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Simultaneous measurements of the ac susceptibility and the dc magnetization of an untwinned single-crystal YBa 2 Cu 3 O 7 have been carried out to clarify the nature of vortex lattice melting. The first-order melting transition appears as a jump in the dc magnetization. Evidence for effectual pinning at temperatures above the melting transition is obtained as a sharp transition in Ј and a sharp peak in Љ of width 0.2 K in 10 kG. In addition, a precursor lattice softening phenomenon can be seen in Ј and Љ at temperatures below the melting temperature. This sequential change is more visible when the ac susceptibility is given in the Ј-Љ representation. It has been confirmed that there exists a melting transition of YBa 2 Cu 3 O 7 even below 10 kG.

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Confinement of hydrogen molecules at graphene–substrate interface has presented significant importance from the viewpoints of development of fundamental understanding of two-dimensional material interface and energy storage system. In this study, we investigate H2 confinement at a graphene–Au interface by combining selective proton permeability of graphene and the electrochemical hydrogen evolution reaction (electrochemical HER) method. After HER on a graphene/Au electrode in protonic acidic solution, scanning tunneling microscopy finds that H2 nanobubble structures can be produced between graphene and the Au surface. Defect dependence of the bubble formation suggests that intrinsic defects in graphene, which have high hydrogen permeation barrier but are permeable for protons, are involved in the fundamental mechanism of bubble formation. Strain analysis by Raman spectroscopy also shows that atomic size roughness on the graphene/Au surface originating from the HER-induced strain relaxation of graphene plays significant role in formation of the nucleation site and H2 storage capacity. The result presented herein would provide further understanding of molecular confinement at graphene-based interface and development of novel energy material.