Zhongwei Dai

Lawrence Berkeley National Laboratory | LBL

Topological crystalline insulators have been recently predicted and observed in rock-salt structure SnSe {111} thin films. Previous studies have suggested that the Se-terminated surface of this thin film with hydrogen passivation has a reduced surface energy and is thus a preferred configuration. In this paper, synchrotron-based angle-resolved phot...

α-RuCl3, a layered 2D material, was recently identified as a promising candidate for realizing a Kitaev quantum spin liquid. However one fundamental property, the crystal structure, has not been well resolved yet due to difficulty of bulk diffraction techniques caused by layer stacking faults. Furthermore, the surface relaxation of monolayer-level...

Flat band electronic states are proposed to be a fundamental tool to achieve various quantum states of matter at higher temperatures due to the enhanced electronic correlations. However, materials with such peculiar electronic states are rare and often rely on subtle properties of the band structures. Here, by using angle-resolved photoemission spe...

We present experimental evidence of electronic and optical interlayer resonances in graphene van der Waals heterostructure interfaces. Using the spectroscopic mode of a low-energy electron microscope (LEEM), we characterized these interlayer resonant states up to 10 eV above the vacuum level. Compared with nontwisted, AB-stacked bilayer graphene (A...

The surface structure of phosphorene crystals materials is determined using surface sensitive dynamical micro-spot low energy electron diffraction ({\mu}LEED) analysis using a high spatial resolution low energy electron microscopy (LEEM) system. Samples of (\textit{i}) crystalline cleaved black phosphorus (BP) at 300 K and (\textit{ii}) exfoliated...

Here, by using angle-resolved photoemission spectroscopy, we showed that Bi2−xCrxSe3 single crystals have a distinctly well-defined band structure with a large bulk band gap and undistorted topological surface states. These spectral features are unlike their thin film forms in which a large nonmagnetic gap with a distorted band structure was report...

Flat band electronic states are proposed to be a fundamental tool to achieve various quantum states of matter at higher temperatures due to the enhanced electronic correlations. However , materials with such peculiar electronic states are rare and often rely on subtle properties of the band structures. Here, by using angle-resolved photoemission sp...

Recently, ultrathin metal-oxide thin film transistors (TFTs) have shown very high on-off ratio and ultra-sharp subthreshold swing, making them promising candidates for applications beyond conventional large-area electronics. While the on-off operation in typical TFTs results primarily from the modulation of charge carrier density by gate voltage, t...

Dispersionless flat bands are proposed to be a fundamental ingredient to achieve the various sought after quantum states of matter including high-temperature superconductivity 1-4 and fractional quantum Hall effect 5-6. Materials with such peculiar electronic states, however, are very rare and often exhibit very complex band structures. Here, we re...

The transition-metal dichalcogenide compounds MoTe2 and WTe2 are polymorphic with both semiconducting and metallic phases. The thermodynamically stable phase of WTe2 at room temperature is orthorhombic and metallic and displays a wide range of interesting phenomena including type-II Weyl fermions, titanic magnetoresistance and superconductivity in...

PLEASE, the Python Low-energy Electron Analysis SuitE, provides an open source and cross-platform graphical user interface (GUI) for rapid analysis and visualization of low energy electron microscopy (LEEM) data sets. LEEM and the associated technique, selected area micro-spot low energy electron diffraction (μ-LEED), are powerful tools for analysi...

The surface structure of phosphorene crystals materials is determined using surface sensitive dynamical micro-spot low energy electron diffraction ({\mu}LEED) analysis using a high spatial resolution low energy electron microscopy (LEEM) system. Samples of (\textit{i}) crystalline cleaved black phosphorus (BP) at 300 K and (\textit{ii}) exfoliated...

Topological crystalline insulators have been recently predicted and observed in rock-salt structure SnSe $\{111\}$ thin films. Previous studies have suggested that the Se-terminated surface of this thin film with hydrogen passivation, has a reduced surface energy and is thus a preferred configuration. In this paper, synchrotron-based angle-resolved...

We have used selected area low energy electron diffraction intensity-voltage (μLEED-IV) analysis to investigate the surface structure of crystalline 2H molybdenum disulfide (MoS2) and mechanically exfoliated and suspended monolayer MoS2. Our results show that the surface structure of bulk 2H-MoS2 is distinct from its bulk and that it has a slightly...

The unidirectional transmission of acoustic waves is realized by a simple geometrically asymmetric steel grating structure. This exotic phenomenon stems from the one-way diffraction effect induced by the different periods of the slits on the both surfaces of the sample. And the frequency range of unidirectional transmission is simply determined by...