7 research outputs found
Experimental and Theoretical Electronic Structure and Symmetry Effects in Ultrathin NbSe2 Films
Layered quasi-two-dimensional transition metal dichalcogenides (TMDCs), which
can be readily made in ultrathin films, offer excellent opportunities for
studying how dimensionality affects electronic structure and physical
properties. Among all TMDCs, NbSe2 is of special interest; bulk NbSe2 hosts a
charge-density-wave phase at low temperatures and has the highest known
superconducting transition temperature, and these properties can be
substantially modified in the ultrathin film limit. Motivated by these effects,
we report herein a study of few-layer NbSe2 films, with a well-defined
single-domain orientation, epitaxially grown on Gallium Arsenide (GaAs).
Angle-resolved photoemission spectroscopy (ARPES) was used to determine the
electronic band structure and the Fermi surface as a function of layer
thickness; first-principles band structure calculations were performed for
comparison. The results show interesting changes as the film thickness
increases from a monolayer (ML) to several layers. The most notable changes
occur between a ML and a bilayer, where the inversion symmetry in bulk NbSe2 is
preserved in the bilayer but not in the ML. The results illustrate some basic
dimensional effects and provide a basis for further exploring and understanding
the properties of NbSe2.Comment: 15 pages, 4 figure
Gapped Electronic Structure of Epitaxial Stanene on InSb(111)
Stanene (single-layer grey tin), with an electronic structure akin to that of
graphene but exhibiting a much larger spin-orbit gap, offers a promising
platform for room-temperature electronics based on the quantum spin Hall (QSH)
effect. This material has received much theoretical attention, but a suitable
substrate for stanene growth that results in an overall gapped electronic
structure has been elusive; a sizable gap is necessary for room-temperature
applications. Here, we report a study of stanene epitaxially grown on the
(111)B-face of indium antimonide (InSb). Angle-resolved photoemission
spectroscopy (ARPES) measurements reveal a gap of 0.44 eV, in agreement with
our first-principles calculations. The results indicate that stanene on
InSb(111) is a strong contender for electronic QSH applications.Comment: 15 pages, 4 figure
Elemental topological Dirac semimetal: {\alpha}-Sn on InSb(111)
Three-dimensional (3D) topological Dirac semimetals (TDSs) are rare but
important as a versatile platform for exploring exotic electronic properties
and topological phase transitions. A quintessential feature of TDSs is 3D Dirac
fermions associated with bulk electronic states near the Fermi level. Using
angle-resolved photoemission spectroscopy (ARPES), we have observed such bulk
Dirac cones in epitaxially-grown {\alpha}-Sn films on InSb(111), the first such
TDS system realized in an elemental form. First-principles calculations confirm
that epitaxial strain is key to the formation of the TDS phase. A phase diagram
is established that connects the 3D TDS phase through a singular point of a
zero-gap semimetal phase to a topological insulator (TI) phase. The nature of
the Dirac cone crosses over from 3D to 2D as the film thickness is reduced
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Dirac Nodal Line in Hourglass Semimetal Nb3SiTe6
Glide-mirror symmetry in nonsymmorphic crystals can foster the emergence of novel hourglass nodal loop states. Here, we present spectroscopic signatures from angle-resolved photoemission of a predicted topological hourglass semimetal phase in Nb3SiTe6. Linear band crossings are observed at the zone boundary of Nb3SiTe6, which could be the origin of the nontrivial Berry phase and are consistent with a predicted glide quantum spin Hall effect; such linear band crossings connect to form a nodal loop. Furthermore, the saddle-like Fermi surface of Nb3SiTe6 observed in our results helps unveil linear band crossings that could be missed. In situ alkali-metal doping of Nb3SiTe6 also facilitated the observation of other band crossings and parabolic bands at the zone center correlated with accidental nodal loop states. Overall, our results complete the system's band structure, help explain prior Hall measurements, and suggest the existence of a nodal loop at the zone center of Nb3SiTe6