By adapting the concept of epitaxy to two-dimensional space, we show the growth of a single-atomic-layer, in-plane heterostructure of a prototypical material system--graphene and hexagonal boron nitride (h-BN). Monolayer crystalline h-BN grew from fresh edges of monolayer graphene with atomic lattice coherence, forming an abrupt one-dimensional interface, or boundary. More important, the h-BN lattice orientation is solely determined by the graphene, forgoing configurations favored by the supporting copper substrate.

Two-dimensional interfaces between crystalline materials have been shown to generate unusual interfacial electronic states in complex oxides. Recently, a one-dimensional interface has been realized in hexagonal boron nitride and graphene planar heterostructures, where a polar-on-nonpolar one-dimensional boundary is expected to possess peculiar electronic states associated with edge states of graphene and the polarity of boron nitride. Here we present a combined scanning tunnelling microscopy and first-principles theory study of the graphene-boron nitride boundary to provide a first glimpse into the spatial and energetic distributions of the one-dimensional boundary states down to atomic resolution. The revealed boundary states are about 0.6 eV below or above the Fermi level depending on the termination of the boron nitride at the boundary, and are extended along but localized at the boundary. These results suggest that unconventional physical effects similar to those observed at two-dimensional interfaces can also exist in lower dimensions.

No abstract

Au-induced atomic wires on the Ge(001) surface were recently claimed to be an ideal 1D metal and their tunneling spectra were analyzed as the manifestation of a Tomonaga-Luttinger liquid (TLL) state. We reinvestigate this system for atomically well-ordered areas of the surface with high resolution scanning tunneling microscopy and spectroscopy (STS). The local density-of-states maps do not provide any evidence of a metallic 1D electron channel along the wires. Moreover, the atomically resolved tunneling spectra near the Fermi energy are dominated by local density-of-states features, deviating qualitatively from the power-law behavior. On the other hand, the defects strongly affect the tunneling spectra near the Fermi level. These results do not support the possibility of a TLL state for this system. An 1D metallic system with well-defined 1D bands and without defects are required for the STS study of a TLL state. DOI:PACS number(s): 71.10. Pm, 68.37.Ef, 73.20.Mf, 68.47.Fg Tomonaga-Luttinger liquid (TLL) is undoubtedly one of the most important theoretical models for interacting electrons in one dimension (1D) [1][2][3]. Over past decades, many efforts were made to experimentally observe a TLL state. The evidence for a TLL state has been accumulated in carbon nanotubes [4,5], strongly anisotropic bulk crystals [6][7][8], fractional-quantum-hall-effect edge states [9], and 1D electron gases of quantum wires [10].Along a largely different direction, the possibility of a TLL state was also discussed in metallic atomic wires selforganized on semiconductor surfaces, in particular, for Au-induced atomic wire arrays on vicinal silicon surfaces [11]. However, no clear indication of a TLL state has been identified for these systems so far [12][13][14][15]. As the most recent system in this line of researches, Au-induced atomic wires on the Ge(001) surface (hereafter, the Au-Ge wires) were suggested as an ideal 1D metallic system [16], with a clear signature of a TLL state in their scanning tunneling spectroscopy (STS) spectra [17]. However, not only the chemical composition and the atomic structure [18][19][20][21][22][23][24], but also their band structure is uncertain at present [25,26]. Most notably, a recent angle-resolved photoemission spectroscopy (ARPES) study, the first such study for a single domain surface, showed an anisotropic but 2D metallic band, which disperses more strongly in the direction perpendicular to the wire [27,28].This situation apparently and urgently requests the confirmation of the existence of a 1D metallic state itself in the Au-Ge wire and the TLL behavior of its tunneling spectra. We also note that while the importance of STS has been mentioned for a few 1D metallic systems [7,29], no detailed atomic scale investigation of STS spectra of a TLL system is available. For such an atomic scale study, a well ordered surface 1D metallic system would definitely be beneficial. Therefore, the Au-Ge wire could be an important model system to unveil a largely

The spatially resolved thermoelectric power is studied on epitaxial graphene on SiC with direct correspondence to graphene atomic structures by a scanning tunneling microscopy (STM) method. A thermovoltage arises from a temperature gradient between the STM tip and the sample, and variations of thermovoltage are distinguished at defects and boundaries with atomic resolution. The epitaxial graphene has a high thermoelectric power of 42 µV/K with a big change (9.6 µV/K) at the monolayer-bilayer boundary. Long-wavelength oscillations are revealed in thermopower maps which correspond to the Friedel oscillations of electronic density of states associated with the intravalley scattering in graphene. On the same terrace of a graphene layer, thermopower distributions show domain structures that can be attributed to the modifications of local electronic structures induced by microscopic distortions (wrinkles) of graphene sheet on the SiC substrate. The thermoelectric power, the electronic structure, the carrier concentration, and their interplay are analyzed on the level of individual defects and boundaries in graphene.

The magnetic domains in 2D layered material Fe 3 GeTe 2 are studied by using variabletemperature scanning tunneling microscope with a magnetic tip after in situ cleaving of single crystals. A stripy domain structure is revealed in a zero-field cooled sample below the ferromagnetic transition temperature of 205 K, which is replaced by separate double-walled domains and bubble domains when cooling the sample under a magnetic field of a ferromagnetic 3 3 Ni tip. The Ni tip can further convert the double-walled domain to a bubble domain pattern as well as move the Neel-type chiral bubble in sub-micrometer distance. The temperaturedependent evolutions of both zero-field cooled and field cooled domain structures correlate well with the bulk magnetization from magnetometry measurements. Atomic resolution scanning tunneling images and spectroscopy are acquired to understand the atomic and electronic structures of the material, which are further corroborated by first-principles calculations.

We investigated Pt-induced nanowires on the Si(110) surface using scanning tunneling microscopy (STM) and angle-resolved photoemission. High resolution STM images show a well-ordered nanowire array of 1.6 nm width and 2.7 nm separation. Angle-resolved photoemission reveals fully occupied one-dimensional (1D) bands with a Rashba-type split dispersion. Local dI/dV spectra further indicate well-confined 1D electron channels on the nanowires, whose density of states characteristics are consistent with the Rashba-type band splitting. The observed energy and momentum splitting of the bands are among the largest ever reported for Rashba systems, suggesting the Pt-Si nanowire as a unique 1D giant Rashba system. This self-assembled nanowire can be exploited for silicon-based spintronics devices as well as the quest for Majorana fermions.

No abstract