Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSpin filtering and thermopower in star coupled quantum dot devices
62
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We analyze the linear thermoelectric transport properties of devices with three quantum dots in a star configuration. A central quantum dot is tunnel-coupled to source and drain electrodes and to two additional quantum dots. For a wide range of parameters, in the absence of an external magnetic field, the system is a singular Fermi liquid with a non-analytic behavior of the electric transport properties at low energies. The singular behavior is associated with the development of a ferromagnetic or an underscreened Kondo effect, depending on the parameter regime. A magnetic field drives the system into a regular Fermi liquid regime and leads to a large peak ($sim k_B/|e|$) in the spin thermopower as a function of the temperature, and to a $sim 100%$ spin polarized current for a wide range of parameters due to interference effects. We find a qualitatively equivalent behavior for systems with a larger number of side coupled quantum dots, with the maximum value of the spin thermopower decreasing as the number of side-coupled quantum dots increases.
rate research
Read More
The zero-temperature magnetic field-dependent conductance of electrons through a one-dimensional non-interacting tight-binding chain with an interacting {it side} dot is reviewed and analized further. When the number of electrons in the dot is odd, and the Kondo effect sets in at the impurity site, the conductance develops a wide minimum as a function of the gate voltage, being zero at the unitary limit. Application of a magnetic field progressively destroys the Kondo effect and, accordingly, the conductance develops pairs of dips separated by $U$, where $U$ is the repulsion between two electrons at the impurity site. Each one of the two dips in the conductance corresponds to a perfect spin polarized transmission, opening the possibility for an optimum spin filter. The results are discussed in terms of Fano resonances between two interfering transmission channels, applied to recent experimental results, and compared with results corresponding to the standard substitutional configuration, where the dot is at the central site of the non-interacting chain.
We study a symmetrical double quantum dot (DD) system with strong capacitive inter-dot coupling using renormalization group methods. The dots are attached to separate leads, and there can be a weak tunneling between them. In the regime where there is a single electron on the DD the low-energy behavior is characterized by an SU(4)-symmetric Fermi liquid theory with entangled spin and charge Kondo correlations and a phase shift $pi/4$. Application of an external magnetic field gives rise to a large magneto-conductance and a crossover to a purely charge Kondo state in the charge sector with SU(2) symmetry. In a four lead setup we find perfectly spin polarized transmission.
We study the thermoelectric response of a device containing a pair of helical edge states contacted at the same temperature $T$ and chemical potential $mu$ and connected to an external reservoir, with different chemical potential and temperature, through a side quantum dot. Different operational modes can be induced by applying a magnetic field $B$ and a gate voltage $V_g$ at the quantum dot. At finite $B$, the quantum dot acts simultaneously as a charge and a spin filter. Charge and spin currents are induced, not only through the quantum dot, but also along the edge states. We focus on linear response and analyze the regimes, which we identify as charge heat engines or refrigerator, spin heat engine and spin refrigerator.
We demonstrate that hexagonal graphene nanoflakes with zigzag edges display quantum interference (QI) patterns analogous to benzene molecular junctions. In contrast with graphene sheets, these nanoflakes also host magnetism. The cooperative effect of QI and magnetism enables spin-dependent quantum interference effects that result in a nearly complete spin polarization of the current, and holds a huge potential for spintronic applications. We understand the origin of QI in terms of symmetry arguments, which show the robustness and generality of the effect. This also allows us to devise a concrete protocol for the electrostatic control of the spin polarization of the current by breaking the sublattice symmetry of graphene, by deposition on hexagonal boron nitride, paving the way to switchable spin-filters. Such a system benefits of all the extraordinary conduction properties of graphene, and at the same time, it does not require any external magnetic field to select the spin polarization, as magnetism emerges spontaneously at the edges of the nanoflake.
Silicon quantum dots are attractive candidates for the development of scalable, spin-based qubits. Pauli spin blockade in double quantum dots provides an efficient, temperature independent mechanism for qubit readout. Here we report on transport experiments in double gate nanowire transistors issued from a CMOS process on 300 mm silicon-on-insulator wafers. At low temperature the devices behave as two few-electron quantum dots in series. We observe signatures of Pauli spin blockade with a singlet-triplet splitting ranging from 0.3 to 1.3 meV. Magneto-transport measurements show that transitions which conserve spin are shown to be magnetic-field independent up to B = 6 T.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
