The quantum Hall effect is one of the most important scientific discoveries in the field of condensed matter physics since the 20th century. So far, four Nobel Prizes have been directly related to it. But for more than a century, scientists have been studying the quantum Hall effect in a two-dimensional system.
In order to achieve breakthroughs in this field, Xiu Faxian, a physics department of Fudan University, led his group to observe direct evidence of a new three-dimensional quantum Hall effect formed by the Orbital trajectory in topological semi-metal cadmium cadmium nanosheets. A key step from 2D to 3D. Relevant research results were published online in the main issue of Nature on December 18th, Beijing time.
As early as more than 130 years ago, the American physicist Hall discovered that the magnetic field perpendicular to the direction of the current is applied to the energized conductor, and the trajectory of the electron will be deflected to generate a voltage in the longitudinal direction of the conductor. This electromagnetic phenomenon is "huo Effect." However, previous experiments have shown that the quantum Hall effect only occurs in two-dimensional or quasi-two-dimensional systems. Is there a quantum Hall effect in a three-dimensional system? If so, what is the mechanism of motion of electrons?
To answer this question, the Sui Faxian team observed a three-dimensional quantum Hall effect in a special material system, namely the topological Dirac semi-metal cadmium arsenide material. This effect is different from the traditional two-dimensional quantum Hall. There is a special electron orbit, called the outer orbit. The electron can pass from the upper surface to the lower surface and then back to the upper surface.
Xiu Xianxian said that the difficulty of the subject lies in the preparation of materials and the measurement of devices. First of all, the material requirements are very high, the thickness must be precisely controlled, and there must be a high mobility. The research team started to grow this material in 2014. After almost five years of exploration, the thickness can be controlled (50-100 nm) and the mobility rate reaches 100,000. The second difficulty is that measurements must be made under extreme conditions: low temperatures and strong magnetic fields. The temperature is in the tens of milli-K (that is, more than 270 degrees below zero), and the strong magnetic field is more than thirty Tesla (a million times the geomagnetic field).
"Our research belongs to the basic research of free exploration. In the aspect of condensed matter physics, we have discovered the three-dimensional quantum Hall effect, which can provide a certain experimental basis for further research and exploration in the future. In addition, this material system has application Very high mobility, fast transmission and response, and some prototype devices for infrared detection and electron spin." Xia Xianxian said.
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