Enhancing the Superconducting Transition Temperature of the Heavy Fermion CompoundCeIrIn5in the Absence of Spin Correlations

Abstract

We report on a pressure(P )-induced evolution of superconductivity and spin correlations in CeIrIn5 via the 115 In nuclear-spin-lattice-relaxation rate measurements. We find that applying pressure suppresses dramatically the antiferromagnetic fluctuations that are strong at ambient pressure. At P = 2.1 GPa, Tc increases to Tc = 0.8 K that is twice Tc(P = 0 GPa), in the background of Fermi liquid state. This is in sharp contrast with the previous case in which negative, chemical pressure (replacing Ir with Rh) enhances magnetic interaction and increases Tc. Our results suggest that multiple mechanisms work to produce superconductivity in the same compound CeIrIn5.The cerium (Ce)-based heavy-fermion compounds CeMIn 5 (M = Co, Rh, and Ir) discovered a few years ago provides a unique opportunity to investigate the interplay between antiferromagnetism and superconductivity [1,2,3]. Among CeMIn 5 , CeIrIn 5 and CeCoIn 5 show superconductivity at P = 0 below T c = 0.4 K and 2.3 K, respectively [2,3]. Antiferromagnet CeRhIn 5 becomes superconducting at relatively lower critical pressure P c ∼ 1.6 GPa and yet exhibits a higher T c ∼ 2 K [1]. Measurements of nuclear-quadrupole-resonance (NQR) [4,5,6,7], thermal transport and heat capacity [8] on CeMIn 5 found that the superconductivity is unconventional, with line-nodes in the superconducting gap function. NQR [4,5,7,9] and inelastic neutron diffraction [10] measurements also found strong antiferromagnetic spin fluctuations in the normal state. In addition, in CeIrIn 5 , the antiferromagnetic spin fluctuations are found to be anisotropic [4], namely, a magnetic correlation length ξ plane within the tetragonal plane grows up more dominantly than ξ c along the c-axis associated with their two-dimensional crystal structure. The nuclearspin-lattice-relaxation rate(1/T 1 ) was found to follow the relation of 1/T 1

Physical properties of Cd doped CeIrIn5 under pressure

“…With increasing pressure, Tsc increases and reaches a maximum value of 1 K at around 3 GPa [7,8]. The mechanism of SC in CeIrIn5 has not been clear yet.…”

CeIrIn5: Superconductivity on a magnetic instability

“…CeIrIn 5 was argued to exist far from an AFM QCP and be located at a cusp-like minimum of T sc which bridges the two superconducting domes [16]. Accordingly, superconductivity of CeIrIn 5 was proposed to be mediated by valence fluctuations rather than by spin fluctuations [16][17][18], which are more commonly taken to mediate pairing in HF superconductors (Scenario I in Fig. 1) [13,19].…”

“…1) [13,19]. 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].…”

Zero-field NMR and NQR measurements of the antiferromagnet URhIn5

“…8 Systematic nuclear magnetic resonance (NMR) investigations of the Ce115 systems have established that these superconductors have d-wave superconducting gaps, [9][10][11][12] and that antiferromagnetic (AFM) spin interactions play an active role in the superconducting pairing. [13][14][15][16] In the Pu115 systems, NMR measurements show d-wave-like superconducting gap behavior, 17,18 with T c 's an order of magnitude higher than those for the Ce115. In heavy-fermion 115 systems, recent systematic NMR experiments have suggested that AFM XYtype anisotropy is more favorable for d-wave superconductivity than Ising-type or isotropic fluctuations.…”