Strain-switchable field-induced superconductivity

Abstract

Field-induced superconductivity is a rare phenomenon where an applied magnetic field enhances or induces superconductivity. Here, we use applied stress as a control switch between a field-tunable superconducting state and a robust non–field-tunable state. This marks the first demonstration of a strain-tunable superconducting spin valve with infinite magnetoresistance. We combine tunable uniaxial stress and applied magnetic field on the ferromagnetic superconductor Eu(Fe 0.88 Co 0.12 ) 2 As 2 to shift the field-induced zero-resistance temperature between 4 K and a record-high value of 10 K. We use x-ray diffraction and spectroscopy measurements under stress and field to reveal that strain tuning of the nematic order and field tuning of the ferromagnetism act as independent control parameters of the superconductivity. Combining comprehensive measurements with DFT calculations, we propose that field-induced superconductivity arises from a novel mechanism, namely, the uniquely dominant effect of the Eu dipolar field when the exchange field splitting is nearly zero.

Perspective: probing elasto-quantum materials with x-ray techniques and in situ anisotropic strain

“…The competition between nematicity and superconductivity was further explored in a recent study on Co-doped EuFe 2 As 2 , a member of the 122 iron pnictide family [28]. In this study, stress was applied in the FeAs direction, inducing B 1g orthorhombicity (figure 2(d)).…”

“…This enhances the superconductivity, yielding a reduced resistivity value. From [28]. Reprinted with permission from AAAS.…”

“…The applied stress strongly tunes the resistivity but has virtually no effect on the Eu moment saturation field or value. From [28]. Reprinted with permission from AAAS.…”

“…A second study [28] examined the optimal-doped compound Eu(Fe 0.88 Co 0.12 ) 2 As 2 , which has a superconducting transition onset temperature (T SC ) of 20 K and an Eu ferromagnetic transition temperature (T FM ) of 17 K. The result is summarized in figure 3(b). The coexistence of the two phases results in the rare phenomenon of ferromagnetic superconductivity.…”