Temperature-pressure phase diagram of CeCoSi: Pressure-induced high-temperature phase

Abstract

We have studied the temperature-pressure phase diagram of CeCoSi by electrical-resistivity experiments under pressure. Our measurements revealed a very unusual phase diagram. While at low pressures no dramatic changes and only a slight shift of the Ne\'el temperature ${T}_{N}$ ($\ensuremath{\approx}$10 K) are observed, at about 1.45 GPa a sharp and large anomaly, indicative of the opening of a spin-density wave gap, appears at a comparatively high temperature ${T}_{S}\ensuremath{\approx}38$ K. With further increasing pressure, ${T}_{S}$ shifts rapidly to low temperatures and disappears at about 2.15 GPa, likely continuously in a quantum critical point, but without evidence for superconductivity. Even more surprisingly, we observed a clear shift of ${T}_{S}$ to higher temperatures upon applying a magnetic field. We discuss two possible origins for ${T}_{S}$: magnetic ordering of Co and a metaorbital type of transition of Ce.