Entropic signatures of the single-impurity Kondo state

Johann Drayne; Silvia Lüscher; Will Grant; Vahid Movahed; Tim Child; Saeed Fallahi; Geoffrey C. Gardner; Michael J. Manfra; Yaakov Kleeorin; Yigal Meir; Joshua Folk

arXiv · 2607.27502

Entropic signatures of the single-impurity Kondo state

Johann Drayne·Silvia Lüscher·Will Grant·Vahid Movahed·Tim Child·Saeed Fallahi·Geoffrey C. Gardner·Michael J. Manfra·Yaakov Kleeorin·Yigal Meir·Joshua Folk

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Abstract

The Kondo singlet---a many-body state formed by entanglement between a localized spin and the Fermi sea---has been studied extensively through its transport signatures in quantum dots. Here we report a thermodynamic measurement of the entropy suppression associated with the formation of the Kondo singlet, using temperature-dependent charge sensing and a Maxwell relation to track the suppression of spin entropy as the first electron is added to a strongly-coupled GaAs quantum dot. Plotting $dN/dT$ against the simultaneously measured occupation $N$ reveals an asymmetric lineshape with its peak shifted to $N>1/2$---a hallmark of Kondo screening---that weakens with increasing temperature and is qualitatively reproduced by numerical renormalization group (NRG) calculations, with a small but persistent offset to lower occupation relative to the theory. An independent measurement of conductance versus occupation on the same device provides a test of these quantities through the mixed-valence crossover and matches NRG within experimental uncertainty.

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Johann Drayne, Silvia Lüscher, Will Grant, Vahid Movahed, Tim Child, Saeed Fallahi, Geoffrey C. Gardner, Michael J. Manfra, Yaakov Kleeorin, Yigal Meir, Joshua Folk. 2026-07-29. Entropic signatures of the single-impurity Kondo state. https://arxiv.org/abs/2607.27502

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