81 research outputs found
Non-Kondo-like Electronic Structure in the Correlated Rare-Earth Hexaboride YbB
We present angle-resolved photoemission studies on the rare-earth hexaboride
YbB, which has recently been predicted to be a topological Kondo insulator.
Our data do not agree with the prediction and instead show that YbB
exhibits a novel topological insulator state in the absence of a Kondo
mechanism. We find that the Fermi level electronic structure of YbB has
three 2D Dirac cone like surface states enclosing the Kramers' points, while
the f-orbital which would be relevant for the Kondo mechanism is eV
below the Fermi level. Our first-principles calculation shows that the
topological state which we observe in YbB is due to an inversion between Yb
and B bands. These experimental and theoretical results provide a new
approach for realizing novel correlated topological insulator states in
rare-earth materials.Comment: 5 pages, 4 figures, Submitted in 2014. Published in 2015, Phys. Rev.
Lett. 114, 01640
Surface Versus Bulk Dirac States Tuning in a Three-Dimensional Topological Dirac Semimetal
Recently, crystalline-symmetry-protected three-dimensional (3D) bulk Dirac
semimetal phase has been experimentally identified in a stoichiometric
high-mobility compound, Cd3As2. The Dirac state observed in Cd3As2 has been
attributed to originate mostly from the bulk state while calculations show that
the bulk and surface states overlap over the entire Dirac dispersion energy
range. In this study, we unambiguously reveal doping induced evolution of the
ground state of surface and bulk electron dynamics in a 3D Dirac semimetal. We
develop a systematic technique to isolate the surface and bulk states in
Cd3As2, by simultaneously utilizing angle-resolved photoemission spectroscopy
(ARPES) and in-situ surface deposition. Our experimental results provide a
method for tuning the chemical potential as well as to observe surface states
degenerate with bulk states, which will be useful for future applications of 3D
Dirac semimetal.Comment: 5 pages, 4 figure
Bulk crystal growth and electronic characterization of the 3D Dirac Semimetal Na3Bi
High quality hexagon plate-like Na3Bi crystals with large (001) plane
surfaces were grown from a molten Na flux. The freshly cleaved crystals were
analyzed by low temperature scanning tunneling microscopy (STM) and
angle-resolved photoemission spectroscopy (ARPES), allowing for the
characterization of the three-dimensional (3D) Dirac semimetal (TDS) behavior
and the observation of the topological surface states. Landau levels (LL) were
observed, and the energy-momentum relations exhibited a linear dispersion
relationship, characteristic of the 3D TDS nature of Na3Bi. In transport
measurements on Na3Bi crystals the linear magnetoresistance and Shubnikov-de
Haas (SdH) quantum oscillations are observed for the first time.Comment: To be published in a special issue of APL Material
Momentum space imaging of Cooper pairing in a half-Dirac-gas topological superconductor (a helical 2D topological superconductor)
Superconductivity in Dirac electrons has recently been proposed as a new
platform between novel concepts in high-energy and condensed matter physics. It
has been proposed that supersymmetry and exotic quasiparticles, both of which
remain elusive in particle physics, may be realized as emergent particles in
superconducting Dirac electron systems. Using artificially fabricated
topological insulator-superconductor heterostructures, we present direct
spectroscopic evidence for the existence of Cooper pairing in a half Dirac gas
2D topological superconductor. Our studies reveal that superconductivity in a
helical Dirac gas is distinctly different from that of in an ordinary
two-dimensional superconductor while considering the spin degrees of freedom of
electrons. We further show that the pairing of Dirac electrons can be
suppressed by time-reversal symmetry breaking impurities removing the
distinction. Our demonstration and momentum-space imaging of Cooper pairing in
a half Dirac gas and its magnetic behavior taken together serve as a critically
important 2D topological superconductor platform for future testing of novel
fundamental physics predictions such as emergent supersymmetry and quantum
criticality in topological systems.Comment: Submitted June'14; Accepted to NaturePhysics, to appear AOP (2014
- …