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Ca-intercalation has enabled superconductivity in graphene on SiC. However, the atomic and electronic structures that are critical for superconductivity are still under discussion. We find an essential role of the interface between monolayer graphene and the SiC substrate for superconductivity. In the Ca-intercalation process, at the interface a carbon layer terminating SiC changes to graphene by Ca-termination of SiC (monolayer graphene becomes a bilayer), inducing more electrons than a free-standing model. Then, Ca is intercalated in between the graphene layers, which shows superconductivity with the updated critical temperature (T C ) of up to 5.7 K. In addition, the relation between T C and the normal-state conductivity is unusual, "dome-shaped". These findings are beyond the simple C 6 CaC 6 model in which s-wave BCS superconductivity is theoretically predicted. This work proposes a general picture of the intercalation-induced superconductivity in graphene on SiC and indicates the potential for superconductivity induced by other intercalants.

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As a new scheme of treating the tensor interaction of the nucleon-nucleon interaction, there is a proposal of a tensor-optimized shell-model (TOSM) for the study of medium and heavy nuclei. The TOSM includes the deuteron-like tensor correlation and provides quite a good reproduction of the binding energy and the size of 4 He as compared with rigorous few body calculations. We propose a tensor-optimized few-body model (TOFM) using the spirit of the TOSM approximation in the few body framework with bare nucleon-nucleon interaction. We find that the TOFM can account for the strength of the tensor interaction very well and almost reproduces the full energy and various energy components as compared with rigorous few body calculations. 21.10.Dr It is very important to describe nuclear structure by using bare nucleon-nucleon (NN) interaction. Such an effort has been made for a few body [1] and light mass nuclei up to about A∼12 [2]. The difficulty of solving nuclear ground states by using the NN interaction is the presence of the strong short range repulsion and the medium range tensor interaction caused by the pion exchange. The calculated results on the deuteron indicate that the s-wave component has a distinct dip at the short distance and the probability of the d-wave component is of order of 5%. Although the d-wave component is small, the dominant attraction of order of 80% is caused by the tensor interaction to provide the small binding energy by canceling with a large kinetic energy for the case of the AV8' interaction. These features have to be handled in any theoretical frameworks for a quantitative account of nuclear states. The calculated results of few body frameworks provide extremely a good account of nuclear ground states and a few excited states by including a phenomenological three body interaction [2].In recent years, two very important methods were proposed for the description of finite nuclei. One is the unitary correlation operator method (UCOM) and the other is the tensor optimized shell model (TOSM). The UCOM is a method to handle the short range correlation in terms of the unitary correlation operator by truncating the resulting many body operators at the 2 body level [3]. The TOSM is a method to treat the strong tensor interaction in the 2p-2h model space in the shell model basis [4]. Hence, we are able to calculate medium and heavy nuclei by using bare NN interaction. We discuss here the essence of the TOSM approximation. The strong tensor interaction acting on two nucleons in a spin-saturated * Electronic address: horii@rcnp.osaka-u.ac.jp † Electronic address: toki@rcnp.osaka-u.ac.jp ‡ Electronic address: myo@ge.oit.ac.jp § Electronic address: k-ikeda@riken.go.jp shell model state oughts to excite them into two particle states. Hence, it is a minimum requirement to take 2p-2h excitations in order to treat the tensor interaction, which provides a large attraction to form nucleus. Another important feature is to use various range (short range in particular) gaussian wave functions so that the...