127 research outputs found
Electrical transport properties of single-crystal CaB6, SrB6, and BaB6
The electrical resistivity and Hall effect of alkaline-earth-metal hexaboride single crystals are measured as a function of temperature, hydrostatic pressure, and magnetic field. The transport properties vary weakly with the external parameters and are modeled in terms of intrinsic variable-valence defects. These defects can stay either in (1) delocalized shallow levels or in (2) localized levels resonant with the conduction band, which can be neutral or negatively charged. Satisfactory agreement is obtained for electronic transport properties in a broad temperature and pressure range, although fitting the magnetoresistance is less straightforward and a combination of various mechanisms is needed to explain the field and temperature dependences.We acknowledge support from Grant No. MAT2012-38213-C02-01 from the Ministerio de Economía y Competividad of Spain. Additional support from Diputacion General de Aragon (DGA-CAMRADS) is also acknowledged. Work at Los Alamos was performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences,
Division of Materials Science and Engineering. P.F.S.R. acknowledges a Director’s Postdoctoral Fellowship through the LANL LDRD program. P.S. acknowledges the support by the U.S. Department of Energy (BES) under Grant No. DE-FG02-98ER45707.Peer Reviewe
Magnetic and defect probes of the SmB surface state
The impact of non-magnetic and magnetic impurities on topological insulators
is a central problem concerning their fundamental physics and possible novel
spintronics and quantum computing applications. SmB, predicted to be a
topological Kondo insulator, is considered a benchmark material. Using a
spin-polarized tip in scanning tunneling spectroscopy destroys the signature
peak of the topological surface state, revealing its spin texture. Further,
combining local STS with macroscopic transport measurements on SmB
containing different substitutions enables us to investigate the effect of
impurities. The surface states around impurities are locally suppressed with
different length scales depending on their magnetic properties and, for
sufficiently high impurity level, globally destroyed. Our study points directly
to the topological nature of SmB, and unveils, microscopically and
macroscopically, how impurities -- magnetic or non-magnetic -- affect
topological surface states
Nodeless superconductivity in the noncentrosymmetric ThIrSi compound
The ThIrSi superconductor, with K, is expected to show unusual
features in view of its noncentrosymmetric structure and the presence of heavy
elements featuring a sizable spin-orbit coupling. Here, we report a
comprehensive study of its electronic properties by means of local-probe
techniques: muon-spin rotation and relaxation ({\textmu}SR) and nuclear
magnetic resonance (NMR). Both the superfluid density
(determined via transverse-field {\textmu}SR) and the spin-lattice relaxation
rate (determined via NMR) suggest a nodeless superconductivity.
Furthermore, the absence of spontaneous magnetic fields below , as evinced
from zero-field {\textmu}SR measurements, indicates a preserved time-reversal
symmetry in the superconducting state of ThIrSi. Temperature-dependent upper
critical fields as well as field-dependent superconducting muon-spin
relaxations suggest the presence of multiple superconducting gaps in ThIrSi.Comment: 8 pages, 8 figure
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