Metallic Bi-Rh-O thin films with p-type conduction*

Transition metal oxides with partially filled 4d and 5d orbitals have recently been viewed as promising target materials for the discovery of novel properties, due to their strong spin-orbit coupling that can generate exotic electronic states. Here, we report the fabrication of three kinds of Bi-Rh-O compounds. They are synthesized by the deposition of amorphous films at room temperature by pulsed laser deposition and subsequent annealing in a tube furnace under O₂ atmosphere. On Y-ZrO₂ (111) substrates, two novel compounds with supercell structures [Bi_nO_n]-[RhO₂] (n = 3, 2) are synthesized at annealing temperatures (T_anneal) of 700 °C and 900 °C, respectively. When a buffer layer of pyrochlore oxides is deposited on Y-ZrO₂, single crystalline pyrochlore Bi₂Rh₂O₇ is stabilized at T_anneal of 1,000 °C. These results demonstrate the critical role of the interface-engineering in stabilizing certain crystal structures, which will pave the way for further exploration of Rh oxides and materials design of transition metal oxides. Hall resistivity at 2 K is merely linear to an applied magnetic field with a positive slope for all the compounds, and the estimated carrier densities are p = 3×10²¹ cm^-3 ([Bi₂O₂]-[RhO₂]), 6×10²¹ cm^-3 ([Bi₃O₃]-[RhO₂]), and 1×10²³ cm^-3 (Bi₂Rh₂O₇). The magnetoresistance at 2 K shows quadratic ([Bi₂O₂]-[RhO₂]) and linear ([Bi₃O₃]-[RhO₂], Bi₂Rh₂O₇) field dependence, suggesting strong spin-orbit coupling.