Evidence of unconventional superconducting state in a topological semimetal confirms unprecedented spin-3/2 Cooper pairing.

No abstract

We present details of materials synthesis, crystal structure, and anisotropic magnetic properties of single crystals of CeAlGe, a proposed type-II Weyl semimetal. Single-crystal x-ray diffraction confirms that CeAlGe forms in noncentrosymmetric I41md space group, in line with predictions of non-trivial topology. Magnetization, specific heat and electrical transport measurements were used to confirm antiferromagnetic order below 5 K, with an estimated magnon excitation gap of ∆ = 9.11 K from heat capacity and hole-like carrier density of 1.44 × 10 20 cm −3 from Hall effect measurements. The easy magnetic axis is along the [100] crystallographic direction, indicating that the moment lies in the tetragonal ab-plane below 7 K. A spin-flop transition to less than 1 µB/Ce is observed to occur below 30 kOe at 1.8 K in the M (H) (H a) data. Small magnetic fields of 3 kOe and 30 kOe are sufficient to suppress magnetic order when applied along the a-and c-axes, respectively, resulting in a complex T-H phase diagram for H a and a simpler one for H c.

Single crystals of Ba(Fe 1-x Mn x ) 2 As 2 , 0 < x < 0.148, have been grown and characterized by structural, magnetic, electrical transport, and thermopower measurements. Although growths of single crystals of Ba(Fe 1-x Mn x ) 2 As 2 for the full 0 x 1 range were made, we find evidence for phase separation (associated with some form of immiscibility) starting for x > 0.1-0.2. Our measurements show that whereas the structural/magnetic phase transition found in pure BaFe 2 As 2 at 134 K is initially suppressed by Mn substitution, superconductivity is not observed at any substitution level. Although the effect of hydrostatic pressure up to 20 kbar in the parent BaFe 2 As 2 compound is to suppress the structural/magnetic transition at the approximate rate of 0.9 K/kbar, the effects of pressure and Mn substitution in the x = 0.102 compound are not cumulative. Phase diagrams of transition temperature versus substitution concentration x based on electrical transport, magnetization, and thermopower measurements have been constructed and compared to those of the Ba(Fe 1-x TM x ) 2 As 2 (TM= Co and Cr) series.