The effective mass in physics is a measure of how a particle or object responds to an external force. It is the mass that appears in equations of motion, such as Newton's second law, and describes how an object will accelerate under the influence of a force.
The effective mass can be calculated by taking the second derivative of the energy with respect to the wavevector. This can be represented as m* = ℏ²(d²E/dk²)^-1, where m* is the effective mass, ℏ is the reduced Planck's constant, E is the energy, and k is the wavevector.
The effective mass of a particle can be affected by various factors such as the crystal structure, temperature, and the presence of impurities or defects in the material. It can also be influenced by external electric and magnetic fields.
The effective mass is an important parameter in understanding the electronic properties of materials. It can help predict how a material will behave in different conditions and can be used to design new materials with specific properties. It also plays a crucial role in the field of semiconductor devices.
Some common methods used to measure effective mass include angle-resolved photoemission spectroscopy, cyclotron resonance, and Hall effect measurements. These techniques involve studying the behavior of electrons in a material under the influence of an external force or magnetic field.