Microscopic nature of the Weak Magnetic Order (WMO) phase in UTe2 under pressure

Determine the microscopic nature of the pressure-induced phase in UTe2 referred to as Weak Magnetic Order (WMO), by identifying its underlying order and characteristics at the microscopic level.

Background

Under applied pressure, UTe2 exhibits a superconducting phase (SC2) and additional phase transitions at higher temperatures. One such transition has been proposed to correspond to short-range magnetic order and has been termed Weak Magnetic Order (WMO).

The present calorimetric study finds that WMO is stabilized above SC2 and across a significant pressure range below the antiferromagnetic critical pressure. The authors argue that understanding WMO is central to interpreting the enhancement of the Sommerfeld coefficient and the possible role of quantum criticality associated with WMO, but its microscopic nature has not yet been established.

References

This phase was proposed to be a short-range magnetic order and named “Weak Magnetic Order” (WMO), although its microscopic nature is yet to be determined.

— Quantitative thermodynamic study of superconducting and normal states in UTe2 under pressure  (2603.29760 - Vasina et al., 31 Mar 2026) in Introduction, main text (paragraph discussing the WMO phase)

If the A_0 phase indeed exists and is embedded deep inside the phase diagram, the meeting point is no longer, strictly speaking, a tetracritical point. At present, we do not know the exact critical behavior associated with such a multicritical point, which deserves further theoretical investigation.

— Generic thermodynamics of condensates with extremely small superfluid density ---Application to UTe$_2$ and hidden second phase transition---  (2609.19834 - Machida, 17 Sep 2026) in Section “Phase diagrams under pressure,” subsection “Construction of the phase diagram under P”