441 research outputs found
Measuring thermal conductivity in extreme conditions: sub-Kelvin temperatures and high (27 T) magnetic fields
We present a one-heater-two-thermometer set-up for measuring thermal
conductivity and electric resistivity of a bulk sample at low temperatures down
to 0.1 K and in magnetic fields up to 27 Tesla. The design overcomes the
difficulties emerging in the context of large water-cooled resistive magnets.Comment: 4 pages including 4 figure
On the destruction of the hidden order in URuSi by a strong magnetic field
We present a study of transport properties of the heavy fermion URuSi
in pulsed magnetic field. The large Nernst response of the hidden order state
is found to be suppressed when the magnetic field exceeds 35 T. The combination
of resistivity, Hall and Nernst data outlines the reconstruction of the Fermi
surface in the temperature-field phase diagram. The zero-field ground state is
a compensated heavy-electron semi-metal, which is destroyed by magnetic field
through a cascade of field-induced transitions. Above 40 T, URuSi
appears to be a polarized heavy fermions metal with a large density of carriers
whose effective mass rapidly decreases with increasing magnetic polarization.Comment: published versio
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
Nernst effect in the phase-fluctuating superconductor InO
We present a study of the Nernst effect in amorphous 2D superconductor
InO, whose low carrier density implies low phase rigidity and strong
superconducting phase fluctuations. Instead of presenting the abrupt jump
expected at a BCS transition, the Nernst signal evolves continuously through
the superconducting transition as previously observed in underdoped cuprates.
This contrasts with the case of NbSi, where the Nernst signal
due to vortices below T and by Gaussian fluctuations above are clearly
distinct. The behavior of the ghost critical field in InO points to a
correlation length which does not diverge at , a temperature below which
the amplitude fluctuations freeze, but phase fluctuations survive.Comment: 4 pages, 4 figure
Magnetothermoelectric properties of Bi2Se3
We present a study of entropy transport in Bi2Se3 at low temperatures and
high magnetic fields. In the zero-temperature limit, the magnitude of the
Seebeck coefficient quantitatively tracks the Fermi temperature of the 3D Fermi
surface at \Gamma-point as the carrier concentration changes by two orders of
magnitude (10 to 10cm). In high magnetic fields, the
Nernst response displays giant quantum oscillations indicating that this
feature is not exclusive to compensated semi-metals. A comprehensive analysis
of the Landau Level spectrum firmly establishes a large -factor in this
material and a substantial decrease of the Fermi energy with increasing
magnetic field across the quantum limit. Thus, the presence of bulk carriers
significantly affects the spectrum of the intensively debated surface states in
Bi2Se3 and related materials.Comment: 10 pages, 9 figure
Possible Relevance of Odd Frequency Pairing to Heavy Fermion Superconductivity
What is the character of the gapless quasiparticles in heavy fermion
superconductors (HFSC)? We discuss an odd-frequency pairing interpretation of
HFSC which leads to a two component model for the quasiparticle excitations. In
this picture, line zeroes of unpaired electrons may coexist with gapless
surfaces of paired electrons, with vanishing spin and charge coherence factors
Thermoelectric response of FeTeSe: evidence for strong correlation and low carrier density
We present a study of the Seebeck and Nernst coefficients of
FeTeSe extended up to 28 T. The large magnitude of the
Seebeck coefficient in the optimally doped sample tracks a remarkably low
normalized Fermi temperature, which, like other correlated superconductors, is
only one order of magnitude larger than T. We combine our data with other
experimentally measured coefficients of the system to extract a set of
self-consistent parameters, which identify FeTeSe as a
low-density correlated superconductor barely in the clean limit. The system is
subject to strong superconducting fluctuations with a sizeable vortex Nernst
signal in a wide temperature window.Comment: 4 pages including 4 figure
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
Low-temperature thermopower study of YbRh2Si2
The heavy-fermion compound YbRh2Si2 exhibits an antiferromagnetic (AFM) phase
transition at an extremely low temperature of TN = 70 mK. Upon applying a tiny
magnetic field of Bc = 60 mT the AFM ordering is suppressed and the system is
driven toward a field-induced quantum critical point (QCP). Here, we present
low-temperature thermopower S(T) measurements of high-quality YbRh2Si2 single
crystals down to 30 mK. S(T) is found negative with comparably large values in
the paramagnetic state. In zero field no Landau-Fermi-liquid (LFL) like
behavior is observed within the magnetically ordered phase. However, a sign
change from negative to positive appears at lowest temperatures on the magnetic
side of the QCP. For higher fields B > Bc a linear extrapolation of S to zero
clearly evidences the recovery of LFL regime. The crossover temperature is
sharply determined and coincides perfectly with the one derived from
resistivity and specific heat investigations.Comment: LT25 conference proceedings in Journal of Physics: Conference Serie
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