Giant discrete steps in metal-insulator transition in perovskite manganite wires

Optical lithography is used to fabricate LPCMO wires starting from a single La5=80:3Pr0:3Ca3=8MnO3 (LPCMO) film epitaxially grown on a LaAlO3100 substrate. As the width of the wires is decreased, the resistivity of the LPCMO wires exhibits giant and ultrasharp steps upon varying temperature and magnetic field in the vicinity of the metal-insulator transition. The origin of the ultrasharp transitions is attributed to the effect of spatial confinement on the percolative transport in manganites. The strong spin-charge-lattice interaction in transition metal oxides (TMOs) often leads to a striking phenomenon called electronic phase separation (PS), which is identified with the coexistence of a range of exotic electronic and magnetic phases despite the single crystalline structure [1]. The role of the PS in the related physical properties such as high-T c superconducting and colossal magnetoresistance (CMR) is a hotly debated issue in the field of condensed matter physics. Spatial confinement is a very useful route to gain deeper insight into the nature of PS. In particular, when the spatial dimension of the TMOs is reduced to the characteristic PS length scale, one would expect that changes in the transport properties of the TMOs could be quite dramatic. A model system for this study is La5=8xPrxCa3=8MnO3 (LPCMO), a perovskite manganite that is famously known for its large-scale PS. Transmission electron microscopy has revealed submicrometer-scaled ferromagnetic (FM) and charge ordered (CO) domains [2]. The coexistence of FM=CO phases in LPCMO reflects the competition between the intrinsic properties of its two starting materials, i.e., FM La5=8Ca3=8MnO3 (TC 275 K) and CO antiferro