Von Klitzing constant
Introduction
The Von Klitzing constant, denoted as RK, is a physical constant named after the German physicist Klaus von Klitzing, who discovered the quantized Hall effect. The constant is defined as the resistance value between the voltage and current terminals of a Hall effect device when the conductance is quantized. It is a fundamental constant of nature with a value of approximately 25812.807 ohms.
History
The Von Klitzing constant was discovered during experiments on the quantum Hall effect in 1980. Klaus von Klitzing was investigating the properties of two-dimensional electron systems under strong magnetic fields at low temperatures. He observed that the Hall resistance exhibited step-like increases with magnetic field strength, with each step corresponding to a whole number multiple of a fundamental resistance value. This value was later named the Von Klitzing constant.
Significance
The discovery of the Von Klitzing constant had a profound impact on the field of condensed matter physics. It provided a precise and universal standard for electrical resistance, which is independent of the physical properties of the material and only dependent on the fundamental constants of nature, the charge of the electron, and the Planck constant.
Measurement
The Von Klitzing constant is measured using a device known as a quantum Hall device. This device is typically made from a two-dimensional electron gas, which is created at the interface between two different semiconductor materials. When a strong magnetic field is applied perpendicular to the plane of the electron gas, and the temperature is lowered to near absolute zero, the electrons condense into a quantum fluid state. In this state, the conductance of the device becomes quantized, and the Hall resistance is given by the Von Klitzing constant.
Applications
The Von Klitzing constant is used as a standard for defining the ohm in the International System of Units (SI). Since 1990, the ohm has been defined in terms of the frequency of a specific radiation from the cesium atom, the speed of light, and the Von Klitzing constant. This definition provides a highly accurate and reproducible standard for electrical resistance.