第39回 原研・兵県大合同コロキウム

日時: 平成20年3月3日(月) 16:00〜
Date and time: 3rd Mar. (Mon.) 16:00〜
場所: SPring-8, 萌光館
Place: SPring-8, "HOUKOUKAN" seminar room
Title: Spin excitation spectra of Hyper-Kagome Na4Ir3O8
講演者: 藤山茂樹 氏 (東京大学大学院工学系研究科・物理工学専攻)
Speaker: Dr. Shigeki Fujiyama (Department of Applied Physics, University of Tokyo, CREST-JST)
Abstract: pdficon pdf file

Quest for quantum spin liquid (QSL) in more than one dimensional magnetic materials continues. The QSL state, where magnetic long range order is suppressed by quantum fluctuation, is theoretically proposed to realize by frustrations of antiferromagnetic interactions induced by triangular couplings. In this context, two-dimensional triangular or Kagome lattices with S=1/2 were extensively studied to maximize the quantum fluctuations.

Recently, a spinel-related iridate, Na4Ir3O8, was found to realize quantum spin liquid down to 2 K (∼6×10-3J) by specific heat and our NMR measurements. This material is composed of corner-shared triangles of tetravalent iridiums of low spin state (S=1/2). This is the first example of QSL material with three dimensional network.

We performed 23Na NMR to study the static and dynamical spin susceptibilities of this material. The frequency shifts (K=Aχ(T)/NAμB) and nuclear spin-lattice relaxation rate (1/T1T∝Σq A(q)2χ''(q,ω)/ω ) below 20K (∼0.06J) become independent of temperature, as if spin excitation spectra is continuous, suggesting the emergence of spinons at low temperatures.

In my talk, I will compare physical quantities such as specific heat, susceptibility (frequency shifts), nuclear relaxations of various frustrated materials, and argue possible short ranged chiral order which occur at J/2.