arXiv subjects

Avedis Neehus

Publications and source records attributed to Avedis Neehus.

3 recordsLinked to original sources

arXiv2026

Dichroic Raman probes for chiral edge modes

The identification and manipulation of charge-neutral fractionalized quasi-particles, in particular chiral edge modes (CEM), is a long-standing quest in physics. Remarkably, the microscopically mediated interaction between light and charge-neutral excitations in Mott-Hubbard insulators can take an identical form to the Raman coupling between light and particles with electric charge. However, since CEMs are Raman-inactive due to conservation of lattice momentum, Raman probes have been deemed unsuitable for their identification. Here, using the Kitaev quantum spin liquid (KSL) as an illustrative example, we demonstrate that the long-range correlated disorder inherent to a closed edge can lead to a Raman circular dichroism (RCD) signal that avoids suppression by linear and angular momentum selection rules, and exhibits a dependence on experimentally tunable length and energy scales that are characteristic of CEM. Having calculated the low-frequency RCD response of generic KSL, we argue that the interaction of the chiral matter fermion with the $\Ztwo$ boundary charge leaves a unique fingerprint of the KSL via the anisotropic Zeeman field dependence.

cond-mat.str-el↗

arXiv2025

Projectively implemented altermagnetism in an exactly solvable quantum spin liquid

Altermagnets are a new class of symmetry-compensated magnets with large spin splittings. Here, we show that the notion of altermagnetism extends beyond the realm of Landau-type order: we study exactly solvable $\mathbb{Z}_2$ quantum spin(-orbital) liquids (QSL), which simultaneously support magnetic long-range order as well as fractionalization and $\mathbb{Z}_2$ topological order. Our symmetry analysis reveals that in this model three distinct types of ``fractionalized altermagnets (AM$^*$)'' may emerge, which can be distinguished by their residual symmetries. Importantly, the fractionalized excitations of these states carry an emergent $\mathbb{Z}_2$ gauge charge, which implies that they transform \emph{projectively} under symmetry operations. Consequently, we show that ``altermagnetic spin splittings'' are now encoded in a momentum-dependent particle-hole asymmetry of the fermionic parton bands. We discuss consequences for experimental observables such as dynamical spin structure factors and (nonlinear) thermal and spin transport.

cond-mat.str-el↗

arXiv2024

Genuine topological Anderson insulator from impurity induced chirality reversal

We investigate a model of Dirac fermions with Haldane type mass impurities which open a global topological gap even in the dilute limit. Surprisingly, we find that the chirality of this mass term, i.e., the sign of the Chern number, can be reversed by tuning the magnitude of the single-impurity scattering. Consequently, the disorder induces a phase disconnected from the clean topological phase, i.e., a genuine topological Anderson insulator. In seeming contradiction to the expectation that mass disorder is an irrelevant perturbation to the clean integer quantum Hall transition, the tri-critical point separating these two Chern insulating phases and a thermal metal phase is located at zero impurity density and connected to the appearance of a zero energy bound state in the continuum corresponding to a divergent Haldane mass impurity. Our conclusions based on the T-matrix expansion are substantiated by large scale Chebyshev-Polynomial-Green-Function numerics. We discuss possible experimental platforms.

cond-mat.mes-hall↗