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Register a new userStructural investigations of CeIrIn${_5}$ and CeCoIn${_5}$ on macroscopic and atomic length scales
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For any thorough investigation of complex physical properties, as encountered in strongly correlated electron systems, not only single crystals of highest quality but also a detailed knowledge of the structural properties of the material are pivotal prerequisites. Here, we combine physical and chemical investigations on the prototypical heavy fermion superconductors CeIrIn${_5}$ and CeCoIn${_5}$ on atomic and macroscopic length scale to gain insight into their precise structural properties. Our approach spans from enhanced resolution X-ray diffraction experiments to atomic resolution by means of Scanning Tunneling Microscopy (STM) and reveal a certain type of local features (coexistence of minority and majority structural patterns) in the tetragonal HoCoGa$_5$-type structure of both compounds.
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High--quality single crystals of the heavy fermion superconductors CeCoIn$_5$ and CeIrIn$_5$ have been studied by means of low--temperature Scanning Tunneling Microscopy. Methods were established to facilitate textit{in-situ} sample cleaving. Spectroscopy in CeCoIn$_5$ reveals a gap which persists to above $T_c$, possibly evidencing a precursor state to SC. Atomically resolved topographs show a rearrangement of the atoms at the crystal surface. This modification at the surface might influence the surface properties as detected by tunneling spectroscopy.
We present core level non-resonant inelastic x-ray scattering (NIXS) data of the heavy fermion compounds CeCoIn$_5$ and CeRhIn$_5$ measured at the Ce $N_{4,5}$-edges. The higher than dipole transitions in NIXS allow determining the orientation of the $Gamma_7$ crystal-field ground-state orbital within the unit cell. The crystal-field parameters of the Ce$M$In$_5$ compounds and related substitution phase diagrams have been investigated in great detail in the past; however, whether the ground-state wavefunction is the $Gamma_7^+$ ($x^2,-,y^2$) or $Gamma_7^-$ ($xy$ orientation) remained undetermined. We show that the $Gamma_7^-$ doublet with lobes along the (110) direction forms the ground state in CeCoIn$_5$ and CeRhIn$_5$. For CeCoIn$_5$, however, we find also some contribution of the first excited state crystal-field state in the ground state due to the stronger hybridization of 4$f$ and conduction electrons, suggesting a smaller $alpha^2$ value than originally anticipated from x-ray absorption. A comparison is made to the results of existing density functional theory plus dynamical mean-field theory calculations.
We report a high field investigation (up to 45 T) of the metamagnetic transition in CeIrIn$_5$ with resistivity and de-Haas-van-Alphen (dHvA) effect measurements in the temperature range 0.03-1 K. As the magnetic field is increased the resistivity increases, reaches a maximum at the metamagnetic critical field, and falls precipitously for fields just above the transition, while the amplitude of all measurable dHvA frequencies are significantly attenuated near the metamagnetic critical field. However, the dHvA frequencies and cyclotron masses are not substantially altered by the transition. In the low field state, the resistivity is observed to increase toward low temperatures in a singular fashion, a behavior that is rapidly suppressed above the transition. Instead, in the high field state, the resistivity monotonically increases with temperature with a dependence that is more singular than the iconic Fermi-liquid, temperature-squared, behavior. Both the damping of the dHvA amplitudes and the increased resistivity near the metamagnetic critical field indicate an increased scattering rate for charge carriers consistent with critical fluctuation scattering in proximity to a phase transition. The dHvA amplitudes do not uniformly recover above the critical field, with some hole-like orbits being entirely suppressed at high fields. These changes, taken as a whole, suggest that the metamagnetic transition in CeIrIn$_5$ is associated with the polarization and localization of the heaviest of quasiparticles on the hole-like Fermi surface.
The Ce compounds CeCoIn$_5$ and CeRhIn$_5$ are ideal model systems to study the competition of antiferromagnetism (AF) and superconductivity (SC). Here we discuss the pressure--temperature and magnetic field phase diagrams of both compounds. In CeRhIn$_5$ the interesting observation is that in zero magnetic field a coexistence AF+SC phase exist inside the AF phase below the critical pressure $p_{rm c}^star approx 2$ GPa. Above $p_{rm c}^star$ AF is suppressed in zero field but can be re-induced by applying a magnetic field. The collapse of AF under pressure coincides with the abrupt change of the Fermi surface. In CeCoIn$_5$ a new phase appears at low temperatures and high magnetic field (LTHF) which vanishes at the upper critical field $H_{rm c2}$. In both compounds the paramagnetic pair breaking effect dominates at low temperature. We discuss the evolution of the upper critical field under high pressure of both compounds and propose a simple picture of the glue of reentrant magnetism to the upper critical field in order to explain the interplay of antiferromagnetic order and superconductivity.
We report the magnetic structure of nominally 10% Cd-doped CeIrIn$_5$, CeIr(In$_{0.9}$Cd$_{0.1}$)$_5$, determined by elastic neutron scattering. Magnetic intensity was observed only at the ordering wave vector $Q_{AF} = (1/2,1/2,1/2)$, commensurate with the crystal lattice. A staggered moment of 0.47(3)$mu_B$ at 1.8 K resides on the Ce ion. The magnetic moments are found to be aligned along the crystallographic $c$ axis. This is further confirmed by magnetic susceptibility data, which suggest the $c$ axis to be the easy magnetic axis. The determined magnetic structure is strikingly different from the incommensurate antiferromagnetic ordering of the closely related compound CeRhIn$_5$, in which the magnetic moments are antiferromagnetically aligned within the tetragonal basal plane.
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