Protracting the Weyl phase by a giant negative lattice expansion in Bi doped Sm${}_2$Ir${}_2$O${}_7$

Abstract

We show that the Weyl phase in $\mathrm{S}{\mathrm{m}}_2\mathrm{I}{\mathrm{r}}_2{\mathrm{O}}_7$ is protracted up to at least 2~\% alloying with Bi by an anomalous negative lattice expansion with $\mathrm{\Delta a}\sim -0.01$Å. With further doping, the magnetic ordering disappears and electrical resistivity decreases by orders of magnitude; the resistivity upturn remains but with $1/T$ dependence of Weyl phase changed to $-\mathrm{lnT}$ dependence characteristic of the Quadratic Band Touching (QBT). At the Weyl-QBT phase boundary, a new phase is evidenced whose resistivity scales as $-{\mathrm{T}}^{1/4}$ possibly due to proximity to a quantum critical point proposed several years ago [Phys. Rev. X 4, 041027 (2014)], but whose experimental evidence has remained elusive thus far.

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