  This paper serves as a primer on superconductivity, inviting students for
further investigation. Although the theory of superconductivity is a many-body
quantum theory, here we take a more didactic route based on thermodynamics and
symmetry. We briefly survey the more than a century-old field and provide a
one-sentence definition of a superconductor. Surprisingly, many textbooks lack
such a definition, usually introducing superconductors through their properties
rather than by definition. We explain the concept of an order parameter,
symmetry, and symmetry breaking. Based on this, we clarify the difference
between conventional and unconventional superconductors, which is frequently a
confusing topic for newcomers. We provide the reader with a taste of a current
research topic in the field of unconventional superconductivity and magnetism.
For this, we explain the concept of time-reversal symmetry breaking in
condensed matter physics, which is usually associated with a form of magnetism.
Here, we show that time-reversal symmetry might be broken in superconductors,
leading to magnetic properties due to superconductivity itself. For this
purpose, we utilize the method of the Ginzburg-Landau theory for phase
transitions. We discuss the field of chiral superconductivity and guide the
interested reader to further study.
