Superconductivity and Quantum Criticality in CeCoIn_5

We have studied the temperature-pressure phase diagram of CeCoSi by electrical-resistivity experiments under pressure. Our measurements revealed a very unusual phase diagram. While at low pressures no dramatic changes and only a slight shift of the Ne\'{e}l temperature $T_N$ ($\approx 10$ K) are observed, at about 1.45 GPa a sharp and large anomaly, indicative of the opening of a spin-density-wave (SDW) gap, appears at a comparatively high temperature $T_S \approx 38$ K. With...

The electrical resistivity rho(T) of single crystalline CeCu_5Au under pressure was measured in the temperature range 30mK<T<300K. Pressure suppresses the antiferromagnetic order (T_N=2.35K at ambient pressure) and drives the system into a non-magnetic heavy-fermion state above P_c=4.1(3)GPa. The electrical resistivity shows a deviation from a T^2 dependence of a Fermi-liquid in the pressure range 1.8GPa<=P<=5.15GPa. The rho(T)-curves can be compared with those of CeCu_{6-x}A...

The thermal conductivity kappa of the heavy-fermion metal CeCoIn5 was measured in the normal and superconducting states as a function of temperature T and magnetic field H, for a current and field parallel to the [100] direction. Inside the superconducting state, when the field is lower than the upper critical field Hc2, kappa/T is found to increase as T approaches absolute zero, just as in a metal and in contrast to the behavior of all known superconductors. This is due to u...

We present the results of out-of-plane electrical transport measurements on the heavy fermion superconductor CeCoIn$_{5}$ at temperatures from 40 mK to 400 K and in magnetic field up to 9 T. For $T <$ 10 K transport measurements show that the zero-field resistivity $\rho_{c}$ changes linearly with temperature and extrapolates nearly to zero at 0 K, indicative of non-Fermi-liquid (nFL) behavior associated with a quantum critical point (QCP). The longitudinal magnetoresistance ...

This paper has been withdrawn. Please see cond-mat/0605124 for new and updated data and conclusions pertaining to this study.

The pressure-temperature-phase diagram of the new heavy-fermion superconductor CeAu$_2$Si$_2$ is markedly different from those studied previously. Indeed, superconductivity emerges, not on the verge, but deep inside the magnetic phase. In this context, we have carried out ac-calorimetry, resistivity and thermoelectric power measurements on a CeAu$_2$Si$_2$-single crystal under high-pressure. The principal novelties of this experiment are the observation of a new transition li...

In this paper we review some of our recent experimental and theoretical results on transport and thermodynamic properties of heavy-fermion alloys Ce(1-x)Yb(x)CoIn5. Charge transport measurements under magnetic field and pressure on these single crystalline alloys revealed that: (i) relatively small Yb substitution suppresses the field induced quantum critical point, with a complete suppression for nominal Yb doping x>0.20; (ii) the superconducting transition temperature Tc an...

The low-temperature thermal expansion of CeCoIn5 single crystals measured parallel and perpendicular to magnetic fields B oriented along the c axis yields the volume thermal-expansion coefficient $\beta$. Considerable deviations of $\beta(T)$ from Fermi-liquid behavior occur already within the superconducting region of the (B, T) phase diagram and become maximal at the upper critical field $B^0_{c2}$. However, $\beta(T)$ and the Gr\"uneisen parameter $\Gamma$ are incompatible...

We give a review of recent results on the heavy fermion superconductor CeRhIn$_5$ which presents ideal conditions to study the interplay of antiferromagnetism and superconductivity. The main results are the appearance of domains of microscopic coexistence of antiferromagnetism and superconductivity under both, pressure and magnetic field scans. At zero magnetic field, under pressure coexistence appears from the onset of pressure induced superconductivity up to the critical pr...

Quantum criticality in the normal and superconducting state of the heavy-fermion metal CeCoIn$_5$ is studied by measurements of the magnetic Gr\"{u}neisen ratio, $\Gamma_H$, and specific heat in different field orientations and temperatures down to 50 mK. Universal temperature over magnetic field scaling of $\Gamma_H$ in the normal state indicates a hidden quantum critical point at zero field. Within the superconducting state the quasiparticle entropy at constant temperature ...