Quantum criticality in Ce2PdIn8: A thermoelectric study

Abstract

We report the Nernst effect (ν) and thermoelectric power (S) data for the Ce2PdIn8 heavyfermion compound. Both S and ν behave anomalously at low temperatures: the thermopower shows a Kondo-like maximum at T = 37 K, while the Nernst coefficient becomes greatly enhanced and field dependent below T ≈ 30 K. In the zero-T limit S/T and ν/T diverge logarithmically, what is related to occurrence of the quantum critical point (QCP). Presented results suggest that the antiferromagnetic spin-density-wave scenario may be applicable to QCP in Ce2PdIn8. PACS numbers: 72.15.Jf, 74.40.Kb, 74.70.Tx The physical properties of matter in the vicinity of quantum critical point (QCP) has been intensively studied for the last two decades. A relation between QCP and unconventional superconductivity, as well as other unusual properties of the electronic system near QCP have attracted much attention, although this complex topic is far from being well understood. Measurements of the thermoelectric effects, which are particularly sensitive to distribution of the density of the electronic states and variation of the relaxation time around the Fermi surface, turn out to be an effective method to detect departures from the Landau description of metals [1][2][3][4][5]. However, an interpretation of these anomalies is not straightforward, since there exist a wide variety of overlapping to some extent models that attempt to explain the unusual thermoelectric behavior. For instance, one can mention here the models of d-wave-(dDW) , spin-(SDW), charge-(CDW), and unconventional-(UDW) density-waves [6,7], magnetic-field-induced chiral order [8], superconducting vortices (or vortex-like excitations) [9], superconducting fluctuations [10], current vertex correction [11]. Even though, studies on temperature and/or magnetic field variations of the Nernst coefficient and the thermoelectric power have been recognized as very helpful tools in distinguishing between possible types of quantum criticality [12][13][14].In this Letter we investigate the transport properties of the Ce 2 PdIn 8 heavy-fermion (HF) compound that exhibits unconventional superconductivity below T c = 0.7 K [15]. We focus on the thermoelectric phenomena which appear to be highly anomalous in the low temperature region. Both the Nernst effect and the thermoelectric power show below T ≈ 7 K features that can be attributed to presence of the quantum critical point.High-quality polycrystalline sample of Ce 2 PdIn 8 was prepared and characterized as described in Ref. [16]. The resistivity was measured using the four-probe technique with 25 µm gold wires attached to the bar-shaped sample with two component silver epoxy (EPO-TEK H20E). For the Hall coefficient measurement, the sample was mounted on a rotatable probe and continuously turned by 180 degree (face down and up) in a magnetic field (B) of 12.5 T to effectively reverse the field anti-symmetrical signal. During the thermoelectric power and Nernst coefficient measurements, the sample was clamped between two phosphor bronze blocks,...

Anomalous magnetotransport in the heavy-fermion superconductor Ce2PdIn8

“…Most intriguingly, it has also been suggested that Ce 2 PdIn 8 may fulfill the necessary conditions for the formation of a unique modulated Fulde-Ferrell-Larkin-Ovchinnikov superconducting state [6], which possible occurrence at the magnetic highfield-low-temperature corner of the H − T phase diagram of CeCoIn 5 is presently being hotly debated [11]. The many common features between CeCoIn 5 and Ce 2 PdIn 8 motivate further comprehensive studies of the physical behavior in the latter compound.In this Communication we report on the Hall effect and the transverse magnetoresistivity of Ce 2 PdIn 8 , which both appeared highly anomalous yet consistent with the quantum criticality scenario, previously evoked based on the electrical resistivity [5,6,8], thermoelectric [12] and heat capacity [4,9] data. The polycrystalline sample used in the present study was previously characterized by means of X-ray diffraction, magnetic susceptibility, electrical resistivity and heat capacity measurements [5].…”

“…In this Communication we report on the Hall effect and the transverse magnetoresistivity of Ce 2 PdIn 8 , which both appeared highly anomalous yet consistent with the quantum criticality scenario, previously evoked based on the electrical resistivity [5,6,8], thermoelectric [12] and heat capacity [4,9] data. The polycrystalline sample used in the present study was previously characterized by means of X-ray diffraction, magnetic susceptibility, electrical resistivity and heat capacity measurements [5].…”

“…The good reproducibility of Hall data was proved on another polycrystalline sample (cut from the same ingot) that was notably thicker (0.18 mm), yet had comparable surface dimensions (see the data in Ref. 12). The electrical leads were fabricated using silver paste to attach 50 µm thick silver wires to copper pads located on the sample surface.…”

Anomalous superfluid density in quantum critical superconductors

“…The most studied member of this series is the n = 1 member CeCoIn 5 (T c = 2.3 K) (16), in which clear evidence for non-FL behaviors in the normal state (17,18) and nodal superconductivity has been found (6,19,20). The recent discovery of superconductivity at ambient pressure in the n = 2 member Ce 2 PdIn 8 (T c = 0.68 K) (21), which exhibits very similar non-FL properties (22)(23)(24)(25)(26)(27) to those in CeCoIn 5 , allows a detailed comparison of the superconducting properties to extract common features in these superconductors near the antiferromagnetic QCP.…”

Quasi-two-dimensional Fermi surfaces of the heavy-fermion superconductorCe2PdIn8

“…Non-Fermi-liquid behavior was observed in both macroscopic [6][7][8][9][10] and microscopic [11,12] measurements at low temperature, implying that Ce 2 PdIn 8 is located very close to a QCP. It was further suggested that a twodimensional (2D) SDW-type QCP is induced by magnetic field near the upper critical field, H c2 ≈ 2 T [9].…”