4 Search Results

Lateral heterojunctions of atomically precise graphene nanoribbons (GNRs) hold promise for applications in nanotechnology, yet their charge transport and most of the spectroscopic properties have not been investigated. Here, we synthesize a monolayer of multiple aligned heterojunctions consisting of quasi-metallic and wide-bandgap GNRs, and report characterization by scanning tunneling microscopy, angle-resolved photoemission, Raman spectroscopy, and charge transport. Comprehensive transport measurements as a function of bias and gate voltages, channel length, and temperature reveal that charge transport is dictated by tunneling through the potential barriers formed by wide-bandgap GNR segments. The current-voltage characteristics are in agreement with calculations of tunneling conductancemore » through asymmetric barriers. We fabricate a GNR heterojunctions based sensor and demonstrate greatly improved sensitivity to adsorbates compared to graphene based sensors. This is achieved via modulation of the GNR heterojunction tunneling barriers by adsorbates.« less

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 spectroscopy, we show the emergent flat band in a VSe₂ / Bi₂Se₃ heterostructure. Our photoemission study demonstrates that the flat band covers the entire Brillouin zone and exhibits 2D nature with a complex circular dichroism. In addition, the Dirac cone of Bi₂Se₃ is not reshaped by the flat bandmore » even though they overlap in proximity of the Dirac point. These features make this flat band distinguishable from the ones previously found. Thereby, the observation of a flat band in the VSe₂ / Bi₂Se₃ heterostructure opens a promising pathway to realize strongly correlated quantum effects in topological materials.« less

The recently discovered antiferromagnetic topological insulators in the Mn-Bi-Te family with intrinsic magnetic ordering have rapidly drawn broad interest since its cleaved surface state is believed to be gapped, hosting the unprecedented axion states with a half-integer quantum Hall effect. Here, however, we show unambiguously by using high-resolution angle resolved photoemission spectroscopy that a gapless Dirac cone at the (0001) surface of MnBi2Te4 exists inside the bulk band gap. Such an unexpected surface state remains unchanged across the bulk N´eel temperature, and is even robust against severe surface degradation, indicating additional topological protection. Through symmetry analysis and ab initio calculationsmore » we consider different types of surface reconstruction of the magnetic moments as possible origins giving rise to such linear dispersion. Our results unveil the experimental topological properties of MnBi2Te4, revealing that the intrinsic magnetic topological insulator hosts a rich platform to realize various topological phases by tuning the magnetic or structural configurations, and thus push forward the comprehensive understanding of magnetic topological materials.« less

Unraveling the nature of pseudogap phase in high-temperature superconductors holds the key to understanding their superconducting mechanisms and potentially broadening their applications via enhancement of their superconducting transition temperatures. Angle-resolved photoemission spectroscopy (ARPES) experiments using circularly polarized light have been proposed to detect possible symmetry breaking state in the pseudogap phase of cuprates. Here, the presence (absence) of an electronic order which breaks mirror symmetry of the crystal would in principle induce a finite (zero) circular dichroism in photoemission. Different orders breaking reflection symmetries about different mirror planes can also be distinguished by the momentum dependence of the measured circularmore » dichroism.« less