G. Hechtfischer

Zero-crossing steps in intrinsic Josephson junctions of Bi2Sr2CaCu2O8+δ

We have investigated the response to microwave irradiation of small mesas fabricated on single crystals of Bi2Sr2CaCu2O8+δ. We observe zero-crossing steps in the current-voltage characteristic which are consistent with the intrinsic Josephson junctions in the mesa stack phase-locking to the external microwave field.

Subgap structures in intrinsic Josephson junctions of Tl2Ba2Ca2Cu3O10+δ and Bi2Sr2CaCu2O8+δ

The current voltage characteristics of intrinsic Josephson junctions in thin films of Tl2Ba2Ca2Cu3O10+δ and Bi2Sr2CaCu2O8+δ single crystals show pronounced subgap structures at voltages well below the gap. These voltages are independent of sample geometry, magnetic field and temperature up to 0.5 Tc. We discuss possible explanations and show that the structures could be explained by a peak in the quasiparticle contribution to the total current. For superconducting superlattices a subgap peak in the quasiparticle density of states has been predicted theoretically and could explaine our results.

Supercurrents in c-axis Pb/Bi2Sr2CaCu2O8 tunnel junctions

Abstract We investigated Josephson junctions made on the surface of Bi 2 Sr 2 CaCu 2 O 8 single crystals with Pb as the counterectrode. Junctions exhibit a clear lead gap at low temperatures as well as a nonzero supercurrent. In microwave fields Shapiro steps appear at multiples of hf/2e showing that the supercurrent is of first order. Consequences for a potential s-wave order parameter component in Bi 2 Sr 2 CaCu 2 O 8 are discussed.

Intrinsic Josephson effects in various layered superconductors

Abstract The coherence lenghts of some layered superconductors are comparable to or smaller that the interlayer distance, i.e. the layered crystal structure is mapped to a periodic order parameter modulation. In our measurements on (Bi 1−x Pb x ) 2 Sr 2 CaCu 2 O 8+ϑ , IBi 2 Sr 2 CaCu 2 O 8 , Tl 2 Ba 2 Ca 2 Cu 3 O 10 , Pr 2−x Ce x CuO 4 +ϑ and κ-(BEDT-TTF) 2 Cu(NCS) 2 single crystals with transport perpendicular to the layers, we were able to detect the DC as well as the AC Josephson effects.

C-axis tunneling between adjacent superconducting CuO2 bi- or trilayers

Abstract We have investigated the subgap tunneling characteristics in single crystals of Bi 2 Sr 2 CaCu 2 O 8+δ and thin films of Tl 2 Ba 2 Ca 2 Cu 3 O 10+δ with intrinsic Josephson junctions in the resistive state. The low temperature current voltage characteristics (IVC) exhibits a high subgap conductivity. The results are compared to a calculated IVC for tunnel junctions between two identical d-wave superconductors. The calculated quasiparticle branch agrees reasonable with the measured IVC. However, the presence of a small s-wave component can not be excluded. Besides the global IVC we studied fine structures which were observed in the IVC of both materials. These structures can be explained by a resonant coupling of infrared active c-axis phonons to the Josephson ac currents between adjacent pairs of superconducting layers.