Possible multigap Type-I superconductivity in the layered Boride RuB\(_2\)

• Published in: arXiv.org
• Main Authors: Singh, Jaskaran, Jayaraj, Anooja, Srivastava, D, Gayen, S, Thamizhavel, A, Singh, Yogesh
• Format: Paper
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 20.09.2017
• Subjects: Borides; Fermi surfaces; Ginzburg-Landau parameter; Honeycomb construction; Magnetic permeability; Parameter estimation; Specific heat; Superconductivity; Transition metals
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1709.06954

The structure of the layered transition-metal Borides \(A\)B\(_2\) (\(A =\) Os, Ru) is built up by alternating \(T\) and B layers with the B layers forming a puckered honeycomb. Here we report superconducting properties of RuB\(_2\) with a \(T_c \approx 1.5\)K using measurements of the magnetic susceptibility versus temperature \(T\), magnetization \(M\) versus magnetic field \(H\), resistivity versus \(T\), and heat capacity versus \(T\) at various \(H\). We observe a reduced heat capacity anomaly at \(T_c\) given by \(\Delta C/\gamma T_c \approx 1.1\) suggesting multi-gap superconductivity. Strong support for this is obtained by the successful fitting of the electronic specific heat data to a two-gap model with gap values \(\Delta_1/k_BT_c \approx 1.88\) and \(\Delta_2/k_BT_c \approx 1.13\). Additionally, \(M\) versus \(H\) measurements reveal a behaviour consistent with Type-I superconductivity. This is confirmed by estimates of the Ginzburg-Landau parameter \(\kappa \approx 0.1\)--\(0.66\). These results strongly suggest multi-gap Type-I superconductivity in RuB\(_2\). We also calculate the band structure and obtain the Fermi surface for RuB\(_2\). The Fermi surface consists of one quasi-two-dimensional sheet and two nested ellipsoidal sheets very similar to OsB\(_2\). An additional small \(4^{\rm th}\) sheet is also found for RuB\(_2\). RuB\(_2\) could thus be a rare example of a multi-gap Type-I superconductor.