Mikio Eto
Keio University
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Publication
Featured researches published by Mikio Eto.
Nature | 2000
Satoshi Sasaki; S. De Franceschi; J. M. Elzerman; W. G. van der Wiel; Mikio Eto; S. Tarucha; Leo P. Kouwenhoven
The Kondo effect—a many-body phenomenon in condensed-matter physics involving the interaction between a localized spin and free electrons—was discovered in metals containing small amounts of magnetic impurities, although it is now recognized to be of fundamental importance in a wide class of correlated electron systems. In fabricated structures, the control of single, localized spins is of technological relevance for nanoscale electronics. Experiments have already demonstrated artificial realizations of isolated magnetic impurities at metallic surfaces, nanoscale magnets, controlled transitions between two-electron singlet and triplet states, and a tunable Kondo effect in semiconductor quantum dots. Here we report an unexpected Kondo effect in a few-electron quantum dot containing singlet and triplet spin states, whose energy difference can be tuned with a magnetic field. We observe the effect for an even number of electrons, when the singlet and triplet states are degenerate. The characteristic energy scale is much larger than in the ordinary spin-1/2 case.
Physical Review Letters | 2000
Mikio Eto; Yuli V. Nazarov
We investigate the Kondo effect in a quantum dot with almost degenerate spin-singlet and triplet states for an even number of electrons. We show that the Kondo temperature as a function of the energy difference between the states Delta reaches its maximum around Delta = 0 and decreases with increasing Delta. The Kondo effect is thus enhanced by competition between singlet and triplet states. Our results explain recent experimental findings. We evaluate the linear conductance in the perturbative regime.
Japanese Journal of Applied Physics | 1997
Mikio Eto
The many-body effect on the electronic structures of a few electrons confined in a quantum dot is calculated, under magnetic fields, by the exact diagonalization method. When the Coulomb interaction is comparable to the one-electron level spacings and the magnetic field is not too large, the peak positions of the Coulomb oscillation reflect a shell structure of the one-electron levels, which is in semi-quantitative agreement with experimental results [Tarucha et al.: Phys. Rev. Lett. 77 (1996) 3613]. Under strong magnetic fields, the correlation effect results in transitions of the ground state. These transitions can be observed as cusps of the magnetic-field dependence of the peak positions, in the presence of the Zeeman effect.
Journal of the Physical Society of Japan | 1990
Hiroshi Kamimura; Mikio Eto
By the first-principles variational calculations we show that, with the increase of Sr concentration, the ground state of CuO 6 octahedron in La 2- x Sr x CuO 4 changes from 1 A 1 g to 3 B 1 g near the observed onset concentration of superconductivity while the ground state of the CuO 4 cluster in Nd 2- x Ce x CuO 4 is always 3 B 1 g in the presence of dopant electrons. Based on this result, two kinds of phase diagrams are predicted for hole- and electron-doped superconductors. These results support the spin polaron mechanism proposed by Kamimura et al .
Journal of the Physical Society of Japan | 1998
Tomosuke Aono; Mikio Eto; Kiyoshi Kawamura
The conductance through two quantum dots connected in series is studied below the Kondo temperature, based on the slave boson formalism of the Anderson model. The transport properties are characterized by the ratio of the magnitude of the tunneling coupling between two dots to the width of the level broadening. When the ratio is less than unity, the Kondo resonant states are formed between each dot and an external lead, and the conductance is determined by the hopping between the two resonant states. When the ratio is larger than unity, these Kondo resonances are split into the bonding and antibonding peaks, which are located below and above the Fermi level in the leads, respectively, for low gate voltages. As a result, the conductance is suppressed. The conductance has a maximum of 2e 2 /h when the bonding peak is matched with the Fermi level by controlling the gate voltage.
Journal of the Physical Society of Japan | 2005
Mikio Eto; Tetsuya Hayashi; Yuji Kurotani
Semiconductor point contacts can be a useful tool for producing spin-polarized currents in the presence of spin–orbit (SO) interaction. Neither magnetic fields nor magnetic materials are required. ...
Physical Review B | 2006
Akiko Ueda; Mikio Eto
We theoretically study the resonant tunneling and Fano resonance in quantum dots with electron-phonon (e-ph) interaction. We examine the bias-voltage
Journal of the Physical Society of Japan | 1991
Mikio Eto; Hiroshi Kamimura
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Physical Review B | 2009
Hiroki Morishita; L. S. Vlasenko; H. Tanaka; K. Semba; Kentarou Sawano; Yasuhiro Shiraki; Mikio Eto; Kohei M. Itoh
dependence of the decoherence, using the Keldysh Green function method and perturbation with respect to the e-ph interaction. With optical phonons of energy
Physical Review B | 2001
Mikio Eto; Yuli V. Nazarov
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