Giant nonlinear conduction and thyristor-like negative differential resistance inBaIrO3single crystals

Abstract

We synthesized single-crystalline samples of monoclinic BaIrO 3 using a molten flux method, and measured their magnetization, resistivity, Seebeck coefficient and nonlinear voltage-current characteristics. The magnetization rapidly increases below a ferromagnetic transition temperature T C of 180 K, where the resistivity concomitantly shows a hump-type anomaly, followed by a sharp increase below 30 K. The Seebeck coefficient suddenly increases below T C , and shows linear temperature dependence below 50 K. A most striking feature of this compound is that the anomalously giant nonlinear conduction is observed below 30 K, where a small current density of 20 A/cm 2 dramatically suppresses the sharp increase in resistivity to induce a metallic conduction down to 4 K.

Novel Charge Ordering in the Trimer Iridium Oxide BaIrO3

“…Cao et al [11] measured the transport and optical properties of a single-crystal sample of BaIrO 3 , and found that the ferromagnetic order accompanies rapid increase in the resistivity below T c ∼180 K. In addition, they observed a gap-like structure in the optical conductivity below around 1000 cm −1 , and attributed this transition to charge-density-wave (CDW) formation with ferromagnetic order. They further found the additional two temperature anomalies near 80 and 30 K. Although the 80-K anomaly was ill-defined, the 30-K anomaly was detected by other groups in a muon-spin-relaxation experiment [12] and in a nonlinear conduction measurement [13]. Kini et al [14] measured the specific heat of BaIrO 3 and observed a small jump of 2 J/mol K around 180 K, not around 30 and 80 K. They also found that the thermopower rapidly increases below T c , and pointed out the existence of a charge gap below T c .…”

Synthesis, Crystal Structure, and Physical Properties of the Perovskite Iridates

“…Such discrepancy might arise from the different sample quality. Nevertheless, a clear gap opening is unambiguously evidenced at T c by other experimental probes, such as the Seebeck coefficient [51,58] and the high-resolution photoemission spectroscopy [59]. Currently, it remains elusive whether the gap opening is driven by the magnetic order or the Fermi surface nesting.…”

“…Their observations of the giant nonlinear conduction only appearing below 30 K, well below T c ≈ 180K, questioned the above scenario of a simultaneous onset of a CDW and a ferromagnetic transition. Instead of the sliding motion of CDW, they proposed an interplay between two different bands is likely the origin of the nonlinear conduction observed in BaIrO 3 [51]. Such discrepancy might arise from the different sample quality.…”

“…It is the first known ferromagnetic insulator with T c ≈ 180 K among the 5d TMOs [17]. Detailed studies on single crystals revealed a charge-density-wave (CDW) formation below the ferromagnetic order [18,51]. Recent experimental [52] and theoretical [53] investigations further revealed it as an exotic spin-orbit Mott insulator that is of great current research interest.…”

“…The simultaneous occurrence of ferromagnetic order and CDW formation is quite unusual, and 9R BaIrO 3 has thus been the subject of extensive investigations since then. Later on, Nakano and Terasaki [51] carried out similar current-voltage (I-V) measurements on their single crystals by using a pulsed current in order to exclude the self-heating effects. Their observations of the giant nonlinear conduction only appearing below 30 K, well below T c ≈ 180K, questioned the above scenario of a simultaneous onset of a CDW and a ferromagnetic transition.…”