Shock Waves in Nanomechanical Resonators

The dream of every surfer is an extremely steep wave propagating at the highest speed possible. The best waves for this would be shock waves, but are very hard to surf. In the nanoscopic world the same is true: the surfers in this case are electrons riding through nanomechanical devices on acoustic waves [1]. Naturally, this has a broad range of applications in sensor technology and for communication electronics for which the combination of an electronic and a mechanical degree of freedom is essential. But this is also of interest for fundamental aspects of nano-electromechanical systems (NEMS), when it comes to quantum limited displacement detection [2] and the control of phonon number states [3]. Here, we study the formation of shock waves in a NEMS resonator with an embedded two-dimensional electron gas using surface acoustic waves. The mechanical displacement of the nano-resonator is read out via the induced acoustoelectric current. Applying acoustical standing waves we are able to determine the anomalous acoustocurrent. This current is only found in the regime of shock wave formation. We ontain very good agreement with model calculations.Comment: 14 Pages including 4 figure

Comparing schemes of displacement detection and subharmonic generation in nanomachined mechanical resonators

We present measurements on nanomechanical resonators operating in the radio frequency range. We apply a setup which allows the comparison of two schemes of displacement detection for mechanical resonators, namely conventional power reflection measurements of a probing signal and direct detection by capacitive coupling via a gate electrode. For capacitive detection, we employ an on-chip preamplifier, which enables direct measurements of the resonator's displacement. We observe that the response of the mechanical resonator depends on the detection technique applied, which is verified in model calculations. We show results on the detection of subharmonics.-Paper withdrawnComment: 8 pages, 3 figure

Detection of coherent acoustic oscillations in a quantum electromechanical resonator

Coherent control of occupation numbers in quantum mechanical multilevel systems is widely studied driven by its application in lasers and its prospects for quantum computational elements. Here the authors present a nanoelectromechanical resonator equivalent to the coherent control of a quantum mechanical two level system. The distinct eigenmodes of a nanomechanical beam resonator represent the two levels whose amplitude mode occupation numbers are controlled by a frequency matched acoustic excitation, mediated by a pulsed surface acoustic wave. They show that similar to quantum mechanical systems it is possible to transfer occupation numbers from one mode to another by matched acoustic pulses

Shock waves in suspended low-dimensional electron gases

We study the formation of shock waves in a suspended two-dimensional electron gas using surface acoustic waves. The mechanical displacement of the nano-resonator is read out via the induced acoustoelectric current. Applying acoustical standing waves, we are able to determine the anomalous acoustocurrent. This current is only obtained in the regime of shock wave formation. We find very good agreement with model calculations