Large nonsaturating magnetoresistance and pressure-induced phase transition in the layered semimetal HfTe2

Unusual physical properties like large magnetoresistance (MR) and superconductivity occurring in semimetals with Dirac or Weyl points are often linked to their topologically nontrivial band structures. However, there is an increasing number of reports on semimetals that show large MR in the absence of Dirac or Weyl points. Herein we report an experimental and theoretical study on the layered transition-metal dichalcogenide (TMDC) $\mathrm{HfT}{\mathrm{e}}_{2}$ that shows a large MR of $1350%$ at $T=2$ K and ${\ensuremath{\mu}}_{0}H=9\phantom{\rule{0.16em}{0ex}}\mathrm{T}$ in the absence of Dirac or Weyl points. Moreover, the structure and electrical resistivity under pressure reveal a unique structural transition. These results clearly distinguish $\mathrm{HfT}{\mathrm{e}}_{2}$ from TMDCs like $\mathrm{MoT}{\mathrm{e}}_{2}$ or $\mathrm{WT}{\mathrm{e}}_{2}$ which both exhibit larger MR and are viewed as Weyl semimetals. $\mathrm{HfT}{\mathrm{e}}_{2}$ is an appealing platform for future investigations on the interplay of particular band-structure features and their connection to emerging physical properties.