Thermoelectric transport phenomena in topological semimetals

Date

Nov 29, 2024

Time

10:30 AM - 11:30 AM

Speaker

Shahin Alam

Affiliation

International Research Centre MagTop, Institute of Physics, Polish Academy of Sciences, Warsaw, Pol

Language

en

Main Topic

Materialien

Host

Rita Taubert

Description

The discovery of the quantum Hall effect [1] led to realisation how important is topology of the electronic structure and eventually resulted in the discovery of many classes of topological materials. Among them are topological semimetals that exhibit nontrivial band crossings at or near the Fermi level. The electronic bands at nodal points or lines are populated by relativistic-like quasiparticles such as Dirac and Weyl fermions [2]. These, in turn, contribute to electronic transport and give rise to unique topology-related phenomena. The standard method to study the nontrivial attributes is the measurements of charge transport, although, thermoelectric measurements can provide more comprehensive information about the electronic structure due to their high sensitivity to details of the electronic structure. I will discuss the impact of the electronic structure on the transport properties of three non-trivial topological materials, focusing on phenomena such as quantum oscillations (QOs), the anomalous Hall effect (AHE), the anomalous Nernst effect (ANE), and the chiral anomaly. The key features of relativistic fermions in topological semimetals can be probed through QOs measurements. For example, in TaAs2, we observe an unusual temperature dependence of the fundamental frequency (β) and its second harmonic (2β) in the oscillatory Nernst signal, with β disappearing at T ≈ 25 K, where 2β is still visible. This suggests that the spin-zero effect is linked to the evolution of the Landé g-factor, which may indicate that topological attributes in TaAs2 are temperature dependent. In a Weyl semimetal, Berry curvature (BC) can lead to the development of intrinsic AHE and ANE. We observe in a magnetic Weyl candidate CeAlSi, a sign reversal in the anomalous Hall conductivity (AHC) when the magnetic field is rotated from easy to hard axis. This has been attributed to changes of BC due to spin reorientation. The temperature evolution of AHC and anomalous Nernst conductivity, which persist in the paramagnetic phase, suggest Weyl points are located near the Fermi level. The parallel orientation of the magnetic and electrical field can lead to the charge pumping between two cones within a Weyl pair. This results in the formation of the anomalous chiral current detectable by magnetotransport measurements and we looked for them in α-Sn thin film. In fact, this Dirac semimetal (that becomes Weyl in the presence of magnetic field) shows at low temperature the signatures of anomalous chiral current in parallel and angular dependence measurements of thermoelectric power and resistivity. 1. Markus König et al., Science 318,766-770 (2007) 2. N. P. Armitage et al., Rev. Mod. Phys. 90, 015001 (2018)

Links

• Seminars at the IFW

Last modified: Nov 29, 2024, 7:37:06 AM