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A new model describes the population of black hole binaries without assumptions on the shape of their distribution—a capability that could boost the discovery potential of gravitational-wave observations.

Since the first groundbreaking observation of gravitational waves from a black hole merger [1], a worldwide network of observatories–LIGO, Virgo, and KAGRA—has discovered nearly a hundred mergers involving black holes and neutron stars (Fig. 1). The nature of this population of compact objects has implications for nearly every aspect of astrophysics and cosmology. However, understanding how gravitational-wave sources fit into our astrophysical theories has proved challenging. Many of the discoveries have confirmed our expectations, but some—such as those of asymmetric black hole binaries or of unexpectedly massive black holes—defy them.

About 4.5 billion years ago, a small planet smashed into the young Earth, flinging molten rock into space. Slowly, the debris coalesced, cooled and solidified, forming our moon. This scenario of how the Earth’s moon came to be is the one largely agreed upon by most scientists. But the details of how exactly that happened are “more of a choose-your-own-adventure novel,” according to researchers in the University of Arizona Lunar and Planetary Laboratory who published a paper in Nature Geoscience.

“Our research is inspired by the idea that unconventional superconductivity usually emerges in proximity to magnetism,” Xiang said. “In particular, for copper-based and iron-based , many of the proposed superconducting pairing mechanisms are closely connected to magnetism; moreover, the interplay between magnetism and superconductivity may give birth to more peculiar phases of matter, including the pair-density-wave (PDW) order with a spatially oscillating superconducting order parameter and finite-momentum pairing which has been an intense focus of research recently.”

The EuO/KTO heterostructure examined by Xiang and his colleagues exhibits a strong ferromagnetic proximity effect elicited by the EuO overlayer. This effect makes it an ideal platform to study unconventional superconductivity.

“The first report on the superconductivity at the EuO/KTO interface was published in 2021, focusing on the KTO (111) interface,” Xiang said. “We have since worked on the EuO/KTO (110) interface (considering its improved interface quality), at which we revealed the emergence of two-dimensional superconductivity in a previous paper.”