Chair of Computational Condensed Matter Physics, Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
Laboratory for Quantum Magnetism, Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
Phys Rev Lett. 2020 Feb 21;124(7):077202. doi: 10.1103/PhysRevLett.124.077202.
Establishing the physical mechanism governing exchange interactions is fundamental for exploring exotic phases such as quantum spin liquids in real materials. In this Letter, we address exchange interactions in Sr_{2}CuTe_{x}W_{1-x}O_{6}, a series of double perovskites that realize a spin-1/2 square lattice and are suggested to harbor a quantum spin liquid ground state arising from the random distribution of nonmagnetic ions. Our ab initio multireference configuration interaction calculations show that replacing Te atoms with W atoms changes the dominant couplings from nearest to next-nearest neighbor due to the crucial role of unoccupied states of the nonmagnetic ions in the super-superexchange mechanism. Combined with spin-wave theory simulations, our calculated exchange couplings provide an excellent description of the inelastic neutron scattering spectra of the parent compounds, as well as explaining that the magnetic excitations in Sr_{2}CuTe_{0.5}W_{0.5}O_{6} emerge from bond-disordered exchange couplings. Our results demonstrate the crucial role of the nonmagnetic cations in exchange interactions paving the way to further explore quantum spin liquid phases in bond-disordered materials.
建立控制交换相互作用的物理机制对于探索真实材料中的奇异相，如量子自旋液体，是至关重要的。在这篇文章中，我们研究了 Sr_{2}CuTe_{x}W_{1-x}O_{6}中的交换相互作用，这一系列双钙钛矿实现了一个自旋为 1/2 的正方形晶格，并且由于非磁性离子的无规分布，被认为具有来源于量子自旋液体基态的特性。我们的从头算多参考组态相互作用计算表明，由于非磁性离子的未占据态在超交换机制中起着至关重要的作用，用 W 原子取代 Te 原子会改变相邻和次近邻的主导耦合。结合自旋波理论模拟，我们计算的交换耦合对母体化合物的非弹性中子散射谱进行了很好的描述，同时也解释了 Sr_{2}CuTe_{0.5}W_{0.5}O_{6}中的磁激发来源于无序键的交换耦合。我们的结果表明，非磁性阳离子在交换相互作用中起着至关重要的作用，为进一步探索无序键材料中的量子自旋液体相铺平了道路。
