Quantum Criticality and Heavy Fermion State in YbCo₂Zn₂₀under Pressure and Magnetic Field

Abstract

We studied an effect of pressure on the heavy fermion state of YbCo 2 Zn 20 under magnetic fields. The critical pressure P c , where the electronic state changes from the heavy fermion state to the antiferromagnetic state, is estimated to be P c 1.8 GPa. The super-heavy fermion state in the P c region is found to be strongly destroyed in magnetic fields for H 100 . The field-induced quadrupolar phase, which is most likely realized only for H 111 , is found to be robust even in the antiferromagnetic pressure region.

Field-Induced Order in Heavy-Fermion Compound YbCo2Zn20

“…This result evidences that the field-induced phase has different character from the pressure-induced antiferromagnetic one from a microscopic point of view. This is consistent with the behavior in the pressure-magnetic field phase diagram in which pressure-induced ordered phase does not connect to the field-induced one [5,10].…”

Search for pressure-induced quantum criticality in YbFe2Zn20

“…For Kondo lattice systems, the electrons participating in the spin-dependent screening in the region of the Kondo temperature are intimately related to the Fermi-liquid quasiparticles at low temperatures. With previous results for YbCo 2 Zn 20 having shown indications of a magnetic transition when T FL was suppressed, [14][15][16] it is expected that a quantum critical point will also be reached when T FL in YbFe 2 Zn 20 has been driven to zero.…”

Collapse of the Kondo state and ferromagnetic quantum phase transition in YbFe2Zn20

“…At p c , a possibly ferromagnetic transition T M suddenly appears at ∼ 1 K and stays unchanged with further increasing pressure. This suggests that for YbFe 2 Zn 20 , the quantum criticality is avoided by going through a first-order QPT under pressure, which is in contrast to the YbCo 2 Zn 20 and YbIr 2 Zn 20 , where they enter AFM ordered states through QCP [26,39,44]. At high temperature, a continuously increase of the resistivity with pressure was observed for p p c (Fig.…”

“…Taking GdT 2 Zn 20 series for example, ferromagnetic ordered ground state is found for members in the iron column (T = Fe, Ru and Os) while antiferromagnetic ordered ground state in the cobalt column (T = Co, Rh and Ir) [31]. Moreover, the pressure-induced ordered states in YbCo 2 Zn 20 and YbIr 2 Zn 20 have also been suggested as AFM ordering [39,44]. Taking YbFe 2 Zn 20 in this study together, RT 2 Zn 20 family seems to follow the rule that for the iron column members, ferromagnetic ordering is expected, while for the cobalt column members, antiferromagnetic ordering is expected.…”

“…With this idea, Saiga et al [26] performed a high pressure resistivity measurement on YbCo 2 Zn 20 and observed a pressure induced QCP at a critical pressure ∼ 1 GPa and antiferromagnetic (AFM) ordering at higher pressures. Apart from this, a field induced ordered phase has been observed at the ambient pressure in YbCo 2 Zn 20 , possibly due to the crystal electric field level crossing [36][37][38][39][40][41]. A pressure induced QCP has also been estimated for YbIr 2 Zn 20 (≈ 5.2 GPa) and YbRh 2 Zn 20 (≈ 5.2 GPa), however, for YbRh 2 Zn 20 no pressure induced magnetic transitions have been observed so far [42][43][44][45].…”