Thermodynamic properties of CeCu_6‐xAu_x: Fermi‐liquid vs. non‐Fermi‐liquid behaviour

Abstract

We report on a detailed comparison of the thermodynamic properties of the heavy-fermion system CeCu6 which can be described as a Fermi liquid at low temperatures T < 0.1 K, and CeCus.9Auo.l where strong deviations from the Fermi-liquid behaviour were found previously in the T dependence of the specific heat C , magnetization M and electrical resistivity p. The specific heat, magnetization and elastic constants are investigated in a large range of magnetic fields, corroborating the idea that the non-Fermi-liquid behaviour arises from low-lying spin excitations. For the elastic constants, a striking linear T dependence is found for CeCus 9Auo I in contrast to the T2 Fermiliquid behaviour of CeCus.

Quantum phase transitions

“…8), signahng NFL behavior The anisotropic while the larger T^M toward x = I likely results from the strong AF order Right: x dependence of the staggered moment per Ce ion extracted from elastic neutron scattering. 9 [155,156]. An increase of p{T) below 7N has been observed before in other HFS, for example, in CeRu2-xRhxSi2 as will be discussed below [154].…”

“…An example of resolution-limited magnetic Bragg reflections for x = 0.2 is shown in Fig. SoKd line represents C/T = ain{To/T) with a = 0.578 J/molK^ and To = 6.2 K. From [156]. The magnetic ordering vector is Q = (0.625 0 0.253) for x = 0.2 and remains almost constant up to x = 0.4.…”

Multidimensional entropy landscape of quantum criticality

“…Their determination requires elaborate measurements, as compounds of lower crystal symmetry are characterized by a large number of independent ij c constants. The elastic behavior of CeCu6-xAux is described by nine constants, six of which have been published so far for 0 = x and partly for 0.1 (refs [25][26][27][28]…”

“…). To complete our measurements, we have chosen the ij c data from Weber et al25 due to their better agreement with ours and the low-temperature measurements from Finsterbusch et al28 . By using these constants, we can estimate the dependence of the lattice parameters on arbitrary combinations of stresses.…”

Magnetic and structural quantum phase transitions in CeCu6-xAux are independent

“…The corresponding structural phase transition, which can be viewed as a small shear strain of the a m c m planes, emerges from a softening of transverse acoustic phonons. Neutron-scattering experiments [15], thermal-expansion [6], ultrasound-velocity [16,17], and resistivity measurements [18] unambiguously reveal a continuous, second-order transition. Measurements under pressure indicate that this transition is extremely sensitive to volume changes and can easily be suppressed by reducing ∆V Cu(2) , either by external hydrostatic pressure [6,19], by replacing Ce with smaller rare-earth ions R [20][21][22], or by substituting larger metal ions for Cu(2) [6].…”