Strong magnetic instability in correlated metallic Bi2Ir2O7.

Department of Physics and Astronomy and Center for Advanced Materials, University of Kentucky, Lexington, KY 40506, USA.
Journal of Physics Condensed Matter (Impact Factor: 2.22). 07/2012; 24(34):345601. DOI: 10.1088/0953-8984/24/34/345601
Source: PubMed

ABSTRACT We report an experimental/theoretical study of single-crystal Bi(2)Ir(2)O(7) that possesses a metallic state with strongly exchange-enhanced paramagnetism. The ground state of Bi(2)Ir(2)O(7) is characterized by the following features: (1) a divergent low-temperature magnetic susceptibility that indicates no long-range order down to 50 mK; (2) strongly field-dependent coefficients of the low-temperature T and T(3) terms of the specific heat; (3) a conspicuously large Wilson ratio R(W) ≈ 53.5; and (4) unusual temperature and field dependences of the Hall resistivity that abruptly change below 80 K, without any clear correlation with the magnetic behavior. All these unconventional properties suggest the existence of an exotic ground state in Bi(2)Ir(2)O(7).

  • [Show abstract] [Hide abstract]
    ABSTRACT: We investigated the electronic properties of a single crystal of metallic pyrochlore iridate Bi2Ir2O7 by means of infrared spectroscopy. Our optical conductivity data show the splitting of t2g bands into Jeff ones due to strong spin-orbit coupling. We observed a sizable midinfrared absorption near 0.2 eV which can be attributed to the optical transition within the Jeff,1/2 bands. More interestingly, we found an abrupt suppression of optical conductivity in the very far-infrared region. Our results suggest that the electronic structure of Bi2Ir2O7 is governed by the strong spin-orbit coupling and correlation effects, which are a prerequisite for theoretically proposed nontrivial topological phases in pyrochlore iridates.
    Physical review. B, Condensed matter 05/2013; 87(19). · 3.77 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We study the finite temperature and magnetic field phase diagram of electrons on the pyrochlore lattice subject to a local repulsion as a model for the pyrochlore iridates. We provide the most general symmetry-allowed Hamiltonian, including next-nearest neighbour hopping, and relate it to a Slater-Koster based Hamiltonian for the iridates. It captures Lifshitz and/or thermal transitions between several phases such as metals, semimetals, topological insulators and Weyl semimetals, and gapped antiferromagnets with different orders. Our results on the charge conductivity, both DC and optical, Hall coefficient, magnetization and susceptibility show good agreement with recent experiments and provide new predictions. As such, our effective model sheds light on the pyrochlore iridates in a unified way.
    Physical review. B, Condensed matter 08/2012; 87(15). · 3.77 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Muon spin relaxation measurements on Bi2Ir2O7 show that it undergoes a bulk magnetic transition at 1.84(3) K. This is accompanied by increases in the muon spin relaxation rate and the amplitude of the non-relaxing part of the signal. The magnetic field experienced by muons is estimated to be 0.7 mT at low-temperature, around two orders of magnitude smaller than that in other pyrochlore iridates. These results suggest that the low-temperature state represents ordering of exceptionally small magnetic moments with persistent weak dynamics. The relaxation rate increases further below 0.23(4) K, coincident with a growth in the specific heat, suggesting the existence of a second low-temperature magnetic transition.
    Physical review. B, Condensed matter 02/2013; 87(18). · 3.77 Impact Factor