Individual supermassive binary black holes (SMBBHs) are anticipated to be detected by pulsar timing arrays (PTAs) in the nanohertz band. The gravitational waves (GWs) from some of those individual SMBBHs may be diffractionally lensed by intervening galaxies. If on circular orbits, however, it is difficult to identify these lensed SMBBHs only by their GW signals, as their monochromatic waveforms are different from the original unlensed ones only with a small amplitude amplification and phase shift, which can be fit by unlensed waveforms with larger chirp masses or smaller distances. In this paper, we investigate whether we can identify the lensed nanohertz GW signals from highly eccentric SMBBHs by exploiting the dependence of their amplification on the frequencies of different harmonics. We adopt the second post-Newtonian GW waveform from eccentric SMBBHs and the singular isothermal sphere lens model to calculate the difference between the lensed waveforms and the matched filtering ones with unlensed GW templates for different lensed systems, and find the larger the eccentricity, the larger the difference. Assuming the square kilometer array-PTA configuration, we adopt the fitting factor to justify the distinguishability of lensed GW signals from unlensed ones and find that we may identify some of the lensed sources with higher eccentricities ($\gtrsim 0.6$) via 30-yr observations. The identification of diffraction lensed SMBBHs may provide an important probe to the wave nature of GWs and its astrophysical applications.

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• Gravitational lenses
• Gravitational waves