Odd and even Kondo effects from emergent localization in quantum point contacts

Area of Science:

• Condensed Matter Physics
• Nanoscale Electronics
• Quantum Transport

Background:

• Quantum point contacts (QPCs) are fundamental nanodevices exhibiting quantized conductance due to ballistic electron transport.
• Anomalies in QPC conductance are attributed to electron many-body effects, which remain poorly understood.
• Understanding these many-body effects is crucial for advancing nanoscale electronics and quantum applications.

Purpose of the Study:

• To investigate the origin of anomalies in quantized conductance observed in quantum point contacts.
• To elucidate the role of electron many-body effects, specifically localized states and the Kondo effect, in QPC anomalies.
• To explore the potential of tunable QPCs as a platform for studying many-body physics at the single-site level.

Main Methods:

• Experimental investigation using length-tunable quantum point contacts.
• Analysis of conductance traces to identify quantized plateaux and anomalies.
• Characterization of many-body effects through Kondo signatures, distinguishing between odd and even Kondo effects.

Main Results:

• Identified spontaneously localized states emerging from Friedel oscillations as the source of many-body effects in QPCs.
• Demonstrated that the Kondo effect, associated with localized electron spins, contributes to the formation of these many-body states.
• Observed periodic modulation of many-body properties with alternating odd and even Kondo effects in length-tunable QPCs, directly reflecting the number of localized states.

Conclusions:

• The study reveals that anomalies in QPC conductance are caused by localized states and associated Kondo effects.
• Tunable QPCs provide a versatile platform for probing many-body physics and understanding electron spin interactions at the nanoscale.
• These findings are significant for hybrid devices, spintronics, and quantum information applications.