How hot can it get? The two-stage Kondo effect (KE) behaves pretty much like a set of Russian dolls: open one, and there is a smaller one inside. Through a sequence of quantum dots (QDs) weakly coupled to each other (with only the first one strongly coupled to an electron reservoir), one can observe successive KEs, each one with a lower Kondo temperature TK (by a few orders of magnitude) than the previous one. As TK is in general on the scale of a few Kelvin, already the second stage TK becomes impossible to observe experimentally. In a recent work with CIAM collaborators from Brazil and Chile, we showed that adding a capacitive coupling U’ between the QDs can greatly decrease the ratio between successive TKs. (left-side figure).

Submitted to Phys. Rev. B

Heating-up a very low temperature phenomenon

Materials World Network (USA – Brazil – Chile)George B. Martins, Oakland University, DMR 0710529

Kondo temperature: The characteristic energy of the Kondo state, the Kondo temperature TK , is the only energy scale left in the system when in the Kondo state. Being able to predict how TK varies with the gate voltage Vg (as shown through an analytic expression – magenta curve on the right) is important information. However, its validity is limited to a narrow window of Vg (notice divergence). With CIAM collaborators from Brazil and Chile, a numerical way of calculating an ‘extension’ of TK for a larger window of Vg was devised (see figure). This method is now being refined.

Physical Review B 83, 125404 (2011)

REU funded at Oakland University, RET plannedMaterials World Network (USA – Brazil – Chile) DMR - 0710529

George B. Martins, Oakland University, DMR 0710529

The efforts to continue the outreach to the Pontiac School District (PSD) students has been greatly increased this summer after the approval for three years of an REU site in the Physics Dep. at Oakland University, of which Martins is the PI. We had 7 students this summer, being 5 of them minority students from Pontiac, one of the most underprivileged districts in Michigan. (Notice below a picture of the students while visiting Fermi Lab this past May) This effort will be greatly enhanced in the next year, as Martins will be applying for an RET grant, which will bring the high school teachers from PSD to do research projects in the Physics Dep. at Oakland.