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Kondo insulator
About: Kondo insulator is a research topic. Over the lifetime, 2749 publications have been published within this topic receiving 71820 citations.
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28 Jan 1993TL;DR: In this article, the Kondo problem and the Bethe ansatz have been studied in the context of magnetic impurities and fermi liquid theories, and N-fold degenerate models have been proposed.
Abstract: 1. Models of magnetic impurities 2. Resistivity calculations and the resistance minimum 3. The Kondo problem 4. Renormalization group calculations 5. Fermi liquid theories 6. Exact solutions and the Bethe ansatz 7. N-fold degenerate models I 8. N-fold degenerate models II 9. Theory and experiment 10. Strongly correlated fermions Appendices.
2,763 citations
TL;DR: In this paper, the binding energy of the spin singlet has been observed in a single-electron transistor (SET) with only two electrodes and without control over the structure.
Abstract: How localized electrons interact with delocalized electrons is a central question to many problems in sold-state physics1,2,3. The simplest manifestation of this situation is the Kondo effect, which occurs when an impurity atom with an unpaired electron is placed in a metal2. At low temperatures a spin singlet state is formed between the unpaired localized electron and delocalized electrons at the Fermi energy. Theories predict4,5,6,7 that a Kondo singlet should form in a single-electron transistor (SET), which contains a confined ‘droplet’ of electrons coupled by quantum-mechanical tunnelling to the delocalized electrons in the transistor's leads. If this is so, a SET could provide a means of investigating aspects of the Kondo effect under controlled circumstances that are not accessible in conventional systems: the number of electrons can be changed from odd to even, the difference in energy between the localized state and the Fermi level can be tuned, the coupling to the leads can be adjusted, voltage differences can be applied to reveal non-equilibrium Kondo phenomena7, and a single localized state can be studied rather than a statistical distribution. But for SETs fabricated previously, the binding energy of the spin singlet has been too small to observe Kondo phenomena. Ralph and Buhrman8 have observed the Kondo singlet at a single accidental impurity in a metal point contact, but with only two electrodes and without control over the structure they were not able to observe all of the features predicted. Here we report measurements on SETs smaller than those made previously, which exhibit all of the predicted aspects of the Kondo effect in such a system.
1,723 citations
TL;DR: A tunable Kondo effect has been realized in small quantum dots and measurements of the temperature and magnetic field dependence of a Coulomb-blockaded dot show good agreement with predictions of both equilibrium and nonequilibrium Kondo effects.
Abstract: A tunable Kondo effect has been realized in small quantum dots. A dot can be switched from a Kondo system to a non-Kondo system as the number of electrons on the dot is changed from odd to even. The Kondo temperature can be tuned by means of a gate voltage as a single-particle energy state nears the Fermi energy. Measurements of the temperature and magnetic field dependence of a Coulomb-blockaded dot show good agreement with predictions of both equilibrium and nonequilibrium Kondo effects.
1,316 citations
TL;DR: The Kondo resonance can be tuned reversibly using the gate voltage to alter the charge and spin state of the molecule and persists at temperatures up to 30 K and when the energy separation between the molecular state and the Fermi level of the metal exceeds 100 meV.
Abstract: When an individual molecule1, nanocrystal2,3,4, nanotube5,6 or lithographically defined quantum dot7 is attached to metallic electrodes via tunnel barriers, electron transport is dominated by single-electron charging and energy-level quantization8. As the coupling to the electrodes increases, higher-order tunnelling and correlated electron motion give rise to new phenomena9,10,11,12,13,14,15,16,17,18,19, including the Kondo resonance10,11,12,13,14,15,16. To date, all of the studies of Kondo phenomena in quantum dots have been performed on systems where precise control over the spin degrees of freedom is difficult. Molecules incorporating transition-metal atoms provide powerful new systems in this regard, because the spin and orbital degrees of freedom can be controlled through well-defined chemistry20,21. Here we report the observation of the Kondo effect in single-molecule transistors, where an individual divanadium molecule20 serves as a spin impurity. We find that the Kondo resonance can be tuned reversibly using the gate voltage to alter the charge and spin state of the molecule. The resonance persists at temperatures up to 30 K and when the energy separation between the molecular state and the Fermi level of the metal exceeds 100 meV.
1,311 citations
TL;DR: In this article, it was suggested that a second-order transition from an antiferromagnetic to a Kondo spin-compensated ground state will occur as the exchange coupling constant J is increased to a critical value Jc for systems in which J ≲ Jc.
Abstract: By considering a one-dimensional analog of a system of conduction electrons exchange coupled to a localized spin in each cell of a lattice, it is suggested that a second-order transition from an antiferromagnetic to a Kondo spin-compensated ground state will occur as the exchange coupling constant J is increased to a critical value Jc For systems in which J ≲ Jc, a very weak sublattice magnetization may occur as a result of nearly complete spin-compensation
1,309 citations