Herz, Markus

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Shot Noise of 1,4-Benzenedithiol Single-Molecule Junctions

2016-03-09, Karimi, Mohammad Amin, Bahoosh, Safa G., Herz, Markus, Hayakawa, Ryoma, Pauly, Fabian, Scheer, Elke

We report measurements of the shot noise on single-molecule Au-1,4-benzenedithiol-Au junctions, fabricated with the mechanically controllable break junction (MCBJ) technique at 4.2 K in a wide range of conductance values from 10(-2) to 0.24 conductance quanta. We introduce a simple measurement scheme using a current amplifier and a spectrum analyzer and that does not imply special requirements regarding the electrical leads. The experimental findings provide evidence that the current is carried by a single conduction channel throughout the whole conductance range. This observation suggests that the number of channels is limited by the Au-thiol bonds and that contributions due to direct tunneling from the Au to the π-system of the aromatic ring are negligible also for high conductance. The results are supported by quantum transport calculations using density functional theory.

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Force-noise spectroscopy by tunneling current deflection sensing

2016, Herz, Markus, Scheer, Elke

An electro-mechanical setup for the measurement of force-noise properties in a low-temperature tunnelingmicroscope has been utilized to enable extremely high resolution and acquire force-noise spectra as function of the applied voltage bias. The direct crosstalk of vibrations onto the tunneling current is used to measure the deflection of a force-sensing cantilever. We demonstrate its capability to measure the mechanical energy of the cantilever, caused by the noise of the force from vacuum tunneling between polycrystalline Iridium electrodes. We observe peak levels of the induced cantilever energy at polarity-symmetric voltages corresponding to dominant peaks of the phonon density of states, which suggests that inelastic transport processes contribute to force fluctuations.

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Fundamental quantum noise mapping with tunnelling microscopes tested at surface structures of subatomic lateral size

2013-10-21, Herz, Markus, Bouvron, Samuel, Cavar, Elizabeta, Fonin, Mikhail, Belzig, Wolfgang, Scheer, Elke

We present a measurement scheme that enables quantitative detection of the shot noise in a scanning tunnelling microscope while scanning the sample. As test objects we study defect structures produced on an iridium single crystal at low temperatures. The defect structures appear in the constant current images as protrusions with curvature radii well below the atomic diameter. The measured power spectral density of the noise is very near to the quantum limit with Fano factor F = 1. While the constant current images show detailed structures expected for tunnelling involving d-atomic orbitals of Ir, we find the current noise to be without pronounced spatial variation as expected for shot noise arising from statistically independent events.