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Register a new userTransport through a quantum dot with two parallel Luttinger liquid leads
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We study transport through a quantum dot side-coupled to two parallel Luttinger liquid leads in the presence of a Coulombic dot-lead interaction. This geometry enables an exact treatment of the inter-lead Coulomb interactions. We find that for dots symmetrically disposed between the two leads the correlation of charge fluctuations between the two leads can lead to an enhancement of the current at the Coulomb-blockade edge and even to a negative differential conductance. Moving the dot off center or separating the wires further converts the enhancement to a suppression.
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Electron transport properties in a parallel double-quantum-dot structure with three-terminals are theoretically studied. By introducing a local Rashba spin-orbit coupling, we find that an incident electron from one terminal can select a specific terminal to depart from the quantum dots according to its spin state. As a result, spin polarization and spin separation can be simultaneously realized in this structure. And spin polarizations in different terminals can be inverted by tuning the structure parameters. The underlying quantum interference that gives rise to such a result is analyzed in the language of Feynman paths for the electron transmission.
We study theoretically the transport through a single impurity in a one-channel Luttinger liquid coupled to a dissipative (ohmic) bath . For non-zero dissipation $eta$ the weak link is always a relevant perturbation which suppresses transport strongly. At zero temperature the current voltage relation of the link is $Isim exp(-E_0/eV)$ where $E_0simeta/kappa$ and $kappa$ denotes the compressibility. At non-zero temperature $T$ the linear conductance is proportional to $exp(-sqrt{{cal C}E_0/k_BT})$. The decay of Friedel oscillation saturates for distance larger than $L_{eta}sim 1/eta $ from the impurity.
A correct general formula for the spin current through an interacting quantum dot coupled to ferromagnetic leads with magnetization at an arbitrary angle $theta$ is derived within the framework of the Keldysh formalism. Under asymmetric conditions, the spin current component J_{z} may change sign for $0<theta<pi$. It is shown that the spin current and spin tunneling magnetoresistance exhibit different angle dependence in the free and Coulomb blockade regimes. In the latter case, the competition of spin precession and the spin-valve effect could lead to an anomaly in the angle dependence of the spin current.
We have fabricated a lateral double barrier magnetic tunnel junction (MTJ) which consists of a single self-assembled InAs quantum dot (QD) with ferromagnetic Co leads. The MTJ shows clear hysteretic tunnel magnetoresistance (TMR) effect, which is evidence for spin transport through a single semiconductor QD. The TMR ratio and the curve shapes are varied by changing the gate voltage.
The Tomonaga-Luttinger liquid (TLL) concept is believed to generically describe the strongly-correlated physics of one-dimensional systems at low temperatures. A hallmark signature in 1D conductors is the quantum phase transition between metallic and insulating states induced by a single impurity. However, this transition impedes experimental explorations of real-world TLLs. Furthermore, its theoretical treatment, explaining the universal energy rescaling of the conductance at low temperatures, has so far been achieved exactly only for specific interaction strengths. Quantum simulation can provide a powerful workaround. Here, a hybrid metal-semiconductor dissipative quantum circuit is shown to implement the analogue of a TLL of adjustable electronic interactions comprising a single, fully tunable scattering impurity. Measurements reveal the renormalization group `beta-function for the conductance that completely determines the TLL universal crossover to an insulating state upon cooling. Moreover, the characteristic scaling energy locating at a given temperature the position within this conductance renormalization flow is established over nine decades versus circuit parameters, and the out-of-equilibrium regime is explored. With the quantum simulator quality demonstrated from the precise parameter-free validation of existing and novel TLL predictions, quantum simulation is achieved in a strong sense, by elucidating interaction regimes which resist theoretical solutions.
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