For example if we look Ising model correlation function is(adsbygoogle = window.adsbygoogle || []).push({});

[tex]\langle S_iS_{i+j}\rangle[/tex]

So we can see that if we took into acount just nearest neighbours interraction we also will see that some [tex]i+j[/tex]-th spin feels i-th spin. So there is some correlation between them.

Am I right? This is correlation function. And what is correlation lenght?

Is it lenght between

[itex]\uparrow\uparrow\uparrow\uparrow\downarrow\downarrow[/itex]

the biggest number of align spins?

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# Difference between corelation function and corelation lenght

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