Heavy‐fermion superconductivity and Fermi‐surface properties under pressure

We present an overview of the Fermi‐surface properties for antiferromagnets CeRh2Si2, CeIn3, CeRhIn5, and CeIrSi3, which were clarified from the de Haas–van Alphen (dHvA) experiments under strong magnetic fields up to 170 kOe and high pressures up to 3 GPa. A drastic change of the 4f‐electronic state from a 4f‐localized Fermi surface to a 4f‐itinerant Fermi surface occurs in CeRh2Si2, CeIn3, and CeRhIn5 when the pressure P crosses a critical pressure Pc or $P_{{\rm c}}^{*} $. Here, the Néel temperature TN disappears and the superconducting state appears at around Pc or $P_{{\rm c}}^{*} $. A critical pressure $P_{{\rm c}}^{*} $ in CeRhIn5 is the pressure when TN is extrapolated to zero in the temperature vs. pressure phase diagram, and/or the antiferromagnetic state disappears completely even in magnetic fields. This is because the antiferromagnetic state is stable against magnetic fields, or in other words, the antiferromagnetic state recovers in magnetic fields. CeIrSi3 without inversion symmetry in the tetragonal structure is also similar to CeRhIn5 in the superconducting and Fermi‐surface properties. It is characteristic that a huge upper critical field at zero temperature in superconductivity $H_{{\rm c2}} (0) \simeq 450\,{\rm kOe}$ is realized for $H{\parallel} [001]$ in CeIrSi3 with the superconducting transition temperature Tsc = 1.6 K.