We developed a facile hydrothermal method for synthesizing ultrafine size-controllable earth-abundant Cu₂ZnSnS₄ (CZTS) nanocrystals using simple Cu(II), Zn(II) and Sn(II) inorganic salts and thiourea in a mixed ethylenediamine and di-water solution as precursors. X-ray diffraction, Raman scattering and transmission electron microscopy confirm that pure kesterite structure CZTS nanocrystals have been synthesized at temperatures as low as 180 °C. Broadening of Raman peaks and blue-shift of the absorption edge is attributed to quantum confinement within the nanocrystals. The hydrophilism and tunable band-gap of the CZTS nanocrystals show the potential applications of the nanocrystals for biological labelling and quantum dot based solar cells.

For strongly correlated oxides, it has been a long-standing issue regarding the role of the chemical ordering of the dopants on the physical properties. Here, using unit cell by unit cell superlattice growth technique, we determine the role of chemical ordering of the Pr dopant in a colossal magnetoresistant (La_1−yPr_y)_1−xCa_xMnO₃ (LPCMO) system, which has been well known for its large length-scale electronic phase separation phenomena. Our experimental results show that the chemical ordering of Pr leads to marked reduction of the length scale of electronic phase separations. Moreover, compared with the conventional Pr-disordered LPCMO system, the Pr-ordered LPCMO system has a metal–insulator transition that is ∼100 K higher because the ferromagnetic metallic phase is more dominant at all temperatures below the Curie temperature.

Significance: We report a breakthrough in addressing a long-standing and challenging issue: the physical origin of electronic phase separation phenomena in complex oxides. Using tricolor monoatomic superlattice growth, we provide direct experimental evidence to show that the chemical-dopants-induced disorder is crucial for electronic phase separation and colossal magnetoresistance effect. Conceptually our results are far reaching: we believe that correlated materials in general likely need deviations from ideality to display the crucial nonlinear effects important for devices.

The transition temperatures of molecular ferroelectrics are usually lower than those of inorganic ferroelectrics due to weaker electron–electron and electron–phonon interactions in molecular ferroelectrics. Therefore, above-room-temperature molecular ferroelectrics are very rare which hinders their application in modern electronic fields. Here we report a new kind of above-room-temperature molecular ferroelectric, diisopropylammonium perchlorate (DIPAP), which combines fast switchable molecular dielectrics. The ferroelectric to paraelectric phase transition occurs at about 338 K in the heating process, which was confirmed by structure analysis (from space group of P1 to P2₁/c), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), dielectric permittivity, pyroelectric as well as Raman spectra. The spontaneous polarization measured from pyroelectric current and ferroelectric hysteresis loop is about 0.1 μC cm⁻², while the calculated value by first principles is as high as 20 μC cm⁻². This large theoretical spontaneous polarization value can be achieved through designing and modulating a molecular structure to a fully polarized one.

Ruthenium-based perovskite systems are attractive because their structural, electronic, and magnetic properties can be systematically engineered. The ${\mathrm{SrRuO}}_3/{\mathrm{SrTiO}}_3$ superlattice, with its period consisting of one unit cell each, is very sensitive to strain change. Our first-principles simulations reveal that, in the high tensile strain region, it transits from a ferromagnetic metal to an antiferromagnetic insulator with clear tilted octahedra, while in the low strain region, it is a ferromagnetic metal without octahedra tilting. Detailed analyses of three spin-down $\mathrm{Ru}-t_{2g}$ orbitals just below the Fermi level reveal that the splitting of these orbitals underlies these dramatic phase transitions, with the rotational force constant of ${\mathrm{RuO}}_6$ octahedron high up to $16\mathrm{meV}/{\mathrm{Deg}}^2$, 4 times larger than that of ${\mathrm{TiO}}_6$. Differently from nearly all the previous studies, these transitions can be probed optically through the diagonal and off-diagonal dielectric tensor elements. For a 1% change in strain, our experimental spin moment change is $-0.14\pm 0.06$ ${\mu }_B$, quantitatively consistent with our theoretical value of $-0.1$ ${\mu }_B$.

Ferroelectrics are essential in memory devices for multi-bit storage and high-density integration. Ferroelectricity mainly exists in compounds but rare in single-element materials due to their lack of spontaneous polarization in the latter. However, we report a room-temperature ferroelectricity in quasi-one-dimensional Te nanowires. Piezoelectric characteristics, ferroelectric loops and domain reversals are clearly observed. We attribute the ferroelectricity to the ion displacement created by the interlayer interaction between lone-pair electrons. Ferroelectric polarization can induce a strong field effect on the transport along the Te chain, giving rise to a self-gated ferroelectric field-effect transistor. By utilizing ferroelectric Te nanowire as channel, the device exhibits high mobility (~220 cm²·V⁻¹·s⁻¹), continuous-variable resistive states can be observed with long-term retention (>10⁵ s), fast speed (1.92 TB/cm²). Our work provides opportunities for single-element ferroelectrics and advances practical applications such as ultrahigh-density data storage and computing-in-memory devices.