arXiv subjects

Sam Young Cho

Publications and source records attributed to Sam Young Cho.

46 records · Page 3Linked to original sources

arXiv2003

Quantum Transport and Integrability of the Anderson Model for a Quantum Dot with Multiple Leads

We show that an Anderson Hamiltonian describing a quantum dot connected to multiple leads is integrable. A general expression for the non-linear conductance is obtained by combining the Bethe ansatz exact solution with Landauer-Büttiker theory. In the Kondo regime, a closed form expression is given for the matrix conductance at zero temperature and when all the leads are close to the symmetric point. A bias-induced splitting of the Kondo resonance is possible for three or more leads. Specifically, for $N$ leads, with each at a different chemical potential, there can be $N-1$ Kondo peaks in the conductance.

cond-mat.mes-hall↗

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

Mesoscopic Luttinger Liquid Theory in an Aharonov-Bohm Ring

A careful study on the mesoscopic PC in a Luttinger liquid ring is carried out. It is shown that discreteness plays an important role in calculating the PC caused by the magnetic flux. At zero temperature, the current is shown to be independent of the interaction even when $g=g_2-g_4$ is not zero. The current becomes enhanced at finite temperatures comparing to the non-interacting case, when the parameter g is positive.

cond-mat.str-el↗

arXiv2002

Effects of broken time-reversal symmetry on transmission zeros in the Aharonov-Bohm interferometer

In this paper, we study the behavior of the transmission zeros in the closed Aharonov-Bohm(AB) interferometer with an embedded scattering center in one arm and the corresponding change in the transmission phase when the time-reversal symmetry is broken by magnetic fields. Specifically, we consider three embedded scattering centers: one discrete energy level, a double-barrier well, and a $t$-stub. We find the followings from our model study: (i) The transmission zeros are real when the AB flux is an integer or a half-integer multiple of the flux quantum, and the transmission phase jumps by $π$ at the zeros. (ii) The transmission zeros become complex or are shifted off the real-energy axis when the magnetic AB flux is not an integer or a half-integer multiple of the flux quantum, and the transmission phase evolves continuously. (iii) The distance of the zeros from the real-energy axis or the imaginary part of the transmission zeros is sinusoidal as a function of the magnetic AB phase. We suggest the experimental setup which can test our results.

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↗

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↗

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↗