Kondo ground state in a quantum dot with an even number of electrons in a magnetic field
Abstract
Kondo conduction has been observed in a quantum dot with an even number of electrons at the tripletsinglet degeneracy point produced by applying a small magnetic field B orthogonal to the dot plane. At a much larger field B~B_{*}, orbital effects induce the reversed transition from the singlet to the triplet state. We study the newly proposed Kondo behavior at this point. Here the Zeeman spin splitting cannot be neglected, which changes the nature of the Kondo coupling. On the grounds of exact diagonalization results in a dot with cylindrical symmetry, we show that, at odds with what happens at the other crossing point, close to B_{*}, orbital and spin degrees of freedom are ``locked together,'' so that the Kondo coupling involves a fictitious spin 12 only, which is fully compensated for by conduction electrons under suitable conditions. In this sense, spin at the dot is fractionalized. We derive the scaling equation of the system by means of a nonperturbative variational approach. The approach is extended to the B≠B_{*} case and the residual magnetization on the dot is discussed.
 Publication:

Physical Review B
 Pub Date:
 March 2001
 DOI:
 10.1103/PhysRevB.63.125318
 arXiv:
 arXiv:condmat/0010054
 Bibcode:
 2001PhRvB..63l5318G
 Keywords:

 73.23.Hk;
 72.15.Qm;
 79.60.Jv;
 Coulomb blockade;
 singleelectron tunneling;
 Scattering mechanisms and Kondo effect;
 Interfaces;
 heterostructures;
 nanostructures;
 Condensed Matter  Mesoscale and Nanoscale Physics
 EPrint:
 13 pages, 4 .eps figures