Effect of pressure on competing electronic correlations in the heavy-electron system URu2Si2.

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 \ensuremath{\sim}15.4 kbar on these transitions. For pressures less than 12 kbar, ${T}_{0}$ increases linearly at a rate \ensuremath{\sim}130 mK/kbar, while ${T}_{c}$ decreases linearly at a rate \ensuremath{\sim}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 \ensuremath{\rho}(${T}_{\mathrm{max}}$), scales as a function of reduced temperature T/${T}_{\mathrm{max}(\mathrm{P})}$ from ${T}_{c}$ to well above ${T}_{\mathrm{max}}$, except in the immediate vicinity of ${T}_{0}$.