ABSTRACT
In kagome metal CsV_{3}Sb_{5}, multiple intertwined orders are accompanied by both electronic and structural instabilities. These exotic orders have attracted much recent attention, but their origins remain elusive. The newly discovered CsTi_{3}Bi_{5} is a Ti-based kagome metal to parallel CsV_{3}Sb_{5}. Here, we report angle-resolved photoemission experiments and first-principles calculations on pristine and Cs-doped CsTi_{3}Bi_{5} samples. Our results reveal that the van Hove singularity (vHS) in CsTi_{3}Bi_{5} can be tuned in a large energy range without structural instability, different from that in CsV_{3}Sb_{5}. As such, CsTi_{3}Bi_{5} provides a complementary platform to disentangle and investigate the electronic instability with a tunable vHS in kagome metals.
ABSTRACT
Van Hove singularity (VHS) has been considered as a driving source for unconventional superconductivity. A VHS in two-dimensional (2D) materials consists of a saddle point connecting electron-like and hole-like bands. In a rare case, when a VHS appears at Fermi level, both electron-like and hole-like conduction can coexist, giving rise to an enhanced density of states as well as an attractive component of Coulomb interaction for unconventional electronic pairing. However, this van Hove scenario is often destroyed by an incorrect chemical potential or competing instabilities. Here, by using angle-resolved photoemission measurements, we report the observation of a VHS perfectly aligned with the Fermi level in a kagome superconductor CsV3-xTaxSb5 (x ~ 0.4), in which a record-high superconducting transition temperature is achieved among all the current variants of AV3Sb5 (A = Cs, Rb, K) at ambient pressure. Doping dependent measurements reveal the important role of van Hove scenario in boosting superconductivity, and spectroscopic-imaging scanning tunneling microscopy measurements indicate a distinct superconducting state in this system.
ABSTRACT
Dual-responsive chemosensors have garnered much research interests owing to the ability of recognizing two analytes simultaneously. Herein, the chemosensor BPIS composed of hemicyanine and 2, 2'-dipyridylamine (DPA) was facilely synthesized for sensitive and expeditious recognition of Cu2+ and HSO3- in 100% aqueous solution. By adding Cu2+, BPIS showed substantial spectral changes accompanied by a noticeable color change from pink to yellow under daylight. The absorbance and fluorescence intensity were linearly correlated to the Cu2+ concentration, enabling the quantitative recognition of Cu2+. The limit of detection (LOD) for Cu2+ was down to 4.02 × 10-9 M. The response time of BPIS towards Cu2+ was 10 s, imparting BPIS great potential in real-time detection of Cu2+. Meanwhile, BPIS manifested ratiometric fluorescence response by introducing HSO3- owing to the 1,4-addition between HSO3- and the unsaturated CC bond of BPIS. The color of the BPIS solution progressively faded from pink to colorless with increasing HSO3- concentration, and a LOD of 3.47 × 10-9 M was obtained. In addition, BPIS-coated test paper was found to be an efficient tool for fast, sensitive, portable detection of Cu2+ and HSO3- by naked eyes. More importantly, the precise detection of Cu2+ and HSO3- in real water and sugars were realized, respectively, by capitalizing on BPIS as the signal tool.
Subject(s)
Colorimetry , Fluorescent Dyes , Limit of Detection , Spectrometry, Fluorescence , WaterABSTRACT
A dual-function colorimetric probe (Cz-Cy7) with an electron-donating carbazole tethered at the central position of heptamethine cyanine was designed and synthesized, and the performance on CN- and HClO detection were systematically investigated. With the addition of CN-, Cz-Cy7 exhibited remarkable changes in both UV-vis and fluorescence spectra with a good linear relationship to CN- concentration, and a discernible color change under daylight was observed. The limit of detection for CN- was found to be 9.1â¯nM in DMF and 0.09⯵M in DMF/H2O. Meanwhile, Cz-Cy7 exhibited a highly sensitive response to HClO in the presence of other ROS (reactive oxygen species) based on the sensing mechanism of oxidative cleavage of olefinic Câ¯=â¯â¯=â¯C bond. The limit of detection for HClO was evaluated to be 14â¯nM in PBS buffer solution (containing 50% CH3CN). More importantly, the probe Cz-Cy7 showed good recovery and analytical precision in real water samples for both CN- and HClO detection, indicating it was feasible and reliable for practical application. Moreover, the test strips loaded with Cz-Cy7 were fabricated and validated to be a portable tool for the efficient detection of CN- and HClO by the naked eye.
