Comparative study on aging effect in BiFeO3 thin films substituted at A- and B-site

Typical characteristics of aging effect, double hysteresis loops, were observed in (100)-oriented Bi0.95Ca0.05FeO3 (BCFO) and BiFe0.95Ni0.05O3 (BFNO) films grown on LaNiO3(100)/Si substrates. The double hysteresis loops for BCFO film become less "constrained" with increasing applied voltage compared to that for BFNO, indicating that the aging effect is more severe in the latter. This can be demonstrated by the lower leakage current and smaller dielectric constant for BFNO. These phenomena are explained based on the crystal structure and defect chemistry. The defect states of the Bi, Ca, Fe, Ni and O ions were clarified by the XPS data.Comment: 15 pages, 5 figures, accepted by Applied Physics Letter

Coexistence of multi-photon processes and longitudinal couplings in superconducting flux qubits

In contrast to natural atoms, the potential energies for superconducting flux qubit (SFQ) circuits can be artificially controlled. When the inversion symmetry of the potential energy is broken, we find that the multi-photon processes can coexist in the multi-level SFQ circuits. Moreover, there are not only transverse but also longitudinal couplings between the external magnetic fields and the SFQs when the inversion symmetry of potential energy is broken. The longitudinal coupling would induce some new phenomena in the SFQs. Here we will show how the longitudinal coupling can result in the coexistence of multi-photon processes in a two-level system formed by a SFQ circuit. We also show that the SFQs can become transparent to the transverse coupling fields when the longitudinal coupling fields satisfy the certain conditions. We further show that the quantum Zeno effect can also be induced by the longitudinal coupling in the SFQs. Finally we clarify why the longitudinal coupling can induce coexistence and disappearance of single- and two-photon processes for a driven SFQ, which is coupled to a single-mode quantized field.Comment: 11 pages, 6 figure