Signatures of Fractional Quantum Anomalous Hall States in Twisted MoTe2 Bilayer

The interplay between spontaneous symmetry breaking and topology can result in exotic quantum states of matter. A celebrated example is the quantum anomalous Hall (QAH) state, which exhibits an integer quantum Hall effect at zero magnetic field thanks to its intrinsic ferromagnetism. In the presence of strong electron-electron interactions, exotic fractional-QAH (FQAH) states at zero magnetic field can emerge. These states could host fractional excitations, including non-Abelian anyons - crucial building blocks for topological quantum computation. Flat Chern bands are widely considered as a desirable venue to realize the FQAH state. For this purpose, twisted transition metal dichalcogenide homobilayers in rhombohedral stacking have recently been predicted to be a promising material platform. Here, we report experimental signatures of FQAH states in 3.7-degree twisted MoTe2 bilayer. Magnetic circular dichroism measurements reveal robust ferromagnetic states at fractionally hole filled moir\'e minibands. Using trion photoluminescence as a sensor, we obtain a Landau fan diagram which shows linear shifts in carrier densities corresponding to the v=-2/3 and -3/5 ferromagnetic states with applied magnetic field. These shifts match the Streda formula dispersion of FQAH states with fractionally quantized Hall conductance of -2/3$e^2/h$ and -3/5$e^2/h$, respectively. Moreover, the v=-1 state exhibits a dispersion corresponding to Chern number -1, consistent with the predicted QAH state. In comparison, several non-ferromagnetic states on the electron doping side do not disperse, i.e., are trivial correlated insulators. The observed topological states can be further electrically driven into topologically trivial states. Our findings provide clear evidence of the long-sought FQAH states, putting forward MoTe2 moir\'e superlattices as a fascinating platform for exploring fractional excitations.Comment: 15 pages, 4 figures, v2: extended data (6 figures) is added. Comments are welcom

Atomic Sn–enabled high-utilization, large-capacity, and long-life Na anode

Constructing robust nucleation sites with an ultrafine size in a confined environment is essential toward simultaneously achieving superior utilization, high capacity, and long-term durability in Na metal-based energy storage, yet remains largely unexplored. Here, we report a previously unexplored design of spatially confined atomic Sn in hollow carbon spheres for homogeneous nucleation and dendrite-free growth. The designed architecture maximizes Sn utilization, prevents agglomeration, mitigates volume variation, and allows complete alloying-dealloying with high-affinity Sn as persistent nucleation sites, contrary to conventional spatially exposed large-size ones without dealloying. Thus, conformal deposition is achieved, rendering an exceptional capacity of 16 mAh cm−2 in half-cells and long cycling over 7000 hours in symmetric cells. Moreover, the well-known paradox is surmounted, delivering record-high Na utilization (e.g., 85%) and large capacity (e.g., 8 mAh cm−2) while maintaining extraordinary durability over 5000 hours, representing an important breakthrough for stabilizing Na anode

Multidimensional perovskite solar cells

Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted extensive attention, and their certified power conversion efficiency (PCE) has reached 25.5%. However, the instability of the high-efficiency 3-dimensional (3D) perovskite against ambient conditions (moisture, light and thermal) and the existing defects severely limit its practical applications and commercialization. Unlike 3D perovskites, the large hydrophobic spacer cations in low-dimensional (2D, 1D, and 0D) perovskites are able to effectively improve the stability, but they also weaken the light absorption range and hinder charge transport. The construction of a low-dimensional/3D perovskite multidimensional structure, which can combine the advantages of the high stability of low-dimensional perovskites and the superior efficiency of 3D perovskites, is proposed to achieve high efficiency and ultrastability. Moreover, the proper incorporation of low-dimensional perovskite into 3D perovskite can passivate defects and inhibit ion migration. Herein, this article summarizes the recent research progress of low-dimensional/3D perovskite multidimensional structures for PSCs and provides some perspectives toward developing stable and efficient PSCs

Partial Ion Exchange Derived 2D Cu-Zn-In-S Nanosheets as Sensitizers of 1D TiO2 Nanorods for Boosting Solar Water Splitting

A facile route for the fabrication of a novel ZnS shell/Cu-Zn-In-S nanosheets/TiO2 nanorods heterojunction was reported in this work. Especially, the quaternary Cu-Zn-In-S nanosheets were synthesized creatively from the ternary ZnIn2S4 nanosheets by partial exchange reaction, leading to substantial enhancement on the light absorbance. Such heterojunction could increase the surface area and accelerate the charge transfer resulting from its hierarchical 2D/1D structure and favorable energy bands. Moreover, the ZnS coating acted as a passivation layer as well as a potential barrier, significantly suppressing the interface recombination. The above synergistic effects resulted in the largely increased photocurrent density from 0.34 mA cm(-2) for the pristine TiO2 to 0.81 mA cm(-2) for the heterojunction at 0.8 V vs RHE.</p

Boosting PEC performance of Si photoelectrodes by coupling bifunctional CuCo hybrid oxide cocatalysts

Silicon (Si) is an attractive candidate for photoelectrochemical (PEC) water splitting because of its small band gap, fast carrier mobility and abundant reserves. However, the PEC performance has been severely limited by the sluggish kinetics of oxygen/hydrogen evolution reaction at the Si photoelectrode/electrolyte interface and poor stability in the aqueous environment. Herein, the bifunctional CuCo hybrid oxides (CuCo-HO) cocatalysts have been integrated with ultrathin TiO2 decorated n-type and p-type Si nanowires (NWs) to simultaneously improve the photoactivity and stability of Si photoelectrodes. The thickness of TiO2 layer, the concentration of CuCo-precursor and the hydrothermal reaction time have been investigated to optimize the PEC performance. The enhancement mechanism is studied and mainly ascribed to the increased light harvesting, small charge transfer resistance and high carrier density of Si NWs/TiO2/CuCo-HO photoelectrodes

Boosting PEC performance of Si photoelectrodes by coupling bifunctional CuCo hybrid oxide cocatalysts

Silicon (Si) is an attractive candidate for photoelectrochemical (PEC) water splitting because of its small band gap, fast carrier mobility and abundant reserves. However, the PEC performance has been severely limited by the sluggish kinetics of oxygen/hydrogen evolution reaction at the Si photoelectrode/electrolyte interface and poor stability in the aqueous environment. Herein, the bifunctional CuCo hybrid oxides (CuCo-HO) cocatalysts have been integrated with ultrathin TiO2 decorated n-type and p-type Si nanowires (NWs) to simultaneously improve the photoactivity and stability of Si photoelectrodes. The thickness of TiO2 layer, the concentration of CuCo-precursor and the hydrothermal reaction time have been investigated to optimize the PEC performance. The enhancement mechanism is studied and mainly ascribed to the increased light harvesting, small charge transfer resistance and high carrier density of Si NWs/TiO2/CuCo-HO photoelectrodes

Frequency-selective perovskite photodetector for anti-interference optical communications

Abstract Free-space coupling, essential for various communication applications, often faces significant signal loss and interference from ambient light. Traditional methods rely on integrating complex optical and electronic systems, leading to bulkier and costlier communication equipment. Here, we show an asymmetric 2D–3D–2D perovskite structure device to achieve a frequency-selective photoresponse in a single device. By combining two electromotive forces of equal magnitude in the opposite directions, the device output is attenuated to zero under constant light illumination. Because these reverse photodiodes have different response speeds, the device only responds near a certain frequency, which can be tuned by manipulating the 2D perovskite components. The target device achieves an ultrafast response of 19.7/18.3 ns in the frequency-selective photoresponse range 0.8–9.7 MHz. This anti-interference photodetector can accurately transmit character and video data under strong light interference with a source intensity of up to 454 mW cm−2

Loading Amorphous NiMoO_4–<i>x</i>S_<i>x</i> Nanosheet Cocatalyst to Improve Performance of <i>p</i>‑Silicon Wafer Photocathode

Considering its small band gap and appropriate conduction band level, Si is a suitable semiconductor for photocathodes in a photoelectrochemical (PEC) cell. Unfortunately, its PEC activity is far from desirable because of inferior stability, high recombination of photogenerated electron–hole pairs, and sluggish hydrogen evolution kinetics at the Si/electrolyte interface. The introduction of low-cost and earth-abundant non-noble metal cocatalysts onto the Si photocathode is a promising route to improve its PEC performance. Herein, we fabricate efficient and stable photocathodes by integrating non-noble metal NiMoO_4–<i>x</i>S_<i>x</i> nanosheets with planar p-Si wafers, along with ultrathin TiO₂ as a protective and passivating film at the intermediate and outermost layer. An onset potential of 0.3 V (vs RHE) and a photocurrent density of 5.1 mA cm^–2 at −0.5 V (vs RHE) are obtained for the optimal photocathode, representing significant enhancement compared to the pristine Si wafers. Moreover, long-term measurement demonstrates that the TiO₂ layer can effectively protect the photocathode from degradation of electrolyte and photocorrosion