Speaker
Description
Superconductivity in UTe2 has many striking properties, like extremely high and anisotropic critical fields and the existence of multiple superconducting phases induced by either pressure or magnetic field. However perhaps the most unusual feature is the reinforcement of superconductivity in applied magnetic fields. The usual effect of magnetic field on superconductivity is through the effect of the field on the motion or the spin of the carriers. The effect of magnetic field on the pairing mechanism is absent or negligeable. This is not surprising in conventional superconductors where the pairing mechanism stems from the electron-phonon interaction, but it is also the case in most unconventional superconductors, even when the pairing mechanism has a magnetic origin. UTe2 is one of the few exceptions where an applied magnetic field can enhance the strength of the pairing mechanism and actually reinforce superconductivity. In ambient pressure conditions, this effect is most spectacular when the field is applied along the b-axis of this orthorhombic system, where, above 15T, the superconducting critical temperature increases with increasing field. However under pressure a reinforcement of superconductivity with magnetic field is found for field applied along the c-axis. In both cases the probable origin is the proximity of a magnetic phase transition line that can be crossed by tuning the field. We will show recent calorimetry measurements in extreme conditions of pressure and/or magnetic field that reveal the interactions between the different phases and provide clues for the underlying pairing mechanisms for the unconventional superconducting phases of this fascinating material.