \nu =1 Landau level
attained by a field of 35T. These measurements reveal the presence of
additional oscillations which occur at fields corresponding to simple rational
fractions of the integer Landau indices.Comment: 5 pages, 4 figure
Emission Characteristics of Organic Light-Emitting Diodes and Organic Thin-Films with Planar and Corrugated Structures
In this paper, we review the emission characteristics from organic light-emitting diodes (OLEDs) and organic molecular thin films with planar and corrugated structures. In a planar thin film structure, light emission from OLEDs was strongly influenced by the interference effect. With suitable design of microcavity structure and layer thicknesses adjustment, optical characteristics can be engineered to achieve high optical intensity, suitable emission wavelength, and broad viewing angles. To increase the extraction efficiency from OLEDs and organic thin-films, corrugated structure with micro- and nano-scale were applied. Microstructures can effectively redirects the waveguiding light in the substrate outside the device. For nanostructures, it is also possible to couple out the organic and plasmonic modes, not only the substrate mode
High Photoelectric Conversion Efficiency of Metal Phthalocyanine/Fullerene Heterojunction Photovoltaic Device
This paper introduces the fundamental physical characteristics of organic photovoltaic (OPV) devices. Photoelectric conversion efficiency is crucial to the evaluation of quality in OPV devices, and enhancing efficiency has been spurring on researchers to seek alternatives to this problem. In this paper, we focus on organic photovoltaic (OPV) devices and review several approaches to enhance the energy conversion efficiency of small molecular heterojunction OPV devices based on an optimal metal-phthalocyanine/fullerene (C60) planar heterojunction thin film structure. For the sake of discussion, these mechanisms have been divided into electrical and optical sections: (1) Electrical: Modification on electrodes or active regions to benefit carrier injection, charge transport and exciton dissociation; (2) Optical: Optional architectures or infilling to promote photon confinement and enhance absorption
Electrical Current Aging of Mixed-Host Organic Light-Emitting Devices with Thin Doped Layer
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