IFW Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany.
Swiss Light Source, Paul Scherrer Insitute, CH-5232 Villigen PSI, Switzerland.
Phys Rev Lett. 2015 Mar 6;114(9):096402. doi: 10.1103/PhysRevLett.114.096402. Epub 2015 Mar 4.
Fractionalization of an electronic quasiparticle into spin, charge, and orbital parts is a fundamental and characteristic property of interacting electrons in one dimension. However, real materials are never strictly one dimensional and the fractionalization phenomena are hard to observe. Here we studied the spin and orbital excitations of the anisotropic ladder material CaCu_{2}O_{3}, whose electronic structure is not one dimensional. Combining high-resolution resonant inelastic x-ray scattering experiments with theoretical model calculations, we show that (i) spin-orbital fractionalization occurs in CaCu_{2}O_{3} along the leg direction x through the xz orbital channel as in a 1D system, and (ii) no fractionalization is observed for the xy orbital, which extends in both leg and rung direction, contrary to a 1D system. We conclude that the directional character of the orbital hopping can select different degrees of dimensionality. Using additional model calculations, we show that spin-orbital separation is generally far more robust than the spin-charge separation. This is not only due to the already mentioned selection realized by the orbital hopping, but also due to the fact that spinons are faster than the orbitons.
电子准粒子的自旋、电荷和轨道部分的分数化是一维相互作用电子的基本和特征性质。然而，实际材料从来都不是严格的一维，而且分数化现象很难观察到。在这里，我们研究了各向异性梯状材料 CaCu_{2}O_{3}的自旋和轨道激发，其电子结构不是一维的。通过高分辨率共振非弹性 X 射线散射实验和理论模型计算的结合，我们表明(i) 在 CaCu_{2}O_{3}中，自旋轨道分数化沿腿方向 x 通过 xz 轨道通道发生，就像在一维系统中一样，而(ii) 对于 xy 轨道，没有观察到分数化，这与一维系统相反，xy 轨道在腿和梯级方向上都延伸。我们得出结论，轨道跃迁的方向性可以选择不同程度的维度。使用额外的模型计算，我们表明自旋轨道分离通常比自旋电荷分离更稳健。这不仅是由于轨道跃迁实现的已经提到的选择，还由于自旋子比轨道子快。
