Terahertz direct-detection behavior of niobium nitride superconducting tunnel junctions above liquid helium temperature

Zheng, Wei; Li, Shao-Liang; Li, Jing; Shi, Sheng‐Cai

doi:10.1088/0953-2048/27/7/075003

Cited by 1 publication

(2 citation statements)

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“…Superconducting transition metal nitrides and carbides have been intensely studied due to their physical properties of high hardness and chemical stability as well as transition temperatures, T c , above that of Nb [1]. Potential devices utilizing thin films of transition metal compounds, which might replace those currently using Nb, continue to draw attention [2][3][4][5]. Some transition metal carbides (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Giant two-phonon Raman scattering from nanoscale NbC precipitates in Nb

et al. 2015

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High purity niobium (Nb), subjected to the processing methods used in the fabrication of superconducting RF cavities, displays micron-sized surface patches containing excess carbon.High-resolution transmission electron microscopy and electron energy-loss spectroscopy measurements are presented which reveal the presence of nanoscale NbC coherent precipitates in such regions. Raman backscatter spectroscopy on similar surface regions exhibit spectra consistent with the literature results on bulk NbC but with significantly enhanced two-phonon scattering. The unprecedented strength and sharpness of the two-phonon signal has prompted a theoretical analysis, using density functional theory (DFT), of phonon modes in NbC for two different interface models of the coherent precipitate. One model leads to overall compressive strain and a comparison to ab-initio calculations of phonon dispersion curves under uniform compression of the NbC shows that the measured two-phonon peaks are linked directly to phonon anomalies arising from strong electron-phonon interaction. Another model of the extended interface between Nb and NbC, studied by DFT, gives insight into the frequency shifts of the acoustic and optical mode density of states measured by first order Raman. The exact origin of the stronger two-phonon response is not known at present but it suggests the possibility of enhanced electron-phonon coupling in transition metal carbides under strain found either in the bulk NbC inclusions or at their interfaces with Nb metal. Preliminary tunneling studies using a point contact method show some energy gaps larger than expected for bulk NbC.

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Section: Introductionmentioning

confidence: 99%

“…Potential devices utilizing thin films of transition metal compounds, which might replace those currently using Nb, continue to draw attention [2][3][4][5].…”

mentioning

confidence: 99%