K. Heuser

Crossover to Fermi-Liquid Behavior at Lowest Temperatures in Pure CeNi2Ge2

We present a low temperature study of the nearly antiferromagnetic heavy Fermion compound CeNi2Ge2 including specific heat measurements in magnetic fields up to 13 T, resistivity, magnetization, DC- and AC- susceptibility measurements down to 30 mK. The results show that, although the system is close to a quantum critical point, CeNi2Ge2 exhibits Fermi-liquid behavior below approximately 300 mK. At higher temperatures hyperscaling indicates the existence of strong coupling spin fluctuations responsible for the observed non-Fermi-liquid properties.

Low Temperature Specific Heat of CeRu2Si2 at the Field Induced Metamagnetic Instability

We report specific heat measurements in a broad temperature range between 0.06 and 20 K on single crystalline CeRu2Si2 in magnetic fields applied parallel to the c-direction around the critical field BM, where the metamagnetic transition from the itinerant to the localized state takes place. In the critical field BM ∥ c=7.8 T a distinct deviation from the usual Fermi- liquid behavior is found down to our lowest temperature. Below 1.8 K C/T varies as (1−aT), while for 1.8 K<T<20 K a power law Tλ−1 with λ=0.66 is found. Small deviations from the critical magnetic field leads to the recovery of a Fermi-liquid ground state. The observed behavior of the specific heat at the field induced magnetic instability is discussed in the context of a non-Fermi-liquid state and compared with those for the field-induced nFl CeCu6−xAgx and the recent observation of nFl behavior at BM in UPt3.

Non-Fermi-Liquid Behavior in CePt1+xSi1−x and CePtSi1−yGey

The heavy-fermion system CePtSi is located close to a magnetic instability. In order to study the influence of composition on the physical properties of CePtSi we prepared slightly off-stoichiometric CePt1+xSi1−x polycrystals. CePt1+xSi1−x with x=−0.04 exhibits typical non-Fermi-liquid behavior (C/T∝lnT, χ∝T−0.21, ρ∝T1.5). A scaling analysis of the thermodynamic quantities at magnetic fields up to 10T and temperatures up to 6K points to a quantum phase transition described by some unknown non-Gaussian fixed point. In contrast substitution of Si by Ge leads to a quantum phase transition involving weak-coupling spin fluctuations for CePtSi0.89Ge0.11, which can be described within the framework of the self-consistent renormalization theory.

Quantum phase transitions: experimental facts—a challenge for theory

Abstract Quantum critical phenomena occur in many heavy fermion systems giving rise to non-Fermi liquid behavior at lowest temperatures. Here we report on three systems, namely CeCu 6− x Ag x , CePtSi and UCu 5− x Pd x , where the temperature-dependent specific heat, c ( T ), and resistivity, ρ ( T ), for each system correspond to two different scenarios, depending on whether the long-range antiferromagnetic order is suppressed by magnetic field or chemical pressure, by iso-electronic or non-iso-electronic doping and by change of composition or atomic redistribution, respectively. Theoretically this curious behavior can be thought of as a transition from a weak-coupling scenario to some unknown non-Gaussian fixed point.

Onset of magnetism and Fermi-liquid instabilities in Yb compounds

Abstract YbCu5−xAlx provides the possibility to tune ground state properties by a change of the valence due to the Cu/Al substitution, by pressure as well as by the application of a magnetic field. The former originates long-range magnetic order for x>1.5 and at the critical concentration xcr≈1.5 non-Fermi-liquid (NFL) properties are obvious, e.g., from a − ln T contribution to the specific heat. The latter causes that antiferromagnetic order can be suppressed (x=1.6 and x=1.7) and at a critical magnetic field Hc NFL becomes evident while for H⪢Hc a Fermi-liquid ground state is recovered.

Quantum critical behavior of magnetic field-dependent resistivity of CeCu6−xAgx

Abstract For various antiferromagnetic systems the antiferromagnetic long-range order phase transition can be suppressed by pressure or doping. A crossover from magnetic to Fermi liquid behavior occurs at a critical value of the tuning parameter, where non-Fermi liquid behavior can be observed. We have strong evidence that this scenario works also for an external magnetic field as tuning parameter in the system CeCu6−xAgx.