The effect of high hydrostatic pressure on the magnetic field and temperature dependence of the attenuation of a longitudinal ultrasonic wave propagated along the ⟨100⟩ direction in superconducting ${\mathrm{Sr}}_2\mathrm{Ru}{\mathrm{O}}_4$ has been investigated. The magnetic field dependence of the attenuation suggests the vertical character of the nodes in the superconducting gap. Application of pressure causes a decrease of the critical temperature $T_c$ and critical magnetic field $H_{c2}$; the width of the transition under pressure increases. The dependence of $H_{c2\parallel ab}$ on $T_c$ was found to be linear, in contrast to the quadratic one for $H_{c2\parallel c}$. The slope $d{H}_{c2\parallel ab}∕d{T}_c$ has a universal character; its value does not depend on the physical factor causing reduction of $T_c$, regardless if it is pressure or impurities. The observed effects demonstrate that the pressure application induces an increase in the electron-electron interaction. We show that this increase can be described in terms of a changing electron relaxation time, as in the case of impurities.

• Received 15 December 2007

DOI:https://doi.org/10.1103/PhysRevB.77.052502