Insight
is our reward

Publications in Nature Physics by NOMIS researchers

NOMIS Researcher(s)

Published in

August 10, 2023

Arrays of Josephson junctions are governed by a competition between superconductivity and repulsive Coulomb interactions, and are expected to exhibit diverging low-temperature resistance when interactions exceed a critical level. Here we report a study of the transport and microwave response of Josephson arrays with interactions exceeding this level. Contrary to expectations, we observe that the array resistance drops dramatically as the temperature is decreased—reminiscent of superconducting behaviour—and then saturates at low temperature. Applying a magnetic field, we eventually observe a transition to a highly resistive regime. These observations can be understood within a theoretical picture that accounts for the effect of thermal fluctuations on the insulating phase. On the basis of the agreement between experiment and theory, we suggest that apparent superconductivity in our Josephson arrays arises from melting the zero-temperature insulator. © 2023, The Author(s).

Research field(s)
Natural Sciences

NOMIS Researcher(s)

Published in

May 29, 2023

Under high pressures and temperatures, molecular systems with substantial polarization charges, such as ammonia and water, are predicted to form superionic phases and dense fluid states with dissociating molecules and high electrical conductivity. This behaviour potentially plays a role in explaining the origin of the multipolar magnetic fields of Uranus and Neptune, whose mantles are thought to result from a mixture of H2O, NH3 and CH4 ices. Determining the stability domain, melting curve and electrical conductivity of these superionic phases is therefore crucial for modelling planetary interiors and dynamos. Here we report the melting curve of superionic ammonia up to 300 GPa from laser-driven shock compression of pre-compressed samples and atomistic calculations. We show that ammonia melts at lower temperatures than water above 100 GPa and that fluid ammonia’s electrical conductivity exceeds that of water at conditions predicted by hot, super-adiabatic models for Uranus and Neptune, and enhances the conductivity in their fluid water-rich dynamo layers. © 2023, The Author(s), under exclusive licence to Springer Nature Limited.

Research field(s)
Natural Sciences, Physics & Astronomy, Fluids & Plasmas

NOMIS Researcher(s)

Published in

March 1, 2022

Biomolecular condensates are dense assemblies of proteins that form distinct biochemical compartments without being surrounded by a membrane. Some, such as P granules and stress granules, behave as droplets and contain many millions of molecules. Others, such as transcriptional condensates that form on the surface of DNA, are small and contain thousands of molecules. The physics behind the formation of small condensates on DNA surfaces is still under discussion. Here we investigate the nature of transcription factor condensates using the pioneer transcription factor Krüppel-like factor 4 (Klf4). We show that Klf4 can phase separate on its own at high concentrations, but at low concentrations, Klf4 only forms condensates on DNA. Using optical tweezers, we demonstrate that these Klf4 condensates form on DNA as a type of surface condensation. This surface condensation involves a switch-like transition from a thin adsorbed layer to a thick condensed layer, which shows hallmarks of a prewetting transition. The localization of condensates on DNA correlates with sequence, suggesting that the condensate formation of Klf4 on DNA is a sequence-dependent form of surface condensation. Prewetting together with sequence specificity can explain the size and position control of surface condensates. We speculate that a prewetting transition of pioneer transcription factors on DNA underlies the formation and positioning of transcriptional condensates and provides robustness to transcriptional regulation.

Research field(s)
Natural Sciences, Physics & Astronomy, Fluids & Plasmas