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Proximity-induced pseudogap: evidence for preformed pairs
Ofer Yuli1, Itay Asulin, Yoav Kalcheim
1Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
Physical Review Letters
|April 7, 2010
Summary
Proximity-induced superconducting gaps were observed above the critical temperature in gold/lanthanum cuprate bilayers. This suggests incoherent Cooper pairs penetrating the normal metal, not density-wave order.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Superconductivity
Background:
- The proximity effect describes how superconductivity can be induced in a normal metal adjacent to a superconductor.
- Understanding the temperature dependence of this effect is crucial for applications and fundamental physics.
Purpose of the Study:
- To investigate the temperature evolution of the proximity effect in gold/lanthanum cuprate and lanthanum cuprate/lanthanum cuprate bilayers.
- To determine the mechanism behind the persistence of proximity-induced gaps above the superconducting transition temperature.
Main Methods:
- Scanning tunneling microscopy (STM) was employed to probe the electronic properties of the bilayers.
- Measurements focused on the temperature dependence of tunneling spectra to observe induced gaps.
Main Results:
- Proximity-induced gaps were observed, centered at the chemical potential, persisting above the superconducting transition temperature (Tc).
- These gaps remained observable up to the pseudogap crossover temperature in both investigated bilayer systems.
- The observed behavior was independent of the normal-metal cap layer's specific properties.
Conclusions:
- The findings are incompatible with explanations based on density-wave order.
- Results support a model involving the penetration of incoherent Cooper pairs into the normal metal above Tc.
- This provides new insights into the nature of superconductivity and the pseudogap phase in cuprates.
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