Strain-induced topological insulator phase and effective magnetic interactions in Li2IrO3

Abstract

We present an effective tight-binding Hamiltonian for Li 2 IrO 3 based on maximally localized Wannier functions for states near the Fermi level as obtained from first-principles electronic structure calculations. The majority of the Wannier orbitals are positioned on the center site with dominant j eff = 1/2 character, while relatively small j eff = 3/2 tails lie on the three nearest-neighbor sites. Interestingly, the spin quantization axis of the j eff = 1/2 components deviates from the local octahedral axis and points toward the nearest-neighbor Ir direction. In our tight-binding model, there are relatively strong next-nearest-and the third-nearest-neighbor hopping terms within the two-dimensional Ir honeycomb lattice in addition to the relatively small but significant interlayer hopping terms. The ratio between the nearest-neighbor and the third-nearest-neighbor hoppings, which can be controlled by the lattice strain, plays a critical role in determinating the Z 2 -invariant character of Li 2 IrO 3 . From our tight-binding model, we also derive an effective Hamiltonian and its parameters for the magnetic exchange interactions. Due to the complex spin-dependent next-nearest-neighbor hopping terms, our pseudospin Hamiltonian includes significant next-nearest-neighbor antiferromagnetic Kitaev terms as well as DzyaloshinskiiMoriya and Heisenberg interactions. From our model Hamiltonian we estimate classical energies of collinear magnetic configurations as functions of the Hund's coupling of the Ir atom, from which zigzag-type magnetic order gives the lowest energy.

Magnetic properties ofSr3NiIrO6andSr3CoIrO6: Magnetic hysteresis with coercive fields of up to 55 T

“…Moreover, no structural change was seen at either T 1 or T 2 [13,15]. In conjunction with the magnetization results, neutronscattering data for the low-temperature phases of Sr 3 NiIrO 6 and Sr 3 CoIrO 6 have been interpreted either in terms of amplitude-modulated antiferromagnetism or as a partiallydisordered antiferromagnetic (PDA) state [15,16]. Such PDA states, proposed by Mekata [24], were first reported for the A 3 BB O 6 family in Ref.…”

“…The salient structural details [11,13,15,18] are shown in Figs. 1(a) and 1(b) for Sr 3 NiIrO 6 . The Ni 2+ and Ir 4+ magnetic ions occupy oxygen cages that alternate in chains parallel to the c axis [ Fig.…”

“…This large hysteresis evolves out of a frustrated, antiferromagnetic ground state that incorporates an entangled spin-orbit state on the 5d ion [10]. Sr 3 NiIrO 6 and Sr 3 CoIrO 6 are members of the A 3 BB O 6 family, where A is an alkaline earth and B and B are transition metal ions [11]. Soon after their synthesis [12], it was realized [13,14] that the interplay of electron correlations, magnetic frustration, reduced dimensionality, and magnetocrystalline anisotropy could lead to interesting physics; subsequently the structural and magnetic properties have been the subject of several studies (e.g., Refs.…”

Electronic excitations and structure of Li2IrO3 thin films grown on ZrO2:Y (001) substrates

“…[7][8][9][10] Ultimately, the physical realization of such states of matter is desired with respect to quantum computation proposals. [11][12][13] Subsequently, experiments showed that both materials order magnetically at %15 K: Na 2 IrO 3 is deep within an antiferromagnetically zig-zag ordered phase, [14][15][16][17] whereas Li 2 IrO 3 shows incommensurate spiral order but is placed close to the desired spin liquid phase.…”

“…In fact, both a strain-induced spin liquid and topological insulator phase are proposed to exist. 4,5,9,10 Hence, thin films of this class of material lay a foundation for future experiments including, e.g., studies on the (Na 1Àx Li x ) 2 IrO 3 compounds, which are not available in single crystalline form so far.…”