Seminar by Tomonari Mizoguchi, "Magnetic phase diagram in hyperkagome iridate Na4Ir3O8"

Seminar Information (Theory of Quantum Matter Unit)

• Speaker: Tomonoari Mizoguchi
• Affiliation: Ph.D. student, Department of Physics, University of Tokyo)
• Title: "Magnetic phase diagram in hyperkagome iridate Na4Ir3O8"
• Date/Time: Tuesday, 21st June / 2-3pm
• Venue: C016, Lab1

Magnetic phase diagram in hyperkagome iridate Na4Ir3O8

Tomonari Mizoguchi (University of Tokyo)

Hyperkagome iridate Na4Ir3O8 [1] has attracted a great attention as a candidate for a spin liquid state. In this material, Ir4+ ions possess the pseudospin jeff=1/2, and they are on a hyperkagome lattice (i.e., the corner-sharing triangles in three-dimensions), which is geometrically frustrated. Recently, it has been reported in the muSR [2] and NMR [3] experiments that this material shows the spin freezing behavior below T~ 6-7K.

  Motivated by these experiments, we investigated the effect of small anisotropic spin exchange interactions in addition to a huge antiferromagnetic Heisenberg interaction [4], since small anisotropic interactions may become important in the low temperature region. Actually, previous works have shown that selected sets of anisotropic interactions play an important role in determining the classical ground state of this material [5-7]. For further understanding of the effect of anisotropic interactions, the derivation of the generic spin model is highly desirable.

 In this seminar, I will first show how to derive a generic spin model by considering multiorbital interactions and the spin-orbit coupling for t_2g orbitals. Then I will discuss the magnetic phase diagram of that model at the classical level which is obtained by a combination of Luttinger-Tisza analysis and classical Monte Carlo simulated annealing. We find that there are three q=0 states: Z_2, Z_6^{2p}, and Z_6^{1p} states. The spin configurations of three q=0 states can be characterized by underlying lattice symmetries. Finally, I will present the possible explanation for the spin freezing behavior on the basis of our theoretical analysis.

[1] Y. Okamoto, et al., Phys. Rev. Lett. 99, 137207 (2007).

[2] R. Dally, et al., Phys. Rev. Lett. 113, 247601 (2014).

[3] A. C. Shockley, et al., Phys. Rev. Lett. 115, 047201 (2015).

[4] T. Mizoguchi, et al., arXiv: 1603.00469 (2016).

[5] G. Chen and L. Balents, Phys. Rev. B 78, 094403 (2008).

[6] I. Kimchi and A. Vishwanath, Phys. Rev. B 89, 014414 (2014).

[7] R. Shindou, Phys. Rev. B 93, 094419 (2016).