Quantum paraelectricity in the Kitaev quantum spin liquid candidates H3LiIr2O6 and D3LiIr2O6
Quantum paraelectricity in the Kitaev quantum spin liquid candidates H3LiIr2O6 and D3LiIr2O6
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DOI：
10.1103/physrevb.101.184410
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发表时间：
2020-05-08
影响因子：
3.7
通讯作者：
Loidl, A.
中科院分区：
文献类型：
--
作者：
Geirhos, K.;Lunkenheimer, P.;Loidl, A.
H3LiIr2O6是第一个没有任何长程磁序迹象的蜂窝晶格系统，一直到最低温度，这为实现理想的Kitaev量子自旋液体带来了希望。它的蜂窝层通过层间氢键连接在一起。这些氢键的静态或动态无序被认为强烈地影响了磁交换，并使Kitaev类型的相互作用占优势。利用介电谱，我们提供了H3LiIr2O6和D3LiIr2O6的偶极弛豫的实验证据，这反映了氢键的双势垒势内的质子和氘的动力学。探测到的氢动力学揭示了玻璃冻结，其特征是在冷却下强烈减速，从热激活跳跃到向低温方向的量子力学隧道。因此，这些材料除了是Kitaev量子自旋液体候选材料外，还是量子顺电子材料。然而，在低温下发现的MHz范围内的小驰豫速率实际上实现了准静态氢无序，正如最近的理论工作所假设的那样，解释了这两个化合物的量子-自旋-液体基态。
H3LiIr2O6 is the first honeycomb-lattice system without any signs of long-range magnetic order down to the lowest temperatures, raising the hope for the realization of an ideal Kitaev quantum spin liquid. Its honeycomb layers are coupled by interlayer hydrogen bonds. Static or dynamic disorder of these hydrogen bonds was proposed to strongly affect the magnetic exchange and to make Kitaev-type interactions dominant. Using dielectric spectroscopy, here we provide experimental evidence for dipolar relaxations in H3LiIr2O6 and deuterated D3LiIr2O6, which mirror the dynamics of protons and deuterons within the double-well potentials of the hydrogen bonds. The detected hydrogen dynamics reveals glassy freezing, characterized by a strong slowing down under cooling, with a crossover from thermally activated hopping to quantum-mechanical tunneling towards low temperatures. Thus, besides being Kitaev quantum-spin-liquid candidates, these materials also are quantum paraelectrics. However, the small relaxation rates in the mHz range, found at low temperatures, practically realize quasistatic hydrogen disorder, as assumed in recent theoretical works to explain the quantum-spin-liquid ground state of both compounds.