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Shot noise scanning probe microscopy: probing the dynamics at the atomic scale

Periodic Reporting for period 1 - SN-STM_FM (Shot noise scanning probe microscopy: probing the dynamics at the atomic scale)

Reporting period: 2015-04-01 to 2017-03-31

The dynamics of exotic systems such as high-temperature superconductors and heavy fermion materials is gaining ever increasing interest as it contains important clues to the mechanism driving the often unanticipated and technologically very relevant properties. To address the dynamics at the scale where the action occurs, namely that of the atoms and electrons, this Marie Curie action set out to design and construct a low temperature, finite frequency compatible shot noise scanning tunnelling microscope. Within the scope of this action, atomic scale shot noise measurements of one correlated electron system was anticipated, providing the first time-dependent information at the atomic scale of the system. Indeed, after designing and constructing the novel microscope, and subsequent extensive calibration measurements, atomic scale shot noise measurements of the high temperature superconductor Bi2Sr2CaCu2O8+x have been performed, the results of which will be published soon. Beyond the duration of this action, the new facility will continue to give powerful new information in the time domain of quantum matter systems.
The project proposal consisted of four work packages: design, assembly, commissioning and first scientific study using the new equipment. The design of the microscope head and its construction were swift and successful, allowing for atomic resolution imaging in air of graphite. The design and construction of the probe with which to cool the microscope down to 4K and eventually 0.3K took longer than anticipated – due to a design flaw that had to be corrected and an underestimation of the time it took to receive all components. However, once completed, the microscope has successfully been cooled down to 4K and calibration of both the conventional operation of the microscope at low temperature and the novel circuitry for shot noise measurements followed. Eventually, after fine tuning various components and optimising the circuitry, shot noise could reliably be measured at the atomic scale on a gold surface. The specific method for measuring shot noise using the microscope, and the first atomic scale shot noise measurements performed, will be published in the near future. The final phase of the action was to apply the novel technique to the a correlated electron system. Originally a Kondo system consisting of a cobalt atom on a gold surface were proposed. However, it was decided instead to measure the high temperature superconductor Bi2Sr2CaCuO8+x (e.g. Bi2212) on which high quality conventional STM measurements have been performed with the microscope that was constructed during this action, including atomic resolution topography, spectroscopy and quasi particle interference scattering measurements. The attached image (SN-STM-01.jpg) show the design of the microscope and low temperature probe (left), the actual instrument, and atomic resolution topography (right top) and spectroscopy (right bottom) of Bi2212. Additionally, simultaneous atomic scale shot noise measurements have been performed with a resolution on the slope of the noise – which is directly related to the charge and the Fano factor – of a few percent.
In addition to providing valuable scientific results, at the end of this action the fellow has successfully applied for a permanent CNRS researcher position at the host laboratory.
Design and real instrument plus results