Cai Y Q, Chow P C, Restrepo O D, Takano Y, Togano K, Kito H, Ishii H, Chen C C, Liang K S, Chen C T, Tsuda S, Shin S, Kao C C, Ku W, Eguiluz A G
National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
Phys Rev Lett. 2006 Oct 27;97(17):176402. doi: 10.1103/PhysRevLett.97.176402. Epub 2006 Oct 24.
A sharp feature in the charge-density excitation spectra of single-crystal MgB2, displaying a remarkable cosinelike, periodic energy dispersion with momentum transfer (q) along the c* axis, has been observed for the first time by high-resolution nonresonant inelastic x-ray scattering (NIXS). Time-dependent density-functional theory calculations show that the physics underlying the NIXS data is strong coupling between single-particle and collective degrees of freedom, mediated by large crystal local-field effects. As a result, the small-q collective mode residing in the single-particle excitation gap of the B pi bands reappears periodically in higher Brillouin zones. The NIXS data thus embody a novel signature of the layered electronic structure of MgB2.
通过高分辨率非共振非弹性X射线散射（NIXS）首次观察到单晶MgB₂电荷密度激发光谱中的一个尖锐特征，该特征显示出沿c*轴具有动量转移（q）的显著类余弦周期性能量色散。含时密度泛函理论计算表明，NIXS数据背后的物理机制是单粒子自由度与集体自由度之间的强耦合，由大的晶体局域场效应介导。结果，位于B π带单粒子激发能隙中的小q集体模式在更高的布里渊区中周期性地重新出现。因此，NIXS数据体现了MgB₂层状电子结构的一种新特征。
