M. Helm
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View article: Engineering chlorine-based emitters in silicon carbide for telecom-band quantum technologies
Engineering chlorine-based emitters in silicon carbide for telecom-band quantum technologies Open
View article: Optimal growth conditions for strained GaAs/InxAl1−xAs core–shell nanowires with enhanced electronic properties
Optimal growth conditions for strained GaAs/InxAl1−xAs core–shell nanowires with enhanced electronic properties Open
In material systems such as GaAs core/InxAl1−xAs shell nanowires, the elastic strain and the resulting electronic properties of the core can be continuously tailored via the selection of the ternary shell composition, extending the functio…
View article: Magnetization-controlled terahertz harmonic generation with grating and cavity structures
Magnetization-controlled terahertz harmonic generation with grating and cavity structures Open
Spintronic terahertz (THz) frequency conversion in ferromagnet/heavy metal (FM/HM) heterostructures has the potential to enhance high-speed data communication and advance ultrafast magnetic memory applications. By leveraging ultrafast spin…
View article: Imaging of electrical signals in a quantum SiC microscope
Imaging of electrical signals in a quantum SiC microscope Open
We report the experimental realization of a quantum silicon carbide microscope (QSiCM) and demonstrate its functionality by imaging magnetic fields generated by electrical currents. We employ a dual-frequency sensing protocol to enhance th…
View article: Muon tomography - ready for practical application?
Muon tomography - ready for practical application? Open
Muon tomography uses naturally occurring nuclear particles to 'X-ray' technical objects. It has applications in security and nuclear safeguards, but not yet in civil engineering. The potential is enormous, as muon tomography could replace …
View article: Room-temperature alignment-free magnetometry with boron vacancies in hot-pressed hexagonal boron nitride
Room-temperature alignment-free magnetometry with boron vacancies in hot-pressed hexagonal boron nitride Open
Magnetic field sensing is essential for applications in communication, environmental monitoring, and biomedical diagnostics. Quantum sensors based on solid-state spin defects, such as nitrogen-vacancy centers in diamond or boron vacancies …
View article: Highly efficient broadband THz mixing and upconversion with Dirac materials
Highly efficient broadband THz mixing and upconversion with Dirac materials Open
The use of the THz frequency domain in future network generations offers an unparalleled level of capacity, which can enhance innovative applications in wireless communication, analytics, and imaging. Communication technologies rely on fre…
View article: Metal content in soft drinks depending on packaging and storage time
Metal content in soft drinks depending on packaging and storage time Open
View article: Determination of the effective carrier concentration in GaAs/AlGaAs core-shell nanowires using optical techniques
Determination of the effective carrier concentration in GaAs/AlGaAs core-shell nanowires using optical techniques Open
Determining the concentration of electrically active dopants in III-V core-shell nanowires has long been a problem due to the difficulty of forming ohmic contact with the nanowire core. In this letter, we have used a non-contact optical me…
View article: Photon emission gain in Er doped Si light emitting diodes by impact excitation
Photon emission gain in Er doped Si light emitting diodes by impact excitation Open
This work demonstrates photon emission gain, i.e., emission of multiple photons per injected electron, through impact excitation in Er-doped silicon light-emitting diodes (LEDs). Conventional methods for exciting Er ions in silicon suffer …
View article: Superconductivity in Ga-doped Si<i> <sub>x</sub> </i>Ge<sub>1−<i>x</i> </sub> alloys through ion implantation and flash-lamp annealing
Superconductivity in Ga-doped Si<i> <sub>x</sub> </i>Ge<sub>1−<i>x</i> </sub> alloys through ion implantation and flash-lamp annealing Open
Group-IV superconducting semiconductors present promising opportunities on the development of scalable hybrid platforms for quantum devices. However, achieving superconducting states in semiconductors remains challenging, particularly conc…
View article: Phonon and magnon dynamics across the antiferromagnetic transition in the two-dimensional layered van der Waals material CrSBr
Phonon and magnon dynamics across the antiferromagnetic transition in the two-dimensional layered van der Waals material CrSBr Open
We report temperature-dependent reflectivity spectra of the layered van der Waals magnet CrSBr in the far-infrared region. Polarization-dependent measurements resolve the vibrational modes along the E∥a and b axes and reveal clear structur…
View article: Optical Properties of GePb Alloy Realized by Ion Beam Technology
Optical Properties of GePb Alloy Realized by Ion Beam Technology Open
Incorporating lead (Pb) into the germanium (Ge) lattice emerges as a promising approach for bandgap engineering, enabling luminescence at longer wavelengths and paving the way for enhanced applications in short-wave infrared (SWIR) light s…
View article: Emitter–optomechanical interaction in ultrahigh-Q hBN nanocavities
Emitter–optomechanical interaction in ultrahigh-Q hBN nanocavities Open
A spectral anomaly exhibiting pronounced asymmetry is observed in the emission spectrum for nanocavities when they are pumped by the charged boron vacancy VB− and have a high Q-factor above a threshold of 10 000. In contrast, cavities with…
View article: Optical Whispering‐Gallery Mode as a Fingerprint of Magnetic Ordering in Van der Waals Layered CrSBr
Optical Whispering‐Gallery Mode as a Fingerprint of Magnetic Ordering in Van der Waals Layered CrSBr Open
An ultra‐sensitive nanoscale magnetism sensing of van der Waals layered CrSBr is demonstrated by employing optical whispering‐gallery‐mode (WGM) resonances in a self‐rolled‐up microcavity. CrSBr nanoflakes with and without intercalation ar…
View article: Simple THz Phase Retarder Based on Mach–Zehnder Interferometer for Polarization Control
Simple THz Phase Retarder Based on Mach–Zehnder Interferometer for Polarization Control Open
On-demand polarization control of electromagnetic waves is the fundamental element of modern optics. Its interest has recently been expanded in the terahertz (THz) range for coherent excitation of collective quasiparticles in matters, trig…
View article: Optical spin readout of a silicon color center in the telecom L-band
Optical spin readout of a silicon color center in the telecom L-band Open
Optically active spin systems in silicon are attracting growing interest for quantum technologies, driven by their potential for large-scale photonic integration, long spin coherence times, and compatibility with CMOS fabrication. Efficien…
View article: Ambipolar Transport in Phosphorus-Implanted WS<sub>2</sub> Monolayers
Ambipolar Transport in Phosphorus-Implanted WS<sub>2</sub> Monolayers Open
View article: Optical spin readout of a silicon color center in the telecom L-band
Optical spin readout of a silicon color center in the telecom L-band Open
Silicon-based quantum technologies have gained increasing attention due to their potential for large-scale photonic integration, long spin coherence times, and compatibility with CMOS fabrication. Efficient spin-photon interfaces are cruci…
View article: High-pressure modulation of breathing kagome lattice: Cascade of Lifshitz transitions and evolution of the electronic structure
High-pressure modulation of breathing kagome lattice: Cascade of Lifshitz transitions and evolution of the electronic structure Open
The interplay between electronic correlations, density wave orders, and magnetism gives rise to several fascinating phenomena. In recent years, kagome metals have emerged as an excellent platform for investigating these unique properties, …
View article: High‐Performance and Ultrafast Single Germanium Nanowire Photodetectors
High‐Performance and Ultrafast Single Germanium Nanowire Photodetectors Open
Semiconductor nanowire‐based photodetectors with high sensitivity and fast photoresponse in the near‐infrared wavelength range are crucial for applications in light‐wave communication switches, as well as environmental and atmospheric sens…
View article: A high-performance all-silicon photodetector enabling telecom-wavelength detection at room temperature
A high-performance all-silicon photodetector enabling telecom-wavelength detection at room temperature Open
Photonic integrated circuits (PICs) are crucial for advancing optical communications, promising substantial gains in data transmission speed, bandwidth, and energy efficiency compared to conventional electronics 1 . Telecom-wave…
View article: Simple THz phase retarder based on Mach-Zehnder interferometer for polarization control
Simple THz phase retarder based on Mach-Zehnder interferometer for polarization control Open
On-demand polarization control of electromagnetic waves is the fundamental element of modern optics. Its interest has recently been expanded in the terahertz (THz) range for coherent excitation of collective quasiparticles in matters, trig…
View article: Time-resolved nanospectroscopy of III–V semiconductor nanowires
Time-resolved nanospectroscopy of III–V semiconductor nanowires Open
We investigate ultrafast electron dynamics in GaAs/InGaAs core–shell nanowires. Our findings highlight the potential of time-resolved nanoscopy for contactless probing of carrier mobility and recombination dynamics in nanostructures.
View article: Highly efficient broadband THz upconversion with Dirac materials
Highly efficient broadband THz upconversion with Dirac materials Open
The use of the THz frequency domain in future network generations offers an unparalleled level of capacity, which can enhance innovative applications in wireless communication, analytics, and imaging. Communication technologies rely on fre…
View article: A high-performance all-silicon photodetector enabling telecom-wavelength detection at room temperature
A high-performance all-silicon photodetector enabling telecom-wavelength detection at room temperature Open
Photonic integrated circuits (PICs) are crucial for advancing optical communications, promising substantial gains in data transmission speed, bandwidth, and energy efficiency compared to conventional electronics. Telecom-wavelength photode…
View article: Programmable Activation of Quantum Emitters in High‐Purity Silicon with Focused Carbon Ion Beams
Programmable Activation of Quantum Emitters in High‐Purity Silicon with Focused Carbon Ion Beams Open
Carbon implantation at the nanoscale is highly desired for the engineering of defect‐based qubits in a variety of materials, including silicon, diamond, silicon carbide (SiC) and hexagonal boron nitride (hBN). However, the lack of focused …
View article: Hot-Electron Dynamics in a Semiconductor Nanowire under Intense THz Excitation
Hot-Electron Dynamics in a Semiconductor Nanowire under Intense THz Excitation Open
We report terahertz\n(THz)-pump/mid-infrared probe near-field\nstudies\non Si-doped GaAs–InGaAs core–shell nanowires utilizing\nTHz radiation from the free-electron laser FELBE. Upon THz excitation\nof free carriers, we observe a red shift…
View article: Si1−<i>x</i>−<i>y</i>Ge<i>y</i>Sn<i>x</i> alloy formation by Sn ion implantation and flash lamp annealing
Si1−<i>x</i>−<i>y</i>Ge<i>y</i>Sn<i>x</i> alloy formation by Sn ion implantation and flash lamp annealing Open
For many years, Si1−yGey alloys have been applied in the semiconductor industry due to the ability to adjust the performance of Si-based nanoelectronic devices. Following this alloying approach of group-IV semiconductors, adding tin (Sn) i…
View article: Structural changes in Ge1−<i>x</i>Sn<i>x</i> and Si1−<i>x</i>−<i>y</i>Ge<i>y</i>Sn<i>x</i> thin films on SOI substrates treated by pulse laser annealing
Structural changes in Ge1−<i>x</i>Sn<i>x</i> and Si1−<i>x</i>−<i>y</i>Ge<i>y</i>Sn<i>x</i> thin films on SOI substrates treated by pulse laser annealing Open
Ge1−xSnx and Si1−x−yGeySnx alloys are promising materials for future opto- and nanoelectronics applications. These alloys enable effective bandgap engineering, broad adjustability of their lattice parameter, exhibit much higher carrier mob…