Quantum fluctuations and the magnetic ground state of ${\text{Ce}}_3{\text{Pd}}_{20}{\text{Si}}_6$

The temperature and magnetic field dependence of neutron-scattering studies on the heavy fermion compound ${\text{Ce}}_3{\text{Pd}}_{20}{\text{Si}}_6$ are reported. Inelastic neutron scattering reveals two crystal-field excitations corresponding to the environments of the two distinct rare-earth locations within this cubic compound. Surprisingly, the ground states of the two individual Ce sites are inequivalent with the $4a$ site having a ${\Gamma }_7$ ground state, while the $8c$ site reveals a ${\Gamma }_8$ ground state. This is in contrast to the situation found in the analogous compound ${\text{Ce}}_3{\text{Pd}}_{20}{\text{Ge}}_6$, where the ${\Gamma }_8$ ground state is realized for both Ce sites. In addition, these results reveal an interaction between the $8c$ and $4a$ sites previously believed to be absent. The ground state was probed with uniaxial polarization analysis across the region in which field-induced quantum criticality has previously been determined. In zero applied magnetic field no long-range magnetic order could be determined. However, further evidence of field-induced quantum criticality is presented with the observation of diffuse scattering consistent with quantum fluctuations due to nearest-neighbor spin correlations between the two Ce sites.

Figure 1

(Color online) Crystal structure of ${\text{Ce}}_3{\text{Pd}}_{20}{\text{Si}}_6$. For clarity only the Ce atoms are shown. Green atoms show the $\text{Ce}8c$ sites and yellow atoms show the $\text{Ce}4a$ sites.

Figure 2

(Color online) Inelastic neutron-scattering data at 0.06, 100, and 290 K. The full line shows the crystal-field contributions. The dashed line represents the Lorentzian quasielastic line contribution centered at 0 meV.

Figure 3

(Color online) (a) Temperature dependence of the integrated intensity of the low-energy [0.31(2) meV] excitation. Inset: energy dependence of 0.31(2) meV excitation at 60 mK with data corrected for detailed balance. (b) Temperature dependence of the higher energy [3.91(1) meV] CEF transition. Inset shows the energy dependence at 60 mK.

Figure 4

(Color online) Temperature dependence of the central energy position of the high-energy excitation at 3.91(1) meV. The dashed line is a guide to the eyes. Inset: energy dependence of the scattering at temperatures 0.06, 0.4, 2, and 30 K.

Figure 5

(Color online) Powder diffraction data with the full-profile Rietveld refinement (full line) of CPS at (a) 300 K, (b) 5.5 K, and (c) 0.04 K. The vertical markers in the low-temperature plot (c) indicate the expected positions of magnetic Bragg diffraction, as discussed in the text.

Figure 6

(Color online) Separation of nuclear and magnetic scattering at 60 mK and 0.07 T measured on D7 with incident wavelength $3.1\text{Å}$. The inset shows the nuclear scattering at low wave-vector transfer.

Figure 7

(Color online) Paramagnetic scattering at 20 K and 0.07 T. The dashed red line is the paramagnetic scattering expected for ${\text{Ce}}^{3+}$, $J=5/2$, single-ion behavior and the black dots represent scattering observed in ${\frac{d\sigma }{d\Omega }}_{\text{MAG}}$.

Figure 8

(Color online) (a) Contour plot of the broad diffuse magnetic scattering around the reciprocal space position of $Q=0.82\left(3\right){\text{Å}}^{-1}$. (b) The maximum intensity as a function of applied magnetic field showing the most intense scattering close to the critical field of approximately 1.1 T.

Figure 9

(Color online) Magnetic scattering cross-sections expected due to nearest-neighbor correlations only between Ce1-Ce1, Ce2-Ce2, and Ce1-Ce2 atoms. Dashed line shows the position of the maximum in magnetic scattering from Fig. 8a.