Researchers used a highly sensitive technique to examine 16 samples from two different meteorites to find new superconducting alloys. One meteorite formed in the iron core of an asteroid and one flung off a planet’s surface by a collision.
Above – Credit: Graeme Churchard/flickr. Samples from the Mundrabilla meteorite, which was found in Australia in 1911, contain traces of alloys that are low-temperature superconductors.
They used multiple techniques to identify which materials are responsible. In both samples, they found small amounts of materials that can become superconducting at about –268 °C, although the meteorites would not naturally reach such temperatures. In one case, the material was an alloy of lead, indium, and tin, and in the other it was indium and tin without lead.
Both extraterrestrial superconductors are previously-known materials.
The processes that formed these meteorites—and the superconductors they carry—included high pressures and high temperatures, very slow cooling at a rate of about 3°C per year over millions of years, and shocks from high-impact collisions. Schuller expected that such extremes might form novel superconductors that earthbound materials scientists had not yet discovered.
They developed a new technique called magnetic field modulated microwave spectroscopy. To look for superconductors, the sample is hit with microwaves while under a small, oscillating, magnetic field. Superconducting materials absorb the microwaves differently than non-superconducting ones, and that causes a measurable change in the magnetic field. The technique is capable of detecting superconducting regions as small as one-trillionth of a cubic centimeter.
In this paper, we report the presence of superconducting material in two meteorites. We further characterize these phases as alloys of lead, tin, and indium. These findings could impact our understanding of several astronomical environments. Superconducting particles in cold environments could affect planetary formation, shape and origin of magnetic fields, dynamo effects, motion of charged particles, and other processes.
Meteorites can contain a wide range of material phases due to the extreme environments found in space and are ideal candidates to search for natural superconductivity. However, meteorites are chemically inhomogeneous, and superconducting phases in them could potentially be minute, rendering detection of these phases difficult. To alleviate this difficulty, we have studied meteorite samples with the ultrasensitive magnetic field modulated microwave spectroscopy (MFMMS) technique. MFMMS measurements detected superconducting transitions in samples from each, above 5 K. By subdividing and remeasuring individual samples, grains containing the largest superconducting fraction were isolated. The superconducting grains were then characterized with a series of complementary techniques, including vibrating-sample magnetometry (VSM), energy-dispersive X-ray spectroscopy (EDX), and numerical methods. These measurements and analysis identified the likely phases as alloys of lead, indium, and tin.