Oxides of transition metals such as titanium are of interest for applications, such as hydrogen gas sensors or as catalysts, and have intriguing fundamental physical properties. In particular, the origin of an intermediate temperature phase of the compound Ti4O7 has puzzled scientists for decades.
By studying the different electrical phases of Ti4O7, researchers from the RIKEN SPring-8 Center in Harima, along with colleagues from other institutions in Japan, have now taken important steps towards understanding the fundamental differences between the compound’s electrical conductivity at room and low temperatures, and the enigmatic phase that forms at intermediate temperatures.
At room temperature and down to temperatures of 154 K, Ti4O7 is an excellent conductor, as it allows fast transport of electrical charges. At temperatures below 142 K, the compound is an electrical insulator. Between 142 K and 154 K, however, the mysterious intermediate temperature phase sets in where the compound is semiconducting. Both, the metallic and the insulating phases are well understood by classical theories. The semiconducting phase, however, is very strange and complex; its origin is particularly interesting because it is sandwiched by two such well-known phases, explains Munetaka Taguchi from the research team.
To elucidate the origin of the semiconducting phase, the researchers studied the electronic phases at the top of the valence band and bottom of the conduction band that are responsible for the electrical conduction. They employed the techniques of electron photoemission and x-ray absorption, which combined provide a detailed picture of the electronic phases.
In the high-temperature phase, Taguchi and colleagues found that so-called ‘coherent valence electrons’ extended as far as the conduction band, making it a metallic conductor. In the insulating phase, there is a gap in the electronic band structure and no electrons are available in the conduction band. For the intermediate regime, however, a small number of coherent electronic phases remain close to the conduction band and explain the measured electrical conductivity.
While it is clear that the small number of coherent electrons is a remnant of the metallic phase, the transformation path—from the semiconducting state to both the room-temperature metal and the low-temperature insulating phase—remains unclear, notes Taguchi. With such crucial fundamental questions still unsolved, more work is needed to study the nature of the coherent electronic phases, which Taguchi hopes “will provide us [with] vital clues to a more complete understanding of phase transitions.”
The corresponding author for this highlight is based at the Excitation Order Research Team, RIKEN SPring-8 Center
1. Taguchi, M., Chainan, A., Matsunami, M., Eguchi, R., Takata, Y., Yabashi, M., Tamasaku, K., Nihino, Y., Ishikawa, T., Tsuda, S. et al. Anomalous state sandwiched between fermi liquid and charge ordered Mott-insulating phases of Ti4O7. Physical Review Letters 104, 106401 (2010)
gro-pr | Research asia research news
Supersonic waves may help electronics beat the heat
18.05.2018 | DOE/Oak Ridge National Laboratory
Researchers control the properties of graphene transistors using pressure
17.05.2018 | Columbia University
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A...
A team led by Austrian experimental physicist Rainer Blatt has succeeded in characterizing the quantum entanglement of two spatially separated atoms by observing their light emission. This fundamental demonstration could lead to the development of highly sensitive optical gradiometers for the precise measurement of the gravitational field or the earth's magnetic field.
The age of quantum technology has long been heralded. Decades of research into the quantum world have led to the development of methods that make it possible...
Cardiovascular tissue engineering aims to treat heart disease with prostheses that grow and regenerate. Now, researchers from the University of Zurich, the Technical University Eindhoven and the Charité Berlin have successfully implanted regenerative heart valves, designed with the aid of computer simulations, into sheep for the first time.
Producing living tissue or organs based on human cells is one of the main research fields in regenerative medicine. Tissue engineering, which involves growing...
A team of scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg investigated optically-induced superconductivity in the alkali-doped fulleride K3C60under high external pressures. This study allowed, on one hand, to uniquely assess the nature of the transient state as a superconducting phase. In addition, it unveiled the possibility to induce superconductivity in K3C60 at temperatures far above the -170 degrees Celsius hypothesized previously, and rather all the way to room temperature. The paper by Cantaluppi et al has been published in Nature Physics.
Unlike ordinary metals, superconductors have the unique capability of transporting electrical currents without any loss. Nowadays, their technological...
02.05.2018 | Event News
13.04.2018 | Event News
12.04.2018 | Event News
18.05.2018 | Power and Electrical Engineering
18.05.2018 | Information Technology
18.05.2018 | Information Technology