Scaling behavior of temperature-dependent thermopower inCeAu2Si2under pressure

Abstract

We report a combined study of in-plane resistivity and thermopower of the pressure-induced heavy fermion superconductor CeAu2Si2 up to 27.8 GPa. It is found that thermopower follows a scaling behavior in T /T * almost up to the magnetic critical pressure pc ∼ 22 GPa. By comparing with resistivity results, we show that the magnitude and characteristic temperature dependence of thermopower in this pressure range are governed by the Kondo coupling and crystal-field splitting, respectively. Below pc, the superconducting transition is preceded by a large negative thermopower minimum, suggesting a close relationship between the two phenomena. Furthermore, thermopower of a variety of Ce-based Kondo-lattices with different crystal structures follows the same scaling relation up to T /T * ∼ 2.

High-Pressure Study of the Ground- and Superconducting-State Properties of CeAu2Si2

“…At p = 13 GPa, the extrapolated H c value for T N is roughly 30 T and an analogous relationship for T Figure 4 presents the normal-state (H > H c2 ) thermopower S and S/T as a function of temperature (below 6 K) for different pressures. Between 7.6 and 13.6 GPa, S is negative and exhibit a local maximum or a shoulder at T is in good agreement with our previous study [11]. Similar to S, S/T exhibits a maximum at the temperature T ≈ T max S/T at low pressures, but these two temperatures diverge for high pressures.…”

“…Thus, the features in the thermopower corroborate the interpretation of the T and also Ref. [11]]. A feature in S(T ), induced by a phenomenon such as a magnetic rearrangement, is expected to persist in S(T )/T .…”

“…S/T | T →0 continues to decrease beyond 25 GPa, as shown by data from Ref. [11], reflecting the increasing hybridization of Ce-4f and conduction electrons.…”

“…The valence of the Ce ion is 3.00 [4] and the estimated Kondo temperature is T K = 1.7 K [10]. T K increases by roughly 1-2 orders of magnitude when a hydrostatic pressure of 15 GPa is applied [11]. Inelastic magnetic peaks in the neutron scattering spectra show crystal field excitations [12,13].…”

The dominant role of critical valence fluctuations on high Tc superconductivity in heavy fermions

“…Evidently, a simple fit to χ(T ) yields T cr . The empirical law (T − T cr ) −1 is confirmed by data from several samples of CeCu 2 Si 2 [8], CeAu 2 Si 2 [18,26,27], and CeRhIn 5 [17], which are by the way the compounds with highest T c and least negative T cr . Note that the plot of χ(T ) is limited to a temperature (15 K), which corresponds to a small fraction of the first crystal-field-splitting energy.…”