Licchavi Lyceum


Licchavi Lyceum

Fermi Dirac Distribution

The Fermi Dirac distribution is a statistical distribution that describes the distribution of particles with half-integer spin, called fermions, in a system at thermal equilibrium. It provides insights into the probabilities associated with different energy levels and allows for the calculation of various properties of the system, such as average occupation number and energy distribution.

The distribution is derived based on the principles of quantum statistics and assumes that the fermions follow quantum mechanics. It is applicable to systems where the particles are indistinguishable, and the Pauli exclusion principle applies, which states that no two identical fermions can occupy the same quantum state simultaneously.

The Fermi-Dirac distribution is derived as follows:

  1. Consider a system of fermions at thermal equilibrium.
  2. The distribution assumes that the fermions occupy discrete energy levels, and there is a range of possible energy levels.
  3. The distribution function, denoted as f(E), represents the average occupation probability of finding a fermion at an energy level E.
  4. The Fermi-Dirac distribution function is given by:f(E) = 1 / (e^((E – μ) / (kT)) + 1)where:
    • E is the energy of a specific energy level
    • μ is the chemical potential of the system
    • k is Boltzmann’s constant
    • T is the temperature of the system in Kelvin
  5. The distribution function shows that the average occupation probability is related to the energy level. Higher energy levels have lower average occupation probabilities, while lower energy levels have higher average occupation probabilities.
  6. The distribution also introduces the concept of chemical potential (μ), which determines the average energy per particle and controls the total number of particles in the system. The chemical potential ensures that the Pauli exclusion principle is satisfied, as it prevents two fermions from occupying the same quantum state.

The Fermi-Dirac distribution provides important insights into the behavior of fermionic systems. Some key properties and applications include:

  • Average Occupation Number: The distribution allows us to calculate the average occupation number, which represents the average number of fermions occupying a specific energy level. It provides information about the population distribution among different energy levels.
  • Energy Distribution: The distribution provides information about the probabilities associated with different energy levels. It describes the distribution of energy among the fermions in the system.
  • Fermi Energy: The Fermi energy, denoted as E_F, represents the energy level at which the occupation probability is 0.5, meaning that 50% of the fermions are below the Fermi energy and 50% are above it. The Fermi energy is an important characteristic of fermionic systems.
  • Applications: The Fermi-Dirac distribution is utilized in various fields, including condensed matter physics, electronic band theory, and the behavior of fermionic particles in conductors, semiconductors, and superconductors.

The Fermi-Dirac distribution provides a statistical description of the behavior of fermionic particles, allowing us to understand their energy distribution and calculate various properties associated with fermionic systems.