Small Quantum Ring Research Articles

Many-particle dynamics of bosons and fermions in quasi-one-dimensional flat-band lattices

The difference between boson and fermion dynamics in quasi-one-dimensional lattices is studied with exact simulations of particle motion and by calculating the persistent current in small quantum rings. We consider three different lattices which in the tight binding model exhibit flat bands. The physical realization is considered to be an optical lattice with bosonic or fermionic atoms. The atoms are assumed to interact with a repulsive short range interaction. The different statistics of bosons and fermions causes different dynamics. Spinless fermions are easily trapped in the flat band states due to the Pauli exclusion principle, which prevents them from interacting, while boson are able to push each other out from the flat band states.

Approximate calculation of electronic energy levels of axially symmetric quantum dot and quantum ring by using energy dependent effective mass

Calculations of electronic structures about the semiconductor quantum dot and the semiconductor quantum ring are presented in this paper. To reduce the calculation costs, for the quantum dot and the quantum ring, their simplified axially symmetric shapes are utilized in our analysis. The energy dependent effective mass is taken into account in solving the Schrödinger equations in the single band effective mass approximation. The calculated results show that the energy dependent effective mass should be considered only for relatively small volume quantum dots or small quantum rings. For large size quantum materials, both the energy dependent effective mass and the parabolic effective mass can give the same results. The energy states and the effective masses of the quantum dot and the quantum ring as a function of geometric parameters are also discussed in detail.

Coulomb blockade in an open small ring with strong backscattering

A comparative study of Coulomb blockade oscillations in a small quantum ring with effective radius 100 nm in ordinary tunnelling and anomalous open regimes is performed. We demonstrate that even though there is no tunnelling barrier between the ring and 2D electron sea in this ring, gigantic Coulomb blockade-like oscillations can be observed. Gate voltage, DC bias and temperature dependences of the ring conductance were experimentally studied at temperatures 0.24 – 1.4 K and magnetic fields up to 1.5 T. These studies show the principal differences between Coulomb blockade oscillations in the tunnelling regime and in the open state. The fundamental single-electron period of the oscillations is found to be the same in both regimes. The role of backscattering processes is concluded to be the reason for the existence of strong Coulomb blockade effects in the open state of the ring.

Aharonov–Bohm effect of a quantum ring in the Kondo regime

AbstractWe investigate a small tuneable quantum ring fabricated by direct local oxidation using an atomic force microscope. The device contains very few electrons and is tuned into the Kondo regime. We study this Kondo effect by temperature dependent measurements. At finite bias voltages we observe additional peaks. These vanish with increasing temperature indicating Kondo correlations for these excited states. Additionally, the geometry of our device allows to study Aharonov–Bohm oscillations in the Kondo regime for a device containing less than ten electrons. We observe a modulation of the Kondo effect with a reduced Aharonov–Bohm period explained by electron–electron interaction in our small quantum ring.

Kondo effect in a few-electron quantum ring.

A small quantum ring with less than ten electrons was studied by transport spectroscopy. For strong coupling to the leads a Kondo effect is observed and used to characterize the spin structure of the system in a wide range of magnetic fields. At small magnetic fields Aharonov-Bohm oscillations influenced by Coulomb interaction appear. They exhibit phase jumps by pi at the Coulomb-blockade resonances. Inside Coulomb-blockade valleys the Aharonov-Bohm oscillations can also be studied due to the finite conductance caused by the Kondo effect. Astonishingly, the maxima of the oscillations show linear shifts with increasing magnetic field and gate voltage.

The persistent current in disordered rings

We have calculated the persistent current on small quantum rings taking into account electron-electron interaction and disorder. With the Coulomb interaction two regimes may arise where the suppression of the current by disorder is much smaller than for the case of free electrons. The first regime is the Luttinger liquid and the other one is associated with the fractional 1 N effect [F.V. Kusmartsev, JETP Lett. 60 (1994) 649]. In both cases the main reason preventing the suppression of the persistent current by disorder is spin-charge separation.