arXiv subjects

Peter Märki

Publications and source records attributed to Peter Märki.

10 recordsLinked to original sources

arXiv2026

Small but Tubby: A Magnetic Loop Antenna Made from 100 mm Copper Tubing

This paper presents the electrical model, key equations, and practical construction of a small transmitting magnetic loop antenna built from unusually large 100 mm diameter copper tubing. The large conductor surface area and wide-area transitions to the vacuum capacitors were designed to minimize resistive losses. The frequency range from 1.8 MHz to 31 MHz is unusually wide. Frequency, impedance matching, and azimuth are all adjusted automatically by servo motors. Indoor losses originate predominantly from near-field coupling to the environment rather than from the antenna itself. Temperature-rise measurements confirm that the bulk of the dissipated power is absorbed by the environment, not by the antenna components. The conducted H-field measurements demonstrate good agreement between the measured H-field and the theoretical free-space H-field calculated from the antenna geometry and an estimated loop current. The loop current was estimated from the measured antenna bandwidth and the applied transmit power. The antenna was developed for indoor operation where outdoor installation is not possible.

physics.ins-det↗

arXiv2022

Gate-defined Two-dimensional Hole and Electron Systems in an Undoped InSb Quantum Well

Quantum transport measurements are performed in gate-defined, high-quality, two-dimensional hole and electron systems in an undoped InSb quantum well. For both polarities, the carrier systems show tunable spin-orbit interaction as extracted from weak anti-localization measurements. The effective mass of InSb holes strongly increases with carrier density as determined from the temperature dependence of Shubnikov-de Haas oscillations. Coincidence measurements in a tilted magnetic field are performed to estimate the spin susceptibility of the InSb two-dimensional hole system. The g-factor of the two-dimensional hole system decreases rapidly with increasing carrier density.

cond-mat.mes-hall↗

arXiv2021

Characterization of quasiparticle tunneling in a quantum dot from temperature dependent transport in the integer and fractional quantum Hall regime

We report on magnetoconductance measurements through a weakly coupled quantum dot, containing roughly 900 electrons, in a wide magnetic field range from 0 T to 12 T. We find modulations of the conductance resonances in the quantum Hall regime for higher integer filling factors $6> ν_\mathrm{dot} > 2$, in addition to modulations at $2> ν_\mathrm{dot} > 1$ and at fractional filling factors $ν_\mathrm{dot} \gtrsim 2/3$, $1/3$. Depending on the internal filling factor, edge reconstruction inside the quantum dot leads to the formation of multiple concentric compressible regions, which contain discrete charge and are separated by incompressible rings. Quasiparticle tunneling between different compressible regions results in magnetic-field-(pseudo)-periodic modulations of the Coulomb resonances with different periodicities, additional super-periodicity or non-periodic features. The evolution of the period in magnetic field indicates cyclic depopulation of the inner compressible regions close to integer filing factors. We study the temperature dependence of the conductance resonances for different magnetic fields. While at low fields, the resonance amplitude decays inversely with temperature, corresponding to single-level transport, the temperature dependence of the amplitude evolves continuously into a linearly increasing behavior for dot filling factor $2> ν_\mathrm{dot} > 1$. This coincides with a reduction of the charging energy by approximately a factor of 2 in the same regime. At zero magnetic field, the temperature dependence differs for individual resonances, and is found to depend on the closeness to quantum dot states that couple strongly to the leads. The presented experiments complement and extend previous results on internal rearrangements of quasiparticles for weakly coupled quantum dots in magnetic field.

cond-mat.mes-hall↗

arXiv2021

Observation of quantum Hall interferometer phase jumps due to changing quasiparticle number

We measure the magneto-conductance through a micron-sized quantum dot hosting about 500 electrons in the quantum Hall regime. In the Coulomb blockade, when the island is weakly coupled to source and drain contacts, edge reconstruction at filling factors between one and two in the dot leads to the formation of two compressible regions tunnel coupled via an incompressible region of filling factor $ν=1$. We interpret the resulting conductance pattern in terms of a phase diagram of stable charge in the two compressible regions. Increasing the coupling of the dot to source and drain, we realize a Fabry-Pérot quantum Hall interferometer, which shows an interference pattern strikingly similar to the phase diagram in the Coulomb blockade regime. We interpret this experimental finding using an empirical model adapted from the Coulomb blockaded to the interferometer case. The model allows us to relate the observed abrupt jumps of the Fabry-Pérot interferometer phase to a change in the number of bulk quasiparticles. This opens up an avenue for the investigation of phase shifts due to (fractional) charge redistributions in future experiments on similar devices.

cond-mat.mes-hall↗

arXiv2020

Fractional Coulomb blockade for quasiparticle tunneling between edge channels

We study the magneto-conductance of a $1.4~\mathrm{μm}$-wide quantum dot in the fractional quantum Hall regime. For a filling factor $\approx 2/3$ and $\gtrsim 1/3$ in the quantum dot the observed Coulomb resonances show a periodic modulation in magnetic field. This indicates a non-trivial reconstruction of the 2/3 fractional quantum Hall state in the quantum dot. We present a model for the charge stability diagram of the system assuming two compressible regions separated by an incompressible stripe of filling factor $2/3$ and $1/3$, respectively. From the dependence of the magnetic field period on total magnetic field we construct the zero-field charge density distribution in the quantum dot. The tunneling between the two compressible regions exhibits fractional Coulomb blockade. For both filling factor regions, we extract a fractional charge $e^*/e = 0.32 \pm 0.03$ by comparing to measurements at filling factor 2. With their close relation to quantum Hall Fabry-Pérot interferometers, our investigations on quantum dots in the fractional quantum Hall regime extend and complement interference experiments investigating the nature of anyonic fractional quantum Hall quasiparticles.

cond-mat.mes-hall↗

arXiv2020

Electronic g-factor and Magneto-transport in InSb Quantum Wells

High mobility InSb quantum wells with tunable carrier densities are investigated by transport experiments in magnetic fields tilted with respect to the sample normal. We employ the coincidence method and the temperature dependence of the Shubnikov-de Haas oscillations and find a value for the effective g-factor of $\mid g^{\ast}\mid $ =35$\pm$4 and a value for the effective mass of $m^*\approx0.017 m_0$, where $m_0$ is the electron mass in vacuum. Our measurements are performed in a magnetic field and a density range where the enhancement mechanism of the effective g-factor can be neglected. Accordingly, the obtained effective g-factor and the effective mass can be quantitatively explained in a single particle picture. Additionally, we explore the magneto-transport up to magnetic fields of 35 T and do not find features related to the fractional quantum Hall effect.

cond-mat.mes-hall↗

arXiv2019

Quantum dot thermometry at ultra-low temperature in a dilution refrigerator with a $^4$He immersion cell

Experiments performed at a temperature of a few millikelvin require effective thermalization schemes, low-pass filtering of the measurement lines and low-noise electronics. Here, we report on the modifications to a commercial dilution refrigerator with a base temperature of 3.5 mK that enable us to lower the electron temperature to 6.7 mK measured from the Coulomb peak width of a quantum dot gate-defined in an [Al]GaAs heteostructure. We present the design and implementation of a liquid $^4$He immersion cell tight against superleaks, implement an innovative wiring technology and develop optimized transport measurement procedures.

cond-mat.mes-hall↗

arXiv2016

Measuring the degeneracy of discrete energy levels using a GaAs/AlGaAs quantum dot

We demonstrate an experimental method for measuring quantum state degeneracies in bound state energy spectra. The technique is based on the general principle of detailed balance, and the ability to perform precise and efficient measurements of energy-dependent tunnelling-in and -out rates from a reservoir. The method is realized using a GaAs/AlGaAs quantum dot allowing for the detection of time-resolved single-electron tunnelling with a precision enhanced by a feedback-control. It is thoroughly tested by tuning orbital and spin-degeneracies with electric and magnetic fields. The technique also lends itself for studying the connection between the ground state degeneracy and the lifetime of the excited states.

cond-mat.mes-hall↗

arXiv2015

Equilibrium free energy measurement of a confined electron driven out of equilibrium

We study out-of equilibrium properties of a quantum dot in a GaAs/AlGaAs two-dimensional electron gas. By means of single electron counting experiments, we measure the distribution of work and dissipated heat of the driven quantum dot and relate these quantities to the equilibrium free energy change, as it has been proposed by C. Jarzynski [Phys. Rev. Lett. {\bf78}, 2690 (1997)]. We discuss the influence of the degeneracy of the quantized energy state on the free energy change as well as its relation to the tunnel rates between the dot and the reservoir.

cond-mat.mes-hall↗

arXiv2014

Spectroscopy of Equilibrium and Non-Equilibrium Charge Transfer in Semiconductor Quantum Structures

We investigate equilibrium and non-equilibrium charge-transfer processes by performing high-resolution transport spectroscopy. Using electrostatically defined quantum dots for energy-selective emission and detection, we achieved unprecedented spectral resolution and a high degree of tunability of relevant experimental parameters. Most importantly, we observe that the spectral width of elastically transferred electrons can be substantially smaller than the linewidth of a thermally broadened Coulomb peak. This finding indicates that the charge-transfer process is fast compared to the electron--phonon interaction time. By drawing an analogy to double quantum dots, we argue that the spectral width of the elastic resonance is determined by the lifetime broadening $h\itΓ$ of the emitter and detector states. Good agreement with the model is found also in an experiment in which the charge transfer is in the regime $h\itΓ\gg k_{\rm{B}}T$. By performing spectroscopy below the Fermi energy, we furthermore observe elastic and inelastic transfer of holes.

cond-mat.mes-hall↗