Photoinduced transition from Mott insulator to metal in the undoped cuprates Nd2CuO4 and La2CuO4
Photoinduced transition from Mott insulator to metal in the undoped cuprates Nd2CuO4 and La2CuO4
复制标题
DOI：
10.1103/physrevb.83.125102
复制
发表时间：
2011-03-09
影响因子：
3.7
通讯作者：
Tokura, Y.
中科院分区：
文献类型：
--
作者：
Okamoto, H.;Miyagoe, T.;Tokura, Y.
用飞秒泵浦探测吸收光谱研究了未掺杂的Nd2CuO4和La2CuO4薄膜样品从Mott绝缘体到金属的光致跃迁。在Nd2CuO4中，通过快速的光载流子复合，产生了低激发光子密度小于0.01光子/铜的金属态，并在40fs内衰变。剩余光载流子由于电荷-自旋耦合效应而局域化，表现出粒子和空穴的两个禁带中吸收。La2CuO4还表现出光致Mott绝缘体向金属的转变，而它表现出与Nd2CuO4不同的电荷动力学，即形成金属态的阈值激发光子密度更大，禁带中吸收能量更高，极化子复合速度更慢。这些行为可以用La2CuO4中比Nd2CuO4中更大的电荷-声子耦合强度来解释，这归因于La2CuO4中顶端氧原子的存在。
Photoinduced transitions from a Mott insulator to a metal have been investigated in the undoped cuprates Nd2CuO4 and La2CuO4 by applying femtosecond pump-probe absorption spectroscopy to epitaxially grown thin-film samples. In Nd2CuO4, a metallic state is generated with low excitation photon density less than 0.01 photons/Cu and decays within 40 fs via the rapid photocarrier recombination. Residual photocarriers are localized by the effect of charge-spin coupling, exhibiting two midgap absorptions due to a particle and a hole. La2CuO4 also shows a photoinduced Mott insulator to metal transition, while it exhibits different charge dynamics from those of Nd2CuO4, that is, larger threshold excitation photon density for the formation of the metallic state, higher energies of the midgap absorptions, and slower recombination of polaronic carriers. These behaviors can be explained by the larger charge-phonon coupling strength in La2CuO4 than in Nd2CuO4, which is attributable to the presence of apical oxygen atoms in La2CuO4.