arXiv subjects

Hind Adawi

Publications and source records attributed to Hind Adawi.

3 recordsLinked to original sources

arXiv2026

Dirac-Line Criticality and Emergent Horizons in Weyl Lifshitz Transitions

Type-II Weyl fermions may emerge behind the event horizon of black holes. We employ the Painlev\'e-Gullstrand metric to study the surface of the Lifshitz transition at the horizon, equivalent to the interface separating the type-I and type-II Weyl states. We find several analogies between the black hole horizon and the transformation of type-I to type-II Weyl fermions through the Dirac line. We analyze the symmetry-protected topological order at the Lifshitz transition originating in semimetals. The emergence of Hawking radiation in Weyl semimetals is discussed. We show that the transition state from type-I to type-II Dirac fermions can be viewed as a black-hole horizon, which exhibits unique characteristics, including a Dirac-line Fermi surface with a nontrivial topological invariant and a critical chiral anomaly effect.

cond-mat.mes-hall↗

arXiv2023

Evolution of short-range magnetic correlations in ferromagnetic Ni-V alloys

We experimentally study how the magnetic correlations develop in a binary alloy close to the ferromagnetic quantum critical point with small-angle neutron scattering (SANS). Upon alloying the itinerant ferromagnet nickel with vanadium, the ferromagnetic order is continuously suppressed. The critical temperature Tc vanishes when vanadium concentrations reach the critical value of xc=0.116 indicating a quantum critical point separating the ferromagnetic and paramagnetic phases. Earlier magnetization and $μ$SR data have indicated the presence of magnetic inhomogeneities in Ni(1-x)V(x) and, in particular, recognize the magnetic clusters close to xc, on the paramagnetic and on the ferromagnetic sides with nontrivial dynamical properties [R. Wang et al., Phys. Rev. Lett. 118, 267202 (2017)]. We present the results of SANS study with full polarization analysis of polycrystalline Ni(1-x)V(x) samples with x=0.10 and x=0.11 with low critical temperatures Tc below 50 K. For both Ni-V samples close to xc we find isotropic magnetic short-range correlations in the nanometer-scale persisting at low temperatures. They are suppressed gradually in higher magnetic fields. In addition, signatures of long-range ordered magnetic domains are present below Tc. The fraction of these magnetic clusters embedded in the ferromagnetic ordered phase grows towards xc and agrees well with the cluster fraction estimate from the magnetization and $μ$SR data. Our SANS studies provide new insights into the nature of the inhomogeneities in a ferromagnetic alloy close to a quantum critical point.

cond-mat.str-el↗

arXiv2023

Study of atomic disorder in Ni-V alloys

We present a pair distribution function (PDF) analysis from neutron diffraction data of the Ni$_{1-x}$V$_x$ alloy in the Ni-rich regime. Such structural study aims to clarify the origin of the magnetic inhomogeneities associated with the quantum Griffiths phase close to the ferromagnetic-paramagnetic quantum phase transition. The PDF analysis successfully reveals the details of the structure and chemical distribution of our Ni$_{1-x}$V$_x$ polycrystalline samples prepared with high-temperature annealing and rapid cooling protocol. This study confirms the expectations that all Ni$_{1-x}$V$_x$ samples with 0$ \leq x \leq $0.15 crystallize in a single phase fcc structure with some residual strain. The increase of the lattice constant and the atomic displacement parameter with V-concentration $x$ is consistently explained by a random occupation of V and Ni-atoms on the lattice, with a radius ratio ($r_{V}/r_{Ni}$) of 1.05. Probing alternate, simple models of the local PDF, such as V-clusters or ordered structures (Ni$_8$V, Ni$_3$V) give inferior results compared to a random occupation. This investigation strongly supports that the magnetic clusters in the binary alloy Ni$_{1-x}$V$_x$ originate from Ni-rich regions created from "random" occupation rather than from chemical clusters. It reveals that Ni$_{1-x}$V$_x$ is one of the rare examples of a solid solution in a wide concentration regime (up to x=0.15) persisting down to low temperatures (T=15 K).

cond-mat.str-el↗