Crystalline topological defects within response theory

• Published in: arXiv.org 2024-06
• Main Authors: Hakani, Sami, Kimchi, Itamar
• Format: Article
• Language: English
• Subjects: Antiferromagnetism; Crystal defects; Dimerization; Domain walls; Electric fields; Inelastic scattering; Photon scatter; Photons; Raman spectra; Topology
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2311.00698

Crystal defects can highlight interesting quantum features by coupling to the low-energy Hamiltonian \(H\). Here we show that independently of this \(H\) coupling, topological crystalline defects can generate new features by directly modifying the response theory of electric field probes such as Raman scattering. To show this we consider an antiferromagnetic spin-1/2 model \(H_{spin}\) on a zigzag chain. Crystalline domain walls between two zigzag domains appear as at most local defects in \(H_{spin}\), but as topological (not locally creatable) defects in the Raman operator \(R\) of inelastic photon scattering. Using time evolving block decimation (TEBD) numerics, mean field, and bosonization, we show that a finite density of crystalline domain walls shifts the entire Raman signal to produce an effective gap. This lattice-defect-induced Raman gap closes and reopens in applied magnetic fields. We discuss the effect in terms of photons sensing the lattice defects within \(R\) as spin-dimerization domain walls, with \(Z_2\) character, and a resulting shift of the probed wavevector from \(q=0\) to \(\pi+\delta q\), giving an \(\textit{O}(1)\) change in contrast to local defects. The magneto-Raman singularity from topological lattice defects here relies on the \(H_{spin}\) spinon liquid state, suggesting future applications using lattice topological defects to modify response-theory operators independently of \(H\) and thereby generate new probes of quantum phases.