Effect of pressure on competing electronic correlations in the heavy-electron systemURu2Si2

Abstract

The heavy-electron compound ${\mathrm{URu}}_2$ ${\mathrm{Si}}_2$ exhibits two electronic phase transitions: superconductivity at $T_c$apeq21.5 K and a second transition at $T_0$apeq217.5 K. The specific-heat anomaly associated with the transition at $T_0$ has a mean-field BCS-like form which suggests the formation of a charge- or spin-density wave that partially gaps the Fermi surface. Through electrical-resistivity measurements, we have studied the influence of pressure P up to ∼15.4 kbar on these transitions. For pressures less than 12 kbar, $T_0$ increases linearly at a rate ∼130 mK/kbar, while $T_c$ decreases linearly at a rate ∼95 mK/kbar. The nearly equal but opposite P dependences of $T_0$ and $T_c$ suggest a competition for electronic density of states at the Fermi level. The resistivity, when normalized to its maximum value ρ($T_{\max }$), scales as a function of reduced temperature T/$T_{\max \left(\mathrm{P}\right)}$ from $T_c$ to well above $T_{\max }$, except in the immediate vicinity of $T_0$.