Temperature dependence of the resistivity tensor in superconducting Bi2Sr2.2Ca0.8Cu2O8 crystals

Layer-Dependent Superconductivity in Iron-Based Superconductors CsCa2Fe4As4F2 and CaKFe4As4

In the quasi-two-dimensional superconductor NbSe2, the superconducting transition temperature (Tc) is layer-dependent, decreasing by about 60% in the monolayer limit. However, for the extremely anisotropic copper-based high-Tc superconductor Bi2Sr2CaCu2O8+δ (Bi-2212), the Tc of the monolayer is almost identical with that of its bulk counterpart. To clarify the effect of dimensionality on superconductivity, here, we successfully fabricate ultrathin flakes of iron-based high-Tc superconductors CsCa2Fe4As4F2 and CaKFe4As4. It is found that the Tc of monolayer CsCa2Fe4As4F2 (after tuning to the optimal doping by ionic liquid gating) is about 20% lower than that of the bulk crystal, while the Tc of three-layer CaKFe4As4 decreases by 46%, showing a more pronounced dimensional effect than that of CsCa2Fe4As4F2. By carefully examining their anisotropy and the c-axis coherence length, we reveal the general trend and empirical law of the layer-dependent superconductivity in these quasi-two-dimensional superconductors.

Absence of superconductivity in I4/mmm-FeH5: experimental evidence

The experimentally discovered FeH5 exhibits a structure built of atomic hydrogen that only has bonding between hydrogen and iron atoms [C. M. Pepin, G. Geneste, A. Dewaele, M. Mezouar and P. Loubeyre, Science, 2017, 357, 382]. However, its superconductivity has remained unsolved since its discovery. In this work, we have synthesized I4/mmm-FeH5 at 139 GPa combined with laser-heating conditions. The electrical resistance measurements at ultrahigh pressures indicate that no evidence of superconducting transition of FeH5 is observed in the temperature range of 1.5 K to 270 K. These results indicate that I4/mmm-FeH5 does not exhibit superconductivity within the experimental temperature range, and the introduction of iron atoms is not beneficial to the formation of the superconducting phase.

Matter-wave self-imaging by atomic center-of-mass motion induced interference

We demonstrate matter-wave self-imaging resulting from atomic center-of-mass motion-based interference. We show that non-negligible atomic center-of-mass motion and an instantaneous Doppler shift can drastically change the condensate momentum distribution, resulting in a periodic collapse and the recurrence of condensate diffraction probability as a function of the stationary light-field pulsing time. The observed matter-wave self-imaging is characterized by an atomic center-of-mass motion induced population amplitude interference in the presence of the light field that simultaneously minimizes all high (n>or=1) diffraction orders and maximizes the zeroth diffraction component.