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Chinese University of Science and Technology Makes Progress in Research on New Topological Materials Weir Semiconductor
[ Instrument R & D of Instrument Network ] Among the new quantum materials, topological materials with special energy band structure also have novel electronic transport characteristics. Related research can not only deepen the understanding of topological states, but also hope to promote the development of new high-performance electronic devices. A typical representative is the Weir semimetal system that has attracted widespread attention. Its transportation research often shows many characteristics such as large unsaturated magnetoresistance, negative magnetoresistance effect under a parallel magnetic field, and planar Hall effect. Arc also provides an electronic channel with high mobility and low power consumption. These characteristics are derived from the existence of the Fermion near Fermi.
Weyl fermions, or Weyl fermions, are massless fermions and play an important role in quantum theory and standard models. Weir Fermion is considered to be a part of fermion in quantum theory, and is a solution derived from the Dirac equation by Herman Weir, and is called Weir equation. Dirac fermions can be seen as a combination of left-handed Wyle fermions and right-handed Wyle fermions. Waifermions are not considered elementary particles. Waifermions exist in the form of quasi-particle excitation in condensate physics.
Herring (C · Hering) first predicted the existence of Weir Fermion in the solid-state system with energy band structure. Tantalum arsenic crystal is the first crystal structure to discover the existence of Weir fermions. The charged fermions are stable at room temperature.
So far, researches on Weir fermions and Weir physics have been limited to semimetal systems. However, from the perspective of device applications, semiconductors have their unique value relative to semi-metals. Recently, Professor Zeng Changgan and Professor Wang Zhengfei of the Key Laboratory of Strongly Coupling Quantum Materials Physics of the International Functional Materials Quantum Design Center and the Department of Physics of the Hefei National Research Center for Microscale Material Science of the University of Science and Technology of China have collaborated with Wang Zhengfei on experimental and theoretical research. Tellurium discovered chiral anomalies dominated by Weir Fermions and quantum oscillations with the logarithm of the magnetic field as a period, which successfully extended Weir physics to semiconductor systems.
Tellurium is a narrow-band semiconductor. Due to the inversion of symmetry in space inversion and the corresponding strong spin-orbit coupling, there is a weir point where the band crosses near the top of the valence band. The team prepared a high-quality tellurium single crystal by physical vapor deposition, and its hole self-doping characteristics put the Fermi energy level at the top of the valence band, which significantly enhanced the impact of Waifermion on the transport properties. The low-temperature transport study further revealed that tellurium single crystals exhibit typical magnetic transport characteristics due to chiral anomalies, including the negative magnetoresistance effect when the magnetic field is parallel to the current direction, and the planar Hall effect that occurs when the magnetic field is in the sample plane.
The Hall effect is a kind of electromagnetic effect. This phenomenon was discovered by the American physicist Hall (EH Hall, 1855-1938) in 1879 when studying the conduction mechanism of metals. When the current passes through the semiconductor perpendicular to the external magnetic field, the carriers deflect, and an additional electric field is generated perpendicular to the direction of the current and magnetic field, thereby generating a potential difference between the two ends of the semiconductor. This phenomenon is the Hall effect, and this potential difference is also This is called the Hall potential difference. The Hall effect is determined using the left-hand rule.
With the help of the strong magnetic field device of the Hefei Chinese Academy of Sciences Strong Magnetic Field Science Center and the Wuhan National Pulsed Strong Magnetic Field Science Center, the team further discovered rare magnetoresistance and Hall resistance quantum oscillations with a logarithmic magnetic field period. This new type of quantum oscillation is a manifestation of self-similar discrete scale invariance, which can be attributed to the fine structure constant (7.5) in tellurium crystals is much larger than the value of vacuum (1/137), which makes the Waifermions and the opposite charge center Form a quasi-bound state in the form of a resonance state.
This work is the first to realize the "topological Weir semiconductor" which combines novel topological properties and semiconductor properties. If the Fermi energy level is adjusted from the valence band to the energy gap, a metal-insulator transition will occur, accompanied by a topological non-trivial state to a mediocre state. This unique characteristic of Weir semiconductors does not exist in Weir semimetals. The discovery of Waier Semiconductor provides new ideas for designing new topological semiconductor devices.
Source: Encyclopedia, University of Science and Technology of China