Broadband magnetic resonance spectroscopy in MnSc[Formula: see text]S[Formula: see text].

Recent neutron scattering experiments suggested that frustrated magnetic interactions give rise to antiferromagnetic spiral and fractional skyrmion lattice phases in MnSc[Formula: see text]S[Formula: see text] . Here, to trace the signatures of these modulated phases, we studied the spin excitations of MnSc[Formula: see text]S[Formula: see text] by THz spectroscopy at 300 mK and in magnetic fields up to 12 T and by broadband microwave spectroscopy at various temperatures up to 50 GHz. We found a single magnetic resonance with frequency linearly increasing in field.

Gapped magnetic ground state in quantum spin liquid candidate κ-(BEDT-TTF)Cu(CN).

Geometrical frustration, quantum entanglement, and disorder may prevent long-range ordering of localized spins with strong exchange interactions, resulting in an exotic state of matter. κ-(BEDT-TTF)Cu(CN) is considered the prime candidate for this elusive quantum spin liquid state, but its ground-state properties remain puzzling. We present a multifrequency electron spin resonance (ESR) study down to millikelvin temperatures, revealing a rapid drop of the spin susceptibility at 6 kelvin.

Microwave probing of bulk dielectrics using superconducting coplanar resonators in distant-flip-chip geometry.

Dielectric measurements on insulating materials at cryogenic temperatures can be challenging, depending on the frequency and temperature ranges of interest. We present a technique to study the dielectric properties of bulk dielectrics at GHz frequencies. A superconducting coplanar Nb resonator is deposited directly on the material of interest, and this resonator is then probed in distant-flip-chip geometry with a microwave feedline on a separate chip.

Cryogenic frequency-domain electron spin resonance spectrometer based on coplanar waveguides and field modulation.

We present an instrument to perform frequency-domain electron spin resonance experiments that is based on coplanar waveguides and field modulation. A large parameter space in frequency (up to 25 GHz), magnetic field (up to 8 T), and temperature (down to 1.6 K) is accessible.

Characterizing dielectric properties of ultra-thin films using superconducting coplanar microwave resonators.

We present an experimental approach for cryogenic dielectric measurements on ultrathin insulating films. Based on a coplanar microwave waveguide design, we implement superconducting quarter-wave resonators with inductive coupling, which allows us to determine the real part ε of the dielectric function at gigahertz frequencies and sample thicknesses down to a few nanometers. We perform simulations to optimize resonator coupling and sensitivity, and we demonstrate the possibility to quantify ε with a conformal mapping technique in a wide sample-thickness and ε-regime.

Role of non-linear effects and standing waves in microwave spectroscopy: Corbino measurements on superconductors and VO.

Broadband microwave spectroscopy can probe material properties in wide spectral and temperature ranges. The quality of such measurements crucially depends on the calibration, which also removes from the obtained spectra signatures of standing waves. Here we consider cryogenic Corbino-type reflection measurements on superconductors close to the critical temperature.

New insights into MagPI: a promising tool to determine the adhesive capacity of biofilm on the mesoscale.

The adhesiveness and stability of ubiquitously distributed biofilms is a significant issue in many areas such as ecology, biotechnology and medicine. The magnetic particle induction (MagPI) system allows precise determinations of biofilm adhesiveness at high temporal and spatial resolution on the mesoscale. This paper concerns several technical aspects to further improve the performance of this powerful experimental approach and enhance the range of MagPI applications.

Single-Gap Superconductivity and Dome of Superfluid Density in Nb-Doped SrTiO_{3}.

SrTiO_{3} exhibits a superconducting dome upon doping with Nb, with a maximum critical temperature T_{c}≈0.4  K. Using microwave stripline resonators at frequencies from 2 to 23 GHz and temperatures down to 0.

Single spin optically detected magnetic resonance with 60-90 GHz (E-band) microwave resonators.

Magnetic resonance with ensembles of electron spins is commonly performed around 10 GHz, but also at frequencies above 240 GHz and in corresponding magnetic fields of over 9 T. However, experiments with single electron and nuclear spins so far only reach into frequency ranges of several 10 GHz, where existing coplanar waveguide structures for microwave (MW) delivery are compatible with single spin readout techniques (e.g.

Surface-resistance measurements using superconducting stripline resonators.

We present a method to measure the absolute surface resistance of conductive samples at a set of GHz frequencies with superconducting lead stripline resonators at temperatures 1-6 K. The stripline structure can easily be applied for bulk samples and allows direct calculation of the surface resistance without the requirement of additional calibration measurements or sample reference points. We further describe a correction method to reduce experimental background on high-Q resonance modes by exploiting TEM-properties of the external cabling.

Microwave resonances in dielectric samples probed in Corbino geometry: simulation and experiment.

The Corbino approach, where the sample of interest terminates a coaxial cable, is a well-established method for microwave spectroscopy. If the sample is dielectric and if the probe geometry basically forms a conductive cavity, this combination can sustain well-defined microwave resonances that are detrimental for broadband measurements. Here, we present detailed simulations and measurements to investigate the resonance frequencies as a function of sample and probe size and of sample permittivity.

Broadband microwave spectroscopy in Corbino geometry at 3He temperatures.

A broadband microwave spectrometer has been constructed to determine the complex conductivity of thin metal films at frequencies from 45 MHz to 20 GHz working in the temperature range from 0.45 K to 2 K (in a (3)He cryostat). The setup follows the Corbino approach: a vector network analyzer measures the complex reflection coefficient of a microwave signal hitting the sample as termination of a coaxial transmission line.

Fabry-Perot resonances in birefringent YAlO3 analyzed at terahertz frequencies.

We present transmission and phase measurements on a birefringent YAlO(3) crystal that is illuminated with linearly polarized terahertz radiation in a broad frequency range (10 cm(-1) to 16 cm(-1)). The spectra exhibit pronounced and complex Fabry-Perot resonances that depend on the polarization orientation of the incoming light. We present a theoretical description to analyze these data and to obtain the optical constants of the crystal in the terahertz range.

Strip-shaped samples in a microwave Corbino spectrometer.

The Corbino geometry, where a flat sample is pressed against an open end of a coaxial cable, is an established probe layout for broadband microwave spectroscopy. Here we show that besides the conventional case of the sample covering the complete Corbino probe, also strip-shaped samples can be studied with a Corbino spectrometer. This increases the sensitivity for highly conductive samples and furthermore opens the route for the study of anisotropic materials.

Extremely slow Drude relaxation of correlated electrons.

The electrical conduction of metals is governed by how freely mobile electrons can move throughout the material. This movement is hampered by scattering with other electrons, as well as with impurities or thermal excitations (phonons). Experimentally, the scattering processes of single electrons are not observed, but rather the overall response of all mobile charge carriers within a sample.