Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom.
Max-Planck-Institut fur Physik komplexer Systeme, Nothnitzer Straße 38, 01187 Dresden, Germany.
Phys Rev Lett. 2019 Feb 1;122(4):047202. doi: 10.1103/PhysRevLett.122.047202.
The 5d-electron honeycomb compound H_{3}LiIr_{2}O_{6} [K. Kitagawa et al., Nature (London) 554, 341 (2018)NATUAS0028-083610.1038/nature25482] exhibits an apparent quantum spin liquid state. In this intercalated spin-orbital compound, a remarkable pileup of low-energy states was experimentally observed in specific heat and spin relaxation. We show that a bond-disordered Kitaev model can naturally account for this phenomenon, suggesting that disorder plays an essential role in its theoretical description. In the exactly soluble Kitaev model, we obtain, via spin fractionalization, a random bipartite hopping problem of Majorana fermions in a random flux background. This has a divergent low-energy density of states of the required power-law form N(E)∝E^{-ν} with a drifting exponent which takes on the value ν≈1/2 for relatively strong bond disorder. Breaking time-reversal symmetry removes the divergence of the density of states, as does applying a magnetic field in experiment. We discuss the implication of our scenario, both for future experiments and from a broader perspective.
5d 电子的蜂窝状化合物 H_{3}LiIr_{2}O_{6} [K. Kitagawa 等人，《自然》（伦敦）554,341（2018）NATUAS0028-083610.1038/nature25482] 表现出明显的量子自旋液体状态。在这个插层自旋轨道化合物中，在比热和自旋弛豫中实验观察到了显著的低能态堆积。我们表明，无序的 Kitaev 模型可以自然地解释这一现象，表明无序在其理论描述中起着至关重要的作用。在完全可解的 Kitaev 模型中，我们通过自旋分裂得到了 Majorana 费米子在随机磁通背景中的随机双分量子跳跃问题。这具有所需幂律形式 N(E)∝E^{-ν}的发散低能态密度，其中漂移指数对于相对较强的键无序取 ν≈1/2 的值。破坏时间反演对称性会消除态密度的发散，实验中施加磁场也会消除态密度的发散。我们讨论了我们的方案的影响，包括对未来实验和更广泛视角的影响。
