The osmate pyrochlore Cd2Os2O7 supports an antiferromagnet insulator ground state with an all-in/all-out (AIAO) spin ordering at low temperature. Above 225 K, Cd2Os2O7 becomes a paramagnetic metal whereas the mechanism of this metal-to-insulator transition (MIT) remains elusive. In this letter, we use cryogenic near-field technique operating at terahertz frequencies to study the evolution of low-energy response across the MIT. We observed a systematic variation of the magnitude of nano-THz signal across the transition, consistent with the trend in the direct-current conductivity. Conducting domain walls that dominate the nano-scale landscape of the conductivity of a closely related AIAO system Nd2Ir2O7 are not apparent in Cd2Os2O7.
Bibliographical noteFunding Information:
Research on “Terahertz nano-imaging of metal-insulator transition in Cd2Os2O7” at Columbia University is supported entirely by the Center on Precision-Assembled Quantum Materials, funded through the US National Science Foundation (NSF) Materials Research Science and Engineering Centers (award No. DMR-2011738). DNB is Moore Investigator in Quantum Materials EPIQS #9455. DNB is the Vannevar Bush Faculty Fellow ONR-VB: N00014-19-1-2630. DNB, RJ and LX conceived the experiments. RJ and LX performed the THz-near-field imaging experiments. RJ constructed the THz near-field device and beam line. HTH and ZH fabricated the CdOsO sample. RJ conducted the lightning-rod modeling. ASM, YS, XC and ML provided helpful comments. RJ and DNB wrote the paper with input from all coauthors. DNB supervised the project. 2 2 7
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