Charge Density Wave States and Structural Transition in Layered Chalcogenide TaSe_(2-x)Te_x

The structural features and three-dimensional nature of the charge density wave （CDW） state of the layered chalcogenide 1T-TaSe2-xTex （0≤x≤2.0） are characterized by Cs-corrected transmission electron microscopy measurements. Notable changes of both average structure and the CDW state arising from Te substitution for Se are clearly demonstrated in samples with x〉0.3. The commensurate CDW state characterized by the known star-of-David clustering in the 1T-TaSe2 crystal becomes visibly unstable with Te substitution and vanishes when x=0.3. The 1T-TaSe2-xTex （0.3≤x≤1.3） samples generally adopt a remarkable incommensurate CDW state with monoclinic distortion, which could be fundamentally in correlation with the strong qq-dependent electron-phonon coupling-induced period-lattice-distortion as identified in TaTe22. Systematic analysis demonstrates that the occurrence of superconductivity is related to the suppression of the commensurate CDW phase and the presence of discommensuration is an evident structural feature observed in the superconducting samples.

Effect of charge order transition on tunneling resistance in Pr_(0.6)Ca_(0.4)MnO_3/Nb-doped SrTiO_3 heterojunction

An oxide p-n heterojunction composed of Pro.6Ca0.4MnO3 film, with a charge order （CO） transition, and lwt% Nb- doped SrTiO3 substrate is fabricated, and the transport properties of the interface are experimentally studied. The rectifying behavior of the junction, well described by the Newman equation, is observed, indicating that tunneling is the dominant process by which the carriers pass through the interface. Above and below the CO transition temperature, satisfactory linear dependencies of junction resistance on temperature are observed, but the slopes of the two resistance-temperature relations are different. The CO process is believed to be relevant to this difference.

Luminescence of Eu ^(3+) in LnAlO_3 (Ln=Gd,Y) under UV and VUV Excitation

Single phases of LnAlO 3:Eu 3+ (Ln=Gd,Y) were obtained by the process of evaporation of their nitric acid solution, and then pyrolysis of their nitrate salts. On monitoring by 613 nm emission, broad bands at around 270 and 170 nm were observed in the excitation spectrum of Gd 0.95Eu 0.05AlO 3. These peaks could be assigned to charge transfer (CT) transitions of Eu 3+-O 2- and Gd 3+-O 2- respectively. All the transitions observed in Gd 0.95Eu 0.05AlO 3 are faithfully reproduced in the Y 0.95Eu 0.05AlO 3, but with an exception of the 8S 7/2→ 6I 11/2 transition of Gd 3+. The 153 nm broad band could be the CT transition of Y 3+-O 2-. Accordingly, the efficiency luminescence of (Gd,Y)BO 3:Eu 3+ was explained as a result of CT transitions of Gd 3+-O 2- and Y 3+-O 2- under 147 nm excitation. Under VUV excitation, Gd 0.95Eu 0.05AlO 3 exhibits a bright red luminescence with CIE chromaticity coordinates of (0.623, 0.335) with a PL intensity of 30 of the commercial phosphor (Gd,Y)BO 3:Eu 3+ (KX-504A). The PL spectrum of Y 0.95Eu 0.05AlO 3 is similar to that of Gd 0.95Eu 0.05AlO 3. Calculation of the color coordinates gives x=0.636, y=0.340 with a PL intensity of 50 of the (Gd,Y)BO 3:Eu 3+ (KX-504A) for Y 0.95Eu 0.05AlO 3, and confirms that it has the appearance of pure spectral red, corresponding approximately to 608 nm. It can be concluded that LnAlO 3:Eu 3+ is a promising red VUV phosphor.

Relationship between the parent charge transfer gap and maximum transition temperature in cuprates

One of the biggest puzzles concerning the cup- rate high temperature superconductors is what determines the maximum transition temperature （Tc,max）, which varies from less than 30 to above 130 K in different compounds. Despite this dramatic variation, a robust trend is that within each family, the double-layer compound always has higher Tc,max than the single-layer counterpart. Here we use scanning tunneling microscopy to investigate the electronic structure of four cuprate parent compounds belonging to two different families. We find that within each family, the double layer compound has a much smaller charge transfer gap size （ACT）, indicating a clear anticorrelation between AcT and Tc,max. These results suggest that the charge transfer gap plays a key role in the superconducting physics of cuprates, which shed important new light on the high To mechanism from doped Mott insulator perspective.

2D hetero-structures based on transition metal dichalcogenides:fabrication,properties and applications

Recently,two dimensional transition metal dichalcogenides MX_2(M = Mo,W,etc; X = S,Se,Te) have ignited immense interests because of their unique structural and physical properties for the potential applications in the nano-optoelectronics,valley-spintronics etc. In terms of the structural compatibility and van der Waals interaction,two dimensional(2D) MX_2 layers can be fabricated into various lateral and vertical hetero-structures. The atomically-thin hetero-structures comprising different layered MX_2 provide a new platform for exploring fundamental physics and device technologies with unprecedented phenomenon and extraordinary functionalities. In this review,we report the recent progress about the fabrication,properties and applications of 2D hetero-structures based on transition metal dichalcogenides.