arXiv subjects

Joel Kuttruff

Publications and source records attributed to Joel Kuttruff.

7 recordsLinked to original sources

arXiv2026

Two pathways to break the insulating state in a correlated transition metal oxide

Correlated transition metal oxides present exciting prospects as switches or memory and storage devices owing to the possibility to control electronic properties using various external stimuli. While their complex behaviour is known to stem from interplay between electronic correlations, atomic structure and orbital physics, they remain poorly understood on the microscopic level. Here, we investigate such origins as a function of temperature and pressure in the transition metal oxide Ti3O5. We find that the insulating room-temperature phase is characterized by one-dimensional zig-zag chains composed by two types of titanium dimers forming orbital selective valence bonds. At the thermal phase transition, one type of titanium dimer breaks up, resulting in an insulator to metal transition with a large orbital repopulation between the two states. Moreover, optical spectroscopy reveals that an additional pressure-driven insulator to metal transition occurs in Ti3O5 at room temperature. The phenomenology of this novel pressure-induced metallic transition is completely different from the insofar studied transitions and results from a competition between intra- and inter-dimer hopping. Our combined results suggest that Ti3O5 is a prototypical correlated transition metal oxide, where both correlations as well as orbital interactions need to be considered to fully understand the evolution of the electronic states.

cond-mat.str-el↗

arXiv2023

Plasmonic Photochemistry as a Tool to Prepare Metallic Nanopores with Controlled Diameter

We show that plasmonic solid-state nanopores with tunable hole diameter can be prepared via a photocatalytic effect resulting from the enhanced electromagnetic field inside a metallic ring prepared on top of a dielectric nanotube. Under white light illumination, the maximum field intensity in these nanorings induces a site selective metal nucleation and growth. We used this approach to prepare bare Au and bimetallic Au-Ag nanorings and demonstrate the reduction of the initial inner diameter of the nanopore down to 4 nanometers. This process can be applied over large arrays with good reproducibility and good control on the nanopore diameter. The tunability of the nanopore diameter can be used to enable optimized detection of single entities with different size, such as single nanoparticles or biomolecules. As proof-of-concept, we demonstrate the versatility of the platform to perform single object detection of dsDNA, and Au nanoparticles with a diameter of 15 nm and 30 nm. We support our experimental findings with numerical simulations that provide insights into the electromagnetic field intensity distribution, showing that a field intensity enhancement of up to 104 can be achieved inside the nanopores. This strong field confinement inside the final nanopore can be used to perform enhanced optical measurements, and to generate local heating, thereby modifying the ionic conductance of the nanopore

physics.optics↗

arXiv2022

Advances in ultrafast plasmonics

In the past twenty years, we have reached a broad understanding of many light-driven phenomena in nanoscale systems. The temporal dynamics of the excited states are instead quite challenging to explore, and, at the same time, crucial to study for understanding the origin of fundamental physical and chemical processes. In this review we examine the current state and prospects of ultrafast phenomena driven by plasmons both from a fundamental and applied point of view. This research area is referred to as ultrafast plasmonics and represents an outstanding playground to tailor and control fast optical and electronic processes at the nanoscale, such as ultrafast optical switching, single photon emission and strong coupling interactions to tailor photochemical reactions. Here, we provide an overview of the field, and describe the methodologies to monitor and control nanoscale phenomena with plasmons at ultrafast timescales in terms of both modeling and experimental characterization. Various directions are showcased, among others recent advances in ultrafast plasmon-driven chemistry and multi-functional plasmonics, in which charge, spin, and lattice degrees of freedom are exploited to provide active control of the optical and electronic properties of nanoscale materials. As the focus shifts to the development of practical devices, such as all-optical transistors, we also emphasize new materials and applications in ultrafast plasmonics and highlight recent development in the relativistic realm. The latter is a promising research field with potential applications in fusion research or particle and light sources providing properties such as attosecond duration.

physics.optics↗

arXiv2022

Ultrafast collapse of molecular polaritons in photoswitch-nanoantennas at room temperature

Molecular polaritons are hybrid light-matter states that emerge when a molecular transition strongly interacts with photons in a resonator. At optical frequencies, this interaction unlocks a way to explore and control new chemical phenomena at the nanoscale. Achieving such a control at ultrafast timescales, however, is an outstanding challenge, as it requires a deep understanding of the dynamics of the collectively coupled molecular excitation and the nanoconfined electromagnetic fields. Here, we investigate the dynamics of collective polariton states, realized by coupling molecular photoswitches to optically anisotropic plasmonic nanoantennas. Pump-probe experiments reveal an ultrafast collapse of polaritons to a single-molecule transition triggered by femtosecond-pulse excitation at room-temperature. Through a synergistic combination of experiments and quantum mechanical modelling, we show that the response of the system is governed by intramolecular dynamics, occurring one order of magnitude faster with respect to the unperturbed excited molecule relaxation to the ground state.

cond-mat.mes-hall↗

arXiv2021

Magnetic Circular Dichroism in Hyperbolic Metamaterial Nanoparticles

The optical properties of some nanomaterials can be controlled by an external magnetic field, providing active functionalities for a wide range of applications, from single-molecule sensing to nanoscale nonreciprocal optical isolation. Materials with broadband tunable magneto-optical response are therefore highly desired for various components in next-generation integrated photonic nanodevices. Concurrently, hyperbolic metamaterials received a lot of attention in the past decade since they exhibit unusual properties that are rarely observed in nature and provide an ideal platform to control the optical response at the nanoscale via careful design of the effective permittivity tensor, surpassing the possibilities of conventional systems. Here, we experimentally study magnetic circular dichroism in a metasurface made of type-II hyperbolic nanoparticles on a transparent substrate. Numerical simulations confirm the experimental findings, and an analytical model is established to explain the physical origin of the observed magneto-optical effects, which can be described in terms of the coupling of fundamental electric and magnetic dipole modes with an external magnetic field. Our system paves the way for the development of nanophotonic active devices combining the benefits of sub-wavelength light manipulation in hyperbolic metamaterials supporting a large density of optical states with the ability to freely tune the magneto-optical response via control over the anisotropic permittivity of the system.

physics.optics↗

arXiv2021

Second harmonic generation in germanium quantum wells for nonlinear silicon photonics

Second-harmonic generation (SHG) is a direct measure of the strength of second-order nonlinear optical effects, which also include frequency mixing and parametric oscillations. Natural and artificial materials with broken center-of-inversion symmetry in their unit cell display high SHG efficiency, however the silicon-foundry compatible group-IV semiconductors (Si, Ge) are centrosymmetric, thereby preventing full integration of second-order nonlinearity in silicon photonics platforms. Here we demonstrate strong SHG in Ge-rich quantum wells grown on Si wafers. The symmetry breaking is artificially realized with a pair of asymmetric coupled quantum wells (ACQW), in which three of the quantum-confined states are equidistant in energy, resulting in a double resonance for SHG. Laser spectroscopy experiments demonstrate a giant second-order nonlinearity at mid-infrared pump wavelengths between 9 and 12 microns. Leveraging on the strong intersubband dipoles, the nonlinear susceptibility almost reaches 10^5 pm/V

physics.optics↗

arXiv2020

Ultrafast all-optical switching enabled by epsilon-near-zero modes in metal-insulator nanocavities

Ultrafast control of light-matter interactions constitutes a crucial feature in view of new technological frontiers of information processing. However, conventional optical elements are either static or feature switching speeds that are extremely low with respect to the timescales at which it is possible to control light. Here, we exploit high-quality-factor engineered epsilon-near-zero (ENZ) modes of a metal-insulator-metal nanocavity to realize an all-optical ultrafast modulation of the reflectance of light at a tailored wavelength. Our approach is based on the presence of the two, spectrally separated, ENZ absorption resonances of the cavity. Optical pumping of the system at its high energy ENZ mode leads to a strong red-shift of the low energy mode because of the transient increase of the local dielectric function, which leads to a sub-3-ps control of the reflectance at a specific wavelength with a relative modulation depth approaching 120%.

physics.optics↗