Jiasheng Chen

The phase diagram of the heavy fermion compound UTe 2 contains multiple superconducting phases, several of which show characteristics of odd-parity pairing. We have investigated the pressure dependence of the superconducting transition in high-quality crystals of UTe 2 by tracking its signature in the magnetic susceptibility χ ( T ) . A single, sharp superconducting transition is observed at low pressures < 0.3 GPa . At higher pressure, a second feature emerges in χ ( T ) , which is located at the lower-temperature superconducting phase boundary previously identified in specific heat measurements. This second transition anomaly in χ ( T ) can be attributed to a step change in the London penetration depth, providing direct evidence for a change in the superconducting order parameter of UTe 2 . Thermodynamic constraints suggest that the low temperature, high pressure superconducting state is distinct from zero pressure superconductivity as well as from the high pressure, high temperature superconducting state, raising the possibility of multicomponent superconductivity in high pressure UTe 2 . Published by the American Physical Society 2025

Commercial adiabatic demagnetisation refrigerators still employ the same hydrated salts that were first introduced over 85 years ago. The inherent limitations of these insulating magnetocalorics – poor thermal conductivity at sub-Kelvin temperatures, low entropy density, corrosiveness – can be overcome by a new generation of rare-earth based metallic magnetocalorics. Here, we present the metallic magnetocaloric YbNi_1.6Sn as an attractive alternative to conventional refrigerants. YbNi_1.6Sn retains high entropy into the 100 mK regime and avoids the noble metal constituents of alternative refrigerants. Demagnetisation tests demonstrate that YbNi_1.6Sn enables economical and durable alternatives to traditional cooling devices for temperatures reaching below 120 mK. We find that the magnetocaloric properties of this material are facilitated by unusually small Kondo and RKKY interactions, which position YbNi_1.6Sn in the extreme local moment limit on the generalised Kondo lattice phase diagram.

Dy(OH) ₃ has impressive magnetocaloric performance optimised around 20 K making it suitable for hydrogen liquefaction using magnetic cooling.

Relativistic effects play a prominent role in many electronic material properties such as the Rashba and Dresselhaus spin splitting in inversion asymmetric crystals, or the bulk band gap in topological insulators. By contrast, macroscopic material properties are typically not connected to relativistic phenomena. As an exception to this rule, we show that the macroscopic chemical and structural properties of superconducting In₅Bi₃ are driven by relativistic physics. In the non-relativistic limit In₅Bi₃ decomposes into elemental indium and bismuth, but the inclusion of relativistic spin–orbit coupling chemically stabilizes the In₅Bi₃ stoichiometry. Similarly, the structural stability of tetragonal In₅Bi₃ is driven by the spin–orbit interaction, which eliminates a phonon instability present in the non-relativistic limit. Low-temperature resistivity and heat capacity measurements show that In₅Bi₃ is a strong coupling superconductor, with a superconducting critical temperature of 4.2 K and a superconducting critical field of 0.3 T. The unconventional interplay between relativity with chemistry and structure, together with the presence of superconductivity, make In₅Bi₃ a versatile material that provides, for example, a simple model for the study of strong coupling superconductivity in quasiperiodic crystals.