Two different teams of physicists have retracted papers from Physical Review B after realizing that a sample used in the paper published first — and which formed the basis of the second paper — was mislabeled.
Here’s the notice for the first paper, “s-wave superconductivity in barium-doped phenanthrene as revealed by specific-heat measurements,” by Jianjun Ying of the University of Science and Technology of China, Hefei, and colleagues:
We recently published a paper entitled “s-wave superconductivity in Ba-doped phenanthrene as revealed by specific-heat measurements.” The sample studied in that paper as Ba1.5-doped phenanthrene is now found to be La-doped phenanthrene. This error was caused by mislabeling the La-doped phenanthrene sample as Ba1.5-doped phenanthrene. During our experiment, we synthesized La- and Ba-doped phenanthrene in the same furnace because both of them have the same sintering temperatures and procedures. The mislabeling occurred when the samples were taken out of the furnace with incorrect records. In addition, it is now found that both Ba- and La-doped phenanthrene show similar superconducting transition temperatures.
In an earlier paper,1 we reported superconductivity in Ba-doped phenanthrene. At that time, we had not yet begun synthesizing La-doped phenanthrene samples, so it was impossible to have made a similar mislabeling error. Furthermore, we burned the superconducting Sr-doped and Ba-doped phenanthrene samples reported in the earlier paper at 750◦ C in air for 2 h and found that the final products were SrCO3 and BaCO3, respectively, which definitely proves that the samples in the earlier paper, indeed, have the composition reported there.
We are sorry for this error, and we ask that the paper not be regarded as part of the scientific literature. The data in the retracted paper with the correct reanalysis may be reported in a different paper, and the conclusions could be considered valid for La-doped phenanthrene.
The paper has been cited four times, according to Thomson Scientific’s Web of Knowledge.
And here’s the notice for the follow-up paper, “Bulk superconductivity and fully gapped superconducting state in Ba-doped phenanthrene,” by Yuichi Kasahara of the University of Tokyo and colleagues:
After the paper was published, the Ba-doped phenanthrene sample, which was provided by Professor X. H. Chen from the University of Science and Technology of China (as acknowledged in our paper) and which showed a superconducting transition temperature Tc of 4.9 K as derived from magnetization measurements, was investigated further by high-resolution diffraction measurements using synchrotron x-ray radiation. Figure 1(a) shows the comparison of the x-ray diffraction (XRD) patterns [(I) from Fig. 1 of our paper (laboratory XRD data) and (II) synchrotron data] of the “Ba-doped phenanthrene” sample with those of (III) hexagonal-closed-packed (hcp) elemental La and (IV) pristine phenanthrene. The simulated pattern of hcp elemental La [space group P63/mmc, a=3.77 and c=12.159̊A(Ref. 1)] and the XRD profiles of the present sample are very similar to each other as shown in Fig. 1(b), which displays the expanded Q region of the data between 1.7 and 4.0̊A−1. This similarity indicates that both sets of data [(I) and (II)] are completely dominated by the Bragg reflections of the hcp polymorph of the elemental La metal, which is known to be a superconductor with Tc=4.9K.
The authors, whose paper has been cited three times, then go on to describe what happened when they reanalyzed their heat data:
Both sets of data (Figs. 1 and 2) indicate that the sample used in our paper contains a large amount of a hcp polymorph of the elemental La metal, and thus, the specific heat anomaly with Tc=4.9 K is dominated by the La metal rather than by a putative Ba-doped phenanthrene superconductor.
The journal’s editor, Gene Sprouse, tells us:
It appears that Kasahara discovered the error after some further sample characterization motivated by a colleague, and then communicated the error to Ying, who had supplied the sample.