Photocurrent in an array of quantum dots based on Rice-Mele model

The photocurrent, known as the shift current, is generated when the light irradiates homogeneous materials without the space inversion symmetry. This could yield a photovoltaic effect which does not require heterostructures. Recently, the shift current was theoretically proposed using the one-dimensional (1D) Rice-Mele model [1]. In this work, we investigate an array of quantum dots (QDs) described by the Rice-Mele model. We also study a ladder model to include the two-dimensionality and to elucidate the role of symmetry.

The Rice-Mele model considered here has the staggered on-site energies ±ε₀ and hopping parameters t±B/2, which give rise to the broken inversion symmetry. First, we consider a double QD system as a minimal model and show that the photocurrent flows in a specific direction without the bias voltage, using the non-equilibrium Green function method. Then, the photocurrent is examined in longer arrays of QDs to elucidate the finite size effect.

Second, we study the ladder model of the QDs, in which two 1D arrays are interconnected with the hopping parameter Δ. By changing the model parameters, we examine both systems in the presence and absence of the space inversion symmetry. The photocurrent decreases with increasing Δ in the presence of the symmetry, whereas the photocurrent increases with Δ in its absence. This suggests the importance of the broken inversion symmetry for the photocurrent generation even in the finite systems.

[1] H. Ishizuka and N. Nagaosa, New J. Phys. 19, 3, 033015 (2017).