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A low-temperature physicist investigates matter when thermal excitation is small enough for quantum behaviour to become especially prominent. Superconductivity, superfluidity and spin systems are characteristic subjects, although the temperature scale depends on the material and the effect being studied.

The central experimental problem is often controlling unwanted heat transfer while making a measurable electrical, magnetic or mechanical probe. A cryostat supplies a controlled low-temperature environment; thermometry and heat-leak measurements establish what the sample actually experiences. Reducing $k_{B}T$ relative to an excitation energy gap can suppress thermal populations, allowing a quantum ground-state response to be distinguished from a classical high-temperature one.