物性セミナー/物理学教室談話会/第15回 NITEP談話会

Wednesday 28 Apr 2021, 16:00 → 17:30 Asia/Tokyo

講師：寺谷義道（大阪市立大学）
日時：4月28日(水) 16:00-17:30
タイトル：Roles of three-body correlations on nonlinear current and noise through multilevel Anderson impurity
要旨：We study Kondo effect occurring in quantum impurity systems such as magnetic dilute alloys, quantum dots, and ultra-cold atoms. It is a many body phenomenon that is caused by interactions between localized spins and conduction electrons. In addition to the spin, other degrees of freedom bring an interesting variety to the Kondo effect. A carbon nanotube quantum dot has four degenerate localized levels consisting of the spin and orbital degrees of freedom. The four levels give rise to the SU(4) Kondo effect. It is observed by measurements of nonequilibrium current and noise[1] .
 In order to examine the nonlinear transport of an N-level Anderson impurity models at low temperatures T and low-bias voltages eV, Fermi-liquid theory has been expanded to arbitrary cases of electron filling Nd both phenomenologically[2,3] and microscopically[4-6]. The theory shows that the transport coefficients up to order of (eV)³ are determined by Fermi-liquid parameters: phase shifts, linear susceptibilities, and nonlinear three-body susceptibilities. We calculate these parameters as functions of Nd for N=4, 6 and 8 using two methods: Wilson numerical renormalization group (NRG) and 1/(N-1) expansion[7]. The latter one is a large N theory which is exact in the limit of N → ∞.
 The NRG results show that the three-body correlations significantly contribute to the nonequilibrium transport coefficients as Nd deviates from particle-hole symmetric point. We find that the correlations can be described by a single parameter in a wide range of 1 ≤ Nd ≤ N-1 for strong interactions. Such behavior of the correlations is experimentally observed[8]. Furthermore, we compare the NRG results with those obtained by 1/(N-1) expansion and find that the three-body correlations are suppressed already for N=8.
[1] M. Ferrier, T. Arakawa, T. Hata, R. Fujiwara, R. Delagrange, R. Weil, R. Deblock, R. Sakano, A. Oguri, and K. Kobayashi, Nat. Phys. 12, 230 (2016).
[2] C. Mora, and et al, Phys. Rev. B 92, 075120 (2015).
[3] M. Filippone, and et al, Phys. Rev. B 98, 075404 (2018).
[4] A. Oguri and A. C. Hewson, Phys. Rev. B 97, 035435 (2018).
[5] Y. Teratani, R. Sakano, and A. Oguri, Phys. Rev. Lett. 125, 216801 (2020).
[6] Y. Teratani, R. Sakano, T. Hata, T. Arakawa, M. Ferrier, K. Kobayashi, and A. Oguri, Phys. Rev. B 102, 165106 (2020).
[7] A. Oguri, Phys. Rev. B 85, 155404 (2012).
[8] T. Hata, Y. Teratani, T. Arakawa, S. Lee, M. Ferrier, R. Deblock, R. Sakano, A. Oguri, and K. Kobayashi, DOI: 10.21203/rs.3.rs-91730/v1.

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