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Electronic structure of YbB: Is it a Topological Insulator or not?
To resolve the controversial issue of the topological nature of the
electronic structure of YbB, we have made a combined study using density
functional theory (DFT) and angle resolved photoemission spectroscopy (ARPES).
Accurate determination of the low energy band topology in DFT requires the use
of modified Becke-Johnson exchange potential incorporating the spin-orbit
coupling and the on-site Coulomb interaction of Yb electrons as large
as 7 eV. We have double-checked the DFT result with the more precise GW band
calculation. ARPES is done with the non-polar (110) surface termination to
avoid band bending and quantum well confinement that have confused ARPES
spectra taken on the polar (001) surface termination. Thereby we show
definitively that YbB has a topologically trivial B 2-Yb 5
semiconductor band gap, and hence is a non-Kondo non-topological insulator
(TI). In agreement with theory, ARPES shows pure divalency for Yb and a -
band gap of 0.3 eV, which clearly rules out both of the previous scenarios of
- band inversion Kondo TI and - band inversion non-Kondo TI. We
have also examined the pressure-dependent electronic structure of YbB,
and found that the high pressure phase is not a Kondo TI but a
\emph{p}-\emph{d} overlap semimetal.Comment: The main text is 6 pages with 4 figures, and the supplementary
information contains 6 figures. 11 pages, 10 figures in total To be appeared
in Phys. Rev. Lett. (Online publication is around March 16 if no delays.
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The Impact of Data Breaches on Hotel and Restaurant Firm Stock Returns
Hospitality firms are susceptible to data breaches due to the high volume of information they keep on customers and employees. In this paper, we first present an analysis of the stock market’s reaction to data breaches at hospitality firms, and we compare these breaches to a matched-firm sample of retail firm breaches. Abnormal stock market returns indicate that hotel and restaurant firm stock prices went down by approximately 1.24% from data breach announcements. We find that the type of breach or number of times a firm has been breached does not alter the impact of a breach on firm returns. Additionally, we find that data breaches cause a greater loss of value for hotel firms than for restaurants. Finally, we find no support for the idea that hospitality firms exhibit larger negative effects compared to retail firms on a matched-pair analysis
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