Magnetically Tunable Kondo–Aharonov-Bohm Effect in a Triangular Quantum Dot

Abstract

The role of discrete orbital symmetry in mesoscopic physics is manifested in a system consisting of three identical quantum dots forming an equilateral triangle. Under a perpendicular magnetic field, this system demonstrates a unique combination of Kondo and Aharonov-Bohm features due to an interplay between continuous [spin-rotation SU(2)] and discrete (permutation C3v) symmetries, as well as U(1) gauge invariance. The conductance as a function of magnetic flux displays sharp enhancement or complete suppression depending on contact setups.

Antisymmetric Spin–Orbit Coupling Effect on Kondo-Induced Electric Polarization in a Triangular Triple Quantum Dot

“…4.2, the ASO coupling can be considered as a magnetic flux through the TTQD and could be chosen as a controllable parameter for detecting an interference effect on the conductance, as proposed in several theoretical studies on QD systems with various configurations. 10,39,[52][53][54][55][56] This work was supported by JSPS KAKENHI Grant Numbers 16H01070 (J-Physics), 15H05885 (J-Physics), 26400332, and 15K05176.…”

“…42-44, 47, 48, 50) The loop structure of the TTQD also gives rise to interference effects such as the Aharonov-Bohm (AB) effect, 10,[52][53][54][55][56] where a magnetic flux penetrating through the loop affects the molecular orbitals of the TTQD and modifies the Kondo behavior in the absence of a magnetic field. 39,43) However, most of the theoretical studies have mainly focused on the conductance through the TTQD as an observable and controllable physical quantity.…”

“…38) The recent development of a fabrication technique has stimulated theoretical investigations of various TTQD Kondo systems because of the high potentiality for versatile quantum devices. [39][40][41][42][43][44][45][46][47][48][49][50][51] The tunable parameters in the TTQD are interdot electron-hopping matrix elements and intradot orbital energy levels used as a standard theoretical setup. The electron occupation number at each dot changes with the depth of the orbital energy relative to the Coulomb coupling.…”

Kondo screening of a high-spin Nagaoka state in a triangular quantum dot

“…The transport is determined by two phase shifts for quasi-particles with even and odd parities, and then a two-terminal conductance in the series configuration is suppressed gseries ≃ 0, while plateau of a four-terminal parallel conductance reaches a Unitary limit value g parallel ≃ 4e 2 /h of two conducting modes. The Kondo effect in quantum dots is an active field of current research, and recently triple quantum dots with triangle have been examined intensively [1,2].…”

“…The transport is determined by two phase shifts for quasi-particles with even and odd parities, and then a two-terminal conductance in the series configuration is suppressed gseries ≃ 0, while plateau of a four-terminal parallel conductance reaches a Unitary limit value g parallel ≃ 4e 2 /h of two conducting modes. The Kondo effect in quantum dots is an active field of current research, and recently triple quantum dots with triangle have been examined intensively [1,2].One interesting property expected to be seen in a quantum-dot array with closed paths is that some degenerate states could be lifted by circular orbital motions of electrons to form a high-spin ground state due to the Nagaoka mechanism. In this report for clarifying, i) how the Nagaoka ferromagnetism that could manifest in the isolated triangle for a particular charge filling is screened by the conduction electrons, and ii) how it affects the lowtemperature transport bellow the Kondo energy scale T K , we present the results using the NRG approach [3,4,5], which is applicable to low-temperatures T T K .…”