The onset of metallic behavior in strained (LaNiO$_3$)$_n$/(SrMnO$_3$)$_2$ superlattices

Motivated by predictions of collective ordering phenomena in LaNiO$_3$, we have grown strained (LaNiO$_3$)$_n$/(SrMnO$_3$)$_2$ superlattices on SrTiO$_3$ using ozone-assisted molecular beam epitaxy. The superlattices exhibit excellent crystallinity and interfacial roughness of less than one unit cell. The samples undergo a metal-insulator transition as $n$ is reduced from 4 to 2. Both $n$ = 1 and 2 samples are insulating, however, they exhibit different transport behavior. The $n$ = 1 sample acts as a gapped insulator, while the addition of a second LNO layer ($n$ = 2) leads to hopping transport through non-gapped conduction channels. These results will be compared to (LaMnO$_3$)/(SrMnO$_3$) superlattices to highlight how interfacial charge transfer differs in the nickelate/manganite superlattices from their all-manganite counterparts. Supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences under contract DE-AC02-06CH11357.