title: Probing the electronic properties of ternary AnM3n-1B2n(n= 1: A = Ca, Sr; M = Rh, Ir andn= 3: A = Ca, Sr; M = Rh) phases: observation of superconductivity.
abstract: We follow the evolution of the electronic properties of the titled homologous series whennas well as the atomic type of A and M are varied where forn= 1, A = Ca, Sr and M = Rh, Ir while forn= 3, A = Ca, Sr and M = Rh. The crystal structure ofn= 1 members is known to be CaRh2B2-type (Fddd), while that ofn= 3 is Ca3Rh8B6-type (Fmmm); the latter can be visualized as a stacking of structural fragments from AM3B2(P6/mmm) and AM2B2. The metallic properties of then= 1 and 3 members are distinctly different: on the one hand, then= 1 members are characterized by a linear coefficient of the electronic specific heatγ≈ 3 mJ mol-1K-2, a Debye temperatureθD≈ 300 K, a normal conductivity down to 2 K and a relatively strong linear magnetoresistivity for fields up to 150 kOe. Then= 3 family, on the other hand, exhibitsγ≈ 18 mJ mol-1K-2,θD≈ 330 K, a weak linear magnetoresistivity and an onset of superconductivity (for Ca3Rh8B6,Tc= 4.0 K andHc2= 14.5 kOe, while for Sr3Rh8B6,Tc= 3.4 K andHc2≈ 4.0 kOe). These remarkable differences are consistent with the findings of the electronic band structures and density of state (DOS) calculations. In particular, satisfactory agreement between the measured and calculatedγwas obtained. Furthermore, the Fermi level,EF, of Ca3Rh8B6lies at almost the top of a pronounced local DOS peak, while that of CaRh2B2lies at a local valley: this is the main reason behind the differences between the, e.g., superconducting properties. Finally, although all atoms contribute to the DOS atEF, the contribution of the Rh atoms is the strongest.
authors.affiliation: National Institute for Materials Science,1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Takeya
authors.affiliation: Instituto de Fisica, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, 21945-970 Rio de Janeiro, Brazil.
authors.forename: Mohammed
authors.initials: M
authors.lastname: ElMassalami
authors.affiliation: Centro de Educação e Saúde, Universidade Federal de Campina Grande, Cuité, PB 58175-000, Brazil.
authors.forename: Luis A
authors.initials: LA
authors.lastname: Terrazos
authors.affiliation: Instituto de Fisica, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, 21945-970 Rio de Janeiro, Brazil.
authors.forename: Raul E
authors.initials: RE
authors.lastname: Rapp
authors.affiliation: Instituto de Fisica, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, 21945-970 Rio de Janeiro, Brazil.
authors.forename: Rodrigo B
authors.initials: RB
authors.lastname: Capaz
authors.affiliation: National Institute for Materials Science,1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Fujii
authors.affiliation: National Institute for Materials Science,1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan.
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Takano
authors.affiliation: Institut für Festkörperphysik, Technische Universität Dresden, D-01062 Dresden, Germany.
authors.forename: Mathias
authors.initials: M
authors.lastname: Doerr
authors.affiliation: Institut für Festkörperphysik, Technische Universität Dresden, D-01062 Dresden, Germany; Faculty of Physics, M V Lomonossov Moscow State University, 119991 Leninskie Gory, Moscow, Russia.
authors.forename: Sergey A
authors.initials: SA
authors.lastname: Granovsky
keywords: 10.14; 20.07; 30.01; AnM3n−1B2n (A=Ca; CaRh2B2-type structures; Ir); M=Rh; Sr; band structure; heat capacity; ternary superconductors