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For electron or electron holes in a solid, the effective mass is usually stated in units of the true mass of the electron m _{e} (9.11×10 ^{-31} Kg). In these units, it is actually in the range 0.01 to 10, but can also be lower or higher, for example reaching 1,000 in exotic heavy fermion materials, or anywhere from zero to infinity(depending on definition) in graphene. As it simplifies the more general band theory, the efective electronic mass can be seen as an important basic parameter that influences measurable properties of a solid, including everything from the efficiency of the solar cell to the speed of an integrated circuit.

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