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Kondo Cloud in a Superconductor
Cătălin Paşcu Moca1,2, Ireneusz Weymann3, Miklós Antal Werner1,4
1MTA-BME Quantum Dynamics and Correlations Research Group, Eötvös Loránd Research Network, Budapest University of Technology and Economics, Budafoki út 8., H-1111 Budapest, Hungary.
Physical Review Letters
|November 12, 2021
Summary
The Kondo cloud, a key feature of the Kondo effect, exists in both screened and unscreened phases within superconductors. Its integrity, or compensation, is universal and linked to impurity properties, offering new insights into quantum phase transitions.
Area of Science:
- Condensed Matter Physics
- Quantum Materials
- Superconductivity
Background:
- The Kondo effect describes magnetic impurities screened by conduction electrons, forming a Kondo cloud.
- In superconductors, the Kondo state transforms into Yu-Shiba-Rusinov states, leading to quantum phase transitions.
- These transitions occur between screened and unscreened phases based on the superconducting energy gap and Kondo temperature.
Purpose of the Study:
- To investigate the existence and nature of the Kondo cloud in both screened and unscreened phases of a superconductor.
- To characterize the integrity of the Kondo cloud using a universal quantity called compensation.
- To explore the relationship between compensation, the Kondo cloud, and magnetic impurity properties.
Main Methods:
- Theoretical analysis of the Kondo effect in superconducting systems.
- Introduction and application of the compensation quantity to quantify Kondo cloud integrity.
- Exploration of experimental monitoring via bias spectroscopy of magnetic impurity g-factors.
Main Results:
- The Kondo cloud persists even in the unscreened phase, contrary to expectations.
- Screening is complete in the screened phase but only partial in the unscreened phase.
- Compensation is a universal quantity directly related to the magnetic impurity's g-factor.
Conclusions:
- The Kondo cloud is a robust feature across quantum phases in superconductors.
- Partial screening in the unscreened phase highlights complex many-body interactions.
- Compensation offers a universal experimental handle to probe magnetic impurities and their screening behavior.
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