Zero and ultralow-field nuclear magnetic resonance (ZULF NMR) is an NMR modality where experiments are performed in fields at which spin-spin interactions within molecules and materials are stronger than Zeeman interactions. This typically occurs at external fields of microtesla strength or below, considerably smaller than Earth's field. In ZULF NMR, the measurement of spin-spin couplings and spin relaxation rates provides a nondestructive means for identifying chemicals and chemical fragments, and for conducting sample or process analyses. The absence of the symmetry imposed by a strong external magnetic field enables experiments that exploit terms in the nuclear spin Hamiltonian that are suppressed in high-field NMR, which in turn opens up new capabilities in a broad range of fields, from the search for dark matter to the preparation of hyperpolarized contrast agents for clinical imaging. Furthermore, as in ZULF NMR the Larmor frequencies are typically in the audio band, the nuclear spins can be manipulated with d.c. magnetic field pulses, and highly sensitive magnetometers are used for detection. In contrast to high-field NMR, the low-frequency signals readily pass through conductive materials such as metals, and heterogeneous samples do not lead to resonance line broadening, meaning that high-resolution spectroscopy is possible. Notable practical advantages of ZULF NMR spectroscopy are the low cost and relative simplicity and portability of the spectrometer system. In recent years ZULF NMR has become more accessible, thanks to improvements in magnetometer sensitivity and commercial availability, and the development of hyperpolarization methods that provide a simple means to boost signal strengths by several orders of magnitude. These topics are reviewed and a perspective on potential future avenues of ZULF-NMR research is presented.

The less-traveled low road in nuclear magnetic resonance is discussed, honoring the contributions of Prof. Bernhard Blümich, aspiring towards reaching 'a new low.' A history of the subject and its current status are briefly reviewed, followed by an effort to prophesy possible directions for future developments.

Over the last 15 years, the content ofNature Physicshas covered an enormous breadth of subjects at the forefront of physics. The journal's past and present editors recount their favourite papers and what made chaperoning them to publication special.

Attracting youngsters to STEM disciplines is a challenge.But once new students have started their courses, how can they be retained?A study of Justyna Zwolak and colleagues suggests that social integration outside the classroom is an important factor.Zwolak et al. surveyed 273 students (from more than 20 different majors) enrolled in introductory physics courses at Florida International University.Every few weeks they asked them about their interactions with peers inside and outside the classroom and performed a complex social-network analysis of those data.Unsurprisingly, for students with grades clearly above or below average, the best predictor of persistence was the final grade.However, whether students with grades in the 'middle of the pack' chose to commit to their studies depended more on how successfully they built up an out-of-class social network.This finding is in contrast to the role of in-class networks, which are not more correlated with persistence than grades, as these authors had found in earlier work.