We report on a class of quantum spin Hall insulators (QSHIs) in strained-layer InAs/GaInSb quantum wells, in which the bulk gaps are enhanced up to fivefold as compared to the binary InAs/GaSb QSHI. Remarkably, with consequently increasing edge velocity, the edge conductance at zero and applied magnetic fields manifests time reversal symmetry-protected properties consistent with the Z_{2} topological insulator. The InAs/GaInSb bilayers offer a much sought-after platform for future studies and applications of the QSHI.

The fundamental factor (ion migration) affecting the stability of perovskite solar cells and improvement strategies have been reviewed.

The performance of perovskite solar cells (PSCs) relies on the synthesis method and chemical composition of the perovskite materials. So far, PSCs that have adopted two‐step sequential deposited perovskite with the state‐of‐art composition (FAPbI3)1−x(MAPbBr3)x (x < 0.05) have achieved record power conversion efficiency (PCE), while their one‐step antisolvent dripping counterparts with typical composition Cs0.05FA0.81MA0.14Pb(I0.85Br0.15)3 with more bromine have exhibited much better long‐term operational stability. Thus, halogen engineering that aims to elevate bromine content in sequential deposited perovskite film would push operational stability of PSCs toward that of antisolvent dripping deposited perovskite materials. Here, a Br‐rich seeding growth method is devised and perovskite seed solution with high bromine content is introduced into a PbI2 precursor, leading to bromine incorporation in the resulting perovskite film. Photovoltaic devices fabricated by Br‐rich seeding growth method exhibit a PCE of 21.5%, similar to 21.6% for PSCs having lower bromine content. Whereas, the operational stability of PSCs with higher bromine content is significantly enhanced, with over 80% of initial PCE retained after 500 h tracking at maximum power point under 1‐sun illumination. This work highlights the vital importance of halogen composition for the operational stability of PSCs, and introduces an effective way to incorporate bromine into mixed‐cation‐halide perovskite film via sequential deposition method.

We observe the magnetic oscillation of electric conductance in the two-dimensional InAs/GaSb quantum spin Hall insulator. Its insulating bulk origin is unambiguously demonstrated by the antiphase oscillations of the conductance and the resistance.Characteristically, the in-gap oscillation frequency is higher than the Shubnikov-de Haas oscillation close to the conduction band edge in the metallic regime. The temperature dependence shows both thermal activation and smearing effects, which cannot be described by the Lifshitz-Kosevich theory. A two-band Bernevig-Hughes-Zhang model with a large quasiparticle self-energy in the insulating regime is proposed to capture the main properties of the in-gap oscillations. ·1 Introduction.-Magnetic oscillations in metals stem from the Landau quantization of charged particles in magnetic field, and have been a standard tool to measure the Fermi surfaces of metals [1]. In two-dimensional electron systems (2DES), the Shubnikov-de Haas (SdH) oscillation of conductance evolves into the integer quantum Hall effect when only a few Landau levels (LLs) are filled. In the fractional quantum Hall effect, the magnetic oscillations of composite fermions offer an unique window looking into many-body physics in this strongly interacting electron system [2,3].Recently, unconventional magnetization and resistivity oscillations were observed in the Kondo insulators, SmB6 and YbB12 [4][5][6][7][8], which challenged the canonical theory of magnetic oscillations and triggered intense studies and controversies. The first concern is whether these oscillations come from the insulating bulk states. This is obscured by the presence of metallic surface states in the 3D topological Kondo insulators [4,9,10]. Therefore, it is particularly desirable to observe magnetic oscillations in 2D topological insulators, e.g., the InAs/GaSb quantum well (QW) [11], in which the bulk and edge transport channels can be clearly distinguished by designing different sample geometries. This is achieved in this work, and the insulating bulk state is shown to be the origin of the in-gap conductance oscillations.Second, it is not clear whether the in-gap oscillations can be captured by the Landau quantization of gapped single-particle states [12][13][14][15] or whether one must consider some kind of (nearly) gapless charge-neutral excitations [16][17][18][19][20]. In experiments, the absence of low-temperature thermal conductivity [21,22] (cf. Refs. [6,23]) poses a severe constraint on charge-neutral excitations. On the other hand, in single-particle models,