Strong Magnetic Fluctuations in a Superconducting State ofCeCoIn5

Abstract

We show results on the vortex core dissipation through current-voltage measurements under applied pressure and magnetic field in the superconducting phase of CeCoIn5. We find that as soon as the system becomes superconducting, the vortex core resistivity increases sharply as the temperature and magnetic field decrease. The sharp increase in flux flow resistivity is due to quasiparticle scattering on critical antiferromagnetic fluctuations. The strength of magnetic fluctuations below the superconducting transition suggests that magnetism is complimentary to superconductivity and therefore must be considered in order to fully account for the low-temperature properties of CeCoIn5.PACS numbers: 71.10. Hf, 71.27.+a, 74.70.Tx Unconventional superconductivity in heavy-fermion material CeCoIn 5 is a complex state of matter involving magnetic and conduction degrees of freedom strongly coupled with each other [1][2][3][4][5]. Superconductivity emerges at a temperature T c ≃ 2.3 K with the order parameter most likely having d-wave symmetry [6][7][8][9]. The magnitude of the specific heat jump at the superconducting transition temperature [1, 6] indicates the mass enhancement of conduction electrons by several orders of magnitude. Normal state resistivity shows nonFermi liquid linear temperature dependence at low temperatures (< 20 K). Approximately at a temperature T * ≃ 45 K [1, 11], the heavy electrons begin to form due to the strong hybridization between the conduction electrons and localized Ce f -electrons. Despite the significant enhancement of the electronic mass, the magnetic susceptibility shows a Curie-Weiss behavior down to moderately low temperatures [1, 2,12,13] signaling the absence of the fully quenched magnetic moments.The pronounced non-Fermi liquid behavior in the normal state and unconventional superconductivity in CeCoIn 5 are thought to arise from the proximity of the system to a quantum critical point (QCP) separating paramagnetic and antiferromagnetic phases. Specifically, it was recently proposed that the transport and thermodynamic properties of CeCoIn 5 in the normal phase are controlled by an antiferromagnetic QCP at an inaccessible negative pressure [14]. The recovery of a Fermi liquid state at low temperatures and high magnetic fields was reported in Ref.[1], pointing to a field-induced QCP at the zero-temperature upper critical field H c2 (0). However, the location of the field-induced QCP exactly at H c2 (0) seems to be just a coincidence, since, with increasing pressure, this QCP moves inside the superconducting dome to lower fields. In fact, high sensitivity Hall effect measurements have revealed that the field induced QCP is located at H ≃ 4.1 T < H c2 (0), which suggest a possible antiferromagnetic ground state superseded by superconductivity [16]. In addition, low temperature thermal expansion data [17] on identification of the quantum critical line can be consistently interpreted within the same set of ideas as the Hall effect data. Thus, all these observations seem to favor the ant...

Non-Fermi liquid regimes with and without quantum criticality in Ce 1− x Yb x CoIn 5

“…As expected, the value of H QCP of 4.1 T for CeCoIn 5 (Fig. 1C) coincides with the value of H QCP determined previously from both resistivity measurements done in the normal state (26) and I − V characteristics measured in the mixed state (10). Therefore, the measurement of Δρ ⊥ a =ρ a along with the analysis used here constitutes an excellent experimental technique to determine the field-induced QCP in the NFL regime.…”

“…The crossover from NFL to Fermi liquid behavior is thought to be governed by a quantum critical point (QCP), which separates paramagnetic and antiferromagnetic (AFM) phases and is located in the superconducting phase (7,8). Neutron-scattering studies (9) and more recent measurements of the vortex-core dissipation through current-voltage characteristics (10) provide direct evidence for an AFM QCP in CeCoIn 5 that could be accessed by tuning the system via magnetic field or pressure.…”

Pressure studies of the quantum critical alloyCe0.93Yb0.07CoIn5

“…Indeed, quantum fluctuations in this family of heavy fermion superconductors are known to be suppressed by pressure because the AFM order in the Ce-lattice is suppressed. [34][35][36] Figure ure shows that from just above T c to about 4 K, the ρ a (T ) data follow very well a √ T dependence (solid lines are linear fits to the data with ρ a (P, T ) = ρ a0 (P ) + B * (P ) √ T ). The pressure dependence of the coefficient B * is shown in the inset to Fig.…”

Filamentary superconductivity across the phase diagram of Ba(Fe,Co)2As2

“…Inhomogeneity is favorable for a subdominant order to emerge locally, in regions where the competing dominant order vanishes. For example, AFM order can be present inside the vortex core 18 and FLSC nucleates at the domain walls in the antiferromagnetically ordered parent compound. 5 The very similar H − T phase diagrams of undoped BaFe 2 As 2 and undoped antiferromagnetic CaFe 2 As 2 5 show a common signature for FLSC in these parent compounds and, therefore, imply that the AFM order is also a competing order to superconductivity in the BaFe 2 As 2 system.…”