# VietNam 2013

August 4-10, 2013

Nanophysics: from fundamentals to applications

(the return)

Thursday 8
Dots and wires

› 14:00 - 14:20 (20min)
Two-impurity Kondo Effect in Al/AlOx/Y Tunnel Junctions
Yu-Ren Lai  1, *@  , Da-Wei Wang  1@  , Juhn-Jong Lin  1, 2, *@
1 : Institute of Physics , National Chiao Tung University
1001 University Road, Hsinchu 300 -  Taiwan
2 : Department of Electrophysics, National Chiao Tung University
1001 University Road, Hsinchu 300 -  Taiwan
* : Corresponding author

We have fabricated a series of Al/AlOx/Y tunnel junctions and measured the differential conductance G(V; T) at liquid-helium temperatures. We found that the zero-bias conductance G(0; T) increases with reducing T below 40 K, i.e., G(0; T) obeys a -ln T law at a higher T regime (10-25 K) and crosses over to a -$\sqrt{T}$ law at an intermediate T regime (5-20 K). The unique -$\sqrt{T}$ feature is suggestive of a novel Kondo effect. In particular, in this intermediate T regime, we observed that the finite-bias G(V; T) curves at different T's collapse closely with the universal scaling function of the two-impurity Kondo effect.

Furthermore, while the G(V; T) behavior is essentially similar for all junctions at not too low T, we found two kinds of distinct T dependences of G(0; T) at T

The two-impurity Kondo effect arises from a minute number of spin-1/2 yttrium impurities which diffused into the insulating barrier during the junction fabrication process.

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