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Hovan Lee

Publications and source records attributed to Hovan Lee.

9 recordsLinked to original sources
arXiv2026

Identical Particle Systems : Hierarchical Spectral Reconstruction

We identify a hierarchical symmetry structure underlying the Hilbert space of quantum systems made of identical particles. By studying the linear map between single-body and many-body spectra, we show that the resulting spectral organization admits a natural partition into sectors induced by a symmetry governed by cyclotomic fields and their Galois groups. This approach offers a new perspective on the structure of quantum many-body spectra, defining a controlled coarse-graining of the Hilbert space in which degeneracies and spectral features can be systematically organized through a set of new quantum numbers. The resulting structure induces a hierarchy of spectral resolutions following a renormalization flow, which enables information loss control. We demonstrate that this hierarchical decomposition provides an efficient route to approximate MBDoS calculations for any identical particle system, while preserving physically relevant spectral properties. This approach provides a general symmetry-based framework for organizing and approximating many-body spectra, with potential applications to quantum thermalization, spectral statistics, and large-scale quantum simulations.

quant-ph↗
arXiv2023

A language-inspired machine learning approach for solving strongly correlated problems with dynamical mean-field theory

We present SCALINN -- Strongly Correlated Approach with Language Inspired Neural Network -- as a method for solving the Anderson impurity model and reducing the computational cost of dynamical mean-field theory calculations. Inspired by the success of generative Transformer networks in natural language processing, SCALINN utilizes an in-house modified Transformer network in order to learn correlated Matsubara Green's functions, which act as solutions to the impurity model. This is achieved by providing the network with low-cost Matsubara Green's functions, thereby overcoming the computational cost of high accuracy solutions. Across different temperatures and interaction strengths, the performance of SCALINN is demonstrated in both physical observables (spectral function, Matsubara Green's functions, quasi-particle weight), and the mean squared error cost values of the neural network, showcasing the network's ability to accelerate Green's function based calculations of correlated materials.

cond-mat.str-el↗
arXiv2022

Portrait of locally driven quantum phase transition cascades in a molecular monolayer

Strongly interacting electrons in layered materials give rise to a plethora of emergent phenomena, such as unconventional superconductivity. heavy fermions, and spin textures with non-trivial topology. Similar effects can also be observed in bulk materials, but the advantage of two dimensional (2D) systems is the combination of local accessibility by microscopic techniques and tuneability. In stacks of 2D materials, for example, the twist angle can be employed to tune their properties. However, while material choice and twist angle are global parameters, the full complexity and potential of such correlated 2D electronic lattices will only reveal itself when tuning their parameters becomes possible on the level of individual lattice sites. Here, we discover a lattice of strongly correlated electrons in a perfectly ordered 2D supramolecular network by driving this system through a cascade of quantum phase transitions using a movable atomically sharp electrostatic gate. As the gate field is increased, the molecular building blocks change from a Kondo-screened to a paramagnetic phase one-by-one, enabling us to reconstruct their complex interactions in detail. We anticipate that the supramolecular nature of the system will in future allow to engineer quantum correlations in arbitrary patterned structures.

cond-mat.mes-hall↗
arXiv2022

Many body study of iron(III) bound human serum transferrin

Transferrins are proteins responsible for transporting metal ions in all vertebrates. However, the iron binding properties of transferrins remain poorly understood. Iron, as a transition metal, forms ions with partially-occupied 3d subshells. The electrons within the 3d orbitals of iron-bound transferrin are therefore highly localized, and interact with one another in a complex manner that cannot be fully characterized by considering each electron separately. In this work, we make use of dynamical mean field theory, a technique that accounts for the strong interactions between these electrons. This is a higher level of theory than has ever been used to study transferrins. We present novel data on the effective spin, multiplet states and optical spectra of iron-bound human serum transferrin.

cond-mat.str-el↗
arXiv2021

Sensing applied pressure by triggering electronic quantum many-body excitations in an optical waveguide

Recently, nanomaterials are arousing increasing interest and a wide variety of opto-electronic devices have been developed, such as light-emitting diodes, solar cells, and photodetectors. However, the study of the light emission properties of quantum dots under pressure is still limited. By using a joint theoretical and experimental approach, we developed a polymer waveguide doped with CdSe quantum dots for pressure sensing. Absorption and re-emission effects of the quantum dots are affected by the pressure applied on the waveguide. Specifically, since both amplitude and wavelength are modulated, not only the pressure can be detected, but also its location along the waveguide. The calibration results demonstrate the feasibility of the proposed force sensor design. Theoretical model and simulations further validate the presented sensing principle. The proposed prototype benefits from the main advantages of optical sensors, such as their predisposition to miniaturization, small cable sizes and weights, immunity to electromagnetic interference, and safe operation in hazard environments. In addition, bio-compatibility, non-toxicity and flexibility make the presented sensor potentially appealing to various application fields such as nanobiotechnology and robotic sensing.

quant-ph↗
arXiv2021

Ab initio molecular dynamics modelling of organic crystal electro-optical properties

Molecular dynamics calculations were preformed on organic crystals 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST) and 4-N,N-dimethylamino-4'-N'-methylstilbazolium 2,4,6-trimethylbenzenesulfonate (DSTMS). Vibrational modes of the structures were investigated to examine the single unit cell phononic contribution of the organic crystals to their terahertz generating capabilities. Linear optical properties were also calculated from snapshots of the molecular dynamics structures through Green-Kubo relations, and compared with experimental transmission.

cond-mat.mtrl-sci↗
arXiv2021

Ultrafast Electron Dynamics in Magnetic Thin Films

In past decades, ultrafast spin dynamics in magnetic systems have been associated with heat deposition from high energy laser pulses, limiting the selective access to spin order. Here we use a long wavelength terahertz pump optical probe setup to measure structural features in the ultrafast time scale. We find that complete demagnetisation is possible with <6 THz pulses. This occurs concurrently with longitudinal acoustic phonons and an electronic response, followed by the magnetic response. The required fluence for full demagnetisation is low, ruling out the necessity of a high power light source.

cond-mat.mtrl-sci↗
arXiv2018

Self-assembly of correlated Kondo lattices: The Mott to Kondo transition in diluted superlattices

In the field of condensed matter, the quest to obtain an experimental realization of a Kondo lattice has generated a tremendous effort of the community, from both standpoints of experiments and theory. The pursuit of obtaining independent magnetic moments, via charge localization through Coulomb interactions, is paramount for applications in nanotechnology. In particular, systems with simultaneous charge and spin degrees of freedom can manifest both Kondo spin quenching and Mott-Hubbard charge localization. A unified experimental framework illuminating the pathway between the two phenomena is of physical and technological interest, and is (as of yet) hardly observed in real condensed matter systems. Recent developments in the ability to control densities and temperatures of strongly correlated Fermionic impurities on surfaces and substrates has opened up a new paradigm of possibilities for this pathway. In particular, a milestone was recently surpassed through the observation of self-assembled superlattices of f band adatoms on metallic surfaces, such as the deposition of Ce on Ag(111). Such lattices have introduced a mechanism of diluted correlated lattices where the interaction between Kondo and Mott physics can be methodically studied. However, it remains difficult to control the adatom distances and substrate densities in these systems, and the interplay between Kondo physics and charge localization remains elusive. In this work, we systematically investigate the phase diagram of superlattice structures of heavy f elements deposited on metallic substrates, and assess the required conditions to obtain Kondo lattices in superlattices. We unveil a unique pathway between Kondo quenching and Mott localization, and identify a non-trivial charge density wave phase emerging from the competition of charge localization and Kondo physics.

cond-mat.str-el↗