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Jeudi 17 Novembre 2016 14h
Amphi Holweck, Esc C
1ème etage
Fermi Surface Topology and Chirality in Putative Weyl Semimetals
Elena Hassinger, F. Arnold, M. Naumann, SC. Wu, Y. Sun, M. Schmidt, H. Borrmann, C. Felser, B. Yan
Weyl Fermions are the solution of the massless Dirac equations and have been long sought after in high energy physics [1]. Electrons in Weyl semimetals are thought to be the solid state realization of these massless chiral Fermions. Recently the non-centrosymmetric mono-pnictides (Ta,Nb)(P,As) were predicted to be Weyl semimetals by ab initio DFT calculations [2]. The presence of Weyl nodes and Fermi arc surface states in these materials was later confirmed by ARPES [3]. Here, we present the precise Fermi surface topology of our TaP and TaAs single crystals with millielectronvolt Fermi energy precision as determined by quantum oscillation measurements and ab intio bandstructure calculations. It will be shown that chirality in TaP is ill-defined due to a large energy separation of the Fermi energy from the Weyl points [4]. In TaAs, on the other hand, “Weyl” Fermi surface pockets of well defined opposite chirality exist [5]. Thus special quantum phenomena due to chirality are only expected in TaAs. As an example we demonstrate that the quantum oscillations in the magnetization from these Weyl pockets are phase-shifted by a pi Berry whereas they are not for the trivial bands. As a second point, we also show evidence that experimental results of the longitudinal magnetoresistance in these compounds can easily be dominated by effects of a field-induced resistance anisotropy. This so-called current jetting [6] can lead to an apparent “negative magnetoresistance” as expected for the chiral anomaly [7].
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S.-Y. Xu et al. Science 349, 613 (2015)
[4] F. Arnold et al. Nat. Comm. 7, 11615 (2016)
[5] F. Arnold et al. arXiv:1603.08846 (2016)
[6] K. Yoshida, JPSJ 41, 574 (1975)
[7] R. Dos Reis, NJP 18, 085006 (2016)