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In physics, 'long-range order' characterizes physical systems in which remote portions of the same sample exhibit correlated behavior.
This can be seen with a correlation function, namely the spin-spin correlation function:
$G(x,x\text{'})\; =\; langle\; s(x)s(x\text{'})$
angle.
This function is equal to unity when $x=x\text{'}$ and decreases as the distance $|x-x\text{'}|$ increases. Typically, it decays exponentially to zero at large distances, and the system is considered to be disordered. If, however, the correlation function decays to a constant value at large $|x-x\text{'}|$ then the system is said to possess long-range order. If it decays to zero algebraically (i.e., as a rational function) then it is called quasi-long-range order.

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See also

See also

★ order-disorder