arXiv subjects

M. Oudah

Publications and source records attributed to M. Oudah.

5 recordsLinked to original sources

arXiv2025

Frustrated S = 1/2 Chains in One-Dimensional Correlated Metal Ti4MnBi2

Electronic correlations lead to heavy quasiparticles in three-dimensional (3D) metals, and their collapse can destabilize magnetic moments. It is an open question whether there is an analogous instability in one-dimensional (1D) systems, unanswered due to the lack of metallic spin chain materials. We report neutron scattering measurements and Density Matrix Renormalization Group calculations establishing spinons in the correlated metal Ti4MnBi2, confirming that its magnetism is 1D. Ti4MnBi2 is inherently frustrated, forming near a quantum critical point (QCP) separating different temperature T = 0 phases of the J1-J2 XXZ model. 1D magnetism dominates to the lowest T, and is barely affected by weak interchain coupling. Ti4MnBi2 is the first metallic spin chain where 3D conduction electrons become strongly correlated due to their coupling to 1D magnetic moments.

cond-mat.str-el↗

arXiv2025

Topology meets time-reversal symmetry breaking in FeSe$_{1-x}$Te$_{x}$ superconductor

Time-reversal symmetry breaking (TRSB) in magnetic topological insulators induces a Dirac gap in the topological surface state (TSS), leading to exotic phenomena such as the quantum anomalous Hall effect. Yet, the interplay between TRSB and topology in superconductors remains underexplored due to limited suitable materials. Here we employ zero-field muon spin relaxation ($μ$SR) as a sensitive probe of TRSB to map out the electronic phase diagrams of iron-chalcogenide superconductors FeSe$_{1-x}$Te$_{x}$. For the Te composition $x=0.64$ with the highest superconducting transition temperature $T_{\rm c}=14.5$ K, which is known to host a TSS and Majorana zero modes within vortices, we detect spontaneous magnetic fields below $T_{\rm c}$ distinct from a magnetic order. This signifies a TRSB superconducting state in the bulk, revealing the convergence of unconventional TRSB superconductivity with topologically nontrivial electronic structures in FeSe$_{1-x}$Te$_{x}$. Given the relatively high $T_{\rm c}$ and the tunability of the Fermi level through chemical substitution, iron-chalcogenide superconductors offer an intriguing platform for investigating the synergy between topological superconductivity and TRSB.

cond-mat.supr-con↗

arXiv2024

Electronic switching of topology in LaSbTe

In the past two decades, various classes of topological materials have been discovered, yet the deliberate control of topology in a single material remains largely unexplored. Here, we demonstrate full experimental control over the topological nodal loop in the square-net material LaSb$_x$Te$_{2-x}$ by chemical substitution and electron doping. Using angle-resolved photoemission spectroscopy (ARPES), we show that changing the antimony concentration x from 0.9 to 1.0 in the bulk opens a gap larger than 400~meV in the nodal loop. Symmetry analysis establishes that this effect originates from the breaking of \textit{n} glide symmetry in the square-net layer. Remarkably, the same topological phase transition can also be driven reversibly on the surface of LaSb$_x$Te$_{2-x}$ by \textit{in situ} chemical gating via potassium deposition, enabling on-demand switching of topology. The control parameter for both the bulk and surface transition is the electron concentration, providing a pathway towards applications based on switching topology by electrostatic gating.

cond-mat.mtrl-sci↗

arXiv2024

Time-Reversal Symmetry Breaking Superconductivity in CaSb$_2$

CaSb$_2$ is a bulk superconductor and a topological semimetal, making it a great platform for realizing topological superconductivity. In this work, we investigate the superconducting upper and lower critical field anisotropy using magnetic susceptibility, and study the superconducting state using muon spin-relaxation. The temperature dependence of transverse-field relaxation rate can be fitted with a single-gap model or two-gap model. Zero-field relaxation shows little temperature dependence when the muon-spin is parallel to the $c*$-axis, while an increase in relaxation appears below 1 K when the muon-spin is parallel to the $ab$-plane. We conclude an $s+is$ order parameter considering the breaking of time-reversal symmetry (TRS), which originates from competing interband interactions between the three bands of CaSb$_2$. To explain the direction-dependent breaking of TRS we suggest loop currents developing in the plane of distorted square-net of Sb atoms.

cond-mat.supr-con↗

arXiv2022

Superconductivity and Quantum Oscillations in Single Crystals of the Compensated Semimetal CaSb$_{2}$

Bulk superconductivity in a topological semimetal is a first step towards realizing topological superconductors, which can host Majorana fermions allowing us to achieve quantum computing. Here, we report superconductivity and compensation of electrons and holes in single crystals of the nodal-line semimetal CaSb$_2$. We characterize the superconducting state and find that Cooper pairs have moderate-weak coupling, and the superconducting transition in specific heat down to 0.22 K deviates from that of a BCS superconductor. The non-saturating magnetoresistance and electron-hole compensation at low temperature are consistent with density functional theory (DFT) calculations showing nodal-line features. Furthermore, we observe de Haas-van Alphen (dHvA) oscillations consistent with a small Fermi surface in the semimetallic state of CaSb$_2$. Our DFT calculations show that the two electron bands crossing the Fermi level are associated with Sb1 zig-zag chains, while the hole band is associated with Sb2 zig-zag chains. The Sb1 zig-zag chains form a distorted square net, which may relate the $M$Sb$_2$ family to the well known $M$SbTe square net semimetals. Realization of superconductivity and a compensated semimetal state in single crystals of CaSb$_2$ establishes the diantimonide family as a candidate class of materials for achieving topological superconductivity.

cond-mat.supr-con↗