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Register a new userMagnetic Properties of Heavy Fermion Superconductors CeRhIn5 and Ce2RhIn8
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Some recent neutron scattering works on CeRhIn5 and Ce2RhIn8, together with related resistivity and specific heat measurements, are summarized. In spite of its layered crystal structure, CeRhIn5 is shown to be 3-dimensional both magnetically and in transport. We also find that the Fisher-Langer behavior is closely followed in CeRhIn5. This may circumvent the Kondo lattice model and support applying established Fermi-liquid superconductivity theory to heavy fermion superconductors.
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A Kondo lattice of strongly interacting f-electrons immersed in a sea of conduction electrons remains one of the unsolved problems in condensed matter physics. The problem concerns localized f-electrons at high temperatures which evolve into hybridized heavy quasi-particles at low temperatures, resulting in the appearance of a hybridization gap. Here, we unveil the presence of hybridization gap in Ce2RhIn8 and find the surprising result that the temperature range at which this gap becomes visible by angle-resolved photoemission spectroscopy is nearly an order of magnitude lower than the temperature range where the magnetic scattering becomes larger than the phonon scattering, as observed in the electrical resistivity measurements. Furthermore the spectral gap appears at temperature scales nearly an order of magnitude higher than the coherent temperature. We further show that when replacing In by Cd to tune the local density of states at the Ce3+ site, there is a strong reduction of the hybridization strength, which in turn leads to the suppression of the hybridization gap at low temperatures.
Anisotropic, spatially textured electronic states often emerge when the symmetry of the underlying crystalline structure is lowered. However, the possibility recently has been raised that novel electronic quantum states with real-space texture could arise in strongly correlated systems even without changing the underlying crystalline structure. Here we report evidence for such texture in the superconducting quantum fluid that is induced by pressure in the heavy-fermion compound CeRhIn5. When long-range antiferromagnetic order coexists with unconventional superconductivity, there is a significant temperature difference between resistively- and thermodynamically-determined transitions into the superconducting state, but this difference disappears in the absence of magnetism. Anisotropic transport behaviour near the superconducting transition in the coexisting phase signals the emergence of textured superconducting planes that are nucleated preferentially along the {100} planes and that appear without a change in crystal symmetry. We show that CeRhIn5 is not unique in exhibiting a difference between resistive and bulk superconducting transition temperatures, indicating that textured superconductivity may be a general consequence of coexisting orders.
We use angle-resolved photoemission spectroscopy to study heavy fermion superconductor Ce2RhIn8. The Fermi surface is rather complicated and consists of several hole and electron pock- ets. We do not observe kz dispersion of Fermi sheets, which is consistent with 2D character of the electronic structure. Comparison of the ARPES data and band structure calculations points to a localized picture of f electrons. Our findings pave the way for understanding the transport and thermodynamical properties of this material.
A technique for measuring the electrical resistivity and absolute thermopower is presented for pressures up to 30 GPa, temperatures down to 25 mK and magnetic fields up to 10 T. With the examples of CeCu2Ge2 and CeCu2Si2 we focus on the interplay of normal phase and superconducting properties. With increasing pres- sure, the behaviour of CeCu2Ge2 evolves from that of an antiferromagnetically ordered Kondo system to that characteristic of an intermediate valence compound as the Kondo temperature increases by about two orders of magnitude. In the pressure window 8-10 < P < 20 GPa, a superconducting phase occurs which com- petes at low pressure with magnetic ordering. For CeCu2Si2 the effective mass of carriers is probed by both the coefficient of the Fermi liquid law and the ini- tial slope of the upper critical field. The magnetic instability is studied no- tably for CeRu2Ge2 and Yb-based compounds for which pressure-induced magnetic ordering tends to develop. Finally, contrary to conventional wisdom, we argue that in heavy fermions a large part of the residual resistivity is most likely not independent of temperature; tentatively ascribed to Kondo hole, it can be very pressure as well as sample dependent. [electrical resistivity, thermoelectric power, heavy fermion, magnetic order, superconductivity]
The physical properties of the very heavy fermion YbCu$_4$Ni were characterized through structural, magnetic, thermal and transport studies along nearly four decades of temperature ranging between 50 milikelvin and 300 K. At high temperature, the crystal electric field levels splitting was determined with $Delta_1 (Gamma_6)= 85$ K and $Delta_2 (Gamma_8) approx 200$ K, the latter being a quartet in this cubic symmetry. An effective magnetic moment $mu_{eff} approx 3mu_B$ is evaluated for the $Gamma_7$ ground state, while at high temperature the value for a Yb$^{3+}$ ion is observed. At low temperature this compounds shows the typical behavior of a magnetically frustrated system undergoing a change of regime at a characteristic temperature $T^*approx 200$ mK into a sort of Fermi-liquid type plateauof the specific heat: $C_m/T|_{Tto 0}$ = const. The change in the temperature dependence of the specific heat coincides with a maximum and a discontinuity in respective inductive and dissipative components of the ac-susceptibility. More details from the nature of this ground state are revealed by the specific heat behavior under applied magnetic field.
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