- #1

ice109

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## Homework Statement

Assume that H0 describes a paramagnetic system that couples to a magnetic field via

the Zeeman effect, i.e. V = −μB, where μ is the magnetic moment. Note that for the

unperturbed paramagnetic system the probability of having an up-spin is equal to that for

a down-spin. Show that the magnetic susceptibility, defined as E = EGS −[itex]\frac{1}{2}\chi B^2[/itex], where

EGS is the ground state energy in the absence of field, is always non-negative. Write down

the expression for the susceptibility.

Note: A similar expression for a susceptibility is valid for an arbitrary perturbation. This

is known as the Lehmann representation applied to the linear response of the system to

the perturbation.

## Homework Equations

## The Attempt at a Solution

i have no idea what's being asked here? is the perturbation −μB to a free particle hamiltonian?

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