156 research outputs found
Determination of the Energy Band Gap of Bi₂Se₃
Despite intensive investigations of Bi2Se3 in past few years, the size and nature of the bulk energy band gap of this well-known 3D topological insulator still remain unclear. Here we report on a combined magneto-transport, photoluminescence and infrared transmission study of Bi2Se3, which unambiguously shows that the energy band gap of this material is direct and reaches Eg = (220 ± 5) meV at low temperatures
Non-uniform carrier density in CdAs evidenced by optical spectroscopy
We report the detailed optical properties of CdAs crystals in a wide
parameter space: temperature, magnetic field, carrier concentration and crystal
orientation. We investigate high-quality crystals synthesized by three
different techniques. In all the studied samples, independently of how they
were prepared and how they were treated before the optical experiments, our
data indicate conspicuous fluctuations in the carrier density (up to 30%).
These charge puddles have a characteristic scale of 100 m, they become
more pronounced at low temperatures, and possibly, they become enhanced by the
presence of crystal twinning. The Drude response is characterized by very small
scattering rates ( meV) for as-grown samples. Mechanical treatment,
such as cutting or polishing, influences the optical properties of single
crystals, by increasing the Drude scattering rate and also modifying the high
frequency optical response. Magneto-reflectivity and Kerr rotation are
consistent with electron-like charge carriers and a spatially non-uniform
carrier density.Comment: Accepted in Physical Review
Red Clover Improves the Energy to Protein Balance of Lucerne-Grass Herbage
Low ratio of readily fermentable carbohydrate to soluble protein concentrations in lucerne (Medicago sativa L.) leads to inefficient use of herbage N by ruminants. To improve the energy to protein balance in lucerne-grass herbage, four proportions of lucerne:red clover (Trifolium pratense L.) were compared in mixtures with and without grasses: timothy (Phleum pratense L.) and tall fescue (Schedonorus arundinaceus Schreb. Dumort.) in Quebec (QC, Canada). In the first post-seeding year, red clover proportion averaged (across grasses and four harvests) 0, 37, 59, and 74% in herbage mixtures. Increasing the proportion of red clover caused a slight but significant decrease in herbage total nitrogen (TN) concentration (32 to 31 g kg-1 DM) but substantial decreases in non-protein N (PA), rapidly (PB1) and moderately (PB2) degraded protein fractions, and a significant increase in the slowly degraded protein fractions (PB3+PC) (157 to 308 g kg-1 TN). With the inclusion of 74% of red clover, the ratio of soluble sugar to crude protein (CP) in herbage increased from 0.25 to 0.36 because of the increase in the soluble sugar concentration (48 to 66 g kg-1 DM). The inclusion of red clover in mixture with lucerne improved the energy to CP balance compared to lucerne alone, and caused a linear increase in the herbage in vitro neutral detergent fiber digestibility from 568 to 639 g kg-1 aNDF with similar herbage dry matter yield (10.3 Mg ha-1)
Magneto-optical signature of massless Kane electrons in Cd3As2
We report on optical reflectivity experiments performed on Cd3As2 over a
broad range of photon energies and magnetic fields. The observed response
clearly indicates the presence of 3D massless charge carriers. The specific
cyclotron resonance absorption in the quantum limit implies that we are probing
massless Kane electrons rather than symmetry-protected 3D Dirac particles. The
latter may appear at a smaller energy scale and are not directly observed in
our infrared experiments.Comment: 5 pages, 4 figures + supplementary materials (17 pages), to be
published in Phys. Rev. Let
Addition of Red Clover or Birdsfoot Trefoil in Alfalfa-based Mixtures to Improve the Forage Energy to Protein Balance
The low ratio of sugars (S) to crude proteins (CP) in alfalfa (AL, Medicago sativa L.) leads to inefficient use of nitrogen by ruminants. The objective was to determine if adding red clover (RC, Trifolium pratense L.) or birdsfoot trefoil (BT, Lotus corniculatus L.) with or without a grass species to AL improved the forage S/CP ratio. Treatments were 100% AL (control) or AL-based mixtures with RC or BT in three proportions (75, 50, or 25% of seeded legumes) with either no grass or with timothy (Phleum pratense L.) or tall fescue (Schedonorus arundinaceus Schreb. Dumort.), resulting in 21 treatments assigned to a randomized complete block design with four replications at three sites in Canada (Agassiz, BC; St-Anne-de-Bellevue, QC; StAugustin-de-Desmaures, QC). Species contribution and nutritive attributes measured at each harvest were weighted for yield as a proportion of the seasonal yield and expressed yearly for the first two post-seeding years. Regression analyses showed that forage S concentration increased, CP concentration tended to decrease, and the S/CP ratio increased from 0.3 to 0.5 (y = 0.002 x + 0.3; P = 0.003, R2 = 0.53) with the addition of up to 92% RC or up to 66% BT to AL-based mixtures. The addition of up to 61% TI or 55% TF did not impact the S/CP ratio of AL-based mixtures. Further studies are needed to determine if the improved forage S/CP ratio following the addition of RC or BT to AL-based mixtures leads to an improved N-use efficiency in ruminants
Strong interband Faraday rotation in 3D topological insulator Bi2Se3
The Faraday effect is a representative magneto-optical phenomenon, resulting from the transfer of angular momentum between interacting light and matter in which time-reversal symmetry has been broken by an externally applied magnetic field. Here we report on the Faraday rotation induced in the prominent 3D topological insulator Bi2Se3 due to bulk interband excitations. The origin of this non-resonant effect, extraordinarily strong among other non-magnetic materials, is traced back to the specific Dirac-type Hamiltonian for Bi2Se3, which implies that electrons and holes in this material closely resemble relativistic particles with a non-zero rest mass
Energy scale of Dirac electrons in Cd3As2
Cadmium arsenide (Cd3As2) has recently became conspicuous in solid-state physics due to several reports proposing that it hosts a pair of symmetry-protected 3D Dirac cones. Despite vast investigations, a solid experimental insight into the band structure of this material is still missing. Here we fill one of the existing gaps in our understanding of Cd3As2, and based on our Landau-level spectroscopy study, we provide an estimate for the energy scale of 3D Dirac electrons in this system. We find that the appearance of such charge carriers is limited-contrary to a widespread belief in the solid-state community-to a relatively small energy scale (below 40 meV)
- …