Caveats for the use of Web of Science Core Collection in old literature retrieval and historical bibliometric analysis

By using publications from Web of Science Core Collection (WoSCC), Fosso Wamba and his colleagues published an interesting and comprehensive paper in Technological Forecasting and Social Change to explore the structure and dynamics of artificial intelligence (AI) scholarship. Data demonstrated in Fosso Wambas study implied that the year 1991 seemed to be a watershed of AI research. This research note tried to uncover the 1991 phenomenon from the perspective of database limitation by probing the limitations of search in abstract/author keywords/keywords plus fields of WoSCC empirically. The low availability rates of abstract/author keywords/keywords plus information in WoSCC found in this study can explain the watershed phenomenon of AI scholarship in 1991 to a large extent. Some other caveats for the use of WoSCC in old literature retrieval and historical bibliometric analysis were also mentioned in the discussion section. This research note complements Fosso Wamba and his colleagues study and also helps avoid improper interpretation in the use of WoSCC in old literature retrieval and historical bibliometric analysis.

Anomalous CDW ground state in Cu$_2$Se: a wave-like fluctuation of $it{dc}$ I-V curve near 50 K

A charge density wave (CDW) ground state is observed in polycrystalline Cu$_2$Se below 125 K, which corresponds to an energy gap of 40.9 meV and an electron-phonon coupling constant of 0.6. Due to the polycrystalline structure, the Peierls transition process has been expanded to a wide temperature range from 90 to 160 K. The Hall carrier concentration shows a continuous decrease from 2.1$times$10$^{20}$ to 1.6$times$10$^{20}$ cm$^{-3}$ in the temperature range from 160 K to 80 K, while almost unchanged above 160 K and below 90 K. After entering the CDW ground state, a wave-like fluctuation was observed in the I-V curve near 50 K, which exhibits as a periodic negative differential resistivity in an applied electric field due to the current. We also investigated the doping effect of Zn, Ni, and Te on the CDW ground state. Both Zn and Ni doped Cu$_2$Se show a CDW character with increased energy gap and electron-phonon coupling constant, but no notable Peierls transition was observed in Te doped Cu$_2$Se. Similar wave-like I-V curve was also seen in Cu$_{1.98}$Zn$_{0.02}$Se near 40 K. The regular fluctuation in $it{dc}$ I-V curve was not magnetic field sensitive, but temperature and sample size sensitive.