207 research outputs found
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
Emptying Dirac valleys in bismuth using high magnetic fields
The Fermi surface of elemental bismuth consists of three small rotationally
equivalent electron pockets, offering a valley degree of freedom to charge
carriers. A relatively small magnetic field can confine electrons to their
lowest Landau level. This is the quantum limit attained in other dilute metals
upon application of sufficiently strong magnetic field. Here, we report on the
observation of another threshold magnetic field never encountered before in any
other solid. Above this field, , one or two valleys become
totally empty. Drying up a Fermi sea by magnetic field in the Brillouin zone
leads to a manyfold enhancement in electric conductance. We trace the origin of
the large drop in magnetoresistance across to transfer of
carriers between valleys with highly anisotropic mobilities. The
non-interacting picture of electrons with field-dependent mobility explains
most results. Coulomb interaction may play a role in shaping the fine details.Comment: 19 pages, 5 figures, Supplemental Material available upon reques
T-square electronic thermal resistivity in metallic strontium titanate
The temperature dependence of the phase space for electron-electron (e-e)
collisions leads to a T-square contribution to electrical resistivity of
metals. Umklapp scattering are identified as the origin of momentum loss due to
e-e scattering in dense metals. However, in dilute metals like lightly doped
strontium titanate, the origin of T-square electrical resistivity in absence of
Umklapp events is yet to be pinned down. Here, by separating electron and
phonon contributions to heat transport, we extract the electronic thermal
resistivity in niobium-doped strontium titanate and show that it also displays
a T-square temperature dependence. Its amplitude correlates with the T-square
electrical resistivity. The Wiedemann-Franz law strictly holds in the
zero-temperature limit, but not at finite-temperature, because the two T-square
prefactors are different by a factor of , like in other Fermi
liquids. Recalling the case of He, we argue that T-square thermal
resistivity does not require Umklapp events. The approximate recovery of the
Wiedemann-Franz law in presence of disorder would account for a T-square
electrical resistivity without Umklapp.Comment: 7 pages, 4 figures and 2 tables, plus a supplemen
Magnetoresistance of semi-metals: the case of antimony
Large unsaturated magnetoresistance has been recently reported in numerous
semi-metals. Many of them have a topologically non-trivial band dispersion,
such as Weyl nodes or lines. Here, we show that elemental antimony displays the
largest high-field magnetoresistance among all known semi-metals. We present a
detailed study of the angle-dependent magnetoresistance and use a
semi-classical framework invoking an anisotropic mobility tensor to fit the
data. A slight deviation from perfect compensation and a modest variation with
magnetic field of the components of the mobility tensor are required to attain
perfect fits at arbitrary strength and orientation of magnetic field in the
entire temperature window of study. Our results demonstrate that large orbital
magnetoresistance is an unavoidable consequence of low carrier concentration
and the sub-quadratic magnetoresistance seen in many semi-metals can be
attributed to field-dependent mobility, expected whenever the disorder
length-scale exceeds the Fermi wavelength.Comment: Supplementary material on reques
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
Matière quantique sous champ magnétique / Quantum matter under magnetic field
Recherche Page web : https://www.college-de-france.fr/site/young-team-incubator/Presentation__4.htm. Le groupe Matière quantique sous champ magnétique de l’IPCF s’intéresse aux propriétés électroniques des métaux dilués en présence d’un champ magnétique. Sous l’effet du champ magnétique, les électrons se déplacent le long d’une hélice dont le rayon est donné par le rayon cyclotronique (Rc). À mesure que le champ magnétique augmente, Rc diminue, croisant les différentes échelles caractéristiqu..
- …