Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userUniversal Scaling in Non-equilibrium Transport Through a Single-Channel Kondo Dot
280
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Scaling laws and universality play an important role in our understanding of critical phenomena and the Kondo effect. Here we present measurements of non-equilibrium transport through a single-channel Kondo quantum dot at low temperature and bias. We find that the low-energy Kondo conductance is consistent with universality between temperature and bias and characterized by a quadratic scaling exponent, as expected for the spin-1/2 Kondo effect. The non-equilibrium Kondo transport measurements are well-described by a universal scaling function with two scaling parameters.
rate research
Read More
We study the electronic current through a quantum dot coupled to two superconducting leads which is driven by either a voltage $V$ or temperature $Delta T$ bias. Finite biases beyond the linear response regime are considered. The local two-particle interaction $U$ on the dot is treated using an approximation scheme within the functional renormalization group approach set up in Keldysh-Nambu-space with $U$ being the small parameter. For $V>0$ we compare our renormalization group enhanced results for the dc-component of the current to earlier weak coupling approaches such as the Hartree-Fock approximation and second order perturbation theory in $U$. We show that in parameter regimes in which finite bias driven multiple Andreev reflections prevail small $|U|$ approaches become unreliable for interactions of appreciable strength. In the complementary regime the convergence of the current with respect to numerical parameters becomes an issue - but can eventually be achieved - and interaction effects turn out to be smaller then expected based on earlier results. For $Delta T>0$ we find a surprising increase of the current as a function of the superconducting phase difference in the regime which at $T=0$ becomes the $pi$ (doublet) phase.
We investigate non-equilibrium transport in the absence of spin-flip energy relaxation in a few-electron quantum dot artificial atom. Novel non-equilibrium tunneling processes involving high-spin states which cannot be excited from the ground state because of spin-blockade, and other processes involving more than two charge states are observed. These processes cannot be explained by orthodox Coulomb blockade theory. The absence of effective spin relaxation induces considerable fluctuation of the spin, charge, and total energy of the quantum dot. Although these features are revealed clearly by pulse excitation measurements, they are also observed in conventional dc current characteristics of quantum dots.
We investigate the non-equilibrium transport properties of a disordered molecular nanowire. The nanowire is regarded as a quasi-one-dimensional organic crystal composed of self-assembled molecules. One orbital and a single random energy are assigned to each molecule while the intermolecular coupling does not fluctuate. Consequently, electronic states are expected to be spatially localized. We consider the regime of strong localization, namely, the localization length is smaller than the length of the molecular wire. Electron-vibron interaction, taking place in each single molecule, is also taken into account. We investigate the interplay between disorder and electron-vibron interaction in response to either an applied electric bias or a temperature gradient. To this end, we calculate the electric and heat currents when the nanowire is connected to leads, using the Keldysh non-equilibrium Greens function formalism. At intermediate temperature, scattering by disorder dominates both charge and heat transport. We find that the electron-vibron interaction enhances the effect of the disorder on the transport properties due to the exponential suppression of tunneling.
The resonant-level model represents a paradigmatic quantum system which serves as a basis for many other quantum impurity models. We provide a comprehensive analysis of the non-equilibrium transport near a quantum phase transition in a spinless dissipative resonant-level model, extending earlier work [Phys. Rev. Lett. 102, 216803 (2009)]. A detailed derivation of a rigorous mapping of our system onto an effective Kondo model is presented. A controlled energy-dependent renormalization group approach is applied to compute the non-equilibrium current in the presence of a finite bias voltage V. In the linear response regime V ->0, the system exhibits as a function of the dissipative strength a localized-delocalized quantum transition of the Kosterlitz-Thouless (KT) type. We address fundamental issues of the non-equilibrium transport near the quantum phase transition: Does the bias voltage play the same role as temperature to smear out the transition? What is the scaling of the non-equilibrium conductance near the transition? At finite temperatures, we show that the conductance follows the equilibrium scaling for V< T, while it obeys a distinct non-equilibrium profile for V>T. We furthermore provide new signatures of the transition in the finite-frequency current noise and AC conductance via the recently developed Functional Renormalization Group (FRG) approach. The generalization of our analysis to non-equilibrium transport through a resonant level coupled to two chiral Luttinger-liquid leads, generated by the fractional quantum Hall edge states, is discussed. Our work on dissipative resonant level has direct relevance to the experiments in a quantum dot coupled to resistive environment, such as H. Mebrahtu et al., Nature 488, 61, (2012).
Spin and charge transport through a quantum dot coupled to external nonmagnetic leads is analyzed theoretically in terms of the non-equilibrium Green function formalism based on the equation of motion method. The dot is assumed to be subject to spin and charge bias, and the considerations are focused on the Kondo effect in spin and charge transport. It is shown that the differential spin conductance as a function of spin bias reveals a typical zero-bias Kondo anomaly which becomes split when either magnetic field or charge bias are applied. Significantly different behavior is found for mixed charge/spin conductance. The influence of electron-phonon coupling in the dot on tunneling current as well as on both spin and charge conductance is also analyzed.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
