Possible Kondo Physics near a Metal-Insulator Crossover in theA-Site Ordered PerovskiteCaCu3Ir4O12

Abstract

The A-site ordered perovskite (AA(3)')B(4)O(12) can accommodate transition metals on both A' and B sites in the crystal structure. Because of this structural feature, it is possible to have narrow-band electrons interacting with broadband electrons from different sublattices. Here we report a new A-site ordered perovskite (CaCu(3))Ir(4)O(12) synthesized under high pressure. The coupling between localized spins on Cu(2+) and itinerant electrons from the Ir-O sublattice makes Kondo-like physics take place at a temperature as high as 80 K. Results from the local density approximation calculation have confirmed the relevant band structure. The magnetization anomaly found at 80 K can be well rationalized by the two-fluid model.

High electrical conductivity of composite ceramics consisting of insulating oxide and ordered perovskite conducting oxide

“…κ , κ CCRO and κ CuO are the thermal conductivity of the composite, CaCu 3 Ru 4 O 12 and CuO, respectively. κ CCRO and κ CuO are reported to be about 10 W m −1 K −1 at room temperature , and accordingly we assume κ = κ CCRO = κ CuO . We also assume σ CCRO >> σ CuO as is shown in Fig.…”

Competition between heavy fermion and Kondo interaction in isoelectronic A-site-ordered perovskites

“…In this framework the overall ground state is defined by the competition between RKKY type magnetic exchange between magnetic holes on Cu with the Kondo screening by conduction carries from the B-O sublattices. For CCIrO, with a S = 1/2 d-hole localized on Cu, the large magnetic exchange is comparable in strength with the Kondo screening, resulting in the strongly enhanced effective mass observed with transport and thermal measurements [27]. Thus, Cheng et al firmly placed CCIrO into the heavy fermion regime I in Fig.…”

“…Thus, Cheng et al firmly placed CCIrO into the heavy fermion regime I in Fig. 4(b) with the antiferromagnetic local moment short-range magnetism [23,27]. In moving from Ir to Rh and Co, the Kondo energy scale begins to gain due to the collective hybridization of Cu d-holes into the ZR singlets.…”

“…Very recently, Cheng et al showed that this class of materials displays a crossover between the magnetic insulating and paramagnetic metallic states, depending on the Cu-O and B-O bond lengths [27]. It was further suggested that the CaCu 3 Ir 4 O 12 (CCIrO) compound with the bond-length within the crossover region possesses anomalous electronic and magnetic properties arising presumably due to the interaction between the localized Cu and itinerant Ir states [23].…”

“…Within the proposed phase diagram of Cheng et al B = Co occupies the paramagnetic metallic state while CCIrO is at the crossover region as reflected for instance in anomalous d.c. transport properties shown in Fig. 1(b) [22,27].…”