Jul 26, 2018

「Quantum spin liquids: beyond the kagome lattice」
Fabrice BERT 氏


講演題目: Quantum spin liquids: beyond the kagome lattice
講 師 : Fabrice BERT 博士
     Spectroscopies des Materiaux Quantiques, Laboratoire de Physique des Solides, Orsay, France
日 時 : 平成30年7月26日 (木) 16:30~
場 所 : 北海道大学理学部5号館2階 5-205
共 催 : 第248回エンレイソウの会、物理コロキウム
要 旨 :
Beyond the now archetypal spin liquid material herbertsmithite, we have explored different frustrated structures which open new tracks to tackle the still difficult problem of the Heisenberg antiferromagnetic model on the kagome lattice and/or avoid the also difficult problem of defects. In [NH4]2[C7H14N][V7O6F18], the V4+ ions (d1), with less Jahn-Teller effect compared to Cu2+ (3d9), form a unique S = 1/2 breathing kagome lattice which consists of alternating equilateral triangles, preserving the full frustration of the isotropic model and the spin liquid ground state[1,2]. Combining NMR measurement of the local susceptibility and state-of-the-art series expansion analysis, we could evaluate the ratio J’/J=0.55 for the interactions of the two sets of triangles. In line with recent theoretical results from variational methods and DMRG[3], we found that the spinon excitations are gapless and lead to a metallic-like low T heat capacity in this strong insulator. This experimental study should trigger novel theory approaches of the kagome problem through a J’-> J limit. PbCuTe2O6 emerged recently as a unique example of a Cu2+ (S=1/2) based quantum spin liquid (QSL) with a three dimensional lattice and dominant interactions building up a 3D network of corner sharing triangles, coined “hyperkagome”. We used sub-kelvin magnetization, NMR and muSR to establish the absence of magnetic freezing down to 20mK and the persistence of slow fluctuations [4]. The finite susceptibility at low T suggests a QSL state with a spinon Fermi Surface. A recent inelastic neutron scattering experiment revealed the fractional nature of the magnetic excitations forming a continuum of spinons, thus providing the last important evidence for the spin liquid nature of the ground state [5]. References [1] L. Clark, J.-C. Orain, F. Bert, M.A. De Vries, F.H. Aidoudi, R.E. Morris, P. Lightfoot, J.S. Lord, M.T.F. Telling, P. Bonville, J.P. Attfield, P. Mendels and A. Harrison, Phys. Rev. Lett. 110, 207208 (2013) [2] J.-C. Orain, B. Bernu, P. Mendels, L. Clark, F. H. Aidoudi, P. Lightfoot, R. E. Morris and F. Bert, Phys. Rev. Lett. 118, 237203 (2017) [3] C. Repellin, Y-C He, F. Pollmann, Phys. Rev. B 96, 205124 (2017); Y. Iqbal, D. Poilblanc, R. Thomale, F. Becca, Phys. Rev. B 97, 115127 (2018) [4] P. Khuntia, F. Bert, P. Mendels, B. Koteswararao, A. V. Mahajan, M. Baenitz, F. C. Chou, C. Baines, A. Amato, and Y. Furukawa, Phys. Rev. Lett. 116, 107203 (2016) [5] S. Chillal et al, preprint arXiv:1712.07942

世話人  井原 慶彦

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