Electronic band structure and Fermi surface of CaB6 studied by angle-resolved photoemission spectroscopy

Direct evidence for the dirac-cone topological surface states in the ternary chalcogenide TlBiSe₂

We have performed angle-resolved photoemission spectroscopy on TlBiSe₂, which is a member of the ternary chalcogenides theoretically proposed as candidates for a new class of three-dimensional topological insulators. We found direct evidence for a nontrivial surface metallic state showing an "X"-shaped energy dispersion within the bulk-band gap. The present result unambiguously establishes that TlBiSe₂ is a strong topological insulator with a single Dirac cone at the Brillouin-zone center. The observed bulk-band gap of 0.35 eV is the largest among known topological insulators, making TlBiSe₂ the most promising material for studying room-temperature topological phenomena.

Synthesis and characterization of single-crystal strontium hexaboride nanowires

Catalyst-assisted growth of single-crystal strontium hexaboride (SrB6) nanowires was achieved by pyrolysis of diborane (B2H6) over SrO powders at 760-800 degrees C and 400 mTorr in a quartz tube furnace. Raman spectra demonstrate that the nanowires are SrB6, and transmission electron microscopy along with selected area diffraction indicate that the nanowires consist of single crystals with a preferred [001] growth direction. Electron energy loss data combined with the TEM images indicate that the nanowires consist of crystalline SrB 6 cores with a thin (1 to 2 nm) amorphous oxide shell. The nanowires have diameters of 10-50 nm and lengths of 1-10 microm.

Revelation of the role of impurities and conduction electron density in the high resolution photoemission study of ferromagnetic hexaborides

We investigate the temperature evolution of the electronic structure of ferromagnetic CaB6 using ultrahigh resolution photoemission spectroscopy; the electronic structure of paramagnetic LaB6 is used as a reference. High resolution spectra of CaB6 reveal a finite density of states at the Fermi level E(F) at all the temperatures and evidence of impurity induced localized features in the vicinity of E(F), which are absent in the spectra of LaB6. Analysis of the high resolution spectra suggests that disorder in the B sublattice inducing partial localization in the mobile electrons and low electron density at E(F) is important to achieve ferromagnetism in these systems.

Double exchange model for magnetic hexaborides

A microscopic theory for rare-earth ferromagnetic hexaborides, such as Eu1-xCaxB6, is proposed on the basis of the double-exchange Hamiltonian. In these systems, the reduced carrier concentrations place the Fermi level near the mobility edge, introduced in the spectral density by the disordered spin background. We show that the transport properties such as the Hall effect, magnetoresistance, frequency dependent conductivity, and dc resistivity can be quantitatively described within the model. We also make specific predictions for the behavior of the Curie temperature T(C) as a function of the plasma frequency omega(p).

Photoinduced emission of cooper pairs from superconductors

Under certain conditions specified in this work, a Cooper pair can be emitted from a superconductor upon the absorption of one ultraviolet photon. The spectra of the excited electron pair carry direct information on the energy and angular pair correlation. These statements are concluded from a formal and numerical analysis based on the Bardeen-Cooper-Schrieffer theory for superconductivity.