arXiv subjects

Heinz Schmid

Publications and source records attributed to Heinz Schmid.

15 recordsLinked to original sources

arXiv2026

Radiative-channel valley topological laser

Active topological photonic systems enable robust light control and new pathways for semiconductor lasing. However, their intrinsically non-Hermitian nature, combining gain, radiation leakage, and material loss, makes the underlying physics more complex, and prior studies have mostly focused on gain competition while the influence of loss channels is less examined. Here, we experimentally demonstrate radiative-channel-driven topological lasing in a valley photonic crystal consisting of isolated InP nanorods on an insulator, achieving room-temperature single-mode operation within an about 4 lambda scale cavity. Loss-included simulations show that material absorption and radiative leakage can be exploited to establish the lasing pathway. Local off-edge pumping provides spatial evidence of topological edge-guided lasing. Berry-curvature calculations, reflecting unit-cell symmetry breaking, verify the valley-Hall interface in a triangular lattice. Geometry and temperature tuning identify a narrow spectral window where the above-light-line edge branch matches the gain-loss balance and remains decoupled from bulk bands. These results clarify how the loss landscape governs topological lasing and establish a radiative-edge design framework for active topological photonics. The substrate-supported nanorod architecture additionally offers a scalable route for on-chip implementation.

physics.optics↗

arXiv2026

Few-Shot Neuromorphic Vision in a Nonlinear Photonic Network Laser

With the growing prevalence of AI, demand increases for hardware that mimics the brain's ability to extract structure from limited data. In the retina, ganglion cells detect features from sparse inputs via lateral inhibition, where neurons antagonistically suppress activity of neighbouring cells. Biological neurons exhibit diverse heterogeneous nonlinear responses, linked to robust learning and strong performance in low-data regimes. Here, we introduce a retinally-inspired photonic computing system where spatially-competing lasing modes in a random network laser act as heterogeneous, inhibitively-coupled neurons - enabling feature detection, few-shot classification, and segmentation. This silicon-compatible scheme harnesses heterogeneous excitatory and inhibitory nonlinear physical dynamics which give rise to emergent photonic computing behaviour, including parallel feature detection and strong performance when training data is scarce. We report 98.05% and 87.85% accuracy on MNIST and Fashion-MNIST, and 90.12% on BreaKHis cancer diagnosis - outperforming software CNNs including EfficientNetV2 and the vision transformer ViT in few-shot and class-imbalanced regimes with training sets of up to several hundred images. We demonstrate combined segmentation and classification on the HAM10k skin lesion dataset, achieving DICE and Jaccard scores of 84.49% and 74.80%. These results demonstrate the potential of random lasing networks as nonlinear photonic learning systems, and highlight the ability of heterogeneous nonlinear dynamics to support strong learning in challenging low-data scenarios.

cond-mat.dis-nn↗

arXiv2026

Trap-dependent current suppression of optically excited III-V nanowires at cryogenic temperatures

The advancement of quantum technology networks necessitates high-speed, low-thermal load, and minimal-noise communication links between cryogenic and room-temperature components. At the heart of modern telecommunication, lay optical interconnects allowing for large data transfer capabilities via optical fibers. However, cryogenic photonic technologies remain largely unexplored and require a detailed understanding of material behavior and defect dynamics at low temperatures. In this work, we present the first comprehensive study of integrated III-V heterostructures operating at cryogenic temperatures down to 5K. Using an integrated n-InP/i-InGaAs/p-InP/p-InGaAs stack monolithically grown on silicon, we identify a temperature-dependent current-lowering mechanism arising from trap states becoming increasingly active below 140K. We demonstrate for the first time that these traps can be equivalently excited and controlled through either thermal or optical energy, revealing a dual modulation mechanism. These findings provide new insights into carrier transport and defect behavior in III-V heterostructures at cryogenic temperatures, advancing the field of cryogenic photonics and offering a non-destructive approach for identifying and characterizing material impurities in integrated quantum and optoelectronic devices.

physics.optics↗

arXiv2025

Electrical Characterization of hexagonal SiGe

We report electrical measurements on hexagonal silicon-germanium (hex-SiGe), a group IV alloy with direct bandgap. Electrical contacts are formed by metal alloying and doping is achieved using ion implantation. The metastable hex-SiGe phase is successfully recovered after implantation by solid phase recrystallization. Independent of the metal used, contacts on n-type resulted in Schottky barriers due to Fermi level pinning of hex-SiGe. Overall, this constitutes a first step towards use of hex-SiGe for optoelectronic applications.

cond-mat.mtrl-sci↗

arXiv2025

Engineering Magnetotransport Through Hierarchical Symmetry in Weyl Semimetal Superlattices

Superlattice engineering is a powerful way to tune the transport properties of a material. In this work we show that magnetotransport can be modified by superlattices in 3D materials based on the relative symmetry between the Fermi-surface and superlattice. We demonstrate commensuration oscillations in the ballistic transport regime of a nanostructured 3D material with the Weyl semimetal NbP, a signature typically limited to superlattices in 2D materials. The behavior of the oscillations encodes information about the shared properties between the quasiparticles at the Fermi-surface--including their momentum, charge, mass, and rotational symmetry--and the structure of the superlattice. The magnetic field and temperature dependence of the commensuration oscillations enables us to extract the Fermi-momenta and quasiparticle mass at an order of magnitude lower magnetic field and higher temperature than Shubnikov-de Haas quantum oscillations. Furthermore, we use a chiral superlattice to engineer asymmetric longitudinal magnetoresistance based on the charge of the quasiparticles and superlattice enantiomer. These results demonstrate nanopatterned superlattices as an effective method for fermiology, and also point towards new ways of engineering quantum transport in these systems based on the mutual properties of the superlattice and Fermi-surface.

cond-mat.mes-hall↗

arXiv2025

Orientation Dependent Resistivity Scaling in Mesoscopic NbP Crystals

The scaling of Si transistor technology has resulted in a remarkable improvement in the performance of integrated circuits over the last decades. However, scaled transistors also require reduced electrical interconnect dimensions, which lead to greater losses and power dissipation at circuit level. This is mainly caused by enhanced surface scattering of charge carriers in copper interconnect wires at dimensions below 30 nm. A promising approach to mitigate this issue is to use directional conductors, i.e. materials with anisotropic Fermi surface, where proper alignment of crystalline orientation and transport direction can minimize surface scattering. In this work, we perform a resistivity scaling study of the anisotropic semimetal NbP as a function of crystalline orientation. We use here focused ion beam to pattern and scale down NbP crystallites to dimensions comparable to the electron scattering length at cryogenic temperatures. The experimental transport properties are correlated with the Fermi surface characteristics through a theoretical model, thus identifying the physical mechanisms that influence the resistivity scaling of anisotropic conductors. Our methodology provides an effective approach for early evaluation of anisotropic materials as future ultra-scalable interconnects, even when they are unavailable as epitaxial films.

cond-mat.mes-hall↗

arXiv2024

Surface lattice resonance lasers with epitaxial InP gain medium

Surface lattice resonance (SLR) lasers, where gain is supplied by a thin film active material and the feedback comes from multiple scattering by plasmonic nanoparticles, have shown both low threshold lasing and tunability of the angular and spectral emission. However, typically used materials such as organic dyes and QD films suffer from photo-degradation which hampers practical applications. Here, we demonstrate photo-stable single-mode lasing of SLR modes sustained in an epitaxial solid-state InP slab waveguide. The nanoparticle array is weakly coupled to the optical modes, which decreases the scattering losses and hence the experimental lasing threshold is as low as 90 $μ$J/cm$^{2}$. The nanoparticle periodicity defines the lasing wavelength and enables tuneable emission wavelengths over a 70 nm spectral range. Combining plasmonic nanoparticles with an epitaxial solid-state gain medium paves the way for large-area on-chip integrated SLR lasers for applications including optical communication, optical computing, sensing, and LiDAR.

physics.optics↗

arXiv2023

Single mode laser in the telecom range by deterministic amplification of the topological interface mode

Photonic integrated circuits are paving the way for novel on-chip functionalities with diverse applications in communication, computing, and beyond. The integration of on-chip light sources, especially single-mode lasers, is crucial for advancing those photonic chips to their full potential. Recently, novel concepts involving topological designs introduced a variety of options for tuning device properties such as the desired single mode emission. Here we introduce a novel cavity design that allows to amplify the topological interface mode by deterministic placement of gain material within the topological lattice. The proposed design is experimentally implemented by a selective epitaxy process resulting in Si and InGaAs nanorods embedded within the same topological lattice. This results in the first demonstration of a single-mode laser in the telecom band using the concept of amplified topological modes.

physics.optics↗

arXiv2023

Controlling lasing around Exceptional Points in Coupled Nanolasers

Coupled nanolasers are of growing interest for on-chip optical computation and data transmission, which requires an understanding of how lasers interact to form complex systems. The non-Hermitian interaction between two coupled resonators, when excited selectively, can lead to parity-time symmetry, the formation of exceptional points, and subsequently spectral control and increased sensitivity. These investigations have been limited to pump energies close to the lasing threshold, and large or narrow-line lasers. Here, by programmable optical excitation we study two coupled nanolasers significantly above threshold, where mode instability plays an important role. We map the mode evolution around two exceptional points, and observe lasing gaps due to reversed pump dependence which compare well with nonlinear theory. Finally, the coupling can be exploited to control the lasing threshold and wavelength, and for frequency switching around the lasing gap. Controlled and integrated nanolasers constitutes a promising platform for future highly sensitive and programmable on-chip laser sources.

physics.optics↗

arXiv2022

Waveguide coupled III-V photodiodes monolithically integrated on Si

The seamless integration of III-V nanostructures on silicon is a long-standing goal and an important step towards integrated optical links. In the present work, we demonstrate scaled and waveguide coupled III-V photodiodes monolithically integrated on Si, implemented as InP/In0.5Ga0.5As/InP p-i-n structure. The waveguide coupled devices show a dark current down to 0.048 A/cm2 at -1 V and a responsivity up to 0.2 A/W at -2 V. Using grating couplers centered around 1320 nm, we observed a cutoff frequency f3dB exceeding 70 GHz and data reception at 50 GBd with OOK and 4PAM. When operated in forward bias as light emitting diode, the devices emit light centered at 1550 nm. Furthermore, we also investigate the self-heating of the devices using scanning thermal microscopy and find a temperature increase of only ~15 K during the device operation as emitter, in accordance with thermal simulation results.

physics.app-ph↗

arXiv2021

Single-Mode Emission in InP Microdisks on Si using Au Antenna

An important building block for on-chip photonic applications is a scaled emitter. Whispering gallery mode cavities based on III-Vs on Si allow for small device footprints and lasing with low thresholds. However, multimodal emission and wavelength stability over a wider range of temperature can be challenging. Here, we explore the use of Au nanorods on InP whispering gallery mode lasers on Si for single mode emission. We show that by proper choice of the antenna size and positioning, we can suppress the side-modes of a cavity and achieve single mode emission over a wide excitation range. We establish emission trends by varying the size of the antenna and show that the far-field radiation pattern differs significantly for devices with and without antenna. Furthermore, the antenna-induced single mode emission is dominant from room temperature (300 K) down to 200 K, whereas the cavity without an antenna is multimodal and its dominant emission wavelength is highly temperature dependent.

physics.optics↗

arXiv2020

Sondheimer oscillations as a probe of non-ohmic flow in type-II Weyl semimetal WP$_2$

As conductors in electronic applications shrink, microscopic conduction processes lead to strong deviations from Ohm's law. Depending on the length scales of momentum conserving ($l_{MC}$) and relaxing ($l_{MR}$) electron scattering, and the device size ($d$), current flows may shift from ohmic to ballistic to hydrodynamic regimes and more exotic mixtures thereof. So far, an in situ, in-operando methodology to obtain these parameters self-consistently within a micro/nanodevice, and thereby identify its conduction regime, is critically lacking. In this context, we exploit Sondheimer oscillations, semi-classical magnetoresistance oscillations due to helical electronic motion, as a method to obtain $l_{MR}$ in micro-devices even when $l_{MR}\gg d$. This gives information on the bulk $l_{MR}$ complementary to quantum oscillations, which are sensitive to all scattering processes. We extract $l_{MR}$ from the Sondheimer amplitude in the topological semi-metal WP$_2$, at elevated temperatures up to $T\sim 50$~K, in a range most relevant for hydrodynamic transport phenomena. Our data on micrometer-sized devices are in excellent agreement with experimental reports of the large bulk $l_{MR}$ and thus confirm that WP$_2$ can be microfabricated without degradation. Indeed, the measured scattering rates match well with those of theoretically predicted electron-phonon scattering, thus supporting the notion of strong momentum exchange between electrons and phonons in WP$_2$ at these temperatures. These results conclusively establish Sondheimer oscillations as a quantitative probe of $l_{MR}$ in micro-devices in studying non-ohmic electron flow.

cond-mat.mes-hall↗

arXiv2020

Hybrid III-V Silicon Photonic Crystal Cavity Emitting at Telecom Wavelengths

Photonic crystal (PhC) cavities are promising candidates for Si photonics integrated circuits due to their ultrahigh quality (Q)-factors and small mode volumes. Here, we demonstrate a novel concept of a one-dimensional hybrid III-V/Si PhC cavity which exploits a combination of standard silicon-on-insulator technology and active III-V materials. Using template-assisted selective epitaxy, the central part of a Si PhC lattice is locally replaced with III-V gain material. The III-V material is placed to overlap with the maximum of the cavity mode field profile, while keeping the major part of the PhC in Si. The selective epitaxy process enables growth parallel to the substrate and hence, in-plane integration with Si, and in-situ in-plane homo- and heterojunctions. The fabricated hybrid III-V/Si PhCs show emission over the entire telecommunication band from 1.2 μm to 1.6 μm at room temperature validating the device concept and its potential towards fully integrated light sources on silicon.

physics.app-ph↗

arXiv2020

Wurtzite InP Microdisks: from Epitaxy to Room-Temperature Lasing

Metastable wurtzite crystal phases of semiconductors comprise enormous potential for high-performance electro-optical devices, owed to their extended tunable direct band gap range. However, synthesizing these materials in good quality and beyond nanowire size constraints has remained elusive. In this work, the epitaxy of wurtzite InP microdisks and related geometries on insulator for optical applications is explored. This is achieved by an elaborate combination of selective area growth of fins and a zipper-induced epitaxial lateral overgrowth, which enables co-integration of diversely shaped crystals at precise position. The grown material possesses high phase purity and excellent optical quality characterized by STEM and $μ$-PL. Optically pumped lasing at room temperature is achieved in microdisks with a lasing threshold of 365 $μJ/cm^2$, thus demonstrating promise for a wide range of photonic applications.

physics.app-ph↗

arXiv2010

Single photon emission and detection at the nanoscale utilizing semiconductor nanowires

We report recent progress toward on-chip single photon emission and detection in the near infrared utilizing semiconductor nanowires. Our single photon emitter is based on a single InAsP quantum dot embedded in a p-n junction defined along the growth axis of an InP nanowire. Under forward bias, light is emitted from the single quantum dot by electrical injection of electrons and holes. The optical quality of the quantum dot emission is shown to improve when surrounding the dot material by a small intrinsic section of InP. Finally, we report large multiplication factors in excess of 1000 from a single Si nanowire avalanche photodiode comprised of p-doped, intrinsic, and n-doped sections. The large multiplication factor obtained from a single Si nanowire opens up the possibility to detect a single photon at the nanoscale.

cond-mat.mes-hall↗