arXiv subjects

Haydn S. Adlong

Publications and source records attributed to Haydn S. Adlong.

7 recordsLinked to original sources

arXiv2026

Microscopic Model of Exciton Polarons in 2D Wigner Crystals

Monolayer transition-metal dichalcogenides (TMDs) provide a platform for realizing Wigner crystals and enable their detection via exciton spectroscopy. We develop a microscopic theoretical model for excitons interacting with the localized electrons of the Wigner crystal, including their vibrational motion. In addition to the previously observed exciton-Umklapp feature, the theory reproduces and explains the higher-band attractive-polaron resonances recently reported experimentally. Our model further uncovers that the appearance of two equal-strength and parallel attractive polarons, as commonly observed in WSe$_2$ and WS$_2$, is a signature of strong correlations in the electronic system. Altogether, our results demonstrate that accounting for electronic interactions is essential to reproduce and interpret the exciton-polaron spectra of TMDs.

cond-mat.str-el↗

arXiv2026

Wigner polarons reveal Wigner crystal dynamics in a monolayer semiconductor

Wigner crystals, lattices made purely of electrons, are a quintessential paradigm of studying correlation-driven quantum phase transitions. Despite decades of research, the internal dynamics of Wigner crystals has remained extremely challenging to access, with most experiments probing only static order or collective motion. Here, we establish monolayer WSe2 as a new materials platform to host zero-field Wigner crystals and then demonstrate that exciton spectroscopy provides a direct means to probe both static and dynamic properties of these electron lattices. We uncover striking optical resonances that we identify as Wigner polarons, quasiparticles formed when the electron lattice is locally distorted by exciton-Wigner crystal coupling. We further achieve all-optical control of spins in the Wigner crystal, directly probing valley-dependent Wigner polaron scattering well above the magnetic ordering temperature and in the absence of any external magnetic field. Finally, we demonstrate optical melting of the Wigner crystal and observe intriguingly different responses of the umklapp (static) and Wigner polaron (dynamic) resonances to optical excitation. Our results open up exciting new avenues for elucidating electron dynamics and achieving ultrafast optical control of interaction-driven quantum phase transitions in strongly correlated electron systems.

cond-mat.mes-hall↗

arXiv2025

Microscopic theory of the Hubbard interaction in low-dimensional optical lattices

The Hubbard model is a paradigmatic model of strongly correlated quantum matter, thus making it desirable to investigate with quantum simulators such as ultracold atomic gases. Here, we consider the problem of two atoms interacting in a quasi-one- or quasi-two-dimensional optical lattice, geometries which are routinely realized in quantum-gas-microscope experiments. We perform an exact calculation of the low-energy scattering amplitude which accounts for the effects of the transverse confinement as well as all higher Bloch bands. This goes beyond standard perturbative treatments and allows us to precisely determine the effective Hubbard on-site interaction for arbitrary $s$-wave scattering length (see source code available at [1]). In particular, we find that the Hubbard on-site interaction displays lattice-induced resonances for scattering lengths on the order of the lattice spacing, which are well within reach of current experiments. Furthermore, we show that our results are in excellent agreement with spectroscopic measurements of the Hubbard interaction for a quasi-two-dimensional square optical lattice in a quantum gas microscope. Our formalism is very general and may be extended to multi-band models and other atom-like scenarios in lattice geometries, such as exciton-exciton and exciton-electron scattering in moiré superlattices.

cond-mat.quant-gas↗

arXiv2024

Confined Trions and Mott-Wigner States in a Purely Electrostatic Moiré Potential

Moiré heterostructures consisting of transition metal dichalcogenide (TMD) hetero- and homobilayers have emerged as a promising material platform to study correlated electronic states. Optical signatures of strong correlations in the form of Mott-Wigner states and fractional Chern insulators have already been observed in TMD monolayers and their twisted bilayers. In this work, we use a moiré substrate containing a twisted hexagonal boron nitride (h-BN) interface to externally generate a superlattice potential for the TMD layer: the periodic structure of ferroelectric domains in h-BN effects a purely electrostatic potential for charge carriers. We find direct evidence for the induced moiré potential in the emergence of new excitonic resonances at integer fillings, and our observation of an enhancement of the trion binding energy by $\simeq$ 3 meV. A theoretical model for exciton-electron interactions allows us to directly determine the moiré potential modulation of 30$\pm$5 meV from the measured trion binding energy shift. We obtain direct evidence for charge order linked to electronic Mott-Wigner states at filling factors $ν$ = 1/3 and $ν$ = 2/3 through the associated exciton Umklapp resonances.

cond-mat.str-el↗

arXiv2021

Signatures of the orthogonality catastrophe in a coherently driven impurity

We consider a fixed impurity immersed in a Fermi gas at finite temperature. We take the impurity to have two internal spin states, where the $\uparrow$ state is assumed to interact with the medium such that it exhibits the orthogonality catastrophe, while the $\downarrow$ state is a bare noninteracting particle. Introducing a Rabi coupling between the impurity states therefore allows us to investigate the coupling between a discrete spectral peak and the Fermi-edge singularity, i.e., between states with and without a quasiparticle residue. Combining an exact treatment of the uncoupled impurity Green's functions with a variational approach to treat the Rabi driven dynamics, we find that the system features Rabi oscillations whose frequency scales as a non-trivial power of the Rabi drive at low temperatures. This reflects the power law of the Fermi-edge singularity and, importantly, this behavior is qualitatively different from the case of a mobile impurity quasiparticle where the scaling is linear. We therefore argue that the scaling law serves as an experimentally implementable probe of the orthogonality catastrophe. We additionally simulate rf spectroscopy beyond linear response, finding a remarkable agreement with an experiment using heavy impurities [Kohstall $\textit{et al.}$, Nature $\textbf{485}$, 615 (2012)], thus demonstrating the power of our approach.

cond-mat.quant-gas↗

arXiv2021

Quasiparticle lifetime of the repulsive Fermi polaron

We investigate the metastable repulsive branch of a mobile impurity coupled to a degenerate Fermi gas via short-range interactions. We show that the quasiparticle lifetime of this repulsive Fermi polaron can be experimentally probed by driving Rabi oscillations between weakly and strongly interacting impurity states. Using a time-dependent variational approach, we find that we can accurately model the impurity Rabi oscillations that were recently measured for repulsive Fermi polarons in both two and three dimensions. Crucially, our theoretical description does not include relaxation processes to the lower-lying attractive branch. Thus, the theory-experiment agreement demonstrates that the quasiparticle lifetime is determined by many-body dephasing within the upper repulsive branch rather than by the metastability of the upper branch itself. Our findings shed light on recent experimental observations of persistent repulsive correlations, and have important consequences for the nature and stability of the strongly repulsive Fermi gas.

cond-mat.quant-gas↗

arXiv2021

Thermodynamic signatures of the polaron-molecule transition in a Fermi gas

We consider the highly spin-imbalanced limit of a two-component Fermi gas, where there is a small density of $\downarrow$ impurities attractively interacting with a sea of $\uparrow$ fermions. In the single-impurity limit at zero temperature, there exists the so-called polaron-molecule transition, where the impurity sharply changes its character by binding a $\uparrow$ fermion at sufficiently strong attraction. Using a recently developed variational approach, we calculate the thermodynamic properties of the impurity, and we show that the transition becomes a smooth crossover at finite temperature due to the thermal occupation of excited states in the impurity spectral function. However, remnants of the single-impurity transition are apparent in the momentum-resolved spectral function, which can in principle be probed with Raman spectroscopy. We furthermore show that the Tan contact exhibits a characteristic non-monotonic dependence on temperature that provides a signature of the zero-temperature polaron-molecule transition. For a finite impurity density, we argue that descriptions purely based on the behavior of the Fermi polaron are invalid near the polaron-molecule transition, since correlations between impurities cannot be ignored. In particular, we show that the spin-imbalanced system undergoes phase separation at low temperatures due to the strong attraction between $\uparrow\downarrow$ molecules induced by the Fermi sea. Thus, we find that the impurity spectrum and the induced impurity-impurity interactions are key to understanding the phase diagram of the spin-imbalanced Fermi gas.

cond-mat.quant-gas↗