arXiv subjects

Kicheon Kang

Publications and source records attributed to Kicheon Kang.

54 records · Page 3Linked to original sources

arXiv2002

Tunable Molecular Resonances of Double Quantum Dots Embedded in an Aharonov-Bohm Interferometer

We investigate resonant tunneling through molecular states of coupled double quantum dots embedded in an Aharonov-Bohm (AB) interferometer. The conductance through the system consists of two resonances associated with the bonding and the antibonding quantum states. We predict that the two resonances are composed of a Breit-Wigner resonance and a Fano resonance, those widths and Fano factor depending on the AB phase very sensitively. Further, we point out that the bonding properties, such as the covalent and the ionic bonding, can be identified by the AB oscillations.

cond-mat.mes-hall↗

arXiv2002

Magnetic Polarization Currents in Double Quantum Dot Devices

We investigate coherent electron transport through a parallel circuit of two quantum dots, each of which has a single tunable energy level. Electrons tunneling via each dot from the left lead interfere with each other at the right lead. It is shown that due to the quantum interference of tunneling electrons the double quantum dot device is magnetically polarized by coherent circulation of electrons on the closed path through the dots and the leads. Varying the energy level of each dot one can make the magnetic states of the device to be either {\em up-}, {\em non-}, or {\em down-} polarization. It is shown that for experimentally accessible temperatures and applied biases the magnetic polarization currents should be sufficiently large to observe with current nanotechnology.

cond-mat.mes-hall↗

arXiv2002

Spin Fluctuation Induced Dephasing in a Mesoscopic Ring

We investigate the persistent current in a hybrid Aharonov-Bohm ring - quantum dot system coupled to a reservoir which provides spin fluctuations. It is shown that the spin exchange interaction between the quantum dot and the reservoir induces dephasing in the absence of direct charge transfer. We demonstrate an anomalous nature of this spin-fluctuation induced dephasing which tends to enhance the persistent current. We explain our result in terms of the separation of the spin from the charge degree of freedom. The nature of the spin fluctuation induced dephasing is analyzed in detail.

cond-mat.mes-hall↗

arXiv2001

Effect of Charge Fluctuations on the Persistent Current through a Quantum Dot

We study coherent charge transfer between an Aharonov-Bohm ring and a side-attached quantum dot. The charge fluctuation between the two sub-structures is shown to give rise to algebraic suppression of the persistent current circulating the ring as the size of the ring becomes relatively large. The charge fluctuation at resonance provides transition between the diamagnetic and the paramagnetic states. Universal scaling, crossover behavior of the persistent current from a continuous to a discrete energy limit in the ring is also discussed.

cond-mat.mes-hall↗

arXiv2001

Phase-dependent Kondo Resonance in a Quantum Dot Connected to a Mesoscopic Ring

Phase-sensitive transport through a quantum dot coupled to an Aharonov-Bohm ring is analyzed. In this geometry the spectral density of states is directly related to the conductance. It is shown that the Kondo resonance depends on the phase and on the total number of electrons (modulo 4) in the mesoscopic ring. The effect of the discrete level spacing in the ring and of the coupling to the electrical leads is discussed.

cond-mat.mes-hall↗

arXiv2000

Mesoscopic Kondo Effect in an Aharonov-Bohm Ring

An interacting quantum dot inserted in a mesoscopic ring is investigated. A variational ansatz is employed to describe the ground state of the system in the presence of the Aharonov-Bohm flux. It is shown that, for even number of electrons with the energy level spacing smaller than the Kondo temperature, the persistent current has a value similar to that of a perfect ring with the same radius. On the other hand, for a ring with odd number electrons, the persistent current is found to be strongly suppressed compared to that of an ideal ring, which implies the suppression of the Kondo-resonant transmission. Various aspects of the Kondo-assisted persistent current are discussed.

cond-mat.mes-hall↗

arXiv2000

Spin Fluctuation and Persistent Current in a Mesoscopic Ring Coupled to a Quantum Dot

We investigate the persistent current influenced by the spin fluctuations in a mesoscopic ring weakly coupled to a quantum dot. It is shown that the Kondo effect gives rise to some unusual features of the persistent current in the limit where the charge transfer between two subsystems is suppressed. Various aspects of the crossover from a delocalized to a localized dot limit are discussed in relation with the effect of the coherent response of the Kondo cloud to the Aharonov-Bohm flux.

cond-mat.mes-hall↗

arXiv2000

Anti-Kondo resonance in transport through a quantum wire with a side-coupled quantum dot

An interacting quantum dot side-coupled to a perfect quantum wire is studied. Transport through the quantum wire is investigated by using an exact sum rule and the slave-boson mean field treatment. It is shown that the Kondo effect provides a suppression of the transmission due to the destructive interference of the ballistic channel and the Kondo channel. At finite temperatures, anti-resonance behavior is found as a function of the quantum dot level position, which is interpreted as a crossover from the high temperature Kondo phase to the low temperature charge fluctuation phase.

cond-mat.mes-hall↗

arXiv2000

Parity Effect in a mesoscopic superconducting ring

We study a mesoscopic superconducting ring threaded by a magnetic flux when the single particle level spacing is not negligible. It is shown that, for a superconducting ring with even parity, the behavior of persistent current is equivalent to what is expected in a bulk superconducting ring. On the other hand, we find that a ring with odd parity shows anomalous behavior such as fluxoid quantization at half-integral multiples of the flux quantum and paramagnetic response at low temperature. We also discuss how the parity effect in the persistent current disappears as the temperature is raised or as the size of the ring increases.

cond-mat.mes-hall↗

arXiv2000

Experimental evidences of Luttinger liquid behavior in the crossed multi-wall carbon nanotubes

Luttinger liquid behavior was observed in a crossed junction formed with two metallic multi-wall carbon nanotubes whose differential conductance vanished with the power of bias voltage and temperature. With applying constant voltage or current to one of the two carbon nanotubes in a crossed geometry, the electrical transport properties of the other carbon nanotube were affected significantly, implying there exists strong correlation between the carbon nanotubes. Such characteristic features are in good agreement with the theoretical predictions for the crossed two Luttinger liquids.

cond-mat.mes-hall↗

arXiv1999

Photon-Assisted Quasiparticle Transport and Andreev Transport through an Interacting Quantum Dot

Resonant tunneling through a quantum dot coupled to superconducting reservoirs in the presence of time-dependent external voltage has been studied. A general formula of the current is derived based on the nonequilibrium Green's function technique. Using this formula photon-assisted quasiparticle transport has been investigated for the quantum dot connected to superconductors. In addition, resonant Andreev transport through a strongly correlated quantum dot connected to a normal metallic lead and a superconducting lead is studied.

cond-mat.mes-hall↗

arXiv1998

Coherent Transport through a Quantum Dot Embedded in an Aharonov-Bohm Ring

We study the coherent transport in multi-terminal mesoscopic Aharonov-Bohm ring with a quantum dot embedded in an arm. Employing the Friedel sum rule for the effective single-particle levels in the quantum dot, we explain some anomalous features which have been observed in the experiment. We attribute these anomalies to the result of nontrivial quantum interference of the quantum dot with the attached ring. Further, we propose a new feature of conductance oscillations which can be a test for the validity of our model.

cond-mat.mes-hall↗

arXiv1998

A new perturbation treatment applied to the transport through a quantum dot

Resonant tunnelling through an Anderson impurity is investigated by employing a new perturbation scheme at nonequilibrium. This new approach gives the correct weak and strong coupling limit in $U$ by introducing adjustable parameters in the self-energy and imposing self-consistency of the occupation number of the impurity. We have found that the zero-temperature linear response conductance agrees well with that obtained from the exact sum rule. At finite temperature the conductance shows a nonzero minimum at the Kondo valley, as shown in recent experiments. The effects of an applied bias voltage on the single-particle density of states and on the differential conductances are discussed for Kondo and non-Kondo systems.

cond-mat.str-el↗

arXiv1998

Kondo-resonance, Coulomb blockade, and Andreev transport through a quantum dot

We study resonant tunneling through an interacting quantum dot coupled to normal metallic and superconducting leads. We show that large Coulomb interaction gives rise to novel effects in Andreev transport. Adopting an exact relation for the Green's function, we find that at zero temperature, the linear response conductance is enhanced due to Kondo-Andreev resonance in the Kondo limit, while it is suppressed in the empty site limit. In the Coulomb blockaded region, on the other hand, the conductance is reduced more than the corresponding conductance with normal leads because large charging energy suppresses Andreev reflection.

cond-mat.mes-hall↗

arXiv1998

Transport through an Interacting Quantum Dot Coupled to Two Superconducting Leads

We derive a formula for the current through an interacting quantum dot coupled to two supercouducting leads, using the non-equilibrium Green's function formalism. It is shown that the formula takes an especially simple form, when the Andreev reflections in the junctions are negligible because of large Coulomb repulsion in the dot. Our formalism provides a new framework to investigate many-body effects of mesoscopic systems in the presence of the superconducting leads. For an example, we describe the resonant tunneling of quasiparticles in the presence of strong Coulomb repulsion in the dot. Further, we discuss the boson assisted transport. Multiple sharp peaks are found in the current-voltage curve, which originate from the singularity of BCS density of states and the boson assisted tunneling.

cond-mat.mes-hall↗

arXiv1997

Linear Chain of Coupled Quantum Dots

A linearly coupled chain of spin-polarized quantum dots is investigated under the condition that the number of electrons is equal to or less than the number of the dots. The chemical potential of the system, $μ_{N}=E(N)-E(N-1)$, satisfies, $(μ_{N}+μ_{N_{\ell}+2-N)}/2 \approx V+2t (N, N_{\ell}, V, E(N)$ and $t$ are the number of electrons, the number of dots, and the strength of nearest neighbor electron-electron interactions, the total groundstate energy and the hopping integral between two adjacent dots). This property will be reflected in the spacing between the conductance peaks. The electron density structures are determined using a quantum Monte Carlo method. As the number of electrons is varied several correlated structures are found that are commensurate/incommensurate with the periodic dot system. Hartree-Fock theory fails to predict the correct electronic structures of this system because several nearly degenerate solutions exist.

cond-mat.mes-hall↗

arXiv1997

Effect of Quantum Confinement on Electron Tunneling through a Quantum Dot

Employing the Anderson impurity model, we study tunneling properties through an ideal quantum dot near the conductance minima. Considering the Coulomb blockade and the quantum confinement on an equal footing, we have obtained current contributions from various types of tunneling processes; inelastic cotunneling, elastic cotunneling, and resonant tunneling of thermally activated electrons. We have found that the inelastic cotunneling is suppressed in the quantum confinement limit, and thus the conductance near its minima is determined by the elastic cotunneling at low temperature ($k_BT \ll Γ$, $Γ$: dot-reservoir coupling constant), or by the resonant tunneling of single electrons at high temperature ($k_BT \gg Γ$).

cond-mat.mes-hall↗

arXiv1996

The Finite-$U$ Impurity Anderson Model in the presence of an external magnetic field

We have investigated effects of an external magnetic field in the impurity Anderson model with a finite on-site Coulomb repulsion $U$. Large $N_f$ expansion is employed in the slave boson representation, by taking into account $f^0$, $f^1$, and $f^2$ subspaces. To evaluate the vertex function for the ``empty state boson" self-energy, we have devised two approximations which reduce much computational efforts without losing general features of the model. It is found that the Kondo temperature is reduced by the presence of a magnetic field, and that at low field and at low temperature, the field dependence of both the Kondo temperature and the impurity magnetization exhibits a scaling behavior with high accuracy. Further, some interesting features are found in the field dependence of the impurity magnetization at finite temperature, the physical implications of which are discussed in terms of the renormalized Kondo temperature.

cond-mat↗