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Interplay between magnetism and superconductivity

The interplay of magnetism and superconductivity plays a central role in the continuously-growing field of strongly correlated electron systems. Since already more than two decades, superconductivity has been known to develop in many heavy-fermion magnetic materials. In these systems, both superconductivity and the huge effective mass of the electrons - which is up to 100-1000 times that of the free electron - result from the proximity of a magnetic quantum phase transition and from its associated quantum critical magnetic fluctuations. In organics materials as well as in the recently-discovered iron-based superconductors, superconductivity also often develops in the vicinity of a quantum magnetic phase transition. This suggests that all these very different electronic systems might not be so different, at least concerning the suspected role played by the quantum magnetic fluctuations for the formation of the superconducting Cooper pairs. Understanding how magnetism and superconductivity are connected in these systems should shed light on some of the ingredients necessary to get high-temperature superconductivity, as that observed in the high-temperature superconducting cuprates, and could open a new route to room-temperature superconductivity. The recent discovery of re-entrance of superconductivity in the vicinity of a field-induced magnetic transition in the ferromagnet URhGe confirms the intimate relationship between magnetism and superconductivity in heavy fermions.

Fig. : (left) Phase diagram of the heavy-fermion antiferromagnet CeRh2Si2 under pressure [9]. (right) Phase diagram of the iron-based superconductor Ba(Fe1−xCox)2As2 [10].

References

[9] S. Araki et al., J. Phys.: Condens. Matter 14, L377 (2002).

[10] F. Hardy et al., EPL 91, 47008 (2010).

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