Switching speed limit in magnetite.
Magnetite is a model system for understanding correlated oxides. Nevertheless, the exact mechanism of the insulator–metal, or Verwey, transition has long remained inaccessible. In our Nature Materials paper published in the summer of 2013 we show that we can switch this material from insulating to metallic on unprecedented short time scales.
The Verwey transition was investigated with pump–probe X-ray diffraction and optical reflectivity techniques. The low-T, insulating phase of magnetite, named after the UvA professor and Philips NatLab director E.J.W. Verwey - is due to charges freezing into a pattern also involving ordering of the Fe3d orbitals. Recent X-ray diffraction work showed showed that the Verwey phase possesses 'trimerons', trapping the otherwise mobile charges at three-site, distorted centres in the crystal. Out pump-probe work shows how trimerons become mobile across the insulator–metal transition. We find this to be a two-step process. After an initial 300 fs destruction of individual trimerons, phase separation occurs on a 1.5 +/- 0.2 ps timescale to yield residual insulating and metallic regions. This work establishes the speed limit for switching in future oxide electronics. The research was conducted by a consortium of groups led by Hermann Dürr's group at SIMES in SLAC. Hermann is adjunct professor attached to the QMat group and Mark got involved in this work while on sabbatical at SIMES in the summer of 2012.
Read more on the Nature website or in the pdf.