Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMagnetic field induced two-channel Kondo effect in multiple quantum dots
357
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We study the possibility to observe the two channel Kondo physics in multiple quantum dot heterostructures in the presence of magnetic field. We show that a fine tuning of the coupling parameters of the system and an external magnetic field may stabilize the two channel Kondo critical point. We make predictions for behavior of the scaling of the differential conductance in the vicinity of the quantum critical point, as a function of magnetic field, temperature and source-drain potential.
rate research
Read More
Over-screened Kondo effect is feasible in carbon nanotube quantum dot junction hosting a spin $tfrac{1}{2}$ atom with single $s$-wave valence electron (e.g Au). The idea is to use the two valleys as two symmetry protected flavor quantum numbers $xi={bf K}, {bf K}$. Perturbative RG analysis exposes the finite weak-coupling two-channel fixed point, where the Kondo temperature is estimated to be around $0.5div5$~K. Remarkably, occurrence of two different scaling regimes implies a non-monotonic dependence of the conductance as function of temperature.
Recent experiments have measured the signatures of the Kondo effect in the zero-field thermopower of strongly correlated quantum dots [Svilans {em et al.,} Phys. Rev. Lett. {bf 121}, 206801 (2018); Dutta {em et al.,} Nano Lett. {bf 19}, 506 (2019)]. They confirm the predicted Kondo-induced sign change in the thermopower, upon increasing the temperature through a gate-voltage dependent value $T_{1}gtrsim T_{rm K}$, where $T_{rm K}$ is the Kondo temperature. Here, we use the numerical renormalization group (NRG) method to investigate the effect of a finite magnetic field $B$ on the thermopower of such quantum dots. We show that, for fields $B$ exceeding a gate-voltage dependent value $B_{0}$, an additional sign change takes place in the Kondo regime at a temperature $T_{0}(Bgeq B_{0})>0$ with $T_0<T_1$. The field $B_{0}$ is comparable to, but larger than, the field $B_{c}$ at which the zero-temperature spectral function splits in a magnetic field. The validity of the NRG results for $B_{0}$ are checked by comparison with asymptotically exact higher-order Fermi-liquid calculations [Oguri {em et al.,} Phys. Rev. B {bf 97}, 035435 (2018)]. Our calculations clarify the field-dependent signatures of the Kondo effect in the thermopower of Kondo-correlated quantum dots and explain the recently measured trends in the $B$-field dependence of the thermoelectric response of such systems [Svilans {em et al.,} Phys. Rev. Lett. {bf 121}, 206801 (2018)].
Signatures of the Kondo effect in the electrical conductance of strongly correlated quantum dots are well understood both experimentally and theoretically, while those in the thermopower have been the subject of recent interest. Here, we extend theoretical work [T. A. Costi, Phys. Rev. B {bf 100}, 161106(R) (2019)] on the field-dependent thermopower of such systems, and carry out calculations in order to address a recent experiment on the field dependent thermoelectric response of Kondo-correlated quantum dots [A. Svilans {em et al.,} Phys. Rev. Lett. {bf 121}, 206801 (2018)]. In addition to the sign changes in the thermopower at temperatures $T_1(B)$ and $T_2(B)$ (present also for $B=0$) in the Kondo regime, an additional sign change was found [T. A. Costi, Phys. Rev. B {bf 100}, 161106(R) (2019)] at a temperature $T_0(B)<T_1(B)<T_2(B)$ for fields exceeding a gate-voltage dependent value $B_0$, where $B_0$ is comparable to, but larger, than the field $B_c$ at which the Kondo resonance splits. We describe the evolution of the Kondo-induced sign changes in the thermopower at temperatures $T_0(B),T_1(B)$ and $T_2(B)$ with magnetic field and gate voltage from the Kondo regime to the mixed valence and empty orbital regimes. By carrying out detailed NRG calculations for the above quantities we address the recent experiment by A. Svilans {em et al.,} Phys. Rev. Lett. {bf 121}, 206801 (2018), which measures the field-dependent thermoelectric response of InAs quantum dots exhibiting the Kondo effect, finding good agreement for the overall trends in the measured field- and temperature-dependent thermoelectric response as a function of gate voltage.
We investigate the many-body effects of a magnetic adatom in ferromagnetic graphene by using the numerical renormalization group method. The nontrivial band dispersion of ferromagnetic graphene gives rise to interesting Kondo physics different from that in conventional ferromagnetic materials. For a half-filled impurity in undoped graphene, the presence of ferromagnetism can bring forth Kondo correlations, yielding two kink structures in the local spectral function near the Fermi energy. When the spin splitting of local occupations is compensated by an external magnetic field, the two Kondo kinks merge into a full Kondo resonance characterizing the fully screened ground state. Strikingly, we find the resulting Kondo temperature monotonically increases with the spin polarization of Dirac electrons, which violates the common sense that ferromagnetic bands are usually detrimental to Kondo correlations. Doped ferromagnetic graphene can behave as half metals, where its density of states at the Fermi energy linearly vanishes for one spin direction but keeps finite for the opposite direction. In this regime, we demonstrate an abnormal Kondo resonance that occurs in the first spin direction, while completely absent in the other one.
We study the single-impurity Anderson model out of equilibrium under the influence of a bias voltage $phi$ and a magnetic field $B$. We investigate the interplay between the shift ($omega_B$) of the Kondo peak in the spin-resolved density of states (DOS) and the one ($phi_B$) of the conductance anomaly. In agreement with experiments and previous theoretical calculations we find that, while the latter displays a rather linear behavior with an almost constant slope as a function of $B$ down to the Kondo scale, the DOS shift first features a slower increase reaching the same behavior as $phi_B$ only for $|g| mu_B B gg k_B T_K$. Our auxiliary master equation approach yields highly accurate nonequilibrium results for the DOS and for the conductance all the way from within the Kondo up to the charge fluctuation regime, showing excellent agreement with a recently introduced scheme based on a combination of numerical renormalization group with time-dependent density matrix renormalization group.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
