Tomoko Kita

Thermopower of multiorbital kondo effect via single quantum dot system at finite temperatures

We study the thermopower and some related transport quantities due to the orbital Kondo effect in a single quantum dot system with a finite value of Coulomb repulsion by means of the noncrossing approximation applied to the multiorbital impurity Anderson model. It is elucidated how the asymmetry of the renormalized tunneling resonance due to the two-orbital Kondo effect causes characteristic behavior of the thermopower at finite temperatures under gate-voltage and magnetic-field control, which is compared with that of the ordinary spin Kondo effect.

Resolution of pulmonary arteriovenous fistula by redirection of hepatic venous blood

We report an 8-year-old girl whose unilateral pulmonary arteriovenous fistula (PAVF) disappeared after we redirected hepatic venous blood to the affected lung. This case provides strong evidence that formation of a PAVF depends only on the presence or absence of hepatic venous blood in the pulmonary circulation.

Cellular Dynamical Mean Field Study on Two-Orbital Hubbard Model with Different Bandwidths

We study spin and orbital correlations in the two-orbital Hubbard model with different bandwidths at quarter filling by means of the cellular dynamical mean field theory combined with the noncrossing approximation. We show that the ferromagnetic-antiferro-orbital insulating state is stabilized by the Hunds coupling in the system with the same bandwidths and the antiferromagnetic-ferro-orbital insulating state appears when the difference of bandwidths is quite large. We find that the competition between the two states occurs in the intermediate region and this competition gives rise to the strongly renormalized metallic state.

Spatial fluctuations of spin and orbital nature in the two-orbital Hubbard model

We investigate the quasiparticle dynamics in the two-orbital Hubbard model on the square lattice at quarter filling by means of the cellular dynamical mean-field theory. We show that the Fermi-liquid state is stabilized up to the large Hubbard interactions in the symmetric case without Hunds coupling, and find the heavy quasiparticles around the metal-insulator boundary. It is elucidated that Hunds coupling enhances the antiferro-orbital correlations, which give rise to the pseudogap behavior in the single-particle excitations. We also find the nonmonotonic temperature dependence in the quasiparticle dynamics for intermediate strength of Hunds coupling, and clarify that it is caused by the competition between the Fermi-liquid formation and the antiferro-orbital fluctuations.

Two-orbital Kondo effect in a quantum dot coupled to ferromagnetic leads

We study the Kondo effect of a two-orbital vertical quantum dot (QD) coupled to two ferromagnetic leads by employing an equation of motion method. When the ferromagnetic leads are coupled with parallel spin polarization, we find three peaks in the single-particle excitation spectra. The middle one is the Kondo resonance caused by the orbital degrees of freedom. In magnetic fields, the Kondo effect vanishes. However, at a certain magnetic field new two-fold degenerate states arise and the Kondo effect emerges there. In contrast, when the ferromagnetic leads are coupled with antiparallel spin polarization, the Kondo effect caused by the spin (orbital) degrees of freedom survives (is suppressed) in magnetic fields. We investigate the field dependence of the conductance in the parallel and antiparallel spin polarizations of the leads and find that the conductance changes noticeably in magnetic fields.

Spatial fluctuations of spin and orbital in two-orbital Hubbard model: cluster dynamical mean field study

We investigate the single-particle dynamics and magnetic properties in the two-orbital Hubbard model on the square lattice at quarter filling by using a cluster extension of dynamical mean field theory. We find that the Fermi-liquid state is stabilized up to the large intra- and inter-orbital interactions in the symmetric case without Hunds coupling. It is clarified that the Hunds coupling enhances the antiferro-orbital fluctuations, which gives rise to the pseudo gap behavior in the single-particle excitations. We also find that the Hunds coupling with intermediate strength causes the competition between the Fermi-liquid formation and the antiferro-orbital fluctuations, resulting in the nonmonotonous temperature dependence in the single-particle dynamics.

Three-Orbital Kondo Effect in Single Quantum Dot System with Plural Electrons

We study the Kondo effect and related transport properties in orbitally degenerate vertical quantum dot systems with plural electrons. Applying the non-crossing approximation to the three-orbital Anderson impurity model with the finite Coulomb interaction and Hund-coupling, we investigate the magnetic-field dependence of the conductance and thermopower. We also introduce an additional orbital splitting to take account of the realistic many-body effect in the vertical quantum dot system. It is clarified how the three-orbital Kondo effect influences the transport properties via the modulation of the Kondo temperature and unitary limit of transport quantities due to the change of the symmetry in the system.

Thermopower of Kondo effect in single quantum dot systems with orbital at finite temperatures

We investigate the thermopower due to the orbital Kondo effect in a single quantum dot system by means of the noncrossing approximation. It is elucidated how the asymmetry of tunneling resonance due to the orbital Kondo effect affects the thermopower under gate-voltage and magnetic-field control.

Living-related lobar transplantation and simultaneous atrial septal defect closure in a young patient with irreversible pulmonary hypertension: a case report

A 6-year-old boy was diagnosed as having atrial septal defect with oversystemic pulmonary hypertension, and gradually developed hypoxia and heart failure. At the age of 11, living-related bilateral lobar lung transplantation from his parents was indicated, because of his critical condition. The estimated forced vital capacity calculated by the donors’ lower lobes was 104% of his age. The operation was carried out with simultaneous closure of the atrial septal defect under full cardiopulmonary bypass. The postoperative course was complicated with pulmonary edema and phrenic nerve palsy, which were eventually resolved. Six months after surgery he was free from heart failure and rehabilitating at home without oxygen. The final diagnosis was primary pulmonary hypertension with atrial septal defect. Living-related bilateral lobar lung transplantation with simultaneous intracardiac repair may be an optional strategy for children with Eisenmenger syndrome or primary pulmonary hypertension with intracardiac defect when cadaveric transplantation is not possible.

Spatial fluctuations in two-orbital Hubbard model

We study spin and orbital correlations in the two-orbital Hubbard model with the different bandwidths at quarter filling by means of the cellular dynamical mean field theory combined with the noncrossing approximation. We demonstrate that the ferromagnetic-antiferro-orbital insulating state is stabilized in the system with the same bandwidth and the antiferromagnetic-ferro-orbital insulating state appears when the difference of the bandwidth is quite large. In the intermediate region, we find that the competition between the two states occurs and this competition gives rise to the heavy Fermi-liquid metallic state.