arXiv subjects

Matthew F. Doty

Publications and source records attributed to Matthew F. Doty.

At least 19 recordsLinked to original sources

arXiv2026

Versatile Sleeve-and-Bulk Fabrication of Inversely Designed Nanophotonic Structures with High Pattern Transfer Fidelity

Inverse design is a powerful computational tool for generating nanophotonic devices that should outperform their traditionally designed counterparts. However, translating these theoretical gains into physical devices is challenging because the irregular and non-intuitive features that make inversely designed structures so effective also make them exceptionally difficult to fabricate, typically necessitating substantial process optimization unique to each device design. We describe a versatile two-step nanofabrication process that achieves pattern transfer fidelity in excess of 90% for each of three distinct inverse device designs with no device-specific process optimization.

physics.optics↗

arXiv2026

A high-Q Split Cavity Enabling Independent Electrical Tuning of two Quantum Dots

Cavity-mediated strong coupling is an essential tool for quantum photonics. However, the inherent inhomogeneity in ensembles of matter-based qubits necessitates independent tuning to bring more than one qubit into resonance with a single cavity mode. We present the design, fabrication, and characterization of a GaAs-based photonic crystal split cavity that consists of two electrically-distinct portions, which preserves the ability to apply independent electric fields that would independently tune two distinct qubits based on InAs Quantum Dots (QDs) into resonance with a cavity mode. We show that this device, despite the cut required to electrically isolate the two halves, achieves an average Q $\geq 20,000$, sufficient to enter the strong coupling regime. Moreover, we show that the Q is limited primarily by the precision and accuracy of the e-beam lithography tool, rather than by sidewall scattering. This result creates a realistic experimental path toward devices that use controlled interactions between two InAs QDs, mediated by strong coupling to a single cavity mode, to generate multi-dimensional photon graph states.

physics.optics↗

arXiv2026

A framework for extracting the rates of photophysical processes from biexponentially decaying photon emission data

There is strong interest in designing and realizing optically-active semiconductor nanostructures of greater complexity for applications in fields ranging from biomedical engineering to quantum computing. While these increasingly complex nanostructures can implement progressively sophisticated optical functions, the presence of more material constituents and interfaces also leads to increasingly complex exciton dynamics. In particular, the rates of carrier trapping and detrapping in complex heterostructures are critically important for advanced optical functionality, but they can rarely be directly measured. In this work, we develop a model that includes trapping and release of carriers by optically inactive states. The model explains the widely observed biexponential decay of the photoluminescence signal from neutral excitons in low dimensional semiconductor emitters. The model also allows determination of likelihood intervals for all the transition rates involved in the emission dynamics, without the use of approximations. Furthermore, in cases for which the high temperature limit is suitable, the model leads to specific values of such rates, outperforming reduced models previously used to estimate those quantities. We demonstrate the value of this model by applying it to time resolved photoluminescence measurements of CdSeTe/CdS heterostructures. We obtain values not only for the radiative and nonradiative lifetimes, but also for the delayed photoluminescence originating in trapping and release.

cond-mat.mes-hall↗

arXiv2026

Deterministic Realization of Complex Local Strain Fields and Bandgap Profiles in Two-Dimensional Materials

Emerging classical and quantum device concepts demand precise spatial control over the optoelectronic properties of two-dimensional (2D) materials, but deterministic engineering via local multiaxial strain distributions remains challenging. Using Ga$_2$Se$_2$, we demonstrate a material-agnostic platform in which nanostructure geometry deterministically prescribes in-plane strain profiles in suspended van der Waals membranes. We first use hyperspectral photoluminescence mapping and experimentally-constrained finite element analysis to quantify the experimental biaxial and uniaxial strain gauge factors that relate strain to the change in bandgap. We next show that a two-component analytical model can predict, with less than 12% error, spatially-resolved bandgap shifts arising from multiaxial strain distributions in complex geometries, including the interactions between adjacent nanostructures. Finally, we demonstrate that this approach can be extended to other materials. The results demonstrate that nanostructure design provides a quantitative, deterministic framework for the realization of designed strain and bandgap distributions in 2D materials.

cond-mat.mtrl-sci↗

arXiv2026

Resonance-enhanced super-superexchange yields giant chiral magnon splitting in rutile altermagnets

Altermagnets host momentum-selective spin splitting and chiral-split magnonic excitations despite vanishing net magnetization, enabling spin transport without ferromagnetism. In rutile structures, establishing altermagnetism spectroscopically has been challenging, motivating the search for a rutile platform with a resolvable exchange-driven chiral magnon splitting. Here we combine hybrid-functional first-principles calculations with linear spin-wave theory to show that rutile CuF$_2$ exhibits a meV-scale splitting between magnon modes of opposite chirality along momentum directions dictated by its $d$-wave altermagnetic symmetry. The splitting originates from an anomalously strong long-range super-superexchange channel Cu--F$\cdots$F--Cu, which enhances the symmetry-allowed difference between seventh-neighbour exchanges, $J_{7b} - J_{7a}$, controlling the chiral-mode splitting. We identify an orbital-resonance mechanism: energetic alignment between Cu $3d_{z^2}$ and F $2p_z$ states strengthens virtual hopping along the Cu--F$\cdots$F--Cu path and amplifies the anisotropic long-range exchange. Rutile CuF$_2$ therefore provides an ideal platform to validate rutile altermagnetism and suggests an orbital-energy description for engineering large chiral magnon splittings in insulating altermagnets.

cond-mat.mtrl-sci↗

arXiv2026

Universality and anisotropy of the Photonic Urbach Tail

Disorder in photonic crystals and waveguides creates states inside the photonic band gap. These states are often described as Lifshitz tails despite exhibiting energy distributions inconsistent with Lifshitz statistics near the band edge. Here we show that in photonic-crystal waveguides with intentionally engineered anisotropic disorder, the band-edge tail accessible experimentally follows an Urbach law universally, with cumulative statistics $F(Δ)=\exp[-(Δ/α)^β]$, where $Δ$ is the spectral detuning from the band edge, and an exponent $β\approx 1$ independent of disorder strength and orientation. In contrast to Lifshitz behavior, the density of states is maximal at the band edge and decays into the gap. Crucially, we find that the Urbach energy $α$ is anisotropic, with a pronounced directional splitting and qualitatively different scaling for disorder parallel and perpendicular to the waveguide axis. These conclusions are supported by quantitative agreement between optical measurements of GaAs photonic-crystal waveguides and full-vector simulations. The anisotropic Urbach energy emerges as a sensitive probe of disorder-mode coupling and a practical metric to characterize structural disorder in photonic devices.

physics.optics↗

arXiv2026

Quantifying the Relationship Between Strain and Bandgap in Thin Ga$_2$Se$_2$

We present a rigorous analysis that combines theory, simulation, and experimental measurements to quantify the relationship between strain and bandgap in two dimensional gallium selenide (Ga$_2$Se$_2$). Experimentally, we transfer thin Ga$_2$Se$_2$ flakes onto patterned substrates to deterministically induce multiaxial localized strain. We quantify the local strain using a combination of atomic force microscopy (AFM) measurements and COMSOL Multiphysics simulation. We then experimentally map the strain-induced bandgap shifts using high-resolution hyperspectral PL imaging to generate a robust and statistically significant dataset. We systematically fit this data to extract gauge factors that relate the bandgap shift to the local uniaxial and biaxial strain. We then compute the uniaxial and biaxial strain gauge factors via density functional theory (DFT) and find excellent agreement with the experimentally-determined values. Finally, we show that a simple model that computes bandgap shifts from the local uniaxial and biaxial strain predicts the observed multiaxial bandgap shift with less than 10\% error. The combined results provide a framework for deterministic realization of tailored bandgap profiles induced by controlled strain applied to Ga$_2$Se$_2$, with implications for the future realization of localized quantum emitters for quantum photonic applications.

cond-mat.mtrl-sci↗

arXiv2025

Quantum geometric origins of the orbital degrees of freedom of hybrid bosonic quasiparticles in magnetic systems

The orbital degree of freedom has recently attracted significant attention due to the novel phenomena it enables in condensed matter systems. However, the interpretation of the orbital degree of freedom in bosonic quasiparticles remains conceptually ambiguous and the mechanisms governing the transfer of orbital angular moment (OAM) between distinct quasiparticles, such as magnons and phonons, are not yet fully understood. We investigate orbital dynamics in bosonic systems and identify two origins of OAM: (i) global rotational motion of the system, and (ii) the quantum geometry of wavefunctions. Focusing on the latter, we study strongly coupled magnon-phonon systems in two-dimensional antiferromagnets as a test case. We uncover finite OAM arising from quantum geometric effects via two mechanisms: (a) time-parity symmetry breaking, yielding intra band OAM, and (b) interband coupling, generating interband OAM. We propose that an electrical detection scheme based on the transverse voltage generated by hybrid magnon phonon modes can be used to experimentally probe the bosonic orbital degree of freedom. Our results establish a foundation for the emerging field of phonon orbitronics, providing both a conceptual bridge between phonon and magnon orbitronics and a tool for better understanding magnon-polarons. They also advance a unified framework for harnessing orbital degrees of freedom in bosonic systems and pave the way toward electrical control of magnetization and phononic transport.

cond-mat.mes-hall↗

arXiv2025

Tunable magnon band topology and magnon orbital Nernst effect in noncollinear antiferromagnets

We theoretically investigate the intrinsic magnon orbital Nernst effect (ONE) in noncollinear antiferromagnets with Kagomé spin systems. Our analysis reveals that an externally applied magnetic field induces topological phase transitions in the magnonic system, characterized by the closing and reopening of the band gap between distinct magnon bands. These transitions enable tunable control of the magnon orbital Nernst effect with applied magnetic field, with a pronounced enhancement in magnon orbital Nernst conductivity near the phase transition points. This tunability presents a promising direction for experimental detection of the magnon ONE.

cond-mat.mtrl-sci↗

arXiv2024

Electric polarization induced by magnons and magnon Nernst effects

Magnons offer a promising path toward energy-efficient information transmission and the development of next-generation classical and quantum computing technologies. However, methods to efficiently excite, manipulate, and detect magnons remain a critical need. Here, we show that magnons, despite their charge-neutrality, can induce electric polarization as a result of both their spin and orbital moments. We demonstrate this by calculating the electric polarization induced by magnons in two-dimensional (2D) honeycomb antiferromagnets. The electric polarization becomes finite when the Dzyaloshinskii-Moriya Interaction (DMI) is present and its magnitude can be increased by symmetries of the system. We illustrate this by computing and comparing the electric polarizations induced by the magnon Nernst effects in 2D materials with Néel and Zigzag ordering. Our findings show that in the Zigzag order, where the effect is dominated by the magnon orbital moment, the induced electric polarization is approximately three orders of magnitude greater than in the Néel phase. These findings reveal that electric fields could enable both detection and manipulation of magnons under certain conditions by leveraging their spin and orbital angular moment. They also suggest that the discovery or engineering of materials with substantial magnon orbital moments could lead to more practical use of magnons for future computing and information transmission device applications.

cond-mat.mes-hall↗

arXiv2024

Hybrid terahertz emitter for pulse shaping and chirality control

Terahertz (THz) radiation, spanning from 0.3 to 3x10^12 Hz, fills the crucial gap between the microwave and infrared spectral range. THz technology has found applications in various fields, from imaging and sensing to telecommunication and biosensing. However, the full potential of these applications is often hindered by the need for precise control and manipulation of the frequency and polarization state, which typically requires external THz modulators. Here, we demonstrate a hybrid THz source that overcomes this limitation. Our device consists of two THz emitters integrated into one single device, enabling pulse shaping and chirality control of the emitted radiation without additional external components. The two sources are a spintronic emitter and a semiconductor photoconductive antenna (PCA). Using a combination of dual-wavelength excitation, allowing for control of the relative time delay between the two laser excitation pulses, and tuning external parameters for each emitter (i.e., biasing voltage for the PCA and magnetic field for the spintronic THz emitter) enables precise control of the mixing of the two signals and results in frequency, polarization, and chirality control of the overall THz radiation. This on-chip hybrid emitter provides an essential platform for engineered THz radiation with wide-ranging potential applications.

physics.optics↗

arXiv2024

Incorporation of random alloy GaBi$_{x}$As$_{1-x}$ barriers in InAs quantum dot molecules: alloy strain and orbital effects towards enhanced tunneling

Self-assembled InAs quantum dots (QDs), which have long hole-spin coherence times and are amenable to optical control schemes, have long been explored as building blocks for qubit architectures. One such design consists of vertically stacking two QDs to create a quantum dot molecule (QDM). The two dots can be resonantly tuned to form "molecule-like" coupled hole states from the hybridization of hole states otherwise localized in each respective dot. Furthermore, spin-mixing of the hybridized states in dots offset along their stacking direction enables qubit rotation to be driven optically, allowing for an all-optical qubit control scheme. Increasing the magnitude of this spin mixing is important for optical quantum control protocols. To enhance the tunnel coupling and spin-mixing across the dots, we introduce Bi in the GaAs inter-dot barrier. Previously, we showed how to model InAs/GaBiAs in an atomistic tight-binding formalism, and how the dot energy levels are affected by the alloy. In this paper, we discuss the lowering of the tunnel barrier, which results in a three fold increase of hole tunnel coupling strength in the presence of a 7% alloy. Additionally, we show how an asymmetric strain between the two dots caused by the alloy shifts the resonance. Finally, we discuss device geometries for which the introduction of Bi is most advantageous.

cond-mat.mes-hall↗

arXiv2022

Phonon-mediated strong coupling between a three-dimensional topological insulator and a two-dimensional antiferromagnetic material

Van der Waals antiferromagnetic and topological insulator materials provide powerful platforms for modern optical, electronic, and spintronic devices applications. The interaction between an antiferromagnet (AFM) and a topological insulator (TI), if sufficiently strong, could offer emergent hybrid material properties that enable new functionality exceeding what is possible in any individual material constituent. In this work, we study strong coupling between THz excitations in a three dimensional (3D) topological insulator and a quasi-two dimensional (2D) antiferromagnetic material resulting in a new hybridized mode, namely a surface Dirac plasmon-phonon-magnon polariton. We find that the interaction between a surface Dirac plasmon polariton in the 3D TI and a magnon polariton in the 2D AFM is mediated by the phonon coupling in the 3D TI material. The coupling of phonons with an electromagnetic wave propagating in the 3D TI enhances the permittivity of the TI thin film in a way that results in a strong correlation between the dispersion of Dirac plasmon polaritons on the surfaces of the TI with the thickness of the TI. As a result, the dispersion of surface Dirac plasmon polaritons in the TI can be tuned toward resonance with the magnon polariton in the AFM material by varying the TI's thickness, thereby enhancing the strength of the coupling between the excitations in the two materials. The strength of this coupling, which results in the surface Dirac plasmon-phonon-magnon polariton, can be parameterized by the amplitude of the avoided-crossing splitting between the two polariton branches at the magnon resonance frequency...

cond-mat.mes-hall↗

arXiv2022

Deterministic generation of entangled photonic cluster states from quantum dot molecules

Successful generation of photonic cluster states is the key step in the realization of measurement-based quantum computation and quantum network protocols. Several proposals for the generation of such entangled states from different solid-state emitters have been put forward. Each of these protocols come with their own challenges in terms of both conception and implementation. In this work we propose deterministic generation of these photonic cluster states from a spin-photon interface based on a hole spin qubit hosted in a quantum dot molecule. Our protocol resolves many of the difficulties of existing proposals and paves the way for an experimentally feasible realization of highly entangled multi-qubit photonic states with a high production rate.

quant-ph↗

arXiv2022

Surface plasmon-phonon-magnon polariton in a topological insulator-antiferromagnetic bilayer structure

We present a robust technique for computationally studying surface polariton modes in hybrid materials. We use a semi-classical model that allows us to understand the physics behind the interactions between collective excitations of the hybrid system and develop a scattering and transfer matrix method that imposes the proper boundary conditions to solve Maxwell equations and derive a general equation describing the surface polariton in a heterostructure consisting of N constituent materials. We apply this method to a test structure composed of a topological insulator (TI) and an antiferromagnetic material (AFM) to study the resulting surface Dirac plasmon-phonon-magnon polariton (DPPMP). We find that interactions between the excitations of the two constituents result in the formation of hybridized modes and the emergence of avoided-crossing points in the dispersion relations for the DPPMP. For the specific case of a Bi2Se3 TI material, the polariton branch with low frequency below 2 THz redshifts upon increasing the thickness of TI thin film, which leads to an upper bound on the thickness of the TI layer that will allow an observable signature of strong coupling and the emergence of hybridized states. We also find that the strength of the coupling between the TI and the AFM, which is parameterized by the amplitude of the avoided-crossing splitting between the two polariton branches at the magnon resonance frequency, depends on the magnitude of the magnetic dipole and the line width of the magnon in the AFM material as well as on the Fermi energy of Dirac plasmon in the TI. Finally, we predict that materials with extremely high quality, i.e. low scattering loss rate, are essential to achieve an experimentally-observable strong coupling between a TI and AFM.

cond-mat.mtrl-sci↗

arXiv2022

Avoiding leakage and errors caused by unwanted transitions in Lambda systems

Three-level Lambda systems appear in various quantum information processing platforms. In several control schemes, the excited level serves as an auxiliary state for implementing gate operations between the lower qubit states. However, extra excited levels give rise to unwanted transitions that cause leakage and other errors, degrading the gate fidelity. We focus on a coherent-population-trapping scheme for gates and design protocols that reduce the effects of the unwanted off-resonant couplings and improve the gate performance up to several orders of magnitude. For a particular setup of unwanted couplings, we find an exact solution, which leads to error-free gate operations via only a static detuning modification. In the general case, we improve gate operations by adding corrective modulations to the pulses, thereby generalizing the DRAG protocol to Lambda systems. Our techniques enable fast and high-fidelity gates and apply to a wide range of optically driven platforms, such as quantum dots, color centers, and trapped ions.

quant-ph↗

arXiv2022

Strong coupling between a topological insulator and a III-V heterostructure at terahertz frequency

We probe theoretically the emergence of strong coupling in a system consisting of a topological insulator (TI) and a III-V heterostructure using a numerical approach based on the scattering matrix formalism. Specifically, we investigate the interactions between terahertz excitations in a structure composed of Bi$_{2}$Se$_{3}$ and GaAs materials. We find that the interaction between the Bi$_{2}$Se$_{3}$ layer and AlGaAs/GaAs quantum wells with intersubband transitions (ISBTs) in the terahertz frequency regime creates new hybrid modes, namely Dirac plasmon-phonon-ISBT polaritons. The formation of these hybrid modes results in anti-crossings (spectral mode splitting) whose magnitude is an indication of the strength of the coupling. By varying the structural parameters of the constituent materials, our numerical calculations reveal that the magnitude of splitting depends strongly on the doping level and the scattering rate in the AlGaAs/GaAs quantum wells, as well as on the thickness of the GaAs spacer layer that separates the quantum-well structure from the TI layer. Our results reveal the material and device parameters required to obtain experimentally-observable signatures of strong coupling. Our model includes the contribution of an extra two-dimensional hole gas (2DHG) that is predicted to arise at the Bi$_{2}$Se$_{3}$/GaAs interface, based on density functional theory (DFT) calculations that explicitly account for details of the atomic terminations at the interface. The presence of this massive 2DHG at the TI/III-V interface shifts the dispersion of the Dirac plasmon-ISBT polaritons to higher frequencies. The damping rate at this interface, in contrast, compensates the effect of the 2DHG. Finally, we observe that the phonon resonances in the TI layer are crucial to the coupling between the THz excitations in the TI and III-V materials.

cond-mat.mtrl-sci↗

arXiv2021

Principles of spintronic THz emitters

Significant progress has been made in answering fundamental questions about how and, more importantly, on what time scales interactions between electrons, spins, and phonons occur in solid state materials. These complex interactions are leading to the first real applications of terahertz (THz) spintronics: THz emitters that can compete with traditional THz sources and provide additional functionalities enabled by the spin degree of freedom. This tutorial article is intended to provide the background necessary to understand, use, and improve THz spintronic emitters. A particular focus is the introduction of the physical effects that underlie the operation of spintronic THz emitters. These effects were, for the most part, first discovered through traditional spin-transport and spintronic studies. We therefore begin with a review of the historical background and current theoretical understanding of ultrafast spin physics that has been developed over the past twenty-five years. We then discuss standard experimental techniques for the characterization of spintronic THz emitters and - more broadly - ultrafast magnetic phenomena. We next present the principles and methods of the synthesis and fabrication of various types of spintronic THz emitters. Finally, we review recent developments in this exciting field including the integration of novel material platforms such as topological insulators as well as antiferromagnets and materials with unconventional spin textures.

cond-mat.mtrl-sci↗