Conventional s-Wave Superconductivity in Noncentrosymmetric Ir₂Ga₉: ⁷¹Ga-NQR Evidence

Abstract

Superconductivity without spatial inversion symmetry has begun to attract much attention since the discovery of the superconductor CePt 3 Si.1 It is presumed that the absence of spatial inversion symmetry causes an admixture between even and odd parities of superconducting pairing due to antisymmetric spin-orbit coupling (ASOC).2 However, there has been no clear evidence of the admixture thus far, and hence the spatial noncentrosymmetric effect on superconductivity remains experimentally controversial. Recently, ASOC has also been discussed in transition-metal superconductors. In this system, we can consider ASOC without strongly correlated electron systems, which would be appropriate for tracing the effect of ASOC. Interestingly, in Li 2 Pt 3 B, it was reported that unconventional superconductivity with a line node and a spin-triplet pairing state emerge, which are ascribed to ASOC.3, 4 These reports suggest that ASOC can induce a novel superconducting state even though there is no strong electron correlation.The intermetallic binary Ir 2 Ga 9 does not possess spatial inversion symmetry and becomes superconducting below T c = 2.2 K.5, 6 Specific heat and resistivity measurements showed that the compound is a weak-coupling BCS superconductor with an isotropic gap, and located near the boundary between type-I and type-II superconductivities with an upper critical field H c2 ∼ 150 Oe. 5, 6In this letter, we report on the characteristics of superconductivity in noncentrosymmetric Ir 2 Ga 9 probed by 71 Ga-nuclear-quadrupole-resonance (NQR) measurement at a zero field (H = 0). The spatial noncentrosymmetric effect on the superconducting state is discussed.A single crystal of Ir 2 Ga 9 was grown by the Ga flux method.6 Powder X-ray diffraction indicated that the compound forms in the primitive monoclinic Rh 2 Ga 9 type structure.6, 7 The sample of Ir 2 Ga 9 was crushed into coarse powder for NQR measurement to allow the penetration of the rf field. The NQR measurement was performed by the conventional spin-echo method in the temperature (T ) range of 1-280 K. T 1 was measured at f ∼ 26.45 MHz, which was the 1ν Q (±1/2 ↔ ±3/2) transition of 71 Ga (I = 3/2), as shown in Fig. 1. The NQR

Multiband Superconductivity in Heavy Fermion Compound CePt3Si without Inversion Symmetry: An NMR Study on a High-Quality Single Crystal

“…[15][16][17] This kind of behavior has never been observed in the other HF superconductors such as CeCoIn 5 , CeIrIn 5 , and CeCu 2 Si 2 , which are in a spin-singlet Cooper pairing regime. In the noncentrosymmetric superconductors where the correlation between electrons may be not so significant, however, the characteristic feature for conventional s-wave spin singlet superconducting state has been observed in many compounds, for example, Y 2 C 3 , 18,19) Ir 2 Ga 9 , 20,21) LaPt 3 Si, 22) LaIrSi 3 , 23) Li 2 Pd 3 B, 24) and so on, whereas the parity mixing state has been argued only in the related compound Li 2 Pt 3 B. 25,26) The CePt 3 Si exhibits superconductivity at T c = 0.75 K in an antiferromagnetically ordered state below a Néel temperature of T N = 2.2 K, as reported by Bauer et al 9,27) Neutron-scattering measurement probed an AFM structure with a wave vector Q = (0, 0, 1/2) and a magnetic moment of 0.16µ B lying in the ab-plane of the tetragonal lattice.…”

Applications of nuclear shielding

“…Ir 2 Ga 9 is the conventional s-wave superconductor. 215 Combined application of 69,71 Ga NMR spectroscopy and quantum mechanism calculations reveals the chemical bonding in the digallides of Ca, Sr and Ba. The NMR spectroscopic signal shift is mainly due to the Knight shift and is almost equal for the investigated digallides, whereas the anisotropy of the signal shift decreases with the radius of the alkaline-earth metals.…”