Whereas the discovery of Dirac-and Weyl-type excitations in electronic systems is a major breakthrough in recent condensed matter physics, finding appropriate materials for fundamental physics and technological applications is an experimental challenge. In all of the reported materials, linear dispersion survives only up to a few hundred millielectronvolts from the Dirac or Weyl nodes. On the other hand, real materials are subject to uncontrolled doping during preparation and thermal effect near room temperature can hinder the rich physics. In ZrSiS, angle-resolved photoemission spectroscopy measurements have shown an unusually robust linear dispersion (up to ∼2 eV) with multiple nondegenerate Dirac nodes. In this context, we present the magnetotransport study on ZrSiS crystal, which represents a large family of materials (WHM with W = Zr, Hf; H = Si, Ge, Sn; M = O, S, Se, Te) with identical band topology. Along with extremely large and nonsaturating magnetoresistance (MR), ∼1.4 × 10 5 % at 2 K and 9 T, it shows strong anisotropy, depending on the direction of the magnetic field. Quantum oscillation and Hall effect measurements have revealed large hole and small electron Fermi pockets. A nontrivial π Berry phase confirms the Dirac fermionic nature for both types of charge carriers. The long-sought relativistic phenomenon of massless Dirac fermions, known as the Adler-Bell-Jackiw chiral anomaly, has also been observed.Dirac semimetal | extreme magnetoresistance | chiral anomaly | quantum oscillation | Fermi surface T he discovery of topological insulators (1) and 3D Dirac and Weyl semimetals (2, 3) has emerged as one of the major breakthroughs in condensed matter physics in recent time. Materials with topologically nontrivial band structure serve as a template to explore the quantum dynamics of relativistic particles in low-energy condensed matter systems. In addition to rich physics, these systems offer the possibility of practical applications in magnetic memory, magnetic sensor, or switch and spintronics, due to the novel transport phenomena such as extreme magnetoresistance and ultrahigh mobility (4-6). In Dirac semimetals, bulk valence and conduction bands undergo linear band crossings at fourfold degenerate Dirac points protected by timereversal symmetry (TRS), inversion symmetry (IS), and crystal symmetry (CS) (7,8). By breaking either TRS or IS, each Dirac point can be broken into a pair of doubly degenerate Weyl points, accompanied by the surface Fermi arc (7,8). Theoretical prediction (7, 8) followed by angle-resolved photoemission spectroscopy (ARPES) and transport measurements have verified the existence of bulk Dirac points in Cd3As2 and Na3Bi (2, 9-11) and Weyl nodes in the IS-breaking TX (T = Ta, Nb; X = As, P) family of materials (3,(12)(13)(14) and TRS-breaking YbMnBi2 (15). Apart from these compounds, recently, topological nodal line semimetals (TNLSM) have emerged, where the bands cross along one-dimensional closed lines in k space instead of discrete points. Although proposed in few materials ...

In this report, we present the magnetotransport and magnetization properties of LaSbTe single crystals. Magnetic field-induced turn-on behavior and low-temperature resistivity plateau have been observed. By adopting both metal-semiconductor crossover and Kohler scaling analysis, we have discussed the possible origin of the temperature and magnetic field dependence of resistivity. At 5 K and 9 T, a large, non-saturating transverse magnetoresistance (MR) ∼ 5×10 3 % has been obtained. The MR shows considerable anisotropy, when the magnetic field is applied along different crystallographic directions. The non-linear field dependence of the Hall resistivity confirms the presence of two types of charge carriers. From the semiclassical two-band fitting of Hall conductivity and longitudinal conductivity, very high carrier mobilities and almost equal electron and hole densities have been deduced, which result in large MR. The Fermi surface properties have been analyzed from de Haas-van Alphen oscillation. From the magnetization measurement, the signature of non-trivial surface state has been detected, which confirms that LaSbTe is a topological insulator, consistent with the earlier first-principles calculations. arXiv:1609.09397v3 [cond-mat.mtrl-sci]

Magnetic lanthanide half-Heuslers (RPtBi; R being the lanthanide) represent an attractive subgroup of the Heusler family and have been identified as ideal candidates for time reversal symmetry breaking topological Weyl semimetals. In this paper, we present the detailed analysis of the magnetotransport properties of frustrated antiferromagnet TbPtBi. This material shows large, nonsaturating magnetoresistance (MR) with unusual magnetic field dependence. The MR of TbPtBi is significantly anisotropic with respect to the magnetic field, applied along different crystallographic directions and indicates the anisotropic nature of the Fermi surface. The chiral anomaly induced negative longitudinal magnetoresistance confirms the presence of Weyl fermions. At low temperature, Berry phase driven large anomalous Hall conductivity has been observed. The calculated anomalous Hall angle is the largest reported so far.

The study of electronic properties in topological systems is one of the most fascinating topics in condensed matter physics, which has generated enormous interests in recent times. New materials are frequently being proposed and investigated to identify their non-trivial band structure. While sophisticated techniques such as angle-resolved photoemission spectroscopy have become popular to map the energy-momentum relation, the transport experiments lack any direct confirmation of Dirac and Weyl fermions in a system. From band structure calculations, VAl3 has been proposed to be a type II topological Dirac semimetal. This material represents a large family of isostructural compounds, all having similar electronic band structure and is an ideal system to explore the rich physics of Lorentz symmetry violating Dirac fermions. In this work, we present a detailed analysis on the magnetotransport properties of VAl3. A large, non-saturating magnetoresistance has been observed. Hall resistivity reveals the presence of two types of charge carriers with high mobility.Our measurements show a large planar Hall effect in this material, which is robust and can be easily detectable up to high temperature. This phenomenon originates from the relativistic chiral anomaly and non-trivial Berry curvature, which validates the theoretical prediction of the Dirac semimetal phase in VAl3.