Superconducting, Topological, and Transport Properties of Kagome Metals CsTi3Bi5 and RbTi3Bi5.

The recently discovered ATi3Bi5 (A=Cs, Rb) exhibit intriguing quantum phenomena including superconductivity, electronic nematicity, and abundant topological states. ATi3Bi5 present promising platforms for studying kagome superconductivity, band topology, and charge orders in parallel with AV3Sb5. In this work, we comprehensively analyze various properties of ATi3Bi5 covering superconductivity under pressure and doping, band topology under pressure, thermal conductivity, heat capacity, electrical resistance, and spin Hall conductivity (SHC) using first-principles calculations. Calculated superconducting transition temperature (Tc) of CsTi3Bi5 and RbTi3Bi5 at ambient pressure are about 1.85 and 1.92 K. When subject to pressure, Tc of CsTi3Bi5 exhibits a special valley and dome shape, which arises from quasi-two-dimensional compression to three-dimensional isotropic compression within the context of an overall decreasing trend. Furthermore, Tc of RbTi3Bi5 can be effectively enhanced up to 3.09 K by tuning the kagome van Hove singularities (VHSs) and flat band through doping. Pressures can also induce abundant topological surface states at the Fermi energy (EF) and tune VHSs across EF. Additionally, our transport calculations are in excellent agreement with recent experiments, confirming the absence of charge density wave. Notably, SHC of CsTi3Bi5 can reach up to 226ℏ ·(e· Ω ·cm)-1 at EF. Our work provides a timely and detailed analysis of the rich physical properties for ATi3Bi5, offering valuable insights for further experimental verifications and investigations in this field.

Topological superconductivity and large spin Hall effect in the kagome family Ti6X4 (X = Bi, Sb, Pb, Tl, and In).

Topological superconductors (TSC) become a focus of research due to the accompanying Majorana fermions. However, the reported TSC are extremely rare. Recent experiments reported kagome TSC AV3Sb5 (A = K, Rb, and Cs) exhibit unique superconductivity, topological surface states (TSS), and Majorana bound states. More recently, the first titanium-based kagome superconductor CsTi3Bi5 with nontrivial topology was successfully synthesized as a perspective TSC. Given that Cs contributes little to electronic structures of CsTi3Bi5 and binary compounds may be easier to be synthesized, here, by first-principle calculations, we predict five stable nonmagnetic kagome compounds Ti6X4 (X = Bi, Sb, Pb, Tl, and In) which exhibit superconductivity with critical temperature Tc = 3.8 K - 5.1 K, nontrivial Z 2 band topology, and TSS close to the Fermi level. Additionally, large intrinsic spin Hall effect is obtained in Ti6X4, which is caused by gapped Dirac nodal lines due to a strong spin-orbit coupling. This work offers new platforms for TSC and spintronic devices.

[Reducing Membrane Fouling from Micro-Flocculation in a Humic Acid Ultrafiltration Process].

This study investigated the influence of different floc morphologies produced by micro-flocculation process on filtration of a self-constructed polyvinylidene fluoride (PVDF) ultrafiltration membrane. Aluminum sulfate was used as a flocculant and humic acid (HA) and kaolin as raw water. Both the properties of flocs formed during the micro-flocculation process (floc size and distribution, fractal dimension) and the effects of floc formation on membrane flux under different conditions were investigated. The surface morphology of the contaminated membrane was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and adhesion between the PVDF membrane and organic pollutants was measured to analyze the membrane fouling mechanism. Results showed that the main mechanism during a micro-flocculation process using Al3+ as a flocculant is electrical neutralization to remove organic matter. With an increase in flocculant dosage, floc size increased and the fractal dimension of flocs decreased. The attenuation rate of membrane flux was negatively correlated with floc size. The larger the floc, the lower the membrane flux attenuation rate, and the looser the filter cake layer formed during the ultrafiltration process. Comparatively, membrane fouling caused by flocs with smaller fractal dimension was lighter, and the membrane flux recovery rate was also higher. The interaction force between PVDF and organic matter was positively correlated with the corresponding membrane flux attenuation rate during the initial stage of operation. When dosage of Al3+ was 5 mg·L-1 and initial pH was 7, the HA removal rate was 96.7%, the membrane flux attenuation rate was lowest, and the flux recovery rate reached 88%.