Weyl fermion excitations in the ideal Weyl semimetal CuTlSe_{2}

Abstract

An ideal Weyl semimetal is characterized by a dispersion in which only Weyl cones intersect the Fermi level, with low-energy behavior being governed by Weyl fermions. Although ideal Weyl semimetals have long been anticipated, only a few are realized in nonmagnetic materials. In this study, we confirm the presence of Weyl-fermion excitations in the ideal Weyl semimetal CuTlSe_{2} via a combination of magnetoresistance, Hall-effect, magnetic-susceptibility, nuclear magnetic resonance (NMR), and muon-spin relaxation (µSR) experiments. Magnetoresistance measurements reveal a negative longitudinal magnetoresistance (LMR), which scales as B^{2}, while Hall-effect results indicate a predominant contribution from Weyl fermions with a hole-type charge. Magnetic susceptibility and µSR measurements indicate the lack of any intrinsic spontaneous magnetic moments down to base temperature. Finally, the NMR results can be modeled by a two-component effective Hamiltonian, which reproduces well the temperature-dependent ^{63}Cu NMR (T_{1}T)^{−1} factor, shown to scale as T^{2} below 100 K and as T^{1} above 100 K. Overall, we find that the extremely low concentration (10^{17}cm^{−3}) of carriers in CuTlSe_{2} originates from an ideal nonmagnetic Weyl semimetallic state, persisting up to a thermal excitation energy of 9 meV (100 K), above which trivial electronic bands close to E_{F} take over. Our findings highlight CuTlSe_{2} as a new member of the intriguing class of Weyl semimetals.