After growing successfully TaP single crystal, we measured its longitudinal resistivity (ρxx) and Hall resistivity (ρyx) at magnetic fields up to 9T in the temperature range of 2-300K. It was found that at 2K its magnetoresistivity (MR) reaches to 3.28×105 %, at 300K to 176% at 8T, and both do not appear saturation. We confirmed that TaP is indeed a low carrier concentration, hole-electron compensated semimetal, with a high mobility of hole µ h =3.71×105 cm 2 /V s, and found that a magnetic-field-induced metal-insulator transition occurs at room temperature. Remarkably, as a magnetic field (H ) is applied in parallel to the electric field (E ), the negative MR due to chiral anomaly is observed, and reaches to -3000% at 9T without any signature of saturation, too, which distinguishes with other Weyl semimetals (WSMs). The analysis on the Shubnikov-de Haas (SdH) oscillations superimposing on the MR reveals that a nontrivial Berry's phase with strong offset of 0.3958 realizes in TaP, which is the characteristic feature of the charge carriers enclosing a Weyl nodes. These results indicate that TaP is a promising candidate not only for revealing fundamental physics of the WSM state but also for some novel applications. [8] compound, in which fine-tuning the chemical composition is necessary for breaking inversion symmetry, a WSM has not realized experimentally in any of these compounds due to either no enough large magnetic domain or difficulty to tune the chemical composition within 5%. Very recently, the theoretical proposal [9,10] for a WSM in a class of stoichiometric materials, including TaAs, TaP, NbAs and NbP, which break crystalline inversion symmetry, has been soon confirmed by the experiments [11][12][13][14], except for TaP due to difficulty to grow large crystal. The exotic transport properties exhibiting in these materials ignite an extensive interesting in both the condensed matter physics and material science community, especial for their extremely large magnetoresistance (MR) and ultrahigh mobility of charge carriers.Materials with large MR have been used as magnetic sensors [16], in magnetic memory [17], and in hard drives [18] at room temperature. Large MR is an uncommon property, mostly of magnetic compounds, such as a giant magnetoresistance (GMR) [19] emerging in Fe/Cr thin-film, and colossal magnetoresistance (CMR) in the manganese based perovskites [20,21]. In contrast, ordinary MR, a relatively weak effect, is commonly found in non-magnetic compounds and elements [22]. Magnetic materials typically have negative MR. Positive MR is seen in metals, usually at the level of a few percent, and in some semiconductors, such as 200% at room temperature in Ag 2+δ (Te,Se) [30], comparable with those of materials showing CMR [24], and semimetals, such as high-purity bismuth, graphite [25], and 4.5×10 4 % in WTe 2 [26]. In the semimetals, very high MR is attributed to a balanced hole-electron "resonance" condition, as described in Ref. [26]. WSM provides another possibility to realize extremely large MR, ...

Extremely large magnetoresistance (XMR) was recently discovered in many non-magnetic materials, while its underlying mechanism remains poorly understood due to the complex electronic structure of these materials. Here, we report an investigation of the α-phase WP2, a topologically trivial semimetal with monoclinic crystal structure (C2/m), which contrasts to the recently discovered robust type-II Weyl semimetal phase in β-WP2. We found that α-WP2 exhibits almost all the characteristics of XMR materials: the near-quadratic field dependence of MR, a field-induced up-turn in resistivity following by a plateau at low temperature, which can be understood by the compensation effect, and high mobility of carriers confirmed by our Hall effect measurements. It was also found that the normalized MRs under different magnetic fields has the same temperature dependence in α-WP2, the Kohler scaling law can describe the MR data in a wide temperature range, and there is no obvious change in the anisotropic parameter γ value with temperature. The resistance polar diagram has a peanut shape when field is rotated in ac plane, which can be understood by the anisotropy of Fermi surface. These results indicate that both field-induced-gap and temperature-induced Lifshitz transition are not the origin of up-turn in resistivity in the α-WP2 semimetal. Our findings establish α-WP2 as a new reference material for exploring the XMR phenomena.

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The measurements of magnetization, longitudinal and Hall resistivities are carried out on the intrinsic antiferromagnetic (AFM) topological insulator EuSn 2 As 2. It is confirmed that our EuSn 2 As 2 crystal is a heavily hole doping A-type AFM metal with the Néel temperature T N = 24 K, with a metamagnetic transition from an AFM to a ferromagnetic (FM) phase occurring at a certain critical magnetic field for the different field orientations. Meanwhile, we also find that the carrier concentration does not change with the evolution of magnetic order, indicating that the weak interaction between the localized magnetic moments from Eu 2+ 4f 7 orbits and the electronic states near the Fermi level. Although the quantum anomalous Hall effect (AHE) is not observed in our crystals, it is found that a relatively large negative magnetoresistance (−13%) emerges in the AFM phase, and exhibits an exponential dependence upon magnetic field, whose microscopic origin is waiting to be clarified in future research.