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Hongwei Liu, Junpeng Lu, Xiao Renshaw Wang
In this article, we present a comprehensive review on recent research progress in design and fabrication of active tunable metamaterials and devices based on phase transition of VO2. Firstly, we introduce mechanisms of the metal-to-insulator phase transition (MIPT) in VO2 investigated by ultrafast THz spectroscopies. By analyzing the THz spectra, the evolutions of MIPT in VO2 induced by different external excitations are described. The superiorities of using VO2 as building blocks to construct highly tunable metamaterials are discussed...
December 12, 2017: Nanotechnology
Mangal Das, Amitesh Kumar, Rohit Singh, Myo Than Htay, Shaibal Mukherjee
Single synaptic device with inherent learning and memory functions is demonstrated based on a forming-free amorphous Y2O3 (yttria) memristor fabricated by dual ion beam sputtering system. Synaptic functions such as nonlinear transmission characteristics, long-term plasticity, short-term plasticity and "learning behavior" are achieved using a single synaptic device based on cost-effective metal-insulator- semiconductor (MIS) structure. A "learning behavior" function is demonstrated, for the first time in the literature, for yttria based memristor, which bears resemblance to certain memory functions of biological systems...
December 12, 2017: Nanotechnology
Gerbold C Ménard, Sébastien Guissart, Christophe Brun, Raphaël T Leriche, Mircea Trif, François Debontridder, Dominique Demaille, Dimitri Roditchev, Pascal Simon, Tristan Cren
Just like insulators can present topological phases characterized by Dirac edge states, superconductors can exhibit topological phases characterized by Majorana edge states. In particular, one-dimensional topological superconductors are predicted to host zero-energy Majorana fermions at their extremities. By contrast, two-dimensional superconductors have a one-dimensional boundary which would naturally lead to propagating Majorana edge states characterized by a Dirac-like dispersion. In this paper we present evidences of one-dimensional dispersive in-gap edge states surrounding a two-dimensional topological superconducting domain consisting of a monolayer of Pb covering magnetic Co-Si islands grown on Si(111)...
December 11, 2017: Nature Communications
Xiaojuan Ni, Chao Hui, Ninghai Su, Wei Jiang, Feng Liu
We develop a 2D disk-stick percolation model to investigate the electrical percolation behavior of an insulating thin film reinforced with 1D and 2D conductive nanofillers via Monte Carlo simulation. Numerical predictions of the percolation threshold in single component thin films show good agreement with the previous published work, validating our model for investigating the characteristics of the percolation phenomena. Parametric studies of size effect, i.e., length of 1D nanofiller and diameter of 2D nanofiller, have been carried out to predict the electrical percolation threshold for hybrid systems...
December 11, 2017: Nanotechnology
Paul D Cunningham, Aubrey T Hanbicki, Kathleen M McCreary, Berend T Jonker
Strong Coulombic attraction in monolayer transition metal dichalcogenides gives rise to tightly bound excitons and many body interactions that dominate their optoelectronic properties. However, this Coulombic interaction can be screened through control of the surrounding dielectric environment as well as through applied voltage, which provides a potential means of tuning the bandgap, exciton binding energy, and emission wavelength. Here, we directly show that the bandgap and exciton binding energy can be optically tuned by means of the intensity of the incident light...
December 11, 2017: ACS Nano
Peng Xu, T J Huffman, In Hae Kwak, Amlan Biswas, M M Qazilbash
We investigate the temperature dependence of infrared properties at nanometer length scales in La0.67Sr0.33MnO3 (LSMO) thin film with a thickness of 47 unit cells grown on SrTiO3 substrate. The infrared nano-imaging experiments were performed using a near-field optical microscope in conjunction with a variable temperature heating stage. The near-field infrared data is consistent with the bulk of the LSMO film undergoing the thermally-driven non-percolative second-order transition from a metallic, ferromagnetic phase to an insulating, paramagnetic phase...
December 11, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Yantao Zhang, Liang Wang, Xiaozheng Zhang, Limin Guo, Ying Wang, Zhangquan Peng
Discharging of the aprotic Li-O2 battery relies on O2 reduction to insulating solid Li2 O2 , which can either deposit as thin films on the cathode surface or precipitate as large particles in the electrolyte solution. Toward realizing Li-O2 batteries with high capacity and high rate capability, it is crucially important to discharge Li2 O2 in the electrolyte solution rather than on the cathode surface. Here, a soluble electrocatalyst of coenzyme Q10 (CoQ10 ) that can efficaciously drive solution phase formation of Li2 O2 in current benchmark ether-based Li-O2 batteries is reported, which would otherwise lead to Li2 O2 surface-film growth and premature cell death...
December 11, 2017: Advanced Materials
Si-Jia Chen, Wen Wang, Feng-Yi Zhang, Yan-Long Jia, Xiao-Yin Wang, Xiao Guo, Shao-Nan Chen, Jian-Hui Gao, Tian-Yun Wang
Chinese hamster ovary (CHO) cells are one of the most commonly used expression systems for the production of recombinant proteins but low levels of transgene expression and transgene silencing are frequently encountered. Epigenetic regulatory elements such as the chicken β-globin locus control region hypersensitive site 4 (HS4) and scaffold/matrix attachment regions (S/MARs) have positive effects on transgene expression. In this study, a chimeric HS4-SAR was cloned upstream or downstream of an enhanced green fluorescent protein (eGFP) expression cassette in a eukaryotic vector, and the resulting vectors were transfected into CHO cells...
December 2017: FEBS Open Bio
Srinivas Ramachandran, Kami Ahmad, Steven Henikoff
Nucleosomes are disrupted during transcription and other active processes, but the structural intermediates during nucleosome disruption in vivo are unknown. To identify intermediates, we mapped subnucleosomal protections in Drosophila cells using Micrococcal Nuclease followed by sequencing. At the first nucleosome position downstream of the transcription start site, we identified unwrapped intermediates, including hexasomes that lack either proximal or distal contacts. Inhibiting topoisomerases or depleting histone chaperones increased unwrapping, whereas inhibiting release of paused RNAPII or reducing RNAPII elongation decreased unwrapping...
December 6, 2017: Molecular Cell
Martial Duchamp, Olivier Girard, Giulio Pozzi, Helmut Soltner, Florian Winkler, Rolf Speen, Rafal E Dunin-Borkowski, David Cooper
Off-axis electron holography allows both the amplitude and the phase shift of an electron wavefield propagating through a specimen in a transmission electron microscope to be recovered. The technique requires the use of an electron biprism to deflect an object wave and a reference wave to form an interference pattern. Here, we introduce an approach based on semiconductor processing technology to fabricate fine electron biprisms with rectangular cross-sections. By performing electrostatic calculations and preliminary experiments, we demonstrate that such biprisms promise improved performance for electron holography experiments...
November 22, 2017: Ultramicroscopy
Sophie Charpentier, Luca Galletti, Gunta Kunakova, Riccardo Arpaia, Yuxin Song, Reza Baghdadi, Shu Min Wang, Alexei Kalaboukhov, Eva Olsson, Francesco Tafuri, Dmitry Golubev, Jacob Linder, Thilo Bauch, Floriana Lombardi
Topological superconductivity is central to a variety of novel phenomena involving the interplay between topologically ordered phases and broken-symmetry states. The key ingredient is an unconventional order parameter, with an orbital component containing a chiral p x  + ip y wave term. Here we present phase-sensitive measurements, based on the quantum interference in nanoscale Josephson junctions, realized by using Bi2Te3 topological insulator. We demonstrate that the induced superconductivity is unconventional and consistent with a sign-changing order parameter, such as a chiral p x  + ip y component...
December 8, 2017: Nature Communications
Tingting Wei, Teruo Kanki, Masashi Chikanari, Takafumi Uemura, Tsuyoshi Sekitani, Hidekazu Tanaka
Field-effect transistors using correlated electron materials with an electronic phase transition pave a new avenue to realize steep slope switching, to overcome device size limitations and to investigate fundamental science. Here, we present a new finding in gate-bias-induced electronic transport switching in a correlated electron material, i.e., a VO2 nanowire channel through a hybrid gate, which showed an enhancement in the resistive modulation efficiency accompanied by expansion of metallic nano-domains in an insulating matrix by applying gate biases near the metal-insulator transition temperature...
December 8, 2017: Scientific Reports
Hubert Maier, Johannes Ziegler, Ralf Fischer, Dmitriy Kozlov, Ze Don Kvon, Nikolay Mikhailov, Sergey A Dvoretsky, Dieter Weiss
Transport in topological matter has shown a variety of novel phenomena over the past decade. Although numerous transport studies have been conducted on three-dimensional topological insulators (TIs), study of ballistic motion and thus exploration of potential landscapes on a hundred nanometer scale is for the prevalent TI materials almost impossible due to their low carrier mobility. Therefore, it is unknown whether helical Dirac electrons in TIs, bound to interfaces between topologically distinct materials, can be manipulated on the nanometer scale by local gates or locally etched regions...
December 8, 2017: Nature Communications
Jiaqi Zhang, Yuji Kosugi, Akira Otomo, Yoshiaki Nakano, Takuo Tanemura
Electrically tunable metasurfaces have gained special interest as they can realize ultrathin surface-normal modulators in planar geometries. In this paper, we demonstrate a novel metasurface modulator based on electro-optic (EO) polymer that utilizes bimodal resonance inside a metallic subwavelength grating to increase the modulation efficiency. When two metal-insulator-metal (MIM) resonant modes are excited simultaneously inside the grating, they couple strongly to generate a sharp dip in the reflected spectrum...
November 27, 2017: Optics Express
Jing Du, Jian Wang
Here we design and fabricate a hybrid surface plasmon polarities (SPP) waveguide on the silicon-on-insulator (SOI) photonics platform. The designed hybrid SPP waveguide is composed of a metal ridge, an air gap, and a silicon ridge. We simulate the mode characteristics in the structure and design the waveguide with a wide air gap that can simplify the fabrication process and maintain the advantages of the hybrid SPP mode. The performance of ultrahigh-bandwidth data transmission through the proposed waveguide is then investigated using 161 wavelength-division multiplexing (WDM) channels, each carrying a 11...
November 27, 2017: Optics Express
Xiaobin Hu, Jian Li, Xin Wei
Existing transmission type optical quarter-wave plates based on metallic sub-wavelength structures can hardly realize transmission efficiency above 60%. And their working bandwidths are still very narrow. In this paper, we demonstrate a transmission type quarter-wave plate design with efficiency above 92% over a broad wavelength range (from 1260 nm to 1560 nm). The device proposed is based on a one-dimensional metal-insulator-metal waveguide array buried in silica. Phase difference between transmitted TE and TM components can be tuned continuously...
November 27, 2017: Optics Express
Xu Han, Kebo He, Zhubing He, Zhaoyu Zhang
In this paper, we report the design, fabrication, and characterization of a tungsten-based metamaterial selective solar absorber (SSA) combining a metal-insulator-metal (MIM) structure and simple nanodisk array. The as-fabricated absorber absorbs strongly and selectively in the wavelength range of 0.5-1.75 μm with a characterized absorptance of more than 90%, which drops abruptly to less than 12.6% beyond 2.5 μm. In addition, this broadband and highly selective absorber is polarization-insensitive under incidence of normal plane waves...
November 27, 2017: Optics Express
Honggyu Kim, Patrick B Marshall, Kaveh Ahadi, Thomas E Mates, Evgeny Mikheev, Susanne Stemmer
The lattice response of a prototype Mott insulator, SmTiO_{3}, to hole doping is investigated with atomic-scale spatial resolution. SmTiO_{3} films are doped with Sr on the Sm site with concentrations that span the insulating and metallic sides of the filling-controlled Mott metal-insulator transition (MIT). The GdFeO_{3}-type distortions are investigated using an atomic resolution scanning transmission electron microscopy technique that can resolve small lattice distortions with picometer precision. We show that these distortions are gradually and uniformly reduced as the Sr concentration is increased without any phase separation...
November 3, 2017: Physical Review Letters
K Tomiyasu, J Okamoto, H Y Huang, Z Y Chen, E P Sinaga, W B Wu, Y Y Chu, A Singh, R-P Wang, F M F de Groot, A Chainani, S Ishihara, C T Chen, D J Huang
We carried out temperature-dependent (20-550 K) measurements of resonant inelastic x-ray scattering on LaCoO_{3} to investigate the evolution of its electronic structure across the spin-state crossover. In combination with charge-transfer multiplet calculations, we accurately quantified the renomalized crystal-field excitation energies and spin-state populations. We show that the screening of the effective on-site Coulomb interaction of 3d electrons is orbital selective and coupled to the spin-state crossover in LaCoO_{3}...
November 10, 2017: Physical Review Letters
Takahiro Ohgoe, Masatoshi Imada
Using a variational Monte Carlo method, we study the competition of strong electron-electron and electron-phonon interactions in the ground state of the Holstein-Hubbard model on a square lattice. At half filling, an extended intermediate metallic or weakly superconducting (SC) phase emerges, sandwiched between antiferromagnetic and charge order (CO) insulating phases. By carrier doping into the CO insulator, the SC order dramatically increases for strong electron-phonon couplings, but is largely hampered by wide phase separation (PS) regions...
November 10, 2017: Physical Review Letters
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