Texas Center for Superconductivity

About: Texas Center for Superconductivity is a based out in . It is known for research contribution in the topics: Superconductivity & Thin film. The organization has 1475 authors who have published 2210 publications receiving 52403 citations.

Conducting tin halides with a layered organic-based perovskite structure

Abstract: THE discovery1 of high-temperature superconductivity in layered copper oxide perovskites has generated considerable fundamental and technological interest in this class of materials Only a few other examples of conducting layered perovskites are known; these are also oxides such as (La1-xSrx)n+1 MnnO3n+1 (ref 2), Lan+1NinO3n+1 (ref 3) and Ban+1PbnO3n+1 (ref 4), all of which exhibit a trend from semiconducting to metallic behaviour with increasing number of perovskite layers (n) We report here the synthesis of a family of organic-based layered halide perovskites, (C4H9NH3)2(CH3NH3)n-1Snnl3n+1 which show a similar transition from semiconducting to metallic behaviour with increasing n The incorporation of an organic modulation layer between the conducting tin iodide sheets potentially provides greater flexibility for tuning the electrical properties of the perovskite sheets, and we suggest that such an approach will prove valuable for exploring the range of transport properties possible with layered perovskites

Midgap surface states as a novel signature for dxa2-xb2-wave superconductivity.

Abstract: It is shown that a sizable areal density of midgap states exists on a {110} surface of a ${\mathit{d}}_{\mathit{x}\mathit{a}}^{2}$-${\mathit{x}}_{\mathit{b}}^{2}$-wave superconductor, which can either have vacuum or an insulator at the surface, or be separated from vacuum or an insulator by a clean, size-quantized, normal metal overlayer. These ``midgap'' states have many observable consequences---some of which are briefly discussed here---which can be used as a clear signature to distinguish between d-wave and anisotropic s-wave superconductors.

Conducting Layered Organic-inorganic Halides Containing -Oriented Perovskite Sheets

Abstract: Single crystals of the layered organic-inorganic perovskites, [NH(2)C(I=NH(2)](2)(CH(3)NH(3))m SnmI3m+2, were prepared by an aqueous solution growth technique. In contrast to the recently discovered family, (C(4)H(9)NH(3))(2)(CH(3)NH(3))n-1SnnI3n+1, which consists of (100)-terminated perovskite layers, structure determination reveals an unusual structural class with sets of m -oriented CH(3)NH(3)SnI(3) perovskite sheets separated by iodoformamidinium cations. Whereas the m = 2 compound is semiconducting with a band gap of 0.33 +/- 0.05 electron volt, increasing m leads to more metallic character. The ability to control perovskite sheet orientation through the choice of organic cation demonstrates the flexibility provided by organic-inorganic perovskites and adds an important handle for tailoring and understanding lower dimensional transport in layered perovskites.

Superconductivity up to 164 K in HgBa2Cam-1CumO2m+2+ delta (m=1, 2, and 3) under quasihydrostatic pressures.

Abstract: The superconducting transition temperatures (${\mathit{T}}_{\mathit{c}}$'s) of optimally doped ${\mathrm{HgBa}}_{2}$${\mathrm{Ca}}_{\mathit{m}\mathrm{\ensuremath{-}}1}$${\mathrm{Cu}}_{\mathit{m}}$${\mathrm{O}}_{2\mathit{m}+2+\mathrm{\ensuremath{\delta}}}$ (Hg 1:2:m-1:m) with m=1, 2, and 3 and ${\mathrm{Hg}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Pb}}_{\mathit{x}}$${\mathrm{Ba}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ [Hg(xPb) 1:2:2:3] have been investigated resistively under quasihydrostatic pressures up to 45 GPa. There seems to be a universal upward shift of ${\mathit{T}}_{\mathit{c}}$ under pressure, regardless of m, for all Hg 1:2:m-1:m, implying a common origin for all compounds. Record high ${\mathit{T}}_{\mathit{c}}$'s of 164, 154, and 118 K were reached for the optimally doped Hg 1:2:m-1:m with m=3, 2, and 1, respectively. However, the ${\mathit{T}}_{\mathit{c}}$ enhancement is suppressed by Pb substitution, suggesting the possibility that Hg plays an important role in these compounds.

High thermoelectric performance by resonant dopant indium in nanostructured SnTe

Abstract: From an environmental perspective, lead-free SnTe would be preferable for solid-state waste heat recovery if its thermoelectric figure-of-merit could be brought close to that of the lead-containing chalcogenides. In this work, we studied the thermoelectric properties of nanostructured SnTe with different dopants, and found indium-doped SnTe showed extraordinarily large Seebeck coefficients that cannot be explained properly by the conventional two-valence band model. We attributed this enhancement of Seebeck coefficients to resonant levels created by the indium impurities inside the valence band, supported by the first-principles simulations. This, together with the lower thermal conductivity resulting from the decreased grain size by ball milling and hot pressing, improved both the peak and average nondimensional figure-of-merit (ZT) significantly. A peak ZT of ∼1.1 was obtained in 0.25 atom % In-doped SnTe at about 873 K.