arXiv subjects

Ye-Heng Song

Publications and source records attributed to Ye-Heng Song.

6 recordsLinked to original sources

arXiv2019

Van der Waals heteroepitaxial growth of monolayer Sb in puckered honeycomb structure

Atomically thin two-dimensional (2D) crystals have gained tremendous attentions owing to their potential impacts to the future electronics technologies, as well as the exotic phenomena emerging in these materials. Monolayer of α phase Sb (α-antimonene) that shares the same puckered structure as black phosphorous, has been predicted to be stable with precious properties. However, the experimental realization still remains challenging. Here, we successfully grow high-quality monolayer α-antimonene, with the thickness finely controlled. The α-antimonene exhibits great stability upon exposure to air. Combining scanning tunneling microscope, density functional theory calculations and transport measurement, it is found that the electron band crossing the Fermi level exhibits a linear dispersion with a fairly small effective mass, and thus a good electrical conductivity. All of these properties make the α-antimonene promising in the future electronic applications.

cond-mat.mtrl-sci↗

arXiv2018

Unveiling the Charge Density Wave Inhomogeneity and Pseudogap State in 1T-TiSe2

By using scanning tunneling microscopy (STM) / spectroscopy (STS), we systematically characterize the electronic structure of lightly doped 1T-TiSe2, and demonstrate the existence of the electronic inhomogeneity and the pseudogap state. It is found that the intercalation induced lattice distortion impacts the local band structure and reduce the size of the charge density wave (CDW) gap with the persisted 2x2 spatial modulation. On the other hand, the delocalized doping electrons promote the formation of pseudogap. Domination by either of the two effects results in the separation of two characteristic regions in real space, exhibiting rather different electronic structures. Further doping electrons to the surface confirms that the pseudogap may be the precursor for the superconducting gap. This study suggests that the competition of local lattice distortion and the delocalized doping effect contribute to the complicated relationship between charge density wave and superconductivity for intercalated 1T-TiSe2.

cond-mat.str-el↗

arXiv2017

Observation of Coulomb gap in the quantum spin Hall candidate single-layer 1T'-WTe$_2$

The two-dimensional topological insulators (2DTI) host a full gap in the bulk band, induced by spin-orbit coupling (SOC) effect, together with the topologically protected gapless edge states. However, the SOC-induced gap is usually small, and it is challenging to suppress the bulk conductance and thus to realize the quantum spin Hall (QSH) effect. In this study, we find a novel mechanism to effectively suppress the bulk conductance. By using the quasiparticle interference (QPI) technique with scanning tunneling spectroscopy (STS), we demonstrate that the QSH candidate single-layer 1T'-WTe$_2$ has a semi-metal bulk band structure with no full SOC-induced gap. Surprisingly, in this two-dimensional system, we find the electron interactions open a Coulomb gap which is always pinned at the Fermi energy (E$_F$). The opening of the Coulomb gap can efficiently diminish the bulk state at the E$_F$ and is in favor of the observation of the quantized conduction of topological edge states.

cond-mat.mes-hall↗

arXiv2017

High-buckled R3 stanene with topologically nontrivial energy gap

Stanene has been predicted to be a two-dimensional topological insulator (2DTI). Its low-buckled atomic geometry and the enhanced spin-orbit coupling are expected to cause a prominent quantum spin hall (QSH) effect. However, most of the experimentally grown stanene to date displays a metallic state without a real gap, possibly due to the chemical coupling with the substrate and the stress applied by the substrate. Here,we demonstrate an efficient way of tuning the atomic buckling in stanene to open a topologically nontrivial energy gap. Via tuning the growth kinetics, we obtain not only the low-buckled 1x1 stanene but also an unexpected high-buckled R3xR3 stanene on the Bi(111) substrate. Scanning tunneling microscopy (STM) study combined with density functional theory (DFT) calculation confirms that the R3xR3 stanene is a distorted 1x1 structure with a high-buckled Sn in every three 1x1 unit cells. The high-buckled R3xR3 stanene favors a large band inversion at the Γ point, and the spin orbital coupling open a topologically nontrivial energy gap. The existence of edge states as verified in both STM measurement and DFT calculation further confirms the topology of the R3xR3 stanene. This study provides an alternate way to tune the topology of monolayer 2DTI materials.

cond-mat.mtrl-sci↗

arXiv2017

Direct Visualization of 2D Topological Insulator in Single-layer 1T'-WTe2

We grow nearly freestanding single-layer 1T'-WTe2 on graphitized 6H-SiC(0001) by using molecular beam epitaxy (MBE), and characterize its electronic structure with scanning tunneling microscopy / spectroscopy (STM/STS). We demonstrate the existence of topological edge states at the periphery of single-layer WTe2 islands. Surprisingly, we also find a band gap in the bulk and the semiconducting behaviors of the single-layer WTe2 at low temperature, which is likely resulted from an incommensurate charge density wave (CDW) transition. The realization of two-dimensional topological insulators (2D TIs) in single-layer transition metal dichalcogenide (TMD) thus provides a promising platform for further exploration of the 2D TIs' physics and related applications.

cond-mat.mtrl-sci↗

arXiv2016

Real-space characterization of reactivity towards water at Bi2Te3(111) surface

Surface reactivity is important in modifying the physical and chemical properties of surface sensitive materials, such as the topological insulators (TIs). Even though many studies addressing the reactivity of TIs towards external gases have been reported, it is still under heavy debate whether and how the topological insulators react with H$_2$O. Here, we employ scanning tunneling microscopy (STM) to directly probe the surface reaction of Bi$_2$Te$_3$ towards H$_2$O. Surprisingly, it is found that only the top quintuple layer is reactive to H$_2$O, resulting in a hydrated Bi bilayer as well as some Bi islands, which passivate the surface and prevent from the subsequent reaction. A reaction mechanism is proposed with H$_2$Te and hydrated Bi as the products. Unexpectedly, our study indicates the reaction with water is intrinsic and not dependent on any surface defects. Since water inevitably exists, these findings provide key information when considering the reactions of Bi$_2$Te$_3$ with residual gases or atmosphere.

cond-mat.mtrl-sci↗