Thermodynamic evidence for valley-dependent density of states in bulk bismuth

Electron-like carriers in bismuth are described by the Dirac Hamiltonian, with a band mass becoming a thousandth of the bare electron mass along one crystalline axis. The existence of three anisotropic valleys offers electrons an additional degree of freedom, a subject of recent attention. Here, we map the Landau spectrum by angle-resolved magnetostriction, and quantify the carrier number in each valley: while the electron valleys keep identical spectra, they substantially differ in their density of states at the Fermi level. Thus, the electron fluid does not keep the rotational symmetry of the lattice at low temperature and high magnetic field, even in the absence of internal strain. This effect, reminiscent of the Coulomb pseudo-gap in localized electronic states, affects only electrons in the immediate vicinity of the Fermi level. It presents the most striking departure from the non-interacting picture of electrons in bulk bismuth.Comment: 6 pages, 3 Figure

The Nernst effect and the boundaries of the Fermi liquid picture

Following the observation of an anomalous Nernst signal in cuprates, the Nernst effect was explored in a variety of metals and superconductors during the past few years. This paper reviews the results obtained during this exploration, focusing on the Nernst response of normal quasi-particles as opposed to the one generated by superconducting vortices or by short-lived Cooper pairs. Contrary to what has been often assumed, the so-called Sondheimer cancelation does not imply a negligible Nernst response in a Fermi liquid. In fact, the amplitude of the Nernst response measured in various metals in the low-temperature limit is scattered over six orders of magnitude. According to the data, this amplitude is roughly set by the ratio of electron mobility to Fermi energy in agreement with the implications of the semi-classical transport theory.Comment: Final version, Topical review for JPC

Evidence for a quantum phase transition in electron-doped Pr2−x_{2-x}Cex_{x}CuO4−δ_{4-\delta} from Thermopower measurements

The evidence for a quantum phase transition under the superconducting dome in the high-$T_c$ cuprates has been controversial. We report low temperature normal state thermopower(S) measurements in electron-doped Pr$_{2-x}$Ce$_{x}$CuO$_{4-\delta}$ as a function of doping (x from 0.11 to 0.19). We find that at 2K both S and S/T increase dramatically from x=0.11 to 0.16 and then saturate in the overdoped region. This behavior has a remarkable similarity to previous Hall effect results in Pr$_{2-x}$Ce$_{x}$CuO$_{4-\delta}$ . Our results are further evidence for an antiferromagnetic to paramagnetic quantum phase transition in electron-doped cuprates near x=0.16.Comment: 4 pages, 5 figure

Nernst quantum oscillations in bulk semi-metals

With a widely available magnetic field of 10 T, one can attain the quantum limit in bismuth and graphite. At zero magnetic field, these two elemental semi-metals host a dilute liquid of carriers of both signs. When the quantum limit is attained, all quasi-particles are confined to a few Landau tubes. Each time a Landau tube is squeezed before definitely leaving the Fermi surface, the Nernst response sharply peaks. In bismuth, additional Nernst peaks, unexpected in the non-interacting picture, are resolved beyond the quantum limit. The amplitude of these unexpected Nernst peaks is larger in the samples with the longest electron mean-free-path.Comment: Accepted for publication in Journal of Physics: Condensed Matter's special issue on Strongly Correlated Electron Systems(SCES

Remote Predictive Mapping 4. Utilizing High Resolution Satellite Imagery, Western Minto Inlier, Victoria Island, NWT

The very high spatial resolution and stereo capability of GeoEye-1 images were utilized to map the geology of a part of the western Neoproterozoic Minto Inlier on Victoria Island. To optimize the results of predictive mapping, a LANDSAT-7 image together with a SPOT-5 image were also used in concert with the GeoEye-1 images. The predictive bedrock geology map, interpreted based on 3D stereo visualization, presents much more detailed geological information compared to the existing 1:500,000 scale geological map of the area. The high spatial and moderate spectral resolution of GeoEye images allowed us to distinguish a black shale unit (black shale member), and resolve subtle spectral and textural differences between massive stromatolitic dolostone and dolostone containing fine-grained interlayers in an upper carbonate member. As well, an important distinction could be made between Proterozoic sedimentary strata and unconformably overlying interlayered sandstone and carbonate rocks of Cambro-Ordovician age. The SWIR bands in the LANDSAT and SPOT images proved to be very useful in identifying gabbro sills. A geological map, based on field work, was used to evaluate the remote predictive map. Comparison of the predictive map with the field map shows that the two maps look similar in terms of the regional distribution of the lithological units; however, there are discrepancies between the two maps, especially in areas in which the bedrock is covered by glacial sediments and/or other overburden materials. The spectral similarity between different stratigraphic units comprising similar rock types, also contributed to differences between the predictive map and the field map.Nous avons utilisé la très haute résolution spatiale et les capacités stéréoscopiques des images GeoEye-1 pour cartographier la géologie d’une partie de la partie ouest de l’enclave de Minto, datant du Néoprotérozoïque, de l’île Victoria. Pour optimiser les résultats de la cartographie prédictive, nous avons aussi utilisé une image LANDSAT-7 et une image SPOT-5 avec les images GeoEye-1. Les cartes géologiques prédictives du substratum rocheux, interprétées à partir d’une visualisation stéréoscopique 3D, présentent des renseignements géologiques beaucoup plus détaillés que la carte géologique actuelle de cette zone à l’échelle de 1/500 000. La haute résolution spatiale et la résolution spectrale modérée des images GeoEye nous ont permis de distinguer une unité d’ampélite (membre d’ampélite) et de résoudre des différences spectrales et texturales subtiles entre la dolomie stromatolithique massive et la dolomie contenant des interstrates à grain fin dans un membre carbonaté supérieur. De plus, nous avons pu faire une distinction importante entre les strates sédimentaires du Protérozoïque et les couches interstratifiées de roches carbonatées et de grès du Cambro-Ordovicien qui les surmontent en discordance. Les bandes IRCL des images des satellites LANDSAT et SPOT ont été très utiles pour identifier les filons-couches de gabbro. Une carte géologique basée sur des travaux réalisés sur le terrain a servi à évaluer la carte de télécartographie prédictive. Une comparaison de la carte prédictive et de la carte dressée sur le terrain montre que les deux cartes semblent similaires en ce qui a trait à la répartition régionale des unités lithologiques; mais il y a des différences, surtout aux endroits où le substratum rocheux est couvert de sédiments glaciaires et/ou d’autres matériaux de recouvrement. La similitude spectrale entre les différentes unités stratigraphiques ayant des lithologies similaires a aussi contribué à causer des différences entre la carte prédictive et la carte dressée sur le terrain

Anomalous quasiparticle transport in the superconducting state of CeCoIn5

We report on a study of thermal Hall conductivity k_xy in the superconducting state of CeCoIn_5. The scaling relation and the density of states of the delocalized quasiparticles, both obtained from k_xy, are consistent with d-wave superconducting symmetry. The onset of superconductivity is accompanied by a steep increase in the thermal Hall angle, pointing to a striking enhancement in the quasiparticle mean free path. This enhancement is drastically suppressed in a very weak magnetic field. These results highlight that CeCoIn_5 is unique among superconductors. A small Fermi energy, a large superconducting gap, a short coherence length, and a long mean free path all indicate that CeCoIn_5 is clearly in the superclean regime (E_F/Delta<<l/xi), in which peculiar vortex state is expected.Comment: 5 pages, 5 figure