Towards the Identification of a Quantum Critical Line in the (p,B) Phase Diagram ofCeCoIn5with Thermal-Expansion Measurements

Abstract

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 β. Considerable deviations of β(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, β(T ) and the Grüneisen parameter Γ are incompatible with a quantum critical point (QCP) at B 0 c2 , but allow for a QCP shielded by superconductivity and extending to negative pressures for B < B 0 c2 . Together with literature data we construct a tentative (p, B, T ) phase diagram of CeCoIn5 suggesting a quantum critical line in the (p, B) plane.

CeIrIn5: Superconductivity on a magnetic instability

“…These results resemble those of Cd-doped CeCoIn 5 and pressurized CePd 2 Si 2 and CeRhIn 5 as schematically illustrated in Fig. 1(a) for the scenario I [4][5][6][7][8]11], where SC emerges near an AFM QCP. Our results provide solid evidence that CeIrIn 5 is located near an AFM instability rather than a valence instability and the SC of CeIrIn 5 is associated with critical spin fluctuations, being similar to many other HF superconductors.…”

“…The resulting superconducting phase diagram is nearly identical to that of CeCoIn 5 after a suitable pressure shift [8]. Thus, it has been widely accepted that CeCoIn 5 sits on the threshold of a magnetic instability at ambient pressure [4][5][6][8][9][10].…”

“…Furthermore, application of pressure to the antiferromagnets CeRhIn 5 and CeCo(In,Cd) 5 eventually suppresses the AFM order and induces superconductivity (SC) near an AFM quantum critical point (QCP) (Scenario I in Fig. 1) [4][5][6][7]. The resulting superconducting phase diagram is nearly identical to that of CeCoIn 5 after a suitable pressure shift [8].…”

“…However, no solid evidence of a valence instability has been revealed in CeIrIn 5 , even though nuclear quadrupolar resonance (NQR) experiments detected some differences between the two superconducting domes [17,18]. On the other hand, analyses of nuclear spin-lattice re- [11], which applies to most Ce-based HF superconductors including CeCoIn5 and CeRhIn5 [4][5][6][7][8]. (b) Scenario II: Two superconducting domes (SC I and SC II) develop upon increasing the lattice density [13].…”

Fermi-surface evolution in Yb-substituted CeCoIn5

“…5 As a unique feature, there exists a further magnetic-field-driven antiferromagnetic QCP near the upper critical field. [6][7][8][9] It has been speculated, that at an antiferromagnetic QCP the Fermi surface changes when the system crosses over from a normal antiferromagnetic metal to a strongly correlated Fermi liquid. 10 This makes our study of the influence of Yb doping on the Fermi surface in CeCoIn5 of particular interest.…”