Phase coherence of conduction electrons below the Kondo temperature

Area of Science:

• Condensed Matter Physics
• Quantum Mechanics
• Materials Science

Background:

• Phase decoherence limits quantum coherence in electronic systems.
• Kondo effect describes the screening of magnetic impurities by conduction electrons.
• Understanding decoherence is crucial for quantum information technologies.

Purpose of the Study:

• To measure the phase decoherence rate (tau_{varphi}^{-1}) in disordered silver wires doped with iron (Fe) impurities.
• To investigate the temperature dependence of decoherence, particularly below the Kondo temperature (T_{K}).
• To compare experimental results with existing theoretical models of spin screening and dephasing.

Main Methods:

• Utilizing weak-localization magnetoresistance measurements.
• Implanting silver wires with 2 and 10 ppm of Fe impurities.
• Conducting measurements over a temperature range from 40 mK to 10 K.

Main Results:

• Observed a clear contribution to phase decoherence from Fe impurities between 40 mK and 10 K.
• Found that tau_{varphi}^{-1} decreases rapidly below T_{K} (approximately 4 K) until T/T_{K} ≈ 0.1, matching theoretical predictions.
• Noticed a deviation from theory at lower temperatures (T/T_{K} < 0.1), exhibiting a flatter temperature dependence of tau_{varphi}^{-1}.

Conclusions:

• The study provides experimental evidence for the progressive screening of Fe spins in silver wires.
• The observed anomalous dephasing at low temperatures (T/T_{K} < 0.1) indicates limitations in current theoretical models.
• Further theoretical development, potentially including larger spin or more channels, may be needed to explain the low-temperature behavior.