Novel thermoelectric and elastic responses in Dirac matter
Author
Arjona Romano, VicenteEntity
UAM. Departamento de Física de la Materia CondensadaDate
2019-12-13Subjects
Materia condensada - Tesis doctorales; FísicaNote
Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de la Materia Condensada. Fecha de lectura: 13-12-2019
Esta obra está bajo una licencia de Creative Commons Reconocimiento-NoComercial-SinObraDerivada 4.0 Internacional.
Abstract
This thesis studies some aspects of the physics of topological semimetals, a set of
novel three-dimensional matter systems whose low-energy electronic excitations are
described by Dirac quasiparticles. The unconventional features of these materials,
ranging from basic physics to technological applications, have generated a substantial
research activity during the last years. The interest in crystalline structures
hosting Dirac quasiparticles lies partially on the relativistic nature of their electronic
degrees of freedom, making them an ideal laboratory to test and study fundamental
physics phenomena. This thesis addresses two topics of major interest in the
physics of these systems: the interplay between lattice deformations and electronic
properties, and the influence of anomalies on the thermoelectric response.
In the first part of this thesis, the thermoelectric response of Dirac and Weyl
semimetals is studied in the presence of strong magnetic fields. The anomalous
thermoelectric behaviour is addressed at the charge neutrality point, where a finite
contribution to the thermoelectric coefficient is obtained in the conformal limit.
The thermoelectric coefficients fulfill robust phenomenological relations based
on the Landau-Fermi liquid paradigm of coherent quasiparticles. These relations
may be challenged when the system has strong interactions or when it presents a
poor metallic behaviour. The validity of the Mott relation, a phenomenological law
that relates the thermopower and the electrical conductivity coefficients, is discussed
in the regime of zero doping and zero temperature. In particular, the off-diagonal
components of the electric and thermoelectric tensors are analyzed in the presence
of a magnetic field.
The influence of external deformations on the lattice configuration of topological
semimetals is essential to understand their electronic properties. In these systems,
elastic deformations couple to the low-energy electronic excitations in the form
of elastic gauge fields. The possibility of controlling the dynamics of carriers by
appropriate strain geometries has given rise to a prolific industry associated with
straintronics. In the second part of this thesis, the coupling of lattice deformations to
Dirac quasiparticles in three-dimensional materials is studied by using a symmetry
approach. An interesting aspect is that, in contrast to the two-dimensional case, the
antisymmetric part of the deformation tensor couple to the electronic excitations in
three-dimensional Dirac materials. Finally, the interplay between electromagnetic fields and elastic deformations is
also discussed, in which the collapse of Landau levels is showed in the presence of
strain. The similarities of this mechanism with the case of real magnetic and electric
fields are emphasized, discussing possible strain configurations giving rise to this
effect.
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