Spin-Liquid State in theS=1/2Hyperkagome AntiferromagnetNa4Ir3O8

Abstract

A spinel related oxide, Na4Ir3O8, was found to have a three dimensional network of corner shared Ir 4+ (t2g 5 ) triangles. This gives rise to an antiferromagnetically coupled S = 1/2 spin system formed on a geometrically frustrated hyperkagome lattice. Magnetization M and magnetic specific heat Cm data showed the absence of long range magnetic ordering at least down to 2 K. The large Cm at low temperatures is independent of applied magnetic field up to 12 T, in striking parallel to the behavior seen in triangular and kagome antiferromagnets reported to have a spin-liquid ground state. These results strongly suggest that the ground state of Na4Ir3O8 is a three dimensional manifestation of a spin liquid. PACS numbers: Valid PACS appear hereThe experimental realization of a quantum spin liquid in geometrically frustrated magnets has been one of the biggest challenges in the field of magnetism since Anderson proposed resonating valence bond theory [1] for antiferromagnetically coupled S = 1/2 spins on a triangular lattice. Geometrical frustration in magnets arises from the incompatibility of local spin-spin interactions, which gives rise to macroscopic degeneracy of the ground state. Possible playgrounds for this include triangular, kagome, pyrochlore and garnet lattices essentially consisting of networks of triangles. In real materials, however, it is not easy to prevent spin ordering at substantially lower temperatures than the Curie-Weiss temperature θ W . This is because the spin degeneracy can be lifted by coupling with the other degrees of freedom such as the orbitals, lattice and charges. Such an interplay between the frustrated spins, orbitals and lattice, for example, can be realized in the trimer singlet formation in the S = 1 triangular LiVO 2 [2, 3] with orbital ordering or the spin-Jahn-Teller transition in the S = 3/2 pyrochlore ZnCr 2 O 4 [4]. In addition, only a minute amount of disorder can strongly influence the spin-liquid state in geometrically frustrated magnets and may give rise to the formation of a glassy state of spins.The most likely candidate for the realization of a spinliquid ground state has been the two dimensional kagome antiferromagnet SrCr 9p Ga 12−9p O 19 (S = 3/2) [5,6]. It does not show any evidence for long range ordering down to 100 mK, and a large and field independent magnetic specific heat was observed which was ascribed to spinliquid contributions. Nevertheless, the strong spin glasslike behavior at low temperatures instills a certain ambiguity in identifying the spin-liquid state. Recently, a new generation of spin-liquid compounds has emerged, the S = 1/2 triangular magnet κ-(ET) 2 Cu 2 (CN) 3 [7], an organic Mott insulator, and the S = 1 triangular magnet NiGa 2 S 4 [8]. They were reported to have a spin-liquid ground state or at least a robust liquid phase down to 100 mK. Their magnetic and thermal properties are in striking parallel to those of SrCr 9p Ga 12−9p O 19 but the disorder effect appears to be much weaker.Here we report on a three dimensional analogue of thes...

IrSr2Sm1.15Ce0.85CuColman1, Mclaughlin2 2012Phys. Rev. B

“…These exotic physics range from topological Fermi-arc states in Sr 2 IrO 4 14 to long-range order in Na 2 IrO 3 15 and even a proposed threedimensional quantum spin liquid ground state in the frustrated hyperkagome lattice compound Na 4 Ir 3 O 8 . 16 The possibility of such unusual physical phenomena makes iridium-containing cuprates an obvious synthetic target.…”

Anisotropic Magnetoresistance in AntiferromagneticSr2IrO4

“…The finding of this work opens an entirely new avenue to not only gain a new insight into physics associated with spin-orbit coupling but also to better harness the power of spintronics in a more technically favorable fashion. [13] behaviors, which makes them an attractive playground for studying physics driven by spin-orbit interactions. As AMR is known to be closely associated with spin-orbit interaction, the strong spin-orbit interaction in this 5d transition metal oxide may favor stronger AMR compared to 3d transition metal alloys and oxides.…”

Magnetic and crystal structures ofSr2IrO4: A neutron diffraction study

“…A new balance between the competing energies is therefore established in the iridates and drives exotic quantum phases. Recent experimental observations and theoretical proposals for the iridates have captured the intriguing physics driven by SOI: J eff = 1/2 Mott state, 1-4 superconductivity, 5,6 correlated topological insulator with large gaps, 7,8 spin liquid in hyperkagome structure, 9 Weyl semimetal with Fermi arcs, 10 Kitaev mode, 11,12 and three dimensional (3D) spin liquid with Fermionic spinons. 13 Among all the iridates studied, the single layer Sr 2 IrO 4 has been subjected to the most extensive investigations owing to its structural and electronic similarities to the undoped high-T C cuprates such as La 2 CuO 4 .…”