On Behind the Physics of the Thermoelectricity of Topological Insulators

Topological Insulators are the best thermoelectric materials involving a sophisticated physics beyond their solid state and electronic structure. We show that exists a topological contribution to the thermoelectric effect that arises between topological and thermal quantum field theories applied at very low energies. This formalism provides us with a quantized topological mass proportional to the temperature T leading, through an electric potential V, to a Seebeck coefficient where we identify an anomalous contribution that can be associated to the creation of real electron-hole Schwinger’s pairs close to the topological bands. Finally, we find a general expression for the dimensionless figure of merit of these topological materials, considering only the electronic contribution, getting a value of 2.73 that is applicable to the Bi2Te3, for which it was reported a value of 2.4 after reducing its phononic contribution, using only the most basic topological numbers (0 or 1).Thanks to the CESGA, to AEMAT ED431E 2018/08 and the MAT2016-80762-R project for financial support.S

Emergent topological fields and relativistic phonons within the thermoelectricity in topological insulators

Topological edge states are predicted to be responsible for the high efficient thermoelectric response of topological insulators, currently the best thermoelectric materials. However, to explain their figure of merit the coexistence of topological electrons, entropy and phonons can not be considered independently. In a background that puts together electrodynamics and topology, through an expression for the topological intrinsic field, we treat relativistic phonons within the topological surface showing their ability to modulate the Berry curvature of the bands and then playing a fundamental role in the thermoelectric effect. Finally, we show how the topological insulators under such relativistic thermal excitations keep time reversal symmetry allowing the observation of high figures of merit at high temperatures. The emergence of this new intrinsic topological field and other constraints are suitable to have experimental consequences opening new possibilities of improving the efficiency of this topological effect for their based technologyAuthors acknowledge to CESGA, AEMAT ED431E 2018/08, PID2019-104150RB-I00 and the MAT2016-80762-R project for financial supportS

Anomalous response in the orbital magnetic susceptibility of 2d topological systems

2D compounds with nonzero Berry curvature are ideal systems to study exotic and technologically favorable thermoelectric and magnetoelectric properties. Within this class of materials, the topological trivial and nontrivial regimes have to present very different behaviors, which are encoded for the orbital susceptibility and magnetization. To try to reveal them, it is found that it was necessary to introduce a k-dependent mass term in the relativistic formalism of these materials. Thus, while a topologically trivial insulator is predicted to have a very limited response, in the nontrivial regime, a singular contribution to the orbital magnetic susceptibility, which is inversely proportional to the square of the quantum magnetic flux is unveiled. In this scenario, besides determining the measurement conditions a new route for enhancing the intrinsic orbital magnetism of topological materials widening the range of temperatures and magnetic fields without involving tiny bandgaps is foundThe authors acknowledge PID2019-104150RB-I00, AEMAT ED431E 2018/08 and the MAT2016-80762-R projects for financial support. The authors thank Juan Manuel Faílde for the helpful discussionsS

Topological Insulators: Advances in Thermoelectricity, Orbital Dynamics and Axion Electrodynamics

Topological materials (TMs) are a special class of quantum materials which include Topological Insulators (TIs), Chern Insulators (CIs), Weyl Semimetals, Topological Superconductors and Magnetic Topological Insulators (MTIs). Their non-trivial topology, which differs from the trivial one of conventional systems, give these systems singular thermoelectric and magnetoelectric transport properties. These properties are not only rich from the physical point of view but they can be technologically beneficial for different applications being used such as thermoelectrics, transistors, spintronic devices, superconductors, etc. The origin of this thesis lies in the study of the thermoelectric properties of topological insulators, currently the best thermoelectric materials. Our perspective is theoretical from the beginning given the lack of a microscopic theory in the literature which answers why these systems have such an efficient thermoelectric response, represented by their well known experimental figure of merit. This led us to explore other effects and interactions such as the electron-phonon coupling, thermal excitations, and other orbital magnetic effects and phenomena related to the axion electrodynamics, which are a consequence of their non-trivial topology and shall be developed in this thesis. In addition, we give a new interpretation to the physics of these systems by introducing the concept of a topological intrinsic field which is derived from the Berry curvature defined in the non-trivial topological bands of these materials.2023-03-2