Observation of Low-Energy Einstein Phonon and Superconductivity in Single-Crystalline LaBe₁₃

Abstract

The thermal and electrical transport properties of single-crystalline LaBe 13 have been investigated by specific-heat (C) and electrical-resistivity (ρ) measurements. The specific-heat measurements in a wide temperature range revealed the presence of a hump anomaly near 40 K in the C(T )/T curve, indicating that LaBe 13 has a low-energy Einstein-like-phonon mode with a characteristic temperature of ∼ 177 K. In addition, a superconducting transition was observed in the ρ measurements at the transition temperature of 0.53 K, which is higher than the value of 0.27 K reported previously by Bonville et al. Furthermore, an unusual T 3 dependence was found in ρ(T ) below ∼ 50 K, in contrast to the behavior expected from the electron-electron scattering or the electron-Debye phonon scattering.The beryllides MBe 13 (M = rare earths and actinides) show several novel physical properties depending on the M atom, such as unconventional superconductivity (SC) in UBe 13 , Recently, such cage-structured systems, as represented by filled skutterudites and β-pyrochlores, have been attracting much attention because of the presence of a low-energy

Low-temperature x-ray crystal structure analysis of the cage-structured compounds MBe13(M=La,Sm,and U)

“…[15,19,25]. These results indicate that the MBe 13 systems commonly have relatively high θ D of 600-900 K, although it is necessary to consider an influence of the lowenergy phonon mode for more proper discussion.…”

“…θ D and θ E of the M atom were estimated from the temperature dependence of U eq . The previously reported data are also listed for comparison in this table [15,[18][19][20]25]. [25].…”

“…b Specific heat (Bucher et al) [15]. c Specific heat (Hidaka et al) [19]. d Inelastic neutron (Renker et al) [18].…”

“…For the phonon physics in MBe 13 , previous specific-heat and inelastic neutron scattering (INS) measurements revealed that UBe 13 , ThBe 13 , and possibly LaBe 13 have a low-energy phonon mode, which can be described by an Einstein mode with characteristic temperatures of θ E = 151, 157, and 177 K, respectively [18,19]. To discuss a possibility of an influence of the low-energy phonon mode on novel phenomena in the MBe 13 system, such as unconventional HF superconductivity and non-Fermi-liquid behavior in UBe 13 [20,21] and an intermediate valence state due to the strong c-f hybridization in CeBe 13 [22], it is necessary to elucidate characteristics of the low-energy phonon mode.…”

“…In this study, we investigated structure parameters and phonon properties of a superconductor LaBe 13 with a superconducting transition temperature of ∼0.6 K [19], a possible helical magnet SmBe 13 with a magnetic transition temperature of T M = 8.3 K [15,28,29], and an unconventional HF superconductor UBe 13 [20] by x-ray diffraction (XRD) measurements in temperatures of down to 7 K. The results of the XRD measurements and Rietveld analyses are presented in Sec. III: the temperature dependence of the lattice parameter in subsection A, the fractional (0, y, z) coordinates in subsection B, and isotropic mean-square displacement parameters in subsection C.…”