The Enhancement of the Negative Dynamic Dielectric Constants and the Density of States for the Superconductor/insulator Superlattices

Juh-Tzeng Lue；Yen-Pang Liang；Jian-Shang Sheng

Chinese Journal of Physics

31卷6S期（1993 / 12 / 01）

875 - 883

英文

The real part of the effective dielectric constant is drastically depressed to as low as -15 x 10^4 in the infrared region from 20 to 100 meV as the thickness ratio of the PrBa2Cu3O7/YBa2Cu3O7 superlattice becomes 1.2 nm/2.4 nm by taking account of the coupling of surface plasmon polariton waves excited between neighbouring superconduction layers. The density of states (DOS) at various thickness ratios for superlattices in structure of periodic superconducting/normal materials are calculated by exploiting Green's functions derived in accordance with Kronig-Penny model. The DOS’s sharply increase near the band edges resulting from Fermi-level nesting. Increasing the thickness of superconducting layers, the corresponding DOS of superconducting state will overwhlem that of normal state showing the competition of Cooper paired electrons and normal electrons manipulated by the proximity effect. The enhanced DOS near the band edges is crucial to the retention of high critical temperatures for the recently fabricated YBaCuO/Dy(Pr)BaCuO superlattices.