We demonstrate the operation of coupled-cavity terahertz frequency quantum-cascade lasers composed of two sub-cavities separated by an air gap realized by optical lithography and dry etching. This geometry allows stable, single mode operation with typical side mode suppression ratios in the 30-40 dB range. We employ a transfer matrix method to model the mode selection mechanism. The obtained results are in good agreement with the measurements and allow prediction of the operating frequency. V C 2014 AIP Publishing LLC.[http://dx
Here, we carried out a study on strontium doping effect on the rectifying properties of La2−xSrxCuO4 (LSCO)/NSTO heterojunctions. The intimate relationship between the change in electronic structure of LSCO and the variation of diffusion potential (Vd) of the junction supports opportunities for detecting Fermi level shift and superconducting gap evolution of LSCO upon hole doping. The results agree well to generally perceived viewpoints obtained by other methods. Even the suppression of Fermi level shift in the underdoped regime and weak-coupling d-wave BCS superconductivity behavior in the overdoped regime of LSCO are clearly exhibited by the tuned rectifying behaviors. This work not only reveals rich properties of LSCO/NSTO but also opens an alternative route to monitor the Fermi level and superconducting gap of high-temperature superconductors.
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