Why the crystal momentum k in 2D band structure is defined on a torus?

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SUMMARY

The crystal momentum k in a two-dimensional (2D) band structure is defined on a torus to satisfy the Born–von Karman boundary conditions. This approach is essential for systems like the two-dimensional electronic gas, where periodicity in both x and y directions is established with a period of 2π/a. This toroidal representation allows for a more accurate description of the electronic states in 2D materials, facilitating the analysis of their properties.

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  • Understanding of 2D band structure theory
  • Familiarity with crystal momentum concepts
  • Knowledge of Born–von Karman boundary conditions
  • Basic principles of solid-state physics
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lyylynn
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Hi,

Could someone help to explain that why for the 2 D system, like 2 dimensional electronic gas, the crystal momentum k in 2D band structure is defined on a torus?

Thanks a lot.:)
 
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Probably to satisfy Born–von Karman boundary condition...
 
Because it's periodic in x and y with period 2*pi/a.
 

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