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일시: 7월 15일(금) 오전 11:00

장소: 기초학문관 창의존 (51305)

○ 연사: 백  승  호 박사님 (IFW Dresden)

Title: Observation of a field induced quantum spin liquid in α-RuCl3

○ Abstract: 

Topological states of matter such as quantum spin liquids (QSLs) are of great interest because of their remarkable predicted properties including protection of quantum information and the emergence of Majorana fermions. Such QSLs, however, have proven very difficult to identify experimentally. A major search has centered so far on iridate materials which are proposed to realize the celebrated Kitaev model [1] on a honeycomb lattice — a prototypical topological QSL system in two dimensions (2D). However, at low temperatures long-range magnetic order develops in these iridates due to the presence of significant residual Heisenberg-type of interactions between the spins, which preempt the QSL regime. Recently, studies have shown that the magnetic interactions in a ruthenium-based material, α-RuCl3, are closer to the Kitaev limit, but also this quasi-2D magnetic material exhibits magnetic order at low temperatures [2, 3, 4]. In this talk I will show that an external magnetic field melts the long-range magnetic order in α-RuCl3. Nuclear Magnetic Resonance (NMR) measurements of the spin-relaxation rate evidence that in field larger than ∼ 10 T a spin-gap opens and scales linearly with the magnetic field, whereas at the same time the resonance lines remain very sharp [5]. This indicates that in the spin-gap phase the spins are quantum disordered and locally fluctuating. Our observation of a field- induced QSL in α-RuCl3 within an essentially established theoretical framework holds promise for the future detection, manipulation and eventually braiding of these non-Abelian quasiparticles.

[1] A. Kitaev, Annals of Physics, 321, 2 (2006)
[2] K. W. Plumb et al, PRB 90, 041112 (2014)
[3] L. J. Sandilands, PRL 114, 147201 (2015)
[4] A. Banerjee et al, Nature Materials 15, 733 (2016)
[5] S.-H. Baek et al, (Unpublished, under review).

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