Microscopic and Macroscopic Electronic Properties of the AuCu3-Type Alloys: The LaSn3

Abstract

The bulk properties of the LaSn3"In3(i ) and similar alloy systems display a dramatic, somewhat oscillatory, dependence on the valence-electron concentration. For the LaSn, "In, (, . "& alloy system we have studied the dependence on x of the magnetic susceptibility g and the local electronic behavior at the La and Sn-In sites using the La" and Sn'" nuclear-magnetic-resonance Knight shifts E and spin-lattice relaxation times T,. These results are compared with those for the superconducting transition temperature 1"the electronic-specific-heat coefficient y, and the Debye temperature 8D. Using McMillan's strong-coupling model we have calculated from y and 1,/8D, the electron-phonon coupling parameter X, the bare density of states N(0), and the electron-phonon interaction strength V. For the NMR measurements, the Sn NMR properties follow the behavior of the bulk density of states at the Fermi energy, N(0), considerably better than do the La NMR properties suggesting that the local electronic properties of the Sn-In sites play the dominant role in determining T, . Analysis of the La NMR and y behavior with x indicates the paramagnetic susceptibility of these alloys arises from the La d band with the La d-orbital contribution accounting for most of the large susceptibility for x near LaSn, and LaIn3.

Electron spin resonance study of the LaIn3−xSnxsuperconducting system

“…In the free conduction electron gas model, the Sommerfeld coefficient for a superconductor is given by γ = (2/3)π 2 k 2 B η F (1−λ), where λ is the electron-phonon coupling parameter. For LaIn 3 γ = 6.3 mJ/(mol K 2 ) [9] and λ = 0.55(5) [3]. Hence, we estimate a total density of states at the Fermi level of η F = 0.8(1) states/(eV mol spin).…”

“…The density of states of the LaIn 1.5 Sn 1.5 sample is η F = 0.9(1) states/(eV mol spin) [3]. The ∆g ≃ 30(10)×10 −3 value observed relates to a Korringa rate b = 20(15) Oe/K by Eq.…”

“…Indeed, nuclear magnetic resonance experiments showed that for LaT 3 (T = Sn, In, Pb, Tl, etc.) [1,3,26,27] conduction electron-electron correlations have negligible effect in these compounds. In the free conduction electron gas model, the Sommerfeld coefficient for a superconductor is given by γ = (2/3)π 2 k 2 B η F (1−λ), where λ is the electron-phonon coupling parameter.…”

“…Knowing a Ref. [3] that the density of states for LaIn 2.2 Sn 0.8 is η F = 0.8(1) states/(eV mol spin) [3], from Eq. 2 we find J f s = 32(6) meV (see Table 3).…”

“…From the Sommerfeld coefficient expression and knowing that the LaSn 3 compound has γ = 11.7 mJ/(mol K 2 ) [6] and λ = 0.80(5) [3], we estimate η F = 1.4(1) states/(eV mol spin). The Korringa rate and ∆g found experimentally for La 0.996 Gd 0.004 Sn 3 are 19(1) Oe/K and 20(10)×10 −3 , respectively.…”