Suter A, Mali M, Roos J, Brinkmann D
Physik-Institut, Universitat Zurich, CH-8057 Zurich, Switzerland.
Phys Rev Lett. 2000 May 22;84(21):4938-41. doi: 10.1103/PhysRevLett.84.4938.
We present a 17O nuclear magnetic resonance study in the stoichiometric superconductor YBa2Cu4O8. A double irradiation method enables us to show that, below around 200 K, the spin-lattice relaxation rate of plane oxygen is not only driven by magnetic fluctuations, but also significantly by quadrupolar fluctuations, i. e., low-frequency charge fluctuations. In the superconducting state, on lowering the temperature, the quadrupolar relaxation diminishes faster than the magnetic one. These findings show that, with the opening of the spin pseudogap, a charge degree of freedom of mainly oxygen character is present in the electronic low-energy excitation spectrum.
我们展示了在化学计量比超导体YBa2Cu4O8中进行的17O核磁共振研究。一种双辐照方法使我们能够表明，在约200K以下，平面氧的自旋-晶格弛豫率不仅受磁涨落驱动，还受四极涨落（即低频电荷涨落）的显著影响。在超导状态下，随着温度降低，四极弛豫比磁弛豫衰减得更快。这些发现表明，随着自旋赝能隙的打开，电子低能激发谱中存在主要由氧特征决定的电荷自由度。
