We report a thermodynamic and transport study of the phase diagram of CeRh 1-x Ir x In 5 . Superconductivity is observed over a broad range of doping, 0.3 < x < 1, including a substantial range of concentration (0.3 < x <0.6) over which it coexists with magnetic order (which is observed for 0 < x < 0.6). The anomalous transition to zero resistance that is observed in CeIrIn 5 is robust against Rh substitution. In fact, the observed bulk T c in CeRh 0.5 Ir 0.5 In 5 is more than double that of CeIrIn 5 , whereas the zeroresistance transition temperature is relatively unchanged for 0.5 < x < 1. PACS number(s) 74.70.Tx, 71.27.+a, 75.40.Cx Submitted to PRL

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We report a systematic study of high magnetic field specific heat and resistivity in single crystals of CeCoIn5 for the field oriented in the basal plane (H ab) of this tetragonal heavy fermion superconductor. We observe a divergent electronic specific heat as well as an enhanced A coefficient of the T 2 law in resistivity at the lowest temperatures, as the field approaches the upper critical field of the superconducting transition. Together with the results for field along the tetragonal axis (H c), the emergent picture is that of a magnetic field tuned quantum critical point which exists in the vicinity of the superconducting H 0 c2 despite a variation of a factor of 2.4 in H 0 c2 for different field orientations. This suggests an underlying physical reason exists for the superconducting H 0 c2 to coincide with the quantum critical field. Moreover, we show that the recovery of a Fermi Liquid ground state with increasing magnetic field is more gradual, meaning that the fluctuations responsible for the observed quantum critical phenomena are more robust with respect to magnetic field, when the magnetic field is applied in-plane. Together with the close proximity of the quantum critical point and H 0 c2 in CeCoIn5 for both field orientation, the anisotropy in the recovery of the Fermi liquid state might constitute an important piece of information in identifying the nature of the fluctuations that become critical. PACS numbers:Quantum critical points mark the change in the ground state of a strongly correlated electron system, and the associated quantum fluctuations have tremendous consequences for the properties of the system at finite temperatures. Attention has focused on the heavy fermion superconductor CeCoIn 5 in the context of quantum criticality since its discovery [1]. Superconductivity in this material is not only unconventional (probably d-wave [2, 3]) and Pauli-limited (with the possible presence of a Fulde-Ferrell-Larkin-Ovchinnikov state at low temperatures) [4,5,6] but it is also built out of a normal state displaying Non Fermi Liquid behavior. Indeed, the normal state is characterized by a resistivity almost linear in temperature for a decade above T c in zero field [1], a specific heat coefficient diverging logarithmically over a large temperature range with a similar slope at zero and finite magnetic field [1,7], and a power law behavior in ac-susceptibility [1,7] and the nuclear spin-lattice relaxation rate [8]. All of this suggests the proximity to an antiferromagnetic instability. It is important to note that the specific heat is analogous to UBe 13 [9]. Since the entropy is conserved between the zero field superconducting state and the anomalous normal state at H 0 c2 , this implies that the mass enhancement leading to the heavy fermion ground state is interrupted by the formation of superconductivity and presumably the same spin fluctuations are responsible for both phenomena.The phase diagram of CeCoIn 5 turns out to be rather complex, raising the possibility of one or more quantum critical...

A series of new rare-earth indium-germanides RE 2 InGe 2 (RE ) Sm, Gd, Tb, Dy, Ho, Yb) have been prepared from the corresponding elements through high-temperature reactions using an excess of indium as flux. Single-crystal and powder X-ray diffraction studies showed that these ternary phases crystallize in the tetragonal space group P4/mbm, Z ) 2, Pearson's symbol tP10, and represent new members of the Mo 2 FeB 2 family (an ordered ternary variant of the U 3 Si 2 structure type). The temperature dependence of the dc magnetization (5-300 K) indicates that the RE 2 InGe 2 (RE ) Sm-Ho) compounds order magnetically below ca. 60 K, whereas Yb 2 InGe 2 exhibits Pauli-like temperature-independent paramagnetism. Isothermal magnetization, electrical resistivity, and calorimetry measurements are presented as well and confirm the existence of ordered antiferromagnetic states at low temperatures. The structural trends and the evolution of the magnetic properties are also discussed.