Anomalous lattice contraction and emerging topological phases in Bi-substituted Sm2Ir2O7

Abstract

We demonstrate that substituting Bi for Sm in the pyrochlore Sm2Ir2O7 induces an anomalous lattice contraction, with Å observed at 10% Bi substitution, where 'a' denotes the lattice constant. Beyond 10% Bi substitution, the lattice expands according to Vegard's law. Within this anomalous substitution range, the resistivity shows a behavior up to 2% Bi-substitution, while near 10% substitution a -lnT dependence is observed. These resistivity behaviors suggest the possibility of a Weyl phase up to 2% Bi substitution, which transforms to a semimetallic quadratic band touching (QBT) topological phase near 10%. For the intermediate composition (Sm0.95Bi0.05)2Ir2O7, the resistivity scales as , possibly due to its proximity to a proposed quantum critical point at the Weyl-QBT phase boundary (Savary et al 2014 Phys. Rev. X 4 041027). The samples were characterized using synchrotron powder x-ray diffraction, x-ray near-edge fine structure (XANES), and Extended x-ray absorption fine structure (EXAFS) probes. Additionally, magnetic susceptibility and heat capacity measurements were conducted to provide further support.