Condensed Matter Seminar Series

Observation of photon-induced Kondo satellites in a Single-Electron Transistor

Andrei Kogan

University of Cincinnati

Thursday September 30, 11h00 am, Room 234, Physics Building

Host: Horst Meyer

Abstract: When a magnetic impurity is placed in a host metal, the exchange interaction between the conduction electrons of the metal and the impurity spin produces a dramatic change in the metal ground state : a many-body correlated cloud, which involves both the electrons of the host metal and those localized on the impurity site, is formed. This scenario was proposed by Kondo to explain the anomalous temperature dependence of resistivity of certain "dirty metals", that at the time had remained a real mystery for almost 30 years, and is referred to as the "Kondo Effect".
A wave of renewed interest in this phenomenon has been triggered by the observation of the Kondo effect in a Single-Electron transistor (SET), a device that can be thought of as an "artificially constructed" impurity atom ( a potential well with a few trapped electrons) with macroscopic metallic leads connected to it by tunnel barriers. SETs allow to directly study the many-body correlated state formed on a single impurity, with many relevant parameters ( e.g. the impurity spin and the strength of the exchange coupling) adjustable in-situ during the experiment.
The experiment that I will describe in this talk takes further advantage of the great degree of control offered by the SETs for studying electronic correlations and probes the dynamics of a single Kondo state. We measure the differential conductance of an SET irradiated with microwaves in the Kondo regime. To excite the device, we couple it via a small aperture to a microwave-frequency cavity resonator, excited on one of its fundamental modes. When the energy of the microwave photon hf is comparable to the width of the Kondo peak, satellites to the main zero-bias peak appear at a bias voltage of +- hf/e. These photon-induced features have been predicted theoretically, but experiments done to date concluded that they do not exist, and this finding has even been justified theoretically. I will describe the conditions for observing the satellites, the technical challenges that we faced and compare our findings to theory.

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