Scientists who study matter at very low temperatures are called low-temperature physicists, cryogenicists, or condensed matter physicists (specifically those focusing on low-temperature phenomena).

Here's a breakdown of their specialties:

* Low-temperature physicists: This term broadly encompasses scientists working at very low temperatures, often in the range of millikelvins or even microkelvins (a fraction of a degree above absolute zero). They study various properties of matter at these extreme temperatures, including superconductivity, superfluidity, and quantum phenomena.

* Cryogenicists: These specialists are focused on the science and technology of producing and controlling extremely low temperatures. They develop and operate specialized equipment like cryostats and dilution refrigerators, which are essential for low-temperature research.

* Condensed matter physicists: While not all condensed matter physicists work at low temperatures, many specialize in studying the behavior of matter in its condensed states, which includes solids, liquids, and plasmas. Low-temperature physics is a crucial part of condensed matter research, as it reveals unique quantum properties that are masked at higher temperatures.

In summary, these researchers delve into the intriguing world of matter at its coldest, uncovering fascinating quantum effects and contributing to advancements in fields like quantum computing, high-precision measurements, and material science.