Fermi surface studies near magnetic quantum critical points under high pressure

1.我们研制了适用于测量deHaas-van Alphen（dHvA）效应的活塞-圆柱形高压池，压力可达3GPa，采用非磁性高强度合金NiCrAl。2.我们测量了铁磁超导体UGe_2中的dHvA效应，压力可达1002 GPa，超过临界压力，磁场平行于磁易轴。我们发现，高压下准粒子质量的增加与临界压力下的铁磁-顺磁转变没有直接关系，而是归因于所谓的T_x转变。3.我们测量了ZrZn_2中的dHvA效应。通过对费米面交换劈裂的详细分析，我们发现了磁场诱导的两种磁态之间的交叉，并提出了UGe_2和ZrZn_2可能具有共同的温度-压力-磁场相变。4.我们测量了CeIn_3中的dHvA效应，它在反铁磁-顺磁转变附近表现出超导性，压力高达3GPa。我们发现在反费米磁的临界压力下出现了新的费米面，并且在其它压力下也发现了费米面的显著变化。这些观测结果表明，电子结构的变化伴随着反铁磁-顺磁体转变相继发生。

1.We have developed piston-cylinder high-pressure cells suitable for de Haas-van Alphen (dHvA) effect measurements at pressures up to 3 GPa, using non-magnetic high-strength alloy NiCrAl.2.We have measured the dHvA effect in the ferromagnetic superconductor UGe_2 up to 〜2 GPa, exceeding the critical pressure, for the magnetic field parallel to the magnetic easy a-axis. We have found that the enhancement of quasiparticle mass at high pressures is not directly related to the ferromagnetic-paramagnetic transition at the critical pressure but is ascribed to the so-called T_x transition.3.We have measured the dHvA effect in ZrZn_2, which was reported to be a ferromagnetic superconductor, at pressures up to -2 GPa. We have found from detailed analyzes of exchange splitting of the Fermi surface a crossover between two magnetic states induced by the magnetic field and have proposed that UGe_2 and ZrZn_2 may have a common temperature-pressure-magnetic-field phase diagram.4.We have measured the dHvA effect in CeIn_3, which exhibits superconductivity near the antiferromagnetic-paramagnetic transition, at pressures up to 〜3 GPa. We have found the appearance of new Fermi surfaces at the critical pressure of the antifermmagnetism and have also found pronounced changes of the Fermi surface at other pressures. Those observations indicate that the change of the electronic structure accompanying the antiferromagnetic-paramagnet is transition occurs successively.