4,847 research outputs found
Magnetoresistance from Fermi Surface Topology
Extremely large non-saturating magnetoresistance has recently been reported
for a large number of both topologically trivial and non-trivial materials.
Different mechanisms have been proposed to explain the observed
magnetotransport properties, yet without arriving to definitive conclusions or
portraying a global picture. In this work, we investigate the transverse
magnetoresistance of materials by combining the Fermi surfaces calculated from
first principles with the Boltzmann transport theory approach relying on the
semiclassical model and the relaxation time approximation. We first consider a
series of simple model Fermi surfaces to provide a didactic introduction into
the charge-carrier compensation and open-orbit mechanisms leading to
non-saturating magnetoresistance. We then address in detail magnetotransport in
three representative materials: (i) copper, a prototypical nearly free-electron
metal characterized by the open Fermi surface that results in an intricate
angular magnetoresistance, (ii) bismuth, a topologically trivial semimetal in
which very large magnetoresistance is known to result from charge-carrier
compensation, and (iii) tungsten diphosphide WP2, a recently discovered type-II
Weyl semimetal that holds the record of magnetoresistance in compounds. In all
three cases our calculations show excellent agreement with both the field
dependence of magnetoresistance and its anisotropy measured at low
temperatures. Furthermore, the calculations allow for a full interpretation of
the observed features in terms of the Fermi surface topology. These results
will help addressing a number of outstanding questions, such as the role of the
topological phase in the pronounced large non-saturating magnetoresistance
observed in topological materials.Comment: 13 pages, 9 figure
The Importance of Proper Renormalization Scale-Setting for Testing QCD at Colliders
A primary problem for perturbative QCD analyses is how to set the
renormalization scale of the QCD running coupling in order to achieve maximally
precise fixed-order predictions for physical observables. The Principle of
Maximum Conformality (PMC) eliminates the ambiguities associated with the
conventional renormalization scale-setting procedure, giving predictions which
are independent of the choice of renormalization scheme. The scales of the QCD
couplings and the effective number of quark flavors are set order by order in
the pQCD series. The PMC has a solid theoretical foundation, satisfying the
standard renormalization group invariance and all of the the self-consistency
conditions derived from the renormalization group......In this brief report, we
summarize the results of our recent PMC applications for a number of collider
processes, emphasizing their generality and applicability....... These results
demonstrate that the application of the PMC systematically eliminates a major
theoretical uncertainty for pQCD predictions, thus increasing the sensitivity
of the colliders to possible new physics beyond the Standard Model.Comment: 10 pages, 4 figures. The title has been changed. This review,
submitted to Frontiers of Physics, is based on a contribution by S.J.B. at
the Conference {\it Workshop on Physics at a Future High Intensity Collider @
2-7 GeV in China} Hefei, China January 14-16, 201
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