Halide double perovskites A2B­(I)­B­(III)­X6, in which monovalent B­(I) and trivalent B­(III) cations are arranged in the B-sites of the perovskite structure with a rock-salt ordering, have attracted substantial interest in the field of optoelectronics. However, the rock-salt ordering generally leads to low electronic dimensionality, with relatively large bandgaps and large carrier effective masses. In this work, we demonstrate, by density functional theory (DFT) calculations, that the electronic dimensionality and thus the electronic properties of halide double perovskites can be effectively modulated by manipulating the arrangement of the B-site cations. Through symmetry analysis and DFT calculations, we propose a family of halide double perovskites A2B­(I)­B­(II)­X5 where the B-site cations adopt a columnar-ordered arrangement. Among the considered compounds, Cs2AgPdCl5, Cs2AgPdBr5, and Cs2AgPtCl5 were successfully synthesized as the first examples of the B-site columnar-ordered halide double perovskites. These compounds exhibit small bandgaps of 1.33–1.77 eV that are suitable for visible light absorption, small carrier effective masses along the octahedra chains, and good thermal and air stability. Our work provides a prototype double perovskite structure to incorporate cations in +1 and +2 oxidation states, which may significantly expand the large family of the halide double perovskites and offer a platform to explore prospective optoelectronic semiconductors.

We present the superconducting (SC) property and high-robustness of structural stability of kagome CsV3Sb5 under in situ high pressures. For the initial SC-I phase, its T c is quickly enhanced from 3.5 K to 7.6 K and then totally suppressed at P ∼ 10 GPa. With further increasing pressure, an SC-II phase emerges at P ∼ 15 GPa and persists up to 100 GPa. The T c rapidly increases to the maximal value of 5.2 K at P = 53.6 GPa and slowly decreases to 4.7 K at P = 100 GPa. A two-dome-like variation of T c in CsV3Sb5 is concluded here. The Raman measurements demonstrate that weakening of E 2g mode and strengthening of E 1g mode occur without phase transition in the SC-II phase, which is supported by the results of phonon spectra calculations. Electronic structure calculations reveal that exertion of pressure may bridge the gap of topological surface nontrivial states near E F, i.e., disappearance of Z 2 invariant. Meanwhile, the Fermi surface enlarges significantly, consistent with the increased carrier density. The findings here suggest that the change of electronic structure and strengthened electron-phonon coupling should be responsible for the pressure-induced reentrant SC.