Superlattice formation lifting degeneracy protected by non-symmorphic symmetry through a metal-insulator transition in RuAs

The single crystal of RuAs obtained by Bi-flux method shows obvious successive metal-insulator transitions at T_MI1~255 K and T_MI2~195$ K. The X-ray diffraction measurement reveals a formation of superlattice of 3x3x3 of the original unit cell below T_MI2, accompanied by a change of the crystal system from the orthorhombic structure to the monoclinic one. Simple dimerization of the Ru ions is nor seen in the ground state. The multiple As sites observed in nuclear quadrupole resonance (NQR) spectrum also demonstrate the formation of the superlattice in the ground state, which is clarified to be nonmagnetic. The divergence in 1/T_1 at T_MI1 shows that a symmetry lowering by the metal-insulator transition is accompanied by strong critical fluctuations of some degrees of freedom. Using the structural parameters in the insulating state, the first principle calculation reproduces successfully the reasonable size of nuclear quadrupole frequencies for the multiple As sites, ensuring the high validity of the structural parameters. The calculation also gives a remarkable suppression in the density of states (DOS) near the Fermi level, although the gap opening is insufficient. A coupled modulation of the calculated Ru d electron numbers and the crystal structure proposes a formation of charge density wave (CDW) in RuAs. Some lacking factors remain, but it shows that a lifting of degeneracy protected by the non-symmorphic symmetry through the superlattice formation is a key ingredient for the metal-insulator transition in RuAs.Comment: 10 pages, 10 figure

First-order phase transition to a nonmagnetic ground state in nonsymmorphic NbCrP

We report the discovery of a first-order phase transition at around 125 K in NbCrP, which is a nonsymmorphic crystal with the Pnma space group. From the resistivity, magnetic susceptibility, and nuclear magnetic resonance measurements using crystals made by the Sn-flux method, the high-temperature (HT) phase is characterized to be metallic with a non-negligible magnetic anisotropy. The low-temperature (LT) phase is also found to be a nonmagnetic metallic state with a crystal of lower symmetry. In the LT phase, the spin susceptibility is reduced by ∼30% from that in the HT phase, suggesting that the phase transition is triggered by the electronic instability. The possible origin of the phase transition in NbCrP is discussed based on the electronic structure by comparing it with those in other nonsymmorphic compounds, RuP and RuAs

Large anomalous Hall effect and unusual domain switching in an orthorhombic antiferromagnetic material NbMnP

Abstract Specific antiferromagnetic (AF) spin configurations generate large anomalous Hall effects (AHEs) even at zero magnetic field through nonvanishing Berry curvature in momentum space. In addition to restrictions on AF structures, suitable control of AF domains is essential to observe this effect without cancellations among its domains; therefore, compatible materials remain limited. Here we show that an orthorhombic noncollinear AF material, NbMnP, acquired AF structure-based AHE and controllability of the AF domains. Theoretical calculations indicated that a large Hall conductivity of ~230 Ω−1cm−1 originated from the AF structure of NbMnP. Symmetry considerations explained the production of a small net magnetization, whose anisotropy enabled the generation and cancellation of the Hall responses using magnetic fields in different directions. Finally, asymmetric hysteresis in NbMnP shows potential for the development of controllability of responses in AF materials

First-order phase transition to a nonmagnetic ground state in nonsymmorphic NbCrP

We report the discovery of a first-order phase transition at around 125 K in NbCrP, which is a nonsymmorphic crystal with the Pnma space group. From the resistivity, magnetic susceptibility, and nuclear magnetic resonance measurements using crystals made by the Sn-flux method, the high-temperature (HT) phase is characterized to be metallic with a non-negligible magnetic anisotropy. The low-temperature (LT) phase is also found to be a nonmagnetic metallic state with a crystal of lower symmetry. In the LT phase, the spin susceptibility is reduced by ∼30% from that in the HT phase, suggesting that the phase transition is triggered by the electronic instability. The possible origin of the phase transition in NbCrP is discussed based on the electronic structure by comparing it with those in other nonsymmorphic compounds, RuP and RuAs.</p

Molecular basis for diversification of yeast prion strain conformation

Self-propagating β-sheet–rich fibrillar protein aggregates, amyloidfibers, are often associated with cellular dysfunction and disease.Distinct amyloid conformations dictate different physiological consequences,such as cellular toxicity. However, the origin of the diversityof amyloid conformation remains unknown. Here, we suggest thataltered conformational equilibrium in natively disordered monomericproteins leads to the adaptation of alternate amyloid conformationsthat have different phenotypic effects. We performed acomprehensive high-resolution structural analysis of Sup35NM, anN-terminal fragment of the Sup35 yeast prion protein, and foundthat monomeric Sup35NM harbored latent local compact structuresdespite its overall disordered conformation. When the hidden localmicrostructures were relaxed by genetic mutations or solvent conditions,Sup35NM adopted a strikingly different amyloid conformation,which redirected chaperone-mediated fiber fragmentation and modulatedprion strain phenotypes. Thus, dynamic conformational fluctuationsin natively disordered monomeric proteins represent aposttranslational mechanism for diversification of aggregate structuresand cellular phenotypes