One of the great physicists of the 20th century, Paul Dirac, predicted in 1931 that there could, and probably should, be magnetic monopoles. These are the analogues of electrons and protons, which carry a net electric charge, for magnetism - particles of just north or just south magnetic poles, unlike every magnet that has ever been observed, which is a dipole. Many experiments have looked for magnetic monopoles over the past decades, but no evidence of them has been found.
However, a few days ago, a paper was published that shows synthetic monopoles could be formed using a Bose-Einstein condensate, that strange form of matter where bosons (particles with integer spin) can, when extremely cold (on order of nanokelvin), have such long wavelengths that they superpose and occupy the same quantum state. It appears that by spinning this system and producing a vortex, a version of a magnetic monopole is formed. This would revolutionize the hunt for monopoles because, now being able to isolate and study this synthetic version, one should be able to determine the properties and characteristics of monopoles. Other scientists would then know the signature to look for in other experiments.
Keep in mind that in Dirac's theory, monopoles should exist because the implication would be electric charge must be quantized - it explains what we see with the electrical properties of matter.