Crystal Growth and Study of Unusual Magnetic Anomalies of a Low-Dimensional Iron(III) Oxy-Arsenates:

Our most recent studies have been directed towards the synthesis of low-dimensional magnetic materials as these have drawn continued attention in condensed matter chemistry and physics, owing to their diverse electronic and magnetic properties. One example of such a family is A2Fe2O(AsO4)2 where A = K, Rb. Further, the A2Fe2O(AsO4)2 series show interesting magnetic anomalies regarding stepped magnetization. Also intriguing are the negative magnetizations observed below the ordering temperature in the field cooling (FC) and zero field cooling (ZFC) susceptibility measurements. We have performed the neutron powder diffraction (NPD) measurements using HB-2A in Oakridge National Lab and BT-1 in NIST. Neutron powder diffraction for A2Fe2O(AsO4)2 were collected at various temperatures ranging from 3.3 K to 35 K. The 35 K data has been adequately described with a nuclear model, previously determined using single crystal X-ray diffraction, indicating a lack of long-range magnetic order. The NPD measurements were also conducted in horizontal fields up to 5 T at 2 K. The field dependence of the spin arrangement was used to explain the negative magnetization observed in A2Fe2O(AsO4)2. The neutron scattering measurements of K2Fe2O(AsO4)2 were also carried out using SEQUOIA—Fine-Resolution Fermi Chopper Spectrometer in ORNL

Gapless spin-excitations in the superconducting state of a quasi-one-dimensional spin-triplet superconductor

Majorana zero modes form as intrinsic defects in an odd-orbital one-dimensional superconductor thus motivating the search for such materials in the pursuit of Majorana physics. Here, we present combined experimental results and first principles calculations which suggest that quasi-one-dimensional K$_2$Cr$_3$As$_3$ may be such a superconductor. Using inelastic neutron scattering we probe the dynamic spin-susceptibilities of K$_2$Cr$_3$As$_3$ and K$_2$Mo$_3$As$_3$ and show the presence of antiferromagnetic spin-fluctuations in both compounds. Below the superconducting transition, these fluctuations gap in K$_2$Mo$_3$As$_3$ but not in K$_2$Cr$_3$As$_3$. Using first principles calculations, we show that these fluctuations likely arise from nesting on one dimensional features of the Fermi surface. Considering these results we propose that while K$_2$Mo$_3$As$_3$ is a conventional superconductor, K$_2$Cr$_3$As$_3$ is likely a spin-triplet, and consequently, topological superconductor.Comment: 8 pages, 4 figure