Two-channel Kondo physics in odd impurity chains

We study odd-membered chains of spin-12 impurities, with each end connected to its own metallic lead. For antiferromagnetic exchange coupling, universal two-channel Kondo (2CK) physics is shown to arise at low energies. Two overscreening mechanisms are found to occur depending on coupling strength,...

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Main Authors: Mitchell, A, Logan, D, Krishnamurthy, H
Format: Journal article
Language:English
Published: 2011
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author Mitchell, A
Logan, D
Krishnamurthy, H
author_facet Mitchell, A
Logan, D
Krishnamurthy, H
author_sort Mitchell, A
collection OXFORD
description We study odd-membered chains of spin-12 impurities, with each end connected to its own metallic lead. For antiferromagnetic exchange coupling, universal two-channel Kondo (2CK) physics is shown to arise at low energies. Two overscreening mechanisms are found to occur depending on coupling strength, with distinct signatures in physical properties. For strong interimpurity coupling, a residual chain spin-12 moment experiences a renormalized effective coupling to the leads, while in the weak-coupling regime, Kondo coupling is mediated via incipient single-channel Kondo singlet formation. We also investigate models in which the leads are tunnel-coupled to the impurity chain, permitting variable dot filling under applied gate voltages. Effective low-energy models for each regime of filling are derived, and for even fillings where the chain ground state is a spin singlet, an orbital 2CK effect is found to be operative. Provided mirror symmetry is preserved, 2CK physics is shown to be wholly robust to variable dot filling; in particular, the single-particle spectrum at the Fermi level, and hence the low-temperature zero-bias conductance, is always pinned to half-unitarity. We derive a Friedel-Luttinger sum rule and from it show that, in contrast to a Fermi liquid, the Luttinger integral is nonzero and determined solely by the "excess" dot charge as controlled by gate voltage. The relevance of the work to real quantum dot devices, where interlead charge-transfer processes fatal to 2CK physics are present, is also discussed. Physical arguments and numerical renormalization-group techniques are used to obtain a detailed understanding of these problems. © 2011 American Physical Society.
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spelling oxford-uuid:cee975fa-8aa8-4dcf-b236-69ce52a2234a2022-03-27T07:38:42ZTwo-channel Kondo physics in odd impurity chainsJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:cee975fa-8aa8-4dcf-b236-69ce52a2234aEnglishSymplectic Elements at Oxford2011Mitchell, ALogan, DKrishnamurthy, HWe study odd-membered chains of spin-12 impurities, with each end connected to its own metallic lead. For antiferromagnetic exchange coupling, universal two-channel Kondo (2CK) physics is shown to arise at low energies. Two overscreening mechanisms are found to occur depending on coupling strength, with distinct signatures in physical properties. For strong interimpurity coupling, a residual chain spin-12 moment experiences a renormalized effective coupling to the leads, while in the weak-coupling regime, Kondo coupling is mediated via incipient single-channel Kondo singlet formation. We also investigate models in which the leads are tunnel-coupled to the impurity chain, permitting variable dot filling under applied gate voltages. Effective low-energy models for each regime of filling are derived, and for even fillings where the chain ground state is a spin singlet, an orbital 2CK effect is found to be operative. Provided mirror symmetry is preserved, 2CK physics is shown to be wholly robust to variable dot filling; in particular, the single-particle spectrum at the Fermi level, and hence the low-temperature zero-bias conductance, is always pinned to half-unitarity. We derive a Friedel-Luttinger sum rule and from it show that, in contrast to a Fermi liquid, the Luttinger integral is nonzero and determined solely by the "excess" dot charge as controlled by gate voltage. The relevance of the work to real quantum dot devices, where interlead charge-transfer processes fatal to 2CK physics are present, is also discussed. Physical arguments and numerical renormalization-group techniques are used to obtain a detailed understanding of these problems. © 2011 American Physical Society.
spellingShingle Mitchell, A
Logan, D
Krishnamurthy, H
Two-channel Kondo physics in odd impurity chains
title Two-channel Kondo physics in odd impurity chains
title_full Two-channel Kondo physics in odd impurity chains
title_fullStr Two-channel Kondo physics in odd impurity chains
title_full_unstemmed Two-channel Kondo physics in odd impurity chains
title_short Two-channel Kondo physics in odd impurity chains
title_sort two channel kondo physics in odd impurity chains
work_keys_str_mv AT mitchella twochannelkondophysicsinoddimpuritychains
AT logand twochannelkondophysicsinoddimpuritychains
AT krishnamurthyh twochannelkondophysicsinoddimpuritychains