Cadmium doping the heavy-fermion superconductor CeCoIn(5) at the percent level acts as an electronic tuning agent, sensitively shifting the balance between superconductivity and antiferromagnetism and opening new ambient-pressure phase space in the study of heavy-fermion ground states.

We present the thermopower S (T) and the resistivity ρ (T) of Lu1-x Ybx Rh2 Si2 in the temperature range 3

The electronic band structure of Yb Rh2 Si2 is calculated in a relativistic framework including correlation corrections and magnetization of the Yb ion and compared to detailed angle-resolved photoemission spectra. The photoemission spectra for Lu Rh2 Si2 are used as reference to identify electronic bands with no f symmetry. The calculated band structure manifests a 4 f13 spin-polarized configuration leaving the unoccupied state at 1.4 eV above the Fermi energy. At the band theory level, the 4f bands are located far below the Fermi level and the anisotropic Coulomb interaction within the 4f shell spreads the multilevel into broader 4f complexes below -2.5 eV. The photoemission spectra obtained on Yb Rh2 Si2 show a clear f -multilevel splitting into j=7 2 and 5 2 excitations. The interaction of the 4 f7 2 levels close to the Fermi energy with two conduction bands shows visible hybridization gaps of 45 and 80 meV, respectively. We discuss the origin of these excitations and provide an analysis according to Anderson's single-impurity model with parameters suggested by the band-structure calculation and the photoemission spectra. Both experiment and theory indicate nearly identical Fermi surfaces for Lu Rh2 Si2 and Yb Rh2 Si2. The valency of Yb in Yb Rh2 Si2 is estimated to be close to +3. © 2007 The American Physical Society.

The physical properties of CeM (In1 - x Hgx)5 (M = Rh, Ir) including specific heat and magnetic susceptibility are reported. Two magnetic phases exist in CeRhIn (In1 - x Hgx)5 with some evidence of a change from incommensurate magnetic order to a commensurate structure near 10% nominal Hg substitution. In CeIr (In1 - x Hgx)5, an antiferromagnetic quantum critical point near x = 3 % (followed by robust long-range antiferromagnetism for x > 5 %) appears to be separated from superconductivity in CeIrIn5. The multitude of magnetic ground states observed in the CeM (In1 - x Hgx)5 materials is quite sensitive to doping and magnetic fields. © 2007.

We report on Hall effect measurements on YbRh2Si2 single crystals with different residual resistivity and on LuRh2Si2 single crystal. The temperature dependence of the linear-response Hall coefficient of YbRh2Si2 is described by the anomalous Hall effect and the normal contribution incorporating multi-band effects. Sample dependencies at low T are found and explained by slight changes in the charge-carrier concentrations. © 2007 Elsevier B.V. All rights reserved.

Electron spin resonance (ESR) experiments in YbRh2Si2 Kondo lattice (TK ≃ 25 K) at different field/frequencies (4.1 ≤ ν ≤ 34.4 GHz) and H⊥ c revealed: (i) a strong field dependent Yb3 + spin-lattice relaxation, (ii) a weak field and T-dependent effectiveg -value, (iii) a suppression of the ESR intensity beyond 15% of Lu-doping, and (iv) a strong sample and Lu-doping (≤ 15 %) dependence of the ESR data. These results suggest that the ESR signal in YbRh2Si2 may be due to a coupled Yb3 +-conduction electron resonant collective mode with a subtle field-dependent spins dynamic. © 2009 Elsevier B.V. All rights reserved.

The unconventional nature of the quantum criticality in YbRh 2Si 2 is highlighted on the basis of magnetoresistivity and susceptibility measurements. Results obtained under chemical pressure realized by isoelectronic substitution on the rhodium site are presented. These results illustrate the position of the T*-line associated with a breakdown of the Kondo effect near the antiferromagnetic instability in the low-temperature phase diagram. Whereas at zero temperature the Kondo breakdown and the antiferromagnetic quantum critical point coincide in the proximity of the stoichiometric compound, they are seen to be detached under chemical pressure: For positive chemical pressure the magnetically ordered phase extends beyond the T*(B)-line. For sufficiently high negative pressure the T*(B)-line is separated from the magnetically ordered phase. From our detailed analysis we infer that the coincidence is retained at small iridium concentrations, i.e., at small negative chemical pressure. We outline further measurements which may help to clarify the detailed behavior of the two instabilities. © 2010 Springer Science+Business Media, LLC.

Electron spin resonance (ESR) experiments at different fields or frequencies (4.1≤ν≤34.4 GHz) in the Kondo lattice (TK ≃25 K) YbRh2Si2 single-crystal compounds confirmed the observation of a single anisotropic Dysonian resonance with g⊥c ≅3.55 and no hyperfine components for 4.2≲T≲20 K. However, our studies differently reveal that (i) the ESR spectra for H⊥c show strong-field-dependent spin-lattice relaxation, (ii) a weak-field and temperature-dependent effective g value, (iii) a dramatic suppression of the ESR intensity beyond 15% of Lu doping, and (iv) a strong sample and Lu-doping (≤15%) dependence of the ESR data. These results suggest a different scenario where the ESR signal may be associated to a coupled Yb3+-conduction electron resonant collective mode with a strong bottleneck and dynamiclike behavior. © 2009 The American Physical Society.