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Register a new userCrystalline Electric Field and Kondo Effect in SmOs4Sb12
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Our ultrasound results obtained in pulsed magnetic fields show that the filled-skutterudite compound SmOs$_4$Sb$_{12}$ has the $Gamma_{67}$ quartet crystalline-electric-field ground state. This fact suggests that the multipolar degrees of freedom of the $Gamma_{67}$ quartet play an important role in the unusual physical properties of this material. On the other hand, the elastic response below $approx$ 20 T cannot be explained using the localized 4$f$-electron model, which does not take into account the Kondo effect or ferromagnetic ordering. The analysis result suggests the presence of a Kondo-like screened state at low magnetic fields and its suppression at high magnetic fields above 20 T even at low temperatures.
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We have measured the crystalline electric field (CEF) excitations of the CeMIn5 (M = Co, Rh, Ir) series of heavy fermion superconductors by means of inelastic neutron scattering. Fits to a CEF model reproduce the inelastic neutron scattering spectra and the high temperature magnetic susceptibility. The CEF parameters, energy level splittings, and wavefunctions are tabulated for each member of the CeMIn5 series and compared to each other as well as to the results of previous measurements. Our results indicate that the CEF level splitting in all three materials is similar, and can be thought of as being derived from the cubic parent compound CeIn3 in which an excited state quartet at ~12 meV is split into two doublets by the lower symmetry of the tetragonal environment of the CeMIn5 materials. In each case, the CEF excitations are observed as broad lines in the inelastic neutron scattering spectrum. We attribute this broadening to Kondo hybridization of the localized f moments with the conduction electrons. The evolution of the superconducting transition temperatures in the different members of CeMIn5 can then be understood as a direct consequence of the strength of this hybridization. Due to the importance of Kondo spin fluctuations in these materials, we also present calculations within the non-crossing approximation (NCA) to the Anderson impurity model including the effect of CEF level splitting for the inelastic neutron scattering spectra and the magnetic susceptibility.
Charge-transfer effect under odd-parity crystalline electric field (CEF) is analyzed theoretically. In quantum-critical metal $beta$-YbAlB$_4$, seven-fold configuration of B atoms surrounding Yb atom breaks local inversion symmetry at the Yb site, giving rise to the odd-parity CEF. Analysis of the CEF on the basis of hybridization picture shows that admixture of 4f and 5d wave functions at Yb with pure imaginary coefficient occurs, which makes magnetic-toroidal (MT) and electric-dipole (ED) degrees of freedom active. By constructing the minimal model for periodic crystal $beta$-YbAlB$_4$, we show that the MT as well as ED fluctuation is divergently enhanced at the quantum critical point of valence transition simultaneously with critical valence fluctuations.
We investigate the crystal structure, magnetic properties, and crystalline-electric field of tetragonal, $I4_1/amd$, NaCeO$_2$. In this compound, Ce$^{3+}$ ions form a tetragonally elongated diamond lattice coupled by antiferromagnetic interactions ($Theta_{CW} = -7.69$ K) that magnetically order below $T_N = 3.18$ K. The Ce$^{3+}$ $J = 5/2$ crystalline-electric field-split multiplet is studied via inelastic neutron scattering to parameterize a $J_{eff} = 1/2$ ground state doublet comprised of states possessing mixed $|m_z rangle$ character. Neutron powder diffraction data reveal the onset of $A$-type antiferromagnetism with $mu=0.57(2)$ $mu_B$ moments aligned along the $c$-axis. The magnetic structure is consistent with the expectations of a frustrated Heisenberg $J_1$-$J_2$ model on the elongated diamond lattice with effective exchange values $J_1 > 4 J_2$ and $J_1 > 0$.
The physical properties of single-crystalline SmBe$_{13}$ with a NaZn$_{13}$-type cubic structure have been studied by electrical resistivity ($rho$), specific heat ($C$), and magnetization ($M$) measurements in magnetic fields of up to 9 T. The temperature ($T$) dependence of $rho$ shows normal metallic behavior without showing the Kondo -ln$T$ behavior, suggesting the weak hybridization effect in this system. Analyses of the temperature dependence of $C$ suggest that the Sm ions of this compound are trivalent and that the crystalline-electric-field (CEF) ground state is a $Gamma_8$ quartet with a first-excited state of a $Gamma_7$ doublet located at the energy scale of $sim$ 90 K. Mean-field calculations based on the suggested CEF level scheme can reasonably well reproduce the $T$ dependence of magnetic susceptibility ($chi$) below $sim$ 70 K. These results in the paramagnetic state strongly indicate that the 4$f$ electrons are well localized with the Sm$^{3+}$ configuration. At low temperatures, the 4$f$ electrons undergo a magnetic order at $T_{rm M}$ $sim$ 8.3 K, where $chi$($T$) shows an antiferromagnetic-like cusp anomaly. From the positive Curie--Weiss temperature obtained from the mean-field calculations and from a constructed magnetic phase diagram with multiple regions, we discussed the magnetic structure of SmBe$_{13}$ below $T_{rm M}$, by comparing with other isostructural MBe$_{13}$ compounds showing helical-magnetic ordering.
The crystalline electric field (CEF) energy level scheme of the heavy fermion superconductor CeCoIn_5 has been determined by means of inelastic neutron scattering (INS). Peaks observed in the INS spectra at 8 meV and 27 meV with incident neutron energies between E_i=30-60 meV and at a temperature T = 10 K correspond to transitions from the ground state to the two excited states, respectively. The wavevector and temperature dependence of these peaks are consistent with CEF excitations. Fits of the data to a CEF model yield the CEF parameters B^0_2=-0.80 meV, B^0_4=0.059 meV, and |B^4_4|= 0.137 meV corresponding to an energy level scheme: Gamma_7^(1) (0)[=0.487|+/-5/2> - 0.873|-/+3/2>], Gamma_7^(2) (8.6 meV, 100 K), and Gamma_6 (24.4 meV, 283 K).
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