Abstract
The elastic and anelastic properties of a single crystal of Co-doped pnictide Ba(Fe0.957Co0.043)2As2 have been determined by resonant ultrasound spectroscopy in the frequency range 10–500 kHz, both as a function of temperature through the normal-superconducting transition (Tc ≈ 12.5 K) and as a function of applied magnetic field up to 12.5 T. Correlation with thermal expansion, electrical resistivity, heat capacity, DC and AC magnetic data from crystals taken from the same synthetic batch has revealed the permeating influence of strain on coupling between order parameters for the ferroelastic (QE) and superconducting (QSC) transitions and on the freezing/relaxation behaviour of vortices. Elastic softening through Tc in zero field can be understood in terms of classical coupling of the order parameter with the shear strain e6, λe6, which means that there must be a common strain mechanism for coupling of the form λQE. At fields of ~5 T and above, this softening is masked by Debye-like stiffening and acoustic loss processes due to vortex freezing. The first loss peak may be associated with the establishment of superconductivity on ferroelastic twin walls ahead of the matrix and the second is due to the vortex liquid–vortex glass transition. Strain contrast between vortex cores and the superconducting matrix will contribute significantly to interactions of vortices both with each other and with the underlying crystal structure. These interactions imply that iron-pnictides represent a class of multiferroic superconductors in which strain-mediated coupling occurs between the multiferroic properties (ferroelasticity, antiferromagnetism) and superconductivity.
Highlights
One of the significant achievements of the 20th century was the discovery of high Tc cuprate superconductors which allow electrical conductivity with zero resistance at liquid nitrogen temperatures
Correlation with thermal expansion, electrical resistivity, heat capacity, DC and AC magnetic data from crystals taken from the same synthetic batch has revealed the permeating influence of strain on coupling between order parameters for the ferroelastic (QE) and superconducting (QSC) transitions and on the freezing/relaxation behaviour of vortices
Strain contrast between vortex cores and the superconducting matrix will contribute significantly to interactions of vortices both with each other and with the underlying crystal structure. These interactions imply that iron-pnictides represent a class of multiferroic superconductors in which strain-mediated coupling occurs between the multiferroic properties and superconductivity
Summary
One of the significant achievements of the 20th century was the discovery of high Tc cuprate superconductors which allow electrical conductivity with zero resistance at liquid nitrogen temperatures. In a quite different context, but with equivalent impact, there has been intense interest in multiferroic mat erials, defined as those displaying at least two out of ferroelastic, (anti)ferromagnetic and ferroelectric properties. The latter will be used for device applications, such as memories, with external control by combinations of magnetic, electric and stress fields. In both cases, the underlying physics is that the functional properties of interest are related to the proximity of multiple instabilities. Static magnetic order disappears in overdoped samples (x > ~0.06) but they still display evidence of favourable coupling between spin fluctuations and superconductivity [7, 8]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call