Three-channel Kondo effect discovered in f-electron system for the first time – Bolivar Commercial


In a first-of-its-kind discovery, scientists succeeded in capturing the three-channel Kondo effect in an f-electron system. The three-channel Kondo effect is considered to be the hallmark of the quantum phenomenon.

Discovered by a scientist at Tokyo Metropolitan University, the work could also predict the type of real materials that might show this effect. The researcher showed how electrons around a holmium +3 ion interact with conduction electrons and give rise to a predicted residual entropy value at ultra-low temperatures.

Resistivity in impure metals has been the most curious case of the 20th century. The electrical resistance of metals is largely caused by conduction electrons being dispersed by metal ions undergoing vibrations due to thermal energy. The lower the temperature, the lower the vibration and the weaker the effect; one would expect the resistivity of metals to simply decrease as we approach absolute zero.

However, this is not what happens when the metal is not pure. When the temperature is lowered, the resistivity reaches a minimum before resuming. This effect is known as the Kondo effect after Professor Jun Kondo, who realized that it was due to magnetic impurities interacting with the conduction electrons through a process known as hybridization.

After many breakthroughs in the 1960s and 1970s, physicists began to realize that this was just the beginning. The modes of interaction between the impurity and the conduction electrons could indeed be more complex, in particular when the same impurity could interact with multiple reservoirs of electrons, a “multichannel” Kondo effect. The pioneering work of Nozières and Blandin in 1980 showed how the two-channel Kondo effect resulted in “liquid non-Fermi” behavior. Non-Fermi liquids have, among other things, been linked to high temperature superconductivity.

Now, Professor Takashi Hotta from Tokyo Metropolitan University has examined a three-channel Kondo effect in a digital model of a cubic holmium compound. In the case of holmium 3+ ions, their most energetic electrons are in 4F-orbitals, a subset of the many quantum states that can be occupied by pairs of electrons around an atom. Six fill states of lower energy while four combine in different ways to produce what is called a spin singlet and a spin triplet; these are shown in the diagram, where the rectangle is the triplet, the oval is the singlet, and the differently colored circles denote the four electrons. Together, these create a “spin = 1” impurity which could then hybridize with three different sources of conduction electrons at the same time. Using an algorithm known as the Numerical Renormalization Group Method to model this system, Professor Hotta found an ultra-low temperature residual entropy with the exact value predicted by the three-channel Kondo effect.

Importantly, this new work gives predictions for real materials where the three-channel Kondo effect could be spotted, 1-2-20 compounds consisting of one part holmium, 2 parts transition metal, and 20 parts. aluminum or zinc. Indicators of real experimental systems where the effect could be observed promise to inject new enthusiasm into the search for exotic quantum ground states, with the possibility of discovering new non-Fermi liquids and their potential applications.

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