Weyl (WSMs) evolve from Dirac semimetals in the presence of broken time-reversal symmetry (TRS) or space-inversion symmetry. The WSM phases in TaAs-class materials and photonic crystals are due to the loss of space-inversion symmetry. For TRS-breaking WSMs, despite numerous theoretical and experimental efforts, few examples have been reported. In this Article, we report a new type of magnetic semimetal SrMnSb (y, z < 0.1) with nearly massless relativistic fermion behaviour (m =  0.04 - 0.05m, where m is the free-electron mass). This material exhibits a ferromagnetic order for 304 K < T < 565 K, but a canted antiferromagnetic order with a ferromagnetic component for T < 304 K. The combination of relativistic fermion behaviour and ferromagnetism in SrMnSb offers a rare opportunity to investigate the interplay between relativistic fermions and spontaneous TRS breaking.

Topological insulators are materials characterized by dissipationless, spin-polarized surface states resulting from nontrivial band topologies. Recent theoretical models and experiments suggest that SmB 6 is the first topological Kondo insulator, in which the topologically nontrivial band structure results from electron-electron interactions via Kondo hybridization. Here, we report that the surface conductivity of SmB 6 increases systematically with bulk carbon content. Further, addition of carbon is linked to an increase in n-type carriers, larger low-temperature electronic contributions to the specific heat with a characteristic temperature scale of T Ã ¼ 17 K, and a broadening of the crossover to the insulating state. Additionally, x-ray absorption spectroscopy shows a change in Sm valence at the surface. Our results highlight the importance of phonon dynamics in producing a Kondo insulating state and demonstrate a correlation between the bulk thermodynamic state and the low-temperature resistance of SmB 6 .

PACS number(s): 74.70.AdWe report the synthesis and measurements of magnetic, transport, and thermal properties of polycrystalline Nb 0.18 Re 0.82 , which has a superconducting transition at T c ~ 8.8 K. The noncentrosymmetric α-Mn structure of the compound is confirmed by X-ray diffraction. Using the measured values for the lower critical field H c1 , upper critical field H c2 , and the specific heat C, we estimate the thermodynamic critical field H c (0), coherence length ξ(0), penetration depth λ(0), and the Ginzburg-Landau parameter κ(0). The specific heat jump at T c , ΔC/γT c = 1.86, suggests that Nb 0.18 Re 0.82 is a moderately coupled superconductor. Below T c the electronic specific heat decays exponentially, suggesting that the gap is isotropic. Our data suggest that the triplet admixture is weak in the polycrystalline form of compound. However, the estimated value of the upper critical field H c2 (0) is close to the calculated Pauli limit.

Spin and valley degrees of freedom in materials without inversion symmetry promise previously unknown device functionalities, such as spin-valleytronics. Control of material symmetry with electric fields (ferroelectricity), while breaking additional symmetries, including mirror symmetry, could yield phenomena where chirality, spin, valley, and crystal potential are strongly coupled. Here we report the synthesis of a halide perovskite semiconductor that is simultaneously photoferroelectricity switchable and chiral. Spectroscopic and structural analysis, and first-principles calculations, determine the material to be a previously unknown low-dimensional hybrid perovskite (R)-(−)-1-cyclohexylethylammonium/(S)-(+)-1 cyclohexylethylammonium) PbI3. Optical and electrical measurements characterize its semiconducting, ferroelectric, switchable pyroelectricity and switchable photoferroelectric properties. Temperature dependent structural, dielectric and transport measurements reveal a ferroelectric-paraelectric phase transition. Circular dichroism spectroscopy confirms its chirality. The development of a material with such a combination of these properties will facilitate the exploration of phenomena such as electric field and chiral enantiomer–dependent Rashba-Dresselhaus splitting and circular photogalvanic effects.