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We demonstrate zero-bias mid-infrared photocurrent generation in topological insulator MnBi2Te4 thin films. The symmetry breakings at the surface and interfaces lead to the coexistence of Dirac and Rashba band states, which enable two kinds of photogalvanic responses. One is the magneto-photogalvanic effect in the presence of an external in-plane magnetic field perpendicular to photocurrent direction, and the other is the light-polarization-dependent linear photogalvanic effect arising from in-plane symmetry breakings, both observed up to room temperature. We disentangle these contributions by light-polarization and temperature dependent spectroscopy under the varying magnetic field. [ABSTRACT FROM AUTHOR]

Spatially confined excitons undergo two distinct quantization effects depending on the confinement length, the enhanced binding energy under strong confinement, and the center-of-mass quantization under weak one. However, the transition between them has not been experimentally identified in two-dimensional (2D) materials due to the lack of thin films satisfying large-scale uniformity and atomic-level flatness in a wide thickness range. Here, we reveal the crossover in high-quality epitaxial thin films of a 2D semiconductor PbI2 grown by molecular beam epitaxy. The absorption spectra exhibit oscillatory structures manifesting the exciton center-of-mass quantization, and the quantization energies show an additional blue shift associated with the strong confinement effect below five-layer thickness (35 Å). The precise control of exciton quantum states will lead to the further development of optoelectronic functionalities of 2D materials. [ABSTRACT FROM AUTHOR]

The recently discovered intrinsic magnetic topological insulator MnBi2Te4 has attracted keen interest for exotic quantum states such as a quantum anomalous Hall insulator and an axion insulator. Such quantum states of MnBi2Te4 have been intensively studied mainly in atomically thin exfoliated samples, yet thin film samples with critically tuned Fermi level would be indispensable for further pursuit of topological functionality in MnBi2Te4 and related heterointerfaces. Here, we report on fabrication of an Sb-doped MnBi2Te4 thin film by molecular beam epitaxy and their transport properties. The Sb-substitution induces the change in the carrier type and the subsequent increase in resistivity, demonstrating the tuning of the Fermi level (EF) across the bulk bandgap and the phase change to the topologically nontrivial phase. The EF is further finely controlled in a field-effect transistor device. We observe the enhancement of the anomalous Hall conductivity at the charge neutral point, confirming the opening of the magnetic exchange gap in surface Dirac states. The precise control of the band structure and the Fermi level in the thin-film form will lead to exploring exotic phenomena based on intrinsic magnetic topological insulators. [ABSTRACT FROM AUTHOR]

Perovskitelike RMnO3 (R: rare-earth) exhibits large magnetoelectric effects because of the intimate correlation between magnetic and ferroelectric orders. However, reproducing the multiferroic properties in thin films has been far from straightforward due to the difficulty in the growth of single-crystal films caused by the large orthorhombic distortion in RMnO3. We could overcome the problem and achieve the fabrication of a monodomain single-crystal film of orthorhombic YMnO3 by choosing (0 1 0)-YAlO3 as a substrate. The film showed a ferroelectric transition at 40 K with a saturation polarization of 0.8 μC/cm2. The ferroelectric polarization could be modified by magnetic fields, evidencing the multiferroic state in the film. [ABSTRACT FROM AUTHOR]

We have fabricated epitaxial V1-xWxO2(0≤x≤0.33) thin films on TiO2 (001) substrates. The metal-insulator transition temperature of VO2 is systematically reduced by W doping, and eventually a metallic ground state is realized at 0.08≤x≤0.09. Tiny resistivity upturn around 50 K observed for these films suggests an electronic phase separation between a majority metallic matrix and minority insulating puddles. With further increasing x above 0.095, another insulating phase appears while increasing the metal-insulator transition temperature. The elucidated phase diagram gives basic knowledge for devices based on Mott transition. [ABSTRACT FROM AUTHOR]

The magnetic-field effect on electroluminescence (EL) has been investigated for the tris-(8-hydroxyquinolino) aluminum (Alq3)-based organic light emitting diode. The EL intensity sharply increases up to 8% with increasing magnetic field to 500 Oe at room temperature. The magnetic field effect on EL depends on the interface structure between a hole transporting and a light emitting layers, indicating the importance of the spin-state dynamics of the electron-hole pairs at the interface. [ABSTRACT FROM AUTHOR]

Highly oriented polydiacetylene films have been fabricated by the vacuum deposition method using a new alignment technique. Details of the method are described, and optical and structural properties of typical oriented films of poly[dodecadiyne-1,12-diol- bis(n-butoxycarbonyl-methyl-urethane)][PDA-4BCMU] are reported. [ABSTRACT FROM AUTHOR]