Multi-band effect in the noncentrosymmetric superconductors Mg_{12-\delta}Ir_{19}B_{16} revealed by Hall effect and magnetoresistance measurements

We report the longitudinal resistivity and Hall effect measurements on the noncentrosymmetric superconducting Mg$_{12-\delta}$Ir$_{19}$B$_{16}$ samples with different critical transition temperatures. A strong temperature dependence of the Hall coefficient $R_H$ and nonlinear magnetic field dependence of the Hall resistivity $\rho_{xy}$ in wide temperature region are observed, suggesting a strong multi-band effect in this system. Moreover, a large magnetoresistance up to 20% is found at the field of 9 T. We also observe the violation of the Kohler's rule from our magnetoresistance data, further confirming the presence of multi-band effect in our samples. A detailed analysis shows that the data can't be simply described within the two-band scenario at low temperatures, so we argue that there may be more than two bands contributing to the conduction of the samples.Comment: 4 pages, 4 figure

Universal linear-temperature resistivity: possible quantum diffusion transport in strongly correlated superconductors

The strongly correlated electron fluids in high temperature cuprate superconductors demonstrate an anomalous linear temperature ($T$) dependent resistivity behavior, which persists to a wide temperature range without exhibiting saturation. As cooling down, those electron fluids lose the resistivity and condense into the superfluid. However, the origin of the linear-$T$ resistivity behavior and its relationship to the strongly correlated superconductivity remain a mystery. Here we report a universal relation $d\rho/dT=(\mu_0k_B/\hbar)\lambda^2_L$, which bridges the slope of the linear-$T$-dependent resistivity ($d\rho/dT$) to the London penetration depth $\lambda_L$ at zero temperature among cuprate superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ and heavy fermion superconductors CeCoIn$_5$, where $\mu_0$ is vacuum permeability, $k_B$ is the Boltzmann constant and $\hbar$ is the reduced Planck constant. We extend this scaling relation to different systems and found that it holds for other cuprate, pnictide and heavy fermion superconductors as well, regardless of the significant differences in the strength of electronic correlations, transport directions, and doping levels. Our analysis suggests that the scaling relation in strongly correlated superconductors could be described as a hydrodynamic diffusive transport, with the diffusion coefficient ($D$) approaching the quantum limit $D\sim\hbar/m^*$, where $m^*$ is the quasi-particle effective mass.Comment: 8 pages, 2 figures, 1 tabl

Synthesizing and characterization of hole doped nickel based layer superconductor (La1−x_{1-x}Srx_{x})ONiAs

We report the synthesizing and characterization of the hole doped Ni-based superconductor ($La_{1-x}Sr_{x})ONiAs$. By substituting La with Sr, the superconducting transition temperature $T_c$ is increased from 2.75 K of the parent phase $LaONiAs$ to 3.7 K at the doping levels x= 0.1 - 0.2. The curve $T_c$ versus hole concentration shows a symmetric behavior as the electron doped samples $La(O_{1-x}F_{x})NiAs$. The normal state resistivity in Ni-based samples shows a good metallic behavior and reveals the absence of an anomaly which appears in the Fe-based system at about 150 K, suggesting that this anomaly is not a common feature for all systems. Hall effect measurements indicate that the electron conduction in the parent phase $LaONiAs$ is dominated by electron-like charge carriers, while with more Sr doping, a hole-like band will emerge and finally prevail over the conduction, and accordingly the superconducting transition temperature $T_c$ increases.Comment: 4 pages, 5 figure

Evidence for line nodes in the energy gap of the overdoped Ba(Fe1−x_{1-x}Cox_{x})2_{2}As2_{2} from low-temperature specific heat measurements

Low-temperature specific heat (SH) is measured on Ba(Fe$_{1-x}$Co$_{x}$)$_2$As$_2$ single crystals in a wide doping region under different magnetic fields. For the overdoped sample, we find the clear evidence for the presence of $T^2$ term in the data, which is absent both for the underdoped and optimal doped samples, suggesting the presence of line nodes in the energy gap of the overdoped samples. Moreover, the field induced electron specific heat coefficient $\Delta\gamma(H)$ increases more quickly with the field for the overdoped sample than the underdoped and optimal doped ones, giving another support to our arguments. Our results suggest that the superconducting gap(s) in the present system may have different structures strongly depending on the doping regions.Comment: 5 pages, 4 figure

Transition of stoichiometricSr2VO3FeAs to a superconducting state at 37.2 K

The superconductor Sr4V2O6Fe2As2 with transition temperature at 37.2 K has been fabricated. It has a layered structure with the space group of p4/nmm, and with the lattice constants a = 3.9296Aand c = 15.6732A. The observed large diamagnetization signal and zero-resistance demonstrated the bulk superconductivity. The broadening of resistive transition was measured under different magnetic fields leading to the discovery of a rather high upper critical field. The results also suggest a large vortex liquid region which reflects high anisotropy of the system. The Hall effect measurements revealed dominantly electron-like charge carriers in this material. The superconductivity in the present system may be induced by oxygen deficiency or the multiple valence states of vanadium.Comment: 5 pages, 4 figure

Superconductivity at 15.6 K in Calcium-doped Tb_{1-x}Ca_xFeAsO: the structure requirement for achieving superconductivity in the hole-doped 1111 phase

Superconductivity at about 15.6 K was achieved in Tb_{1-x}Ca_xFeAsO by partially substituting Tb^{3+} with Ca^{2+} in the nominal doping region x = 0.40 \sim 0.50. A detailed investigation was carried out in a typical sample with doping level of x = 0.44. The upper critical field of this sample was estimated to be 77 Tesla from the magnetic field dependent resistivity data. The domination of hole-like charge carriers in the low-temperature region was confirmed by Hall effect measurements. The comparison between the calcium-doped sample Pr_{1-x}Ca_xFeAsO (non-superconductive) and the Strontium-doped sample Pr_{1-x}Sr_xFeAsO (superconductive) suggests that a lager ion radius of the doped alkaline-earth element compared with that of the rare-earth element may be a necessary requirement for achieving superconductivity in the hole-doped 1111 phase.Comment: 7 pages, 7 figure

A readily accessible multifunctional probe: simultaneous recognition of the cation ZN²⁺ and the anion F⁻ via distinguishable wavelengths

The probe 1 was readily prepared via condensation of 8-formyl-7-hydroxy-coumarin and carbonic dihydrazide in a one-step procedure. Probe 1 exhibited high sensitivity and selectivity towards Zn²⁺ and F⁻ through a “turn-on” fluorescence response and/or ratiometric colorimetric response with low detection limits of the order of 10-8 M. The complex behaviour was fully investigated by spectral titration, isothermal titration calorimetry, 1H NMR spectroscopic titration and mass spectrometry. Interestingly, probe 1 not only recognizes the cation Zn²⁺ and the anion F⁻, but can also distinguish between these two ions via the max wavelength in their UV-vis spectra (360 nm for 1-Zn²⁺ versus 400 nm for 1-F⁻ complex) or their fluorescent spectra (λₑₓ / λₑm = 360 nm/ 454 nm for 1-Zn²⁺ versus λₑₓ / λₑm = 400 nm/ 475 nm for 1-F⁻ complex) due to their differing red-shifts. Additionally, probe 1 has been further explored in the detection of Zn²⁺ in living cells

A ratiometric Al³⁺ ion probe based on the coumarin-quinoline FRET system

A coumarin-quinoline based fluorescence resonance energy transfer (FRET) system (TCQ) has been synthesized and employed as a ratiometric fluorescence probe. The selective fluorescent response of the probe TCQ toward Al³⁺ was devised by employing a quinoline moiety as a FRET energy donor with a coumarin moiety as an energy acceptor. The quinoline emission at 390 nm decreased and the coumarin emission at 480 nm increased concurrently on addition of Al³⁺ under excitation wavelength at 253 nm. The TCQ probe exhibited high selectivity for Al³⁺ as compared to other tested metal ions and the ratiometric sensing of Al³⁺ was determined by plotting the fluorescence intensity ratio at 480 nm and 390 nm versus Al³⁺ ion concentration. Moreover, test strips based on TCQ were fabricated, which were found to act as a convenient and efficient Al³⁺ ion detection kit. Furthermore, this system has been used for imaging of Al³⁺ in living cells