Abstrakt
A2Ir2O7 iridates crystalize in the ordered pyrochlore structure (space group Fd-3m) throughout the A rare-earth series. A and Ir ions independently form sublattices of corner-sharing tetrahedra and are surrounded by 8- and 6- coordinate oxygen cages, respectively.
Such geometrical frustration frequently results in many complex (ground) states, e.g., spin liquid, spin ice, or fragmented states have been observed and attracted considerable attention [1,2]. Importantly, the iridium sublattice tends to order in the so-called all-in-all-out (AIAO) magnetic structure [3,4], and the related molecular field significantly influences the magnetic moments on the A sublattice.
A strong spin-orbit coupling is connected with Ir ions, possibly leading to topological phases such as Weyl semimetal or topological Mott insulator [5,6]. Concomitantly with the AIAO ordering of Ir sublattice, a metal/semimetal to insulator transition has been observed in lighter-rare-earth A2Ir2O7 iridates [7].
We present a study of electrical transport properties of heavy-rare-earth A2Ir2O7 iridates (A=Dy-Lu) synthesized employing the CsCl flux method, including so far unprepared A = Tm member. A broad anomaly in the measured data, connected with the semiconductor-insulator transition, is observed in all studied members.
Electrical resistivity increases upon cooling by up to 6 orders of magnitude comparing the room temperature and 2 K data. Electrical resistivity measured in zero and non-zero magnetic field is systematically compared, fitted with multiple models, and discussed with respect to the previous results, including our magnetization, specific heat, and μSR data.
A comprehensive picture of the transport properties of this understudied part of the rare-earth A2Ir2O7 series is drawn. [1] Y. Tokiwa et al., Nat.
Mater. 13, 356-359 (2014). [2] E. Lefrançois et al., Nat.
Commun. 8, 209 (2017). [3] H. Guo et al., Phys.
Rev. B 96, 144415 (2017). [4] H.
Jacobsen et al., Phys. Rev.
B 101, 104404 (2020). [5] W. Witczak-Krempa et al., Annu.
Rev. Condens.
Matter Phys. 5, 57-82 (2014). [6] X. Wan et al., Phys.
Rev. B 83, 205101 (2011). [7] K.
Matsuhira et al., J. Phys.
Soc. Jpn. 80, 094701 (2011).