Origin of the resistivity discrepancy among lightly doped La2CuO4+δ samples

Determine why the temperature dependence of the in-plane resistivity in lightly doped La2CuO4+δ with p ≅ 0.03 differs among studies, specifically why it increases more rapidly below T* in some crystals whereas it decreases below T* in others.

Background

The reported transport behavior of lightly doped La2CuO4+δ is inconsistent across samples. In the crystals studied in the paper, the in-plane resistivity increases below T* ≅ 280 K, while prior studies reported a decrease of the in-plane resistivity below T* comparable to the decrease observed in the out-of-plane resistivity.

The paper identifies possible differences in crystal growth, excess-oxygen introduction, or measurement geometry as sources of the discrepancy, but does not resolve which factor is responsible. Clarifying this issue is important for distinguishing intrinsic transport behavior from sample-preparation or experimental artifacts.

References

Although such a discrepancy for 𝜌∥(𝑇𝑇) seems to be due to differences in the method of sample preparation such as crystal growth and excess oxygen introduction or problems for the resistivity measurement, for example, whether electrical current flows uniformly through sample between voltage electrodes, the reason is unclear at present.

— Magnetism and Electrical Conduction in Lightly-Doped Single-Layer High-$T_c$ Cuprate $\mathrm{La}_2\mathrm{CuO}_{4+δ}$  (2608.18563 - Miyakoshi et al., 19 Aug 2026) in Section 3.2