Li Yuesheng, Adroja Devashibhai, Bewley Robert I, Voneshen David, Tsirlin Alexander A, Gegenwart Philipp, Zhang Qingming
Department of Physics, Renmin University of China, Beijing 100872, People's Republic of China.
Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany.
Phys Rev Lett. 2017 Mar 10;118(10):107202. doi: 10.1103/PhysRevLett.118.107202. Epub 2017 Mar 7.
We apply moderate-high-energy inelastic neutron scattering (INS) measurements to investigate Yb^{3+} crystalline electric field (CEF) levels in the triangular spin-liquid candidate YbMgGaO_{4}. Three CEF excitations from the ground-state Kramers doublet are centered at the energies ℏω=39, 61, and 97 meV in agreement with the effective spin-1/2 g factors and experimental heat capacity, but reveal sizable broadening. We argue that this broadening originates from the site mixing between Mg^{2+} and Ga^{3+} giving rise to a distribution of Yb-O distances and orientations and, thus, of CEF parameters that account for the peculiar energy profile of the CEF excitations. The CEF randomness gives rise to a distribution of the effective spin-1/2 g factors and explains the unprecedented broadening of low-energy magnetic excitations in the fully polarized ferromagnetic phase of YbMgGaO_{4}, although a distribution of magnetic couplings due to the Mg/Ga disorder may be important as well.
我们进行了中高能非弹性中子散射（INS）测量，以研究三角自旋液体候选物YbMgGaO₄中Yb³⁺的晶体电场（CEF）能级。来自基态克莱默斯二重态的三种CEF激发能量集中在ℏω = 39、61和97毫电子伏特，这与有效自旋1/2 g因子和实验热容量一致，但显示出相当大的展宽。我们认为这种展宽源于Mg²⁺和Ga³⁺之间的位点混合，导致Yb - O距离和取向分布，进而导致CEF参数分布，这解释了CEF激发的特殊能量分布。CEF随机性导致有效自旋1/2 g因子分布，并解释了YbMgGaO₄完全极化铁磁相中低能磁激发前所未有的展宽，尽管由于Mg/Ga无序导致的磁耦合分布可能也很重要。
