The material class of rare earth nickelates with high Ni³⁺ oxidation state is generating continued interest due to the occurrence of a metal-insulator transition with charge order and the appearance of non-collinear magnetic phases within this insulating regime. The recent theoretical prediction for superconductivity in LaNiO₃ thin films has also triggered intensive research efforts. LaNiO₃ seems to be the only rare earth nickelate that stays metallic and paramagnetic down to lowest temperatures. So far, centimeter-sized impurity-free single crystal growth has not been reported for the rare earth nickelates material class since elevated oxygen pressures are required for their synthesis. Here, we report on the successful growth of centimeter-sized LaNiO₃ single crystals by the floating zone technique at oxygen pressures of up to 150 bar. Our crystals are essentially free from Ni²⁺ impurities and exhibit metallic properties together with an unexpected but clear antiferromagnetic transition.

A quantum spin liquid (QSL) is an exotic state in which electron spins are highly entangled, yet keep fluctuating even at zero temperature. Experimental realization of model QSLs has been challenging due to imperfections, such as antisite disorder, strain, and extra or a lack of interactions in real materials compared to the model Hamiltonian. Here we report the magnetic susceptibility, thermodynamic, inelastic neutron scattering (INS), and muon-spin relaxation studies on a polycrystalline sample of ${\mathrm{PrZnAl}}_{11}{\mathrm{O}}_{19}$, where the ${\mathrm{Pr}}^{3+}$ ions form an ideal two-dimensional triangular lattice. Our results demonstrate that this system does not order nor freeze, but keeps fluctuating down to 50 mK despite large antiferromagnetic couplings ($\sim -10$ K). Furthermore, the INS and specific-heat data suggest that ${\mathrm{PrZnAl}}_{11}{\mathrm{O}}_{19}$ is best described as a gapless QSL.

Trace NO₂ detection is essential for the production and life, where the sensing strategy is appropriate for rapid detection but lacks molecular specificity. This investigation proposes a sensing mechanism dominated by surface-scattering to achieve the molecularly-specific detection. Two-dimensional Bi₂O₂Se is firstly fabricated into a Schottky-junction-based gas-sensor. Applied with an alternating excitation, the sensor simultaneously outputs multiple response signals (i.e., resistance, reactance, and the impedance angle). Their response times are shorter than 200 s at room temperature. In NO₂ sensing, these responses present the detection limit in ppt range and the sensitivity is up to 16.8 %·ppb⁻¹. This NO₂ sensitivity presents orders of magnitude higher than those of the common gases within the exhaled breath. The impedance angle is involved in the principle component analysis together with the other two sensing signals. Twelve kinds of typical gases containing NO₂ are acquired with molecular characteristics. The change in dipole moment of the target molecule adsorbed is demonstrated to correlate with the impedance angle via surface scattering. The proposed mechanism is confirmed to output ultra-sensitive sensing responses with the molecular characteristic.

A novel electrocatalyst based on the LIFT graphene/Cu_xO with expressive HER activity has successfully been fabricated via one step of laser deposition method. It can be foreseen more electrocatalysts will be obtained inspired by this work.

Frustrated magnets, especially the ones with spin-disordered ground state, have raised intensive attention as excellent magnetocaloric materials for achieving sub-Kelvin magnetic cooling. Here, we investigate the ultralow-temperature magnetic behaviors and magnetocaloric effect (MCE) down to 60 mK on a frustrated Shastry-Sutherland lattice magnet $\mathrm{Y}{\mathrm{b}}_2\mathrm{B}{\mathrm{e}}_2\mathrm{Ge}{\mathrm{O}}_7$ crystallized into the tetragonal structure with space group $P\overline{4}{2}_{1}m$. The magnetic susceptibility, isothermal magnetization $M$($B$), and specific heat results reveal the Ising-like magnetic anisotropy with easy magnetization along the [001] axis. No sign of long-range magnetic order or spin freezing is detected down to 50 mK, where magnetic susceptibility and specific heat data can be understood by a spin dimer system with small spin gap ∼0.78 K. Benefiting from the compatibility of high magnetic ion density ($N_{\mathrm{mag}}$) ∼15.6 $\mathrm{n}{\mathrm{m}}^{-3}$ and large Landé factor $g_{\mathrm{c}}\sim 4.88$ ($B$ // [001]) with the disordered ground state, $\mathrm{Y}{\mathrm{b}}_2\mathrm{B}{\mathrm{e}}_2\mathrm{Ge}{\mathrm{O}}_7$ exhibits an excellent magnetocaloric response in sub-Kelvin temperature regimes. From the analysis of magnetic entropy $S$($T, B$) landscape, it can be cooled down to the minimum temperatures of $T_{\min }\sim 95$ mK and $T_{\min }\sim 240$ mK from $T$ = 2 K after the adiabatic demagnetization from initial fields of $B_i=4$ T and $B_i=2$ T, respectively. The attainable $T_{\min }$ and $N_{\mathrm{mag}}$ of $\mathrm{Y}{\mathrm{b}}_2\mathrm{B}{\mathrm{e}}_2\mathrm{Ge}{\mathrm{O}}_7$ outperform most of Yb-based quantum magnets and the recently reported spin supersolid candidate $\mathrm{N}{\mathrm{a}}_2\mathrm{BaCo}{\left(\mathrm{P}{\mathrm{O}}_4\right)}_2$ in the similar working temperature regimes. Therefore, $\mathrm{Y}{\mathrm{b}}_2\mathrm{B}{\mathrm{e}}_2\mathrm{Ge}{\mathrm{O}}_7$ provides a platform for exploring the exotic magnetic states as well as potential application in magnetic refrigeration at sub-Kelvin temperatures.