The generalized phonon density of states for the high-T c superconductor YBa 2 Cu 3 O 7.1 with high Meissner effect (50%) and for its retreated sample with low Meissner effect (15%) at T=300 K and T=86 K respectively was measured by using inelastic neutron scattering method. The density of states of the superconductor YBa 2 Cu 3 O 7.1 at temperatures of both 300 K and 86 K shows a similar energy spectrum below 95 meV. However, above this energy there are evident softening of modes at 86 K. In addition, a large decrease of 92 meV peak in the density of states for a sample with lower Meissner effect was observed, this effect is supposed to be a result of an increase of vacancies on O 4 site.
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Lead-free BaTiO3 (BTO) film was fabricated by pulsed laser deposition on LaAlO3/SrTiO3 (LAO/STO) heterostructure in oxygen pressure of 2 × 10−3 Pa, which is experimentally required for ensuring the two-dimensional electron gas at LAO/STO heterointerface. Modulation of back-gate voltage on the superconductivity of LAO/STO and BTO/LAO/STO heterointerfaces was studied. The results indicate that the back-gate voltage can adjust the resistance at high temperatures around 300 mK, while it does not modulate the superconducting transition temperature of LAO/STO, which occurs at 160 mK. As for BTO/LAO/STO, it still shows a superconducting transition-like behavior at 110 mK. However, when a negative back-gate voltage is applied, the superconducting transition-like behavior disappears, and after removing the voltage, unlike what was observed for LAO/STO, the superconductivity cannot be recovered. Given this, some underlying mechanisms are proposed.
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