Existence of the LOFF State in Superconducting UPd_2Al_3

TL;DR

This paper investigates the possibility of the LOFF state in UPd_2Al_3, deriving a critical field formula and concluding that the LOFF state alone cannot explain the observed phase diagram, suggesting the need for more complex models.

Contribution

The paper derives a comprehensive formula for the upper critical field of the LOFF state at all temperatures and demonstrates its limitations in explaining UPd_2Al_3's phase diagram.

Findings

LOFF state cannot fully explain UPd_2Al_3 phase diagram

Derived a formula for the upper critical field at all temperatures

Indicates need for models breaking cylindrical symmetry

Abstract

In a recent Letter, Gloos et al have suggested that the heavy fermion superconductor, UPd_2Al_3, has a transition in magnetic field from the normal state to an inhomogeneous superconducting state, known as the LOFF state, followed at lower fields by a first order phase transition to the usual flux lattice state. To investigate this, the author derives a formula for the upper critical field for the LOFF state valid at all temperatures in the clean limit (the previous work of Gruenberg and Gunther was restricted to zero temperature), and shows that the LOFF state cannot quantitatively explain the phase diagram for UPd_2Al_3. This indicates that a more general solution which breaks cylindrical symmetry is necessary to explain the data.