Graphene may command the lion's share of attention but it is not the only material generating buzz in the electronics world. Vanadium dioxide is one of the few known materials that acts like an insulator at low temperatures but like a metal at warmer temperatures starting around 67 degrees Celsius. This temperature-driven metal-insulator transition, the origin of which is still intensely debated, in principle can be induced by the application of an external electric field. That could yield faster and much more energy efficient electronic devices.
"If the origin of this metal-insulator transition is electronic, the application of an electric field should trigger the transition on a picosecond or faster time-scale," says Nagaphani Aetukuri at the IBM-Stanford Spintronic Science and Applications Center (SpinAps). "This would be the basis for an ultrafast electronic switch, in which devices would be activated so quickly that very little energy would be lost through dissipation."
To determine the origin of the metal-insulator transition of vanadium dioxide, Aetukuri and a collaboration of researchers led by Stuart Parkin, of SpinAps and the IBM Almaden Research Center and Hermann Drr of the SLAC National Laboratory, studied thin films of the material at Berkeley Lab's Advanced Light Source (ALS). Using ALS beamline 4.0.2, an undulator beamline that can provide soft X-rays with variable linear polarization, they performed a series of strain-, polarization- and temperature-dependent X-ray absorption spectroscopy tests, in conjunction with X-ray diffraction and electrical transport measurements.
"Our results outlined the electronic properties that govern the metal-insulator transitions in vanadium dioxide and identified for the first time the respective roles of the Pi-symmetry and delta-symmetry electron orbitals," Aetukuri says. "We believe that the metallic phase of vanadium dioxide can be stabilized by populating the Pi-Symmetry orbitals
|Contact: Lynn Yarris|
DOE/Lawrence Berkeley National Laboratory