Abstract
High-pressure experiments have made many important contributions to the field of superconductivity, including studies on the Cu-oxide and Fe-based high-temperature superconductors (HTS). However, for detailed quantitative understanding, the nature of the high-pressure environment acting on the sample must be well defined, a requirement often not met. Since HTS are quasi-2D, all properties are anisotropic. As a result, only a combination of fully hydrostatic and uniaxial pressure experiments are capable of providing the detailed information required. Unfortunately, very few such experiments have been carried out. For both Cu-oxide and Fe-based HTS at optimal doping, Tc is found to be enhanced by either increasing the separation of the superconducting planes or decreasing their area. Future experiments will extend such hydrostatic/uniaxial studies over the entire doping range.
Highlights
Since the discovery of the high-Wf cuprates in 1986 [1] and the Fe-based pnictides in 2008 [2], an enormous volume of experimental and theoretical work has been carried out
In this paper we will attempt to illustrate a few examples of what high-pressure studies have, and have not, taught us about high-temperature superconductors (HTS)
The di!culty is that ‘not all pressures are created equal’ since the nature of high-pressure to which the sample is subjected depends on many factors, the pressure medium used and the temperature at which the pressure is changed. This uncertainty is worrisome for the Fe-based materials since they appear to be exquisitely sensitive to shear stresses which are, surprisingly, found to favor superconductivity
Summary
Since the discovery of the high-Wf cuprates in 1986 [1] and the Fe-based pnictides in 2008 [2], an enormous volume of experimental and theoretical work has been carried out. Hardy et al [21] have determined the uniaxial pressure derivatives along the tetragonal d- and f-axes for the nearly optimally doped single-layer cuprate Hg-1201 and obtain gWf@gSd = +2=3(2) K/GPa and gWf@gSf = 3=6(3) K/GPa. Bringing the CuO2 planes closer together through pressure along the f-axis is seen to rapidly decrease the value of Wf whereas it is increased by reducing the area of the CuO2 plane.
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