Conductance signatures of spin correlations and quantum phase transitions in parallel quantum dots*

Semiconductor quantum dots provide a highly controllable environment to study strongly correlated phenomena and quantum phase transitions (QPT). A parallel double-quantum-dot system, in which dot 1 is in the Kondo regime and dot 2 behaves as a non-interacting resonant level, shows a QPT separating Kondo-screened and local-moment phases [1]. In this work, we use the numerical renormalization-group approach to explore the effect of a nonzero Coulomb interaction $U_{2}$ in dot 2. When dot-2 level is fixed at the Fermi energy, a critical value of $U_{2}$ separates local-moment and Kondo-screened phases. By contrast, if $U_{2}$ is increased keeping particle-hole symmetry in dot 2, the system evolves from a local-moment regime to an underscreened spin-1 regime. Signatures of these behaviors can be experimentally identified through the conductance of the system. We also calculated the spin-spin correlations between the dots and between each dot and the leads to identify how the spin-spin interactions are distributed throughout the structure.\\[0pt] [1] L. G. G. V. Dias da Silva, N. P. Sandler, K. Ingersent, and S. E. Ulloa, Phys. Rev. Lett. 97, 096603 (2006).