Evidence of unconventional superconductivity in the Ni-doped NbB2 system

Abstract

In this paper, a comprehensive study of the effects of Ni-doping on structural, electrical, thermal and magnetic properties of the NbB 2 is presented. Low amounts (≤ 10 %) of Ni substitution on Nb sites cause structural distortions and induce drastic changes in the physical properties, such as the emergence of a bulk superconducting state with anomalous behaviors in the critical fields (lower and upper) and in the specific heat.Ni-doping at the 9 at.% level, for instance, is able to increase the critical temperature (T C ) in stoichiometric NbB 2 (< 1.3 K) to approximately 6.0 K. Bulk superconductivity is confirmed by magnetization, electronic transport, and specific heat measurements. Both H c1 and H c2 critical fields exhibit a linear dependence with reduced temperature (T/T C ), and the specific heat deviates remarkably from the conventional exponential temperature dependence of the single-band BCS theory. These findings suggest multiband superconductivity in the composition range from 0.01 ≤ x ≤ 0.10 (Nb 1-x Ni x B 2 ).

Effect of carbon doping on the structure and superconductivity in AlB2‐type (Mo0.96Ti0.04)0.8${(\text{Mo}_{0.96}\text{Ti}_{0.04})}_{0.8}$B2

“…Transition metal diborides (TMDBs) have attracted a lot of attention over the past few decades due to their diverse properties, [1][2][3] including high hardness and shear strength, [4][5][6][7] excellent corrosion resistance, 8,9 superior catalytic performance, 10,11 notrivial band topology, 12,13 high electrical conductivity and even superconductivity. [14][15][16][17][18] Among existing TMDBs, molybdenum diboride is unique in that it exists in both hexagonal AlB 2 -type and rhombohedral structures. 19 The former is built up by planar transition metal and boron layers stacked alternatively along the 𝑐-axis, and the latter can be derived from the former by puckering half of the boron layers.…”

“…Transition metal diborides (TMDBs) have attracted a lot of attention over the past few decades due to their diverse properties, 1–3 including high hardness and shear strength, 4–7 excellent corrosion resistance, 8,9 superior catalytic performance, 10,11 notrivial band topology, 12,13 high electrical conductivity and even superconductivity 14–18 . Among existing TMDBs, molybdenum diboride is unique in that it exists in both hexagonal AlB 2 ‐type and rhombohedral structures 19 .…”

Effect of carbon doping on the structure and superconductivity in AlB$_{2}$-type (Mo$_{0.96}$Ti$_{0.04}$)$_{0.8}$B$_{2}$

“…Transition metal diborides (TMDBs) have attracted a lot of attention over the past few decades due to their diverse properties [1][2][3], including high hardness and shear strength [4][5][6][7], excellent corrosion resistance [8,9], superior catalytic performance [10,11], notrivial band topology [12,13], high electrical conductivity and even superconductivity [14][15][16][17][18]. Among existing TMDBs, molybdenum diboride is unique in that it exists in both hexagonal AlB 2 -type and rhombohedral structures [19].…”