6 research outputs found
Drumhead Surface States and Topological Nodal-Line Fermions in TlTaSe2
A topological nodal-line semimetal is a new condensed matter state with
one-dimensional bulk nodal lines and two-dimensional drumhead surface bands.
Based on first-principles calculations and our effective k . p model, we
propose the existence of topological nodal-line fermions in the ternary
transition- metal chalcogenide TlTaSe2. The noncentrosymmetric structure and
strong spin-orbit coupling give rise to spinful nodal-line bulk states which
are protected by a mirror reflection symmetry of this compound. This is
remarkably distinguished from other proposed nodal-line semimetals such as
Cu3NPb(Zn) in which nodal lines exist only in the limit of vanishing spin-orbit
coupling. We show that the drumhead surface states in TlTaSe2, which are
associated with the topological nodal lines, exhibit an unconventional chiral
spin texture and an exotic Lifshitz transition as a consequence of the linkage
among multiple drumhead surface-state pockets.Comment: Related papers at
http://physics.princeton.edu/zahidhasangroup/index.htm
Embedded Topological Semimetals
Topological semimetals, such as Dirac, Weyl, or line-node semimetals, are
gapless states of matter characterized by their nodal band structures and
surface states. In this work, we consider layered (topologically trivial)
insulating systems in dimensions that are composed of coupled multi-layers
of -dimensional topological semimetals. Despite being nominal bulk
insulators, we show that crystal defects having co-dimension can harbor
robust lower dimensional topological semimetals embedded in a trivial
insulating background. As an example we show that defect-bound topological
semimetals can be localized on stacking faults and partial dislocations.
Finally, we propose how an embedded topological Dirac semimetal can be
identified in experiment by introducing a magnetic field and resolving the
relativistic massless Dirac Landau level spectrum at low energies in an
otherwise gapped system.Comment: Published Versio
Direct transition resonance in atomically uniform topological Sb(111) thin films
Atomically uniform Sb(111) films are fabricated by the method of molecular beam epitaxy on an optimized Si(111) surface. Two dimensional quantum well states and topological surface states in these films are well resolved as measured by angle-resolved photoemission spectroscopy. We observe an evolution of direct transition resonances by varying the excitation photon energy (and thus the perpendicular crystal momentum). The experimental results are reproduced in a comprehensive model calculation taking into account first-principles calculated initial states and time-reversed low-energy-electron-diffraction final states in the photoexcitation process. The resonant behavior illustrates that the topological surface states and the quantum well states are analytically connected in momentum space in all three dimensions