Seminário do Departamento de Física dos Materiais e Mecânica – FMT
“The Kohn-Sham Anderson system: a hybrid approach for transport in the realistic quantum dots”
Dra. Krissia de Zawadzki - Instituto de Física de São Carlos/USP
Dia: 24 de setembro, segunda-feira, às 15h.
Local: Sala de Seminários José Roberto Leite, Edifício Alessandro Volta (bloco C), IFUSP.
Abstract:
The development of a reliable approach allowing for a realistic description of single-electron transistors (SET) and molecular junctions is a contemporary theoretical challenge. At low temperatures, the transport properties of such quantum dot devices are governed by strong correlations, giving rise to the Kondo physics. This limit is particularly challenging from the theoretical point of view: the ground-state of a Kondo system is characterized by the entanglement between the quantum dot and the free electron gases in the Kondo cloud, a complex state whose final structure is highly sensitive to atomistic details of the materials composing the device. Therefore, an accurate methodology suiting realistic devices is expected to interface a precise band structure calculation and many-body calculation yielding properties in strongly coupled regime. While ab-initio approaches, such as Density-functional Theory (DFT), are the preferred tool at the disposal of condensedmatter theorists interested in the electronic structure of complex materials, the pure DFT route is to be avoided. To date, the few existing approaches for strongly correlated problems have a limited scope of applicability. Previous works based on local and quasi-local approximations for the exchange-correlation functional extracted from the solution of the model Hamiltonians via exact methods, yield only qualitatively descriptions of the low-temperature physical properties of single-electron transistors or molecular junctions. Considering the non-local nature of the ground-state in the Kondo regime, one does not expect to recover experimental realizations of strongly coupled quantum dots by means of local functionals. To tackle this limit, numerical methods, such as implementations of the Renormalization-Group (e.g. NRG and DMRG) offer a reliable framework to diagonalize model Hamiltonians and compute properties along the crossover from the weak to the strongly coupled regime. Nonetheless, in order to perform RG calculations accounting for realistic features of experimental devices (e.g., geometry, band structure and electron-electron interactions in the electron gases) the model parameters must be adjusted conveniently. Motivated by this frustrating dilemma, we propose a novel tool combining the Best ingredients of DFT and RG in a hybrid calculation. Our approach is founded on RG concepts, namely the universality of the zero-bias conductance and the low and high temperature fixed points of the Anderson Hamiltonian. In the present talk, we will present the main ideas underlying our hybrid method and illustrate its application to a relatively simple model: a single-electron transistor modeled by an inhomogeneous Hubbard Hamiltonian. We will show results for the conductance in the limit of low-temperatures and discuss the potential of the new approach to study transport in strongly correlated quantum dots.
