Evidence of Kondo Screening Cloud of Micron Lengths
Speaker:
Ivan Borzenets (City University of Hong Kong)
Event Details
The Kondo effect, known as the archetype of many-body correlations, arises from the interaction
between a localized magnetic moment and surrounding conducting electrons. Advances of
nanotechnology allow us to study the Kondo effect for a single magnetic impurity confined in a
semiconductor quantum dot in contact with electron reservoirs. This development also makes it
possible to embed a Kondo correlated state into an interferometer. Although the Kondo effect is
now a text-book subject of many-body physics, detection of its key object, the Kondo cloud,
remained elusive despite many attempts for the past 50 years.
In this work, we present experimental evidence of a Kondo cloud extending over a length of
micrometers comparable to the theoretical length ξK. Our measurement scheme involves, a
Kondo impurity formed in a quantum dot (QD), and coupled to a quasi- one dimensional channel
that houses a Fabry-Perot (FP) interferometer of variable length L > 1 μm. When we tune a gate
voltage applied to the interferometer end distant from the QD by the length L, we observe
oscillations in measured Kondo temperature: a sign of the cloud at distance L.
Our experiment shows that the Kondo cloud has the main body of size larger than one micrometer
with a tail extending further: in good agreement with our theoretical calculation. This provides
essential insight into the fundamental phenomenon of spin screening in a metal, and opens up a
way of engineering the spin screening and the entanglement.