In rare earth and actinide compounds, fascinating electronic ground states such as magnetic ordering, heavy fermion, and unconventional superconductivity are realized as a result of RKKY interaction, Kondo effect, c-f hybridization. The electronic states in f-electron compounds can be tuned by pressure. For example, in some Ce compounds, the magnetic ordering temperature Tord decreases with increasing pressure and becomes zero at a critical pressure P_c, where a heavy fermion state and, sometimes, pressure-induced unconventional superconductivity are formed. In addition to pressure, the magnetic field is also important tool to investigate the electronic state of heavy-fermion compounds. In the high magnetic fields, for example, the tetragonal symmetry breaking and Fermi surface reconstruction in CeRhIn₅ and field induced quadrupolar ordered phase in YbCo₂Zn₂₀ are observed[1-3].

In my talk, I focus on electronic states of some Ce based compounds under pressure and characteristic phase diagram of heavy-fermion compound CePt₂In₇ under pressure combined with pulsed-high-field using a new generation of pressure cells[4,5]. CePt₂In₇ exhibits an antiferromagnetic transition (AFM) at T_N = 5.5 K [6]. T_N is suppressed by the magnetic field and is expected to become zero at μ₀H_c ~ 40 T for H || c axis [7,8]. TN is also suppressed by pressure above 2 GPa, and seems to become zero at P_C ~ 3.2 GPa, where CePt₂In₇ shows the superconductivity (SC) with the highest transition temperature T_SC ~ 2.1 K [9]. At 2.60 GPa, where AFM and SC coexist, AFM remains robust against the magnetic field and the SC critical field H_C2 is expected to be higher than 10 T. However, restricted magnetic field and pressure windows have prevented from constructing the full (H,P,T) phase diagram.

From measurements of magnetization and magnetoresistance, the H-T phase diagrams of CePt₂In₇ for H || a and c axes are constructed as shown in figure, which is characterized by four states; paramagnetic (PM), correlated paramagnetic (CPM), antiferromagnetic (AF), and polarized paramagnetic (PPM) states. I show the pressure effects on phase diagram and relation between four states.

Figure: Phase diagram of CePt₂In₇ at ambient pressure.

[1] L. Jiao, et al., Proc. Natl. Acad. Sci. 112, 673 (2015).

[2] F. Ronning, et al., Nature 548, 313 (2017).

[3] T. Takeuchi et al., J. Phys. Soc. Jpn. 80, 114703 (2011).

[4] R. Settai et al., Rev. High Press. Sci. and Tec 25, 325 (2015).

[5] D. Braithwaite et al., Rev. Sci. Instrum. 87, 023907 (2016).

[6] E. D. Bauer et al., Phys. Rev. B 81, 180507 (2010).

[7] M. M. Altarawneh et al., Phys. Rev. B 83, 081103 (2011).

[8] Y. Krupko et al., Phys. Rev. B 93, 085121 (2016).

[9] V. A. Sidorov et al., Phys. Rev. B 88, 020503 (2013).