arXiv subjects

Henry Davenport

Publications and source records attributed to Henry Davenport.

10 recordsLinked to original sources

arXiv2026

Exciton Alchemy: Chern Excitons from Trivial Bands

Exciton topology is commonly inherited from the topology of the underlying electronic bands. Recent theoretical work, however, has shown that the exciton Chern number can in general receive an additional contribution from the topology of the exciton envelope wave function, allowing, in principle, interaction-induced topological excitons even when the constituent electronic bands are topologically trivial. Here, we provide an explicit realization of this case by constructing a two-dimensional exciton model with topologically trivial conduction and valence bands that nevertheless hosts a Chern exciton diagnosed by inversion symmetry. Starting from a real-space limit of exponentially localized Wannier states for the conduction and valence bands, we identify the essential ingredients responsible for the emergent exciton topology and formulate a simple construction recipe. Our work demonstrates that interactions alone can generate nontrivial exciton topology, independent of the topology of the underlying electronic bands, and establishes a general framework for designing interaction-induced topological excitons.

cond-mat.mes-hall↗

arXiv2026

Anomalous suppression of quantum chaos between two integrable limits

Level statistics in non-integrable quantum many-body systems with time reversal symmetry are expected to follow the Gaussian Orthogonal Ensemble (GOE), a hallmark of quantum chaos. However, we show that the interacting Su-Schrieffer-Heeger model exhibits a clear suppression of the mean level-spacing ratio $\langle r\rangle$ from the GOE value $\approx 0.535$, persisting deep in the nonintegrable regime. This challenges the conventional association between non-integrability and fully chaotic spectral statistics. Using exact diagonalization supported by semi-analytical arguments, we trace this anomaly to incomplete hybridization of many-body band states inherited from the noninteracting band structure. The resulting restructuring of the spectrum weakens level repulsion without restoring integrability. We show the robustness of this mechanism in extensions of the model which break chiral and inversion symmetry.

cond-mat.stat-mech↗

arXiv2026

Minimising magnetic activity effects in PLATO observations: insights from the Sun-as-a-star

Recent studies showed that magnetic activity effects in solar-type stars can substantially bias seismic inferences, particularly age estimates, regardless of modelling strategy or surface treatment. We quantified how magnetic activity effects in the Sun-as-a-star are smoothed by temporal averaging by analysing 182.5-, 365-, 730-, and 1460-day time series from the BiSON network and the GOLF instrument. We estimated the activity-induced systematic uncertainty using two metrics and compared results across baselines to evaluate how the observing window shapes activity-induced biases. Solar-cycle signatures persist even in 1460-day windows. The suppression of magnetic activity effects with increasing baseline is non-monotonic: one- and four-year windows reduce biases far more effectively than shorter baselines in most cases, whereas 730-day windows provide only limited improvement over 365-day ones. Improvements arise from enhanced frequency determination (dominant at 365 days) and from increasingly efficient temporal averaging of the activity cycle (dominant at 1460 days). In contrast, 730-day is an intermediate regime: frequency accuracy has already plateaued and the observing window remains too short to smooth out cycle-related variability. On average, we find that magnetic activity effects decrease by 24%, 12%, 30%, and 38% when transitioning from 182.5 to 365 days, 365 to 730 days, 730 to 1460 days, and 365 to 1460 days for frequency-based fits; the corresponding improvements for ratio-based fits are 13%, 14%, 20%, and 31%. These results indicate that a continuous single-field four-year PLATO observing programme would provide the most effective suppression of magnetic-activity biases for solar analogues, whereas a 2+2-year strategy (in two distinct fields) is significantly more sensitive to magnetic effects, with limited gains between 365- and 730-day windows.

astro-ph.SR↗

arXiv2026

Composite Quantum Geometry and Semiclassical Dynamics

We derive semiclassical equations of motion for general composite bound states in insulators and semiconductors, covering excitations such as excitons and trions. For neutral composites we find that a uniform external electric field does not couple to a Berry curvature term, contrary to the naive expectation from single-electron dynamics. Instead, a distinct quantum geometric quantity appears generically in the equations of motion. This quantity is the difference between inequivalent Berry connections that can be defined for the composite, generalising the concept of the quantum geometric dipole previously studied for excitons. In the case of charged composites such as trions, we find an additional Berry curvature contribution to the equations of motion. As we demonstrate, however, there is an infinite family of inequivalent composite Berry curvatures, and so care must be taken to make the correct choice that describes the physical dynamics. We explain how this choice should be made dependent on the definition of a spatial centre for the composite. We end by discussing composite dynamics that have no single-electron counterpart. We find that trions in magic-angle twisted bilayer graphene undergo a transverse drift under an applied electric field and that this is driven not only by the Berry curvature contribution but also by the quantum geometric dipole. The interplay of these two geometric contributions further imprints itself on the trion's internal dynamics, causing its dipole moment to oscillate in time.

cond-mat.mes-hall↗

arXiv2026

Stable Wave-Function Zeros Indicate Exciton Topology

Excitons are bound states of electrons and holes whose band topology arises from an interplay between the topology of the underlying electronic bands and the structure of the electron-hole interaction. In crystalline solids, symmetry representations and topological invariants of the conduction and valence bands constrain the structure of the exciton envelope wave function. In particular, we show that crystalline symmetry can enforce stable zeros in the exciton wave function. These occur at high-symmetry momenta, including the optically accessible total momentum p=0. We work out how the stable zeros constrain both the relative exciton-band topology (the difference of exciton and non-interacting topological invariants) and the relative band topology (the difference of valence and conduction band invariants), all without requiring detailed knowledge of the band structure or interactions. We establish these results for two-band excitons in inversion- and rotation-symmetric systems in one and two dimensions, where the relevant topological invariants are the Berry phase in one dimension and the Chern number (modulo the rotation order) in two dimensions. In two dimensions, the exciton Chern number itself can also be constrained by zero patterns.

cond-mat.mes-hall↗

arXiv2026

Exciton Berryology

In translationally invariant semiconductors that host exciton bound states, one can define an infinite number of possible exciton Berry connections. These correspond to the different ways in which a many-body exciton state, at fixed total momentum, can be decomposed into free electron and hole Bloch states that are entangled by an exciton envelope wave function. Inspired by the modern theory of polarization, we define an exciton projected position operator whose eigenvalues single out two unique choices of exciton Berry phase and associated Berry connection - one for electrons, and one for holes. We clarify the physical meaning of these exciton Berry phases and provide a discrete Wilson loop formulation that allows for their numerical calculation without a smooth gauge. As a corollary, we obtain a gauge-invariant expression for the exciton polarisation at a given total momentum, i.e. the mean separation of the electron and hole within the exciton wave function. In the presence of crystalline inversion symmetry, the electron and hole exciton Berry phases are quantized to the same value and we derive how this value can be expressed in terms of inversion eigenvalues of the many-body exciton state. We then consider $C_2 \mathcal{T}$ symmetry, for which no symmetry eigenvalues are available as it is anti-unitary, and confirm that the exciton Berry phase remains quantized and still diagnoses topologically distinct exciton bands. The notion of shift excitons, whose exciton Wannier states are displaced from those of the non-interacting bands by a quantized amount, can therefore be generalised beyond symmetry indicators.

cond-mat.mes-hall↗

arXiv2026

Berry Curvature of Low-Energy Excitons in Rhombohedral Graphene

We investigate low energy excitons in rhombohedral pentalayer graphene encapsulated by hexagonal boron nitride (hBN/R5G/hBN), focusing on the regime at the experimental twist angle $θ= 0.77^\circ$ and with an applied electric field. We introduce a new low-energy two-band model of rhombohedral graphene that captures the band structure more accurately than previous models while keeping the number of parameters low. Using this model, we show that the centres of the exciton Wannier functions are displaced from the moiré unit cell origin by a quantised amount - they are instead localised at $C_3$-symmetric points on the boundary. We also find that the exciton shift is electrically tunable: by varying the electric field strength, the exciton Wannier centre can be exchanged between inequivalent corners of the moiré unit cell. Our results suggest the possibility of detecting excitonic corner or edge modes, as well as novel excitonic crystal defect responses in hBN/R5G/hBN. Lastly, we find that the excitons in hBN/R5G/hBN inherit excitonic Berry curvature from the underlying electronic bands, enriching their semiclassical transport properties. Our results position rhombohedral graphene as a compelling tunable platform for probing exciton topology in moiré materials.

cond-mat.mes-hall↗

arXiv2025

Frequency separation ratios do not suppress magnetic activity effects in solar-like stars

Magnetic activity effects are typically neglected in asteroseismic modelling of solar-type stars, presuming that these effects can be accounted for in the parametrisation of the surface effects. It was however demonstrated that magnetic activity can have a significant impact on the asteroseismic characterisation using both forward and inverse techniques. We investigated whether frequency separation ratios, which are commonly used to efficiently suppress surface effects, are also able to suppress magnetic activity effects. Based on GOLF and BiSON observations of the Sun-as-a-star, we performed asteroseismic characterisations using frequency separation ratios as constraints to measure the apparent temporal evolution of the stellar parameters and their correlation with the 10.7 cm radio flux. Frequency separation ratios do not suppress the effects of magnetic activity. Both $r_{01}$ and $r_{02}$ ratios exhibit a clear signature of the magnetic activity cycle. Consequently, when these ratios are employed as constraints in asteroseismic modelling, magnetic activity effects are propagated to the stellar characterisation. Additionally, most stellar parameters correlate with the activity cycle, unlike the direct fitting of individual frequencies. Magnetic activity effects significantly impact asteroseismic characterisation, regardless of whether forward modelling or inverse methods are used. Standard techniques to suppress surface effects have proven ineffective against magnetic activity influences and systematic uncertainties of 4.7%, 2.9%, and 1.0% should be considered for the stellar age, mass, and radius, respectively. In preparation for future space-based photometry missions, it is therefore essential to enhance our theoretical understanding of these effects and develop a modelling procedure capable of accounting for or efficiently suppressing them.

astro-ph.SR↗

arXiv2025

Momentum-space modulated symmetries in the Luttinger liquid

The chiral Luttinger liquid develops quantum chaos as soon as a -- however slight -- nonlinear dispersion is introduced for the microscopic electronic degrees of freedom. For this nonlinear version of the model, we identify an infinite family of translation-invariant interaction potentials with corresponding modulated symmetries. These symmetries are highly unconventional: they are modulated in momentum space (and do not seem to have an easy physical interpretation). We develop a systematic understanding of these symmetries and study the resulting blocks in the Hamiltonian. In particular, this approach allows us to predict the analytic Hamiltonian block sizes and derive asymptotic scaling laws in the limit of large total momentum. These blocks are reminiscent of Hilbert space fragmentation in that, even though they are labeled by a symmetry, this symmetry is highly nonlocal and does not have a simple interpretation. We corroborate this result by studying entanglement entropy and level statistics.

cond-mat.str-el↗

arXiv2024

Interaction-induced crystalline topology of excitons

We apply the topological theory of symmetry indicators to interaction-induced exciton band structures in centrosymmetric semiconductors. Crucially, we distinguish between the topological invariants inherited from the underlying electron and hole bands, and those that are intrinsic to the exciton wavefunction itself. Focusing on the latter, we show that there exists a class of exciton bands for which the maximally-localised exciton Wannier states are shifted with respect to the electronic Wannier states by a quantised amount; we call these excitons shift excitons. Our analysis explains how the exciton spectrum can be topologically nontrivial and sustain exciton edge states in open boundary conditions even when the underlying noninteracting bands have a trivial atomic limit. We demonstrate the presence of shift excitons as the lowest energy neutral excitations of the Su-Schrieffer-Heeger model in its trivial phase when supplemented by local two-body interactions, and show that they can be accessed experimentally in local optical conductivity measurements.

cond-mat.mes-hall↗