Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userKondo physics in double quantum dot based Cooper pair splitters
175
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The Andreev transport properties of double quantum dot based Cooper pair splitters with one superconducting and two normal leads are studied theoretically in the Kondo regime. The influence of the superconducting pairing correlations on the local density of states, Andreev transmission coefficient and Cooper pair splitting efficiency is thoroughly analyzed. It is shown that finite superconducting pairing potential quickly suppresses the SU(2) Kondo effect, which can however reemerge for relatively large values of coupling to superconductor. In the SU(4) Kondo regime, a crossover from the SU(4) to the SU(2) Kondo state is found as the coupling to superconductor is enhanced. The analysis is performed by means of the density-matrix numerical renormalization group method.
rate research
Read More
We investigate a tunable two-impurity Kondo system in a strongly correlated carbon nanotube double quantum dot, accessing the full range of charge regimes. In the regime where both dots contain an unpaired electron, the system approaches the two-impurity Kondo model. At zero magnetic field the interdot coupling disrupts the Kondo physics and a local singlet state arises, but we are able to tune the crossover to a Kondo screened phase by application of a magnetic field. All results show good agreement with a numerical renormalization group study of the device.
We calculate the nonequilibrium conductance of a system of two capacitively coupled quantum dots, each one connected to its own pair of conducting leads. The system has been used recently to perform pseudospin spectroscopy by controlling independently the voltages of the four leads. The pseudospin is defined by the orbital occupation of one or the other dot. Starting from the SU(4) symmetric point of spin and pseudospin degeneracy in the Kondo regime, for an odd number of electrons in the system, we show how the conductance through each dot varies as the symmetry is reduced to SU(2) by a pseudo-Zeeman splitting, and as bias voltages are applied to any of the dots. We analize the expected behavior of the system in general, and predict characteristic fingerprint features of the SU(4) to SU(2) crossover that have not been observed so far.
We investigate the Fano-Kondo interplay in an Aharonov-Bohm ring with an embedded non-interacting quantum dot and a Coulomb interacting quantum dot. Using a slave-boson mean-field approximation we diagonalize the Hamiltonian via scattering matrix theory, and derive the conductance in the form of a Fano expression, which depends on the mean field parameters. We predict that in the Kondo regime the magnetic field leads to a gapped energy level spectrum due to hybridisation of the non-interacting QD state and the Kondo state, and can quantum-mechanically alter the electrons path preference. We demonstrate that an abrupt symmetry change in the Fano resonance, as seen experimentally, could be a consequence of an underlying Kondo channel.
Tunneling conductance through two quantum dots, which are connected in series to left and right leads, is calculated by using the numerical renormalization group method. As the hopping between the dots increases from very small value, the following states continuously appear; (i) Kondo singlet state of each dot with its adjacent-site lead, (ii) singlet state between the local spins on the dots, and (iii) double occupancy in the bonding orbital of the two dots. The conductance shows peaks at the transition regions between these states. Especially, the peak at the boundary between (i) and (ii) has the unitarity limit value of $2e^{2}/h$ because of coherent connection through the lead-dot-dot-lead. For the strongly correlated cases, the characteristic energy scale of the coherent peak shows anomalous decrease relating to the quantum critical transition known for the two-impurity Kondo effect. The two dots systems give the new realization of the two-impurity Kondo problem.
The Kondo effect is a key many-body phenomenon in condensed matter physics. It concerns the interaction between a localised spin and free electrons. Discovered in metals containing small amounts of magnetic impurities, it is now a fundamental mechanism in a wide class of correlated electron systems. Control over single, localised spins has become relevant also in fabricated structures due to the rapid developments in nano-electronics. Experiments have already demonstrated artificial realisations of isolated magnetic impurities at metallic surfaces, nanometer-scale magnets, controlled transitions between two-electron singlet and triplet states, and a tunable Kondo effect in semiconductor quantum dots. Here, we report an unexpected Kondo effect realised in a few-electron quantum dot containing singlet and triplet spin states whose energy difference can be tuned with a magnetic field. This effect occurs for an even number of electrons at the degeneracy between singlet and triplet states. The characteristic energy scale is found to be much larger than for the ordinary spin-1/2 case.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
