The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
Alexander L. Chudnovskiy - One of the best experts on this subject based on the ideXlab platform.
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From SU(4) to SU(2) Kondo Effect in a double quantum dot
Physica E-low-dimensional Systems & Nanostructures, 2006Co-Authors: Alexander L. ChudnovskiyAbstract:Abstract We consider the spin and orbital Kondo Effect in a parallel arrangement of two strongly electrostatically coupled quantum dots. Increasing the exchange of electrons between the dots through the attached leads induces a transition between the SU(4) spin- and orbital Kondo Effect and SU(2) spin Kondo Effect. Being the same for the SU(4) and SU(2) symmetry points, the Kondo temperature drops slightly in the intermediate regime. Experimentally, two kinds of Kondo Effects can be discriminated by the sensitivity to the suppression of the spin Kondo Effect by Zeeman field. The dependence of the Kondo temperature on Zeeman field and the strength of electronic exchange mediated by the leads is analyzed in detail.
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SU(4) vs. SU(2) Kondo Effect in double quantum dot
Europhysics Letters (EPL), 2005Co-Authors: Alexander L. ChudnovskiyAbstract:We consider the spin and orbital Kondo Effect in a parallel arrangement of two strongly electrostatically coupled quantum dots. Increasing the exchange of electrons between the dots through the attached leads induces a transition between the SU(4) spin and orbital Kondo Effect and SU(2) spin Kondo Effect. Being the same for the SU(4) and SU(2) symmetry points, the Kondo temperature drops slightly in the intermediate regime. Experimentally, two kinds of Kondo Effects can be discriminated by the sensitivity to the suppression of the spin Kondo Effect by Zeeman field. The dependence of the Kondo temperature on Zeeman field and the strength of electronic exchange mediated by the leads is analyzed in detail.
Robert Joynt - One of the best experts on this subject based on the ideXlab platform.
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Spin-valley Kondo Effect in multielectron Si quantum dots
Physical Review B, 2007Co-Authors: Shiue-yuan Shiau, Robert JoyntAbstract:We study the spin-valley Kondo Effect of a silicon quantum dot occupied by $\mathcal{N}$ electrons, with $\mathcal{N}$ up to 4. We show that the Kondo resonance appears in the $\mathcal{N}=1,2,3$ Coulomb blockade regimes, but not in the $\mathcal{N}=4$ one, in contrast to the spin-$1∕2$ Kondo Effect, which only occurs at $\mathcal{N}=\text{odd}$. Assuming large orbital level spacings, the energy states of the dot can be simply characterized by fourfold spin-valley degrees of freedom. The density of states (DOS) is obtained as a function of temperature and applied magnetic field using a finite-$U$ equation-of-motion approach. The structure in the DOS can be detected in transport experiments. The Kondo resonance is split by the Zeeman splitting and valley splitting for double- and triple-electron Si dots, in a similar fashion to single-electron ones. The peak structure and splitting patterns are much richer for the spin-valley Kondo Effect than for the pure spin Kondo Effect.
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Valley Kondo Effect in silicon quantum dots
Physical Review B, 2007Co-Authors: Shiue-yuan Shiau, Sucismita Chutia, Robert JoyntAbstract:Recent progress in the fabrication of quantum dots using silicon has opened the prospect of observing the Kondo Effect associated with a valley degree of freedom. We compute the dot density of states using an Anderson model with infinite Coulomb interaction $U$, whose structure mimics the nonlinear conductance through a dot. The density of states is obtained as a function of temperature and applied magnetic field in the Kondo regime using an equation-of-motion approach. We show that there is a very complex peak structure near the Fermi energy, with several signatures that distinguish this spin-valley Kondo Effect from the usual spin Kondo Effect seen in GaAs dots. We also show that the valley index is generally not conserved when electrons tunnel into a silicon dot, though the extent of this nonconservation is expected to be sample dependent. We identify features of the conductance that should enable experimenters to understand the interplay of Zeeman splitting and valley splitting, as well as the dependence of tunneling on the valley degree of freedom.
Norio Kawakami - One of the best experts on this subject based on the ideXlab platform.
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Laser-Induced Kondo Effect in Ultracold Alkaline-Earth Fermions.
Physical review letters, 2015Co-Authors: Masaya Nakagawa, Norio KawakamiAbstract:We demonstrate that laser excitations can coherently induce a novel Kondo Effect in ultracold atoms in optical lattices. Using a model of alkaline-earth fermions with two orbitals, it is shown that the optically coupled two internal states are dynamically entangled to form the Kondo-singlet state, overcoming the heating Effect due to the irradiation. Furthermore, a lack of SU(N) symmetry in the optical coupling provides a peculiar feature in the Kondo Effect, which results in spin-selective renormalization of Effective masses. We also discuss the Effects of interorbital exchange interactions, and reveal that they induce novel crossover or reentrant behavior of the Kondo Effect owing to control of the coupling anisotropy. The laser-induced Kondo Effect is highly controllable by tuning the laser strength and the frequency, and thus offers a versatile platform to study the Kondo physics using ultracold atoms.
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Thermopower, figure of merit, quantum dot, Kondo Effect, orbital degrees of freedom
arXiv: Mesoscale and Nanoscale Physics, 2007Co-Authors: Rui Sakano, Tomoko Kita, Norio KawakamiAbstract: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.
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Thermopower due to Kondo Effect in Quantum Dot Systems with Orbitals
AIP Conference Proceedings, 2007Co-Authors: Rui Sakano, Norio KawakamiAbstract:We study the thermopower due to the orbital Kondo Effect in single quantum dot systems by exploiting the Bethe ansatz solution of the Anderson impurity model. It is elucidated how the orbital splittings induced by external fields affect the thermopower of the orbital Kondo Effect.
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Conductance via the multiorbital Kondo Effect in single quantum dots
Physical Review B, 2006Co-Authors: Rui Sakano, Norio KawakamiAbstract:We study the Kondo Effect in a single quantum dot system with two or three orbitals by using the Bethe-ansatz exact solution at zero temperature and the non-crossing approximation at finite temperatures. For the two-orbital Kondo Effect, the conductance is shown to be constant at absolute zero in any magnetic fields, but decrease monotonically with increasing fields at finite temperatures. In the case with more orbitals, the conductance increases at absolute zero, while it features a maximum structure as a function of the magnetic field at finite temperatures. We discuss how these characteristic transport properties come from the multi orbital Kondo Effect in magnetic fields.
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Kondo Effect in multiple-dot systems
Physical Review B, 2005Co-Authors: Rui Sakano, Norio KawakamiAbstract:We study the Kondo Effect in multiple-dot systems for which the inter- as well as intra-dot Coulomb repulsions are strong, and the inter-dot tunneling is small. The application of the WardTakahashi identity to the inter-dot dynamical susceptibility enables us to analytically calculate the conductance for a double-dot system by using the Bethe-ansatz exact solution of the SU(4) impurity Anderson model. It is clarified how the inter-dot Kondo Effect enhances or suppresses the conductance under the control of the gate voltage and the magnetic field. We then extend our analysis to multiple-dot systems including more than two dots, and discuss their characteristic transport properties by taking a triple-dot system as an example.
Sho Ozaki - One of the best experts on this subject based on the ideXlab platform.
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Conformal field theory analysis of the QCD Kondo Effect
Physical Review D, 2019Co-Authors: Taro Kimura, Sho OzakiAbstract:We study nonperturbative aspects of the QCD Kondo Effect, which has been recently proposed for the finite density and strong magnetic field systems, using conformal field theory describing the low-energy physics near the IR fixed point. We clarify the symmetry class of the QCD Kondo Effect for both the finite density and magnetic field systems and show how the IR fixed point is nonperturbatively characterized by the boundary condition, which incorporates the impurity Effect in the Kondo problem. We also obtain the low-temperature behavior of several quantities of the QCD Kondo Effect in the vicinity of the IR fixed point based on the conformal field theory analysis.
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Magnetically induced QCD Kondo Effect
Physical Review D, 2016Co-Authors: Sho Ozaki, Kazunori Itakura, Yoshio KuramotoAbstract:The "QCD Kondo Effect" stems from the color exchange interaction in QCD with non-Abelian property, and can be realized in a high-density quark matter containing heavy-quark impurities. We propose a novel type of the QCD Kondo Effect induced by a strong magnetic field. In addition to the fact that the magnetic field does not affect the color degrees of freedom, two properties caused by the Landau quantization in a strong magnetic field are essential for the "magnetically induced QCD Kondo Effect"; (1) dimensional reduction to 1+1-dimensions, and (2) finiteness of the density of states for lowest energy quarks. We demonstrate that, in a strong magnetic field $B$, the scattering amplitude of a massless quark off a heavy quark impurity indeed shows a characteristic behavior of the Kondo Effect. The resulting Kondo scale is estimated as $\Lambda_{\rm K} \simeq \sqrt{e_qB}\ \alpha_{s}^{1/3} {\rm{exp}}\{-{4}\pi/N_{c} \alpha_{s} {\rm{log}}( 4 \pi/\alpha_{s}) \}$ where $\alpha_{s}$ and $N_c$ are the fine structure constant of strong interaction and the number of colors in QCD, and $e_q$ is the electric charge of light quarks.
Leo P. Kouwenhoven - One of the best experts on this subject based on the ideXlab platform.
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Orbital Kondo Effect in carbon nanotubes
Nature, 2005Co-Authors: Pablo Jarillo-herrero, Leo P. Kouwenhoven, Jing Kong, Herre S. J. Van Der Zant, Cees Dekker, Silvano De FranceschiAbstract:Progress in the fabrication of nanometre-scale electronic devices is opening new opportunities to uncover deeper aspects of the Kondo Effect1—a characteristic phenomenon in the physics of strongly correlated electrons. Artificial single-impurity Kondo systems have been realized in various nanostructures, including semiconductor quantum dots2,3,4, carbon nanotubes5,6 and individual molecules7,8. The Kondo Effect is usually regarded as a spin-related phenomenon, namely the coherent exchange of the spin between a localized state and a Fermi sea of delocalized electrons. In principle, however, the role of the spin could be replaced by other degrees of freedom, such as an orbital quantum number9,10. Here we show that the unique electronic structure of carbon nanotubes enables the observation of a purely orbital Kondo Effect. We use a magnetic field to tune spin-polarized states into orbital degeneracy and conclude that the orbital quantum number is conserved during tunnelling. When orbital and spin degeneracies are present simultaneously, we observe a strongly enhanced Kondo Effect, with a multiple splitting of the Kondo resonance at finite field and predicted to obey a so-called SU(4) symmetry.
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Revival of the Kondo Effect
arXiv: Mesoscale and Nanoscale Physics, 2001Co-Authors: Leo P. Kouwenhoven, Leonid GlazmanAbstract:This is a popular review of some recent investigations of the Kondo Effect in a variety of mesoscopic systems. After a brief introduction, experiments are described where a scanning tunneling microscope measures the surroundings of a magnetic impurity on a metal surface. In another set of experiments, Kondo Effect creates a number of characteristic features in the electron transport through small electronic devices -- semiconductor quantum dots or single-molecule transistors which can be tuned by applying appropriate gate voltages. The article contains 5 color figures, photo of Jun Kondo, but no equations.
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Revival of the Kondo Effect
Physics World, 2001Co-Authors: Leo P. Kouwenhoven, Leonid GlazmanAbstract:Why would anyone still want to study a physical phenomenon that was discovered in the 1930s, explained in the 1960s and has been the subject of numerous reviews since the 1970s? Although the Kondo Effect is a well known and widely studied phenomenon in condensed-matter physics, it continues to capture the imagination of experimentalists and theorists alike.
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Kondo Effect in an integer-spin quantum dot
Nature, 2000Co-Authors: S. Sasaki, Wilfred G. Van Der Wiel, J. M. Elzerman, Seigo Tarucha, Mikio Eto, S. De Franceschi, Leo P. KouwenhovenAbstract:The Kondo Effect is a key many-body phenomenon in condensed matter physics. It concerns the interaction between a localised spin and free electrons. Discovered in metals containing small amounts of magnetic impurities, it is now a fundamental mechanism in a wide class of correlated electron systems. Control over single, localised spins has become relevant also in fabricated structures due to the rapid developments in nano-electronics. Experiments have already demonstrated artificial realisations of isolated magnetic impurities at metallic surfaces, nanometer-scale 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 realised in a few-electron quantum dot containing singlet and triplet spin states whose energy difference can be tuned with a magnetic field. This Effect occurs for an even number of electrons at the degeneracy between singlet and triplet states. The characteristic energy scale is found to be much larger than for the ordinary spin-1/2 case.
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Kondo Effect in an integer spin quantum dot
Nature, 2000Co-Authors: S. Sasaki, Wilfred G. Van Der Wiel, J. M. Elzerman, Seigo Tarucha, Mikio Eto, S. De Franceschi, Leo P. KouwenhovenAbstract: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 systems1,2. In fabricated structures, the control of single, localized spins is of technological relevance for nanoscale electronics3,4. Experiments have already demonstrated artificial realizations of isolated magnetic impurities at metallic surfaces5,6, nanoscale magnets7, controlled transitions between two-electron singlet and triplet states8, and a tunable Kondo Effect in semiconductor quantum dots9,10,11,12. 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.
