Complete experimental mapping of the quantum phase diagram for the two-impurity Kondo effect
Yu-Ren Lai1*, Juhn-Jong Lin1,2
1Institute of Physics, National Chiao Tung University, Hsinchu, Taiwan
2Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
* presenting author:賴祐仁, email:Emilio.py97g@g2.nctu.edu.tw
We fabricate a series of copper/aluminum/aluminum-oxide/yttrium planar tunnel junctions. In our design, a few yttrium atoms can diffuse into the insulating barrier during the junction fabrication process, serving as spin-½ magnetic moments. The local magnetic moments can be fully screened by the spins of conduction electrons, leading to a Kondo-screened ground state. The local magnetic moments can also couple with each other via an antiferromagnetic exchange interaction, leading to a spin-singlet ground state. These two ground states are separated by a quantum critical point and it evolves into a quantum critical regime at finite temperatures. We measure the finite bias differential conductance with varied temperature to distinct the ground states of the planar tunnel junction devices. Here we show that the complete experimental mapping of the quantum phase diagram for the two-impurity Kondo effect is possible by using planar tunnel junction system.


Keywords: Planar tunnel junction, Two impurity Kondo effect, Quantum criticality