Green’s Functions at Zero Temperature

Abstract

Many-body calculations are often done for model systems at zero temperature. Of course, real experimental systems are never at zero temperature, although they are often at low temperature. Many quantities are not very sensitive to temperature, particularly at low temperature. Thus, zero temperature calculations are useful even for describing real systems. Furthermore, the zero temperature property of a system is an important conceptual quantity—the ground state of an interacting system. We often describe a system as its ground state plus its excitations, and the ground state may be deduced from a zero temperature calculation. Many zero temperature calculations have been done to deduce, for example, the ground state of the homogeneous electron gas or the ground state of superfluid ⁴He.