三角晶格上的量子电偶极液体
Quantum electric-dipole liquid on a triangular lattice
摘要：
即使在最低温度下，几何挫折和量子力学涨落也可能阻止长程有序的形成，因此可以预期类液体基态。一个很好的例子是受抑磁体中的量子自旋液体，它代表了物质的一种奇异相，吸引了巨大的兴趣。几何挫折和量子涨落可以发生在磁系统之外。在这里，我们提出，量子电偶极子液体，类似于量子自旋液体，可以出现在受挫的电偶极子反铁电耦合的小电偶极子驻留在一个三角形晶格。量子顺电六角铁氧体BaFe_（12）O_（19）是一种具有良好电偶极性能的新型材料，它的电偶极来自于Fe ~（3+）在FeO_5双锥中的偏心位移，构成了一个二维三角晶格。我们提出了一系列的实验证据，包括介电常数，热容，和热导率测量到66 mK，揭示了一个非平凡的基态的存在BaFe 12 O 19，其特征在于巡回低能量激发与一个小的间隙，我们解释为一个奇异的液体状量子相。受挫折的量子电偶极子液体为基础物理学开辟了一个新的领域，也可能在量子信息和计算中找到应用。
英文摘要：
Geometric frustrations and quantum mechanical fluctuations may prohibit the formation of long-range ordering even at the lowest temperature, and therefore liquid-like ground states could be expected. A good example is the quantum spin liquid in frustrated magnets that represents an exotic phase of matter and is attracting enormous interests. Geometric frustrations and quantum fluctuations can happen beyond magnetic systems. Here we propose that quantum electric-dipole liquids, analogs to quantum spin liquids, could emerge in frustrated dielectrics where antiferroelectrically coupled small electric dipoles reside on a triangular lattice. The quantum paraelectric hexaferrite BaFe12O19, in which small electric dipoles originated from the off-center displacement of Fe3+ in the FeO5 bipyramids constitute a two-dimensional triangular lattice, represents a promising candidate to generate the anticipated electric-dipole liquid. We present a series of experimental evidences, including dielectric permittivity, heat capacity, and thermal conductivity measured down to 66 mK, to reveal the existence of a nontrivial ground state in BaFe12O19, characterized by itinerant low-energy excitations with a small gap, to which we interpret as an exotic liquid-like quantum phase. The quantum electric-dipole liquids in frustrated dielectrics open up a fresh playground for fundamental physics and may find applications in quantum information and computation as well.
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