Universal behavior of CePd1−xRhx\rm CePd_{1-x}Rh_x Ferromagnet at Quantum Critical Point

The heavy-fermion metal $\rm CePd_{1-x}Rh_x$ can be tuned from ferromagnetism at $x=0$ to non-magnetic state at some critical concentration $x_c$. The non-Fermi liquid behavior (NFL) at $x\simeq x_c$ is recognized by power low dependence of the specific heat $C(T)$ given by the electronic contribution, magnetic susceptibility $\chi(T)$ and volume expansion coefficient $\alpha(T)$ at low temperatures: $C/T\propto\chi(T)\propto\alpha(T)/T\propto1/\sqrt{T}$. We also demonstrate that the behavior of normalized effective mass $M^*_N$ observed in $\rm CePd_{1-x}Rh_x$ at $x\simeq 0.8$ agrees with that of $M^*_N$ observed in paramagnetic $\rm CeRu_2Si_2$ and conclude that these alloys exhibit the universal NFL thermodynamic behavior at their quantum critical points. We show that the NFL behavior of $\rm CePd_{1-x}Rh_x$ can be accounted for within frameworks of quasiparticle picture and fermion condensation quantum phase transition, while this alloy exhibits a universal thermodynamic NFL behavior which is independent of the characteristic features of the given alloy such as its lattice structure, magnetic ground state, dimension etc.Comment: 5 pages, 3 figure

Energy scales and the non-Fermi liquid behavior in YbRh2Si2

Multiple energy scales are detected in measurements of the thermodynamic and transport properties in heavy fermion metals. We demonstrate that the experimental data on the energy scales can be well described by the scaling behavior of the effective mass at the fermion condensation quantum phase transition, and show that the dependence of the effective mass on temperature and applied magnetic fields gives rise to the non-Fermi liquid behavior. Our analysis is placed in the context of recent salient experimental results. Our calculations of the non-Fermi liquid behavior, of the scales and thermodynamic and transport properties are in good agreement with the heat capacity, magnetization, longitudinal magnetoresistance and magnetic entropy obtained in remarkable measurements on the heavy fermion metal YbRh2Si2.Comment: 8 pages, 8 figure

Asymmetric tunneling, Andreev reflection and dynamic conductance spectra in strongly correlated metals

Landau Fermi liquid theory predicts that the differential conductivity between metallic point and metal is a symmetric function of voltage bias V. This symmetry holds if the particle-hole symmetry is preserved. We show that the situation can be different when one of the two metals is a strongly correlated one whose electronic system can be represented by a heavy fermion liquid. When the heavy fermion liquid undergoes fermion condensation quantum phase transition, the particle-hole symmetry is violated making both the differential tunneling conductivity and dynamic conductance asymmetric as a function of applied voltage. This asymmetry can be observed when the strongly correlated metal is either normal or superconducting. We show that at small values of $V the asymmetric part of the dynamic conductance is a linear function of V and inversely proportional to the maximum value of the gap and does not depend on temperature provided that metal is superconducting, when it becomes normal the asymmetric part diminishes at elevated temperatures.Comment: 8 pages, 7 figure