The change in resistance of a material in a magnetic field reflects its electronic state. In metals with weakly- or non-interacting electrons, the resistance typically increases upon the application of a magnetic field. In contrast, negative magnetoresistance may appear under some circumstances, e.g., in metals with anisotropic Fermi surfaces or with spin-disorder scattering and semimetals with...

By means of detailed electronic structure calculations, we show that strained HgTe(x)S(1-x) alloys show a surprisingly rich topological phase diagram. In the strong topological insulator phase, the spin chirality of the topological nontrivial surface states can be reversed by adjusting the alloy concentration x and the strain. On top of this, we predict two semimetallic topological phases, name...

We show that the pseudorelativistic physics of graphene near the Fermi level can be extended to three dimensional (3D) materials. Unlike in phase transitions from inversion symmetric topological to normal insulators, we show that particular space groups also allow 3D Dirac points as symmetry protected degeneracies. We provide criteria necessary to identify these groups and, as an example, prese...

Weyl and Dirac semimetals recently stimulate intense research activities due to their novel properties. Combining first-principles calculations and effective model analysis, we predict that nonmagnetic compounds BaYBi (Y = Au, Ag and Cu) are Dirac semimetals. As for the magnetic compound EuYBi, although the time reversal symmetry is broken, their long-range magnetic ordering cannot split the Di...

We propose a simple realization of the three-dimensional (3D) Weyl semimetal phase, utilizing a multilayer structure, composed of identical thin films of a magnetically doped 3D topological insulator, separated by ordinary-insulator spacer layers. We show that the phase diagram of this system contains a Weyl semimetal phase of the simplest possible kind, with only two Dirac nodes of opposite ch...

We report an ab initio study of the effect of hydrostatic pressure and uniaxial strain on electronic properties of KNa2Bi, a cubic bialkali bismuthide. It is found that this zero-gap semimetal with an inverted band structure at the Brillouin zone center can be driven into various topological phases under proper external pressure. We show that upon hydrostatic compression KNa2Bi turns into a tri...

Dirac semimetals feature cones with topologically nontrivial states in the bulk that are protected by crystalline symmetries. They attract considerable attention due to rich quantum and properties of interest, such as high Fermi velocities, mobility, small effective masses. Here, we show a ternary intermetallic BaAuSb crystal hosts both trivial topological bulk. The Fermi-surface pocket at Bril...

The recent discovery of Dirac semimetals represents a new achievement in our fundamental understanding of topological states of matter. Due to their topological surface states, high mobility, and exotic properties associated with bulk Dirac points, these new materials have attracted significant attention and are believed to hold great promise for fabricating novel topological devices. For nanos...

Qiang Li, Dmitri E. Kharzeev, 3 Cheng Zhang, Yuan Huang, I. Pletikosić, 5 A. V. Fedorov, R. D. Zhong, J. A. Schneeloch, G. D. Gu, and T. Valla Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, New York 11973, USA Department of Physics, Brookhaven National Laboratory, Upton, New York 11973, USA Department of Physics and Astronomy, Stony Brook University, ...