Extremely Large Magnetoresistance in the Hourglass Dirac Loop Chain Metal β-ReO2.

The transport and thermodynamic properties of β-ReO₂ crystallizing in a nonsymmorphic structure were studied using high-quality single crystals. An extremely large magnetoresistance (XMR) of 22,000% was observed in a transverse magnetic field of 10 T at 2 K. However, unlike other topological semimetals that show XMR, β-ReO₂ has a high electron carrier density of 1 × 10²² cm^-3, as determined by Hall effect measurements and large Fermi surfaces in the electronic structure. In addition, a small Fermi surface with a small effective mass was evidenced by de Haas-van Alphen oscillation measurements. Previous band structure calculations [Wang, et al., Nat. Commun. 8, 1844 (2017)] revealed the existence of two types of loops made of Dirac points of hourglass-shaped dispersions that are connected to each other by a point to form a string of alternating loops, called a Dirac loop chain (DLC), which are protected by multiple glide symmetries. Our first-principles calculations revealed the complex Fermi surfaces, the smallest of which corresponds to the observed small Fermi surface, which is located near the DLC. The XMR of β-ReO₂ is attributed to the small Fermi surface, which is likely caused by the DLC. [ABSTRACT FROM AUTHOR]