arXiv subjects

Péter Makk

Publications and source records attributed to Péter Makk.

At least 19 recordsLinked to original sources

arXiv2026

Capacitance sensing in bilayer graphene with gate reflectometry

In the search for topological states in bilayer graphene, capacitance measurement methods are widely utilized in bridge type readouts or source-drain reflectometry setups. In this paper we demonstrate an alternative readout method based on gate reflectometry. We probe the capacitance of a BLG flake encapsulated between hBN and WSe$_2$ through a lumped-element LC resonator coupled to the top gate electrode of the heterostructure. The microwave readout reliably tracks the opening of a displacement field-induced band gap in the device. Compared to simultaneous DC transport measurements, the RF signal proves to be less affected by the percolating transport channels caused by sample disorder. Furthermore, we use the gate based readout to identify a small-angle alignment between the hBN and BLG flake. From the fixed frequency microwave readout, we extract the device capacitance change between the insulating and metallic state of the bilayer and utilize a comprehensive capacitance network model to explain its origin. Finally, we propose an advanced, multiplexed double-resonator readout scheme capable of simultaneously measuring top and bottom gate capacitances to extract the layer polarizability of the system. This work establishes gate reflectometry as a highly scalable and powerful methodology for exploring topological phases and internal charge dynamics in van der Waals heterostructures.

cond-mat.mes-hall↗

arXiv2026

Efficient non-volatile electric control of magnetosensing in CrSBr

In two-dimensional crystals, electrostatic gating can modulate the charge carrier density, thereby tuning their electrical properties. In magnetic materials such as CrSBr, this approach can also enable direct electrical control of magnetoresistance. Non-volatile gating is particularly attractive since it allows the carrier density to be maintained at a desired level without the need for a continuous gate bias, offering significant advantages for technological applications. Here, we demonstrate a simple device architecture in which a solution-processed ferroelectric P(VDF-TrFE) layer is integrated directly onto a CrSBr channel, enabling non-volatile control of its magnetoresistance. We investigate the magnetotransport response over a broad temperature range and demonstrate a reproducible and robust gate dependence. Notably, the ferroelectric gate achieves a gating efficiency approximately one order of magnitude higher than that of a conventional SiO$_2$ dielectric, highlighting the potential of ferroelectric gating for electrical control of 2D magnetic materials.

cond-mat.mes-hall↗

arXiv2026

Effect of pressure on the magnetic properties of (Co$_{0.5}$Fe$_{0.5}$)$_5$GeTe$_2$

Cobalt-doped Fe$_5$GeTe$_2$ possesses a rich magnetic phase diagram as a function of Co concentration. The nature of magnetic order in (Co$_{0.5}$Fe$_{0.5}$)$_5$GeTe$_2$ is especially interesting, as it has been shown to exhibit ferromagnetic order, A-type antiferromagnetic (AFM) order, or potentially both at the same time. Here we present magnetoresistance measurements on antiferromagnetic (Co$_{0.5}$Fe$_{0.5}$)$_5$GeTe$_2$ at a series of pressures and extract the anisotropy and interlayer exchange fields using the two-sublattice model. We show a 50 % increase of the interlayer exchange at 2 GPa, highlighting the sensitivity of magnetic properties to interlayer distance. In addition, we find that the sharp hysteretic transitions observed within the AFM state can be qualitatively described by a linear chain model, which suggests an even-odd effect as a function of layer number instead of a coexisting ferromagnetic phase.

cond-mat.mes-hall↗

arXiv2026

Universal logic circuit for gate-controlled superconductor-based switches operating at liquid-helium temperatures

The observation of the gate-controlled supercurrent (GCS) effect in superconducting nanostructures initiated major research efforts toward the realisation of superconducting-based computing architectures. Here we introduce a universal logic circuit that can be a promising superconducting building block of classical hybrid supercomputers. We demonstrate a functionally complete set of logic gates by realising the AND, OR, NOT and COPY gates. The general layout and scalability of our device, combined with recent experiments demonstrating fast switching and small voltage signals, make it a functional candidate in superconducting electronics. Our device enables the realization of all classical logic gates and the half-adder combinational logic circuit using at most three nanowires, each uniquely configured with two side-gate electrodes.

cond-mat.mes-hall↗

arXiv2026

Tuning proximity-induced spin-orbit coupling in graphene/WSe$_{2}$ heterostructures

Recently, proximity-induced spin-orbit coupling (SOC) has been observed in heterostructures consisting of monolayer graphene (ML-G) and transition metal dichalcogenides (TMDCs) such as WSe$_{2}$. Successful tuning of SOC in graphene/WSe$_{2}$ heterostructures by applying mechanical pressure and electric fields was also demonstrated in previous studies. In addition, theoretical calculations predicted a strong dependence of the proximity-induced SOC on the twist angle between graphene and TMDC. Here, we put these predictions to experimental test in ML-G/ML-WSe$_{2}$/hBN-heterostructures, where the twist angle is determined by aligning fractured edges, and by crystallographic etching of graphene. By performing weak anti-localization measurements, we determine the strength of the Rasbha-type SOC ($λ_\mathrm{R}$) and the valley-Zeeman-type SOC ($λ_\mathrm{VZ}$). Our experiments confirm a strong twist angle dependence of the proximity-induced SOC in agreement with theoretical predictions. Finally, we demonstrate the tunability of the SOC strength via mechanical pressure, which is in agreement with earlier findings.

cond-mat.mes-hall↗

arXiv2026

Impact of current-induced magnons on spin-orbit torque analysis

The second-harmonic Hall technique is a widely used, sensitive method for studying the spin-orbit torques generated by charge current. It exploits the dependence of the Hall resistance on the magnetization direction, although thermal phenomena also contribute. Historically, deviations from the expected magnetic field dependence have usually been neglected. Based on our studies on permalloy/platinum bilayers, we show that a counterpart to the magnon-related spin-flip unidirectional magnetoresistance - known to appear in the second-harmonic longitudinal resistance - appears in the Hall data, and that describing the results in a wide field range with these contributions is essential to accurately estimate the torques.

cond-mat.mes-hall↗

arXiv2026

Large spin signal and spin rectification in folded-bilayer graphene

Graphene is a promising platform for spin-based non-volatile memory, logic, and neuromorphic computing by combining long-distance spin transport with electrical tunability at room temperature. However, advancing beyond passive spin channels requires devices capable of generating large spin signals with efficient rectification capabilities, which are essential for active spintronic components. Here, we demonstrate a folded-bilayer graphene spin-valve device with giant non-local spin signals in the several mV range with pronounced spin-rectification effects. Efficient spin injection creates a significant spin accumulation of 20 meV and generates a spin diode effect with an asymmetry of over an order of magnitude between forward and reverse bias conditions. This spin-diode effect is expected to arise from nonlinear spin-charge interactions in the folded-bilayer graphene channel. These observed large spin signals and spin-diode effects in graphene systems offer a promising platform for developing active two-dimensional spintronic devices.

physics.app-ph↗

arXiv2025

Increasing the proximity induced spin-orbit coupling in bilayer graphene/WSe$_2$ heterostructures with pressure

Combining graphene with transition metal dichalcogenides (TMDs) leads to enhanced spin-orbit coupling (SOC) in the graphene. The induced SOC has a large effect on the low-energy part of the band structure leading to or stabilizing novel phases such as topological phases or superconductivity. Here, the pressure dependence of the SOC strength is investigated in bilayer graphene/WSe$_2$ heterostructures. We performed magnetoconductance studies, such as weak localization, quantum Hall, and Shubnikov-de Haas oscillation measurements to extract the different SOC terms which determine the low-energy band structure of BLG. We find the proximity-induced SOC strengths increased by more than 50\% as a result of applying 2\,GPa hydrostatic pressure. Our studies highlight the opportunity to increase the SOC coupling strength with pressure, which can be important for correlated phases or spin qubits in BLG/WSe$_2$ heterostructures.

cond-mat.mes-hall↗

arXiv2025

Multimode operation of a superconducting nanowire switch in the nanosecond regime

Superconducting circuits are promising candidates for future computational architectures, however, practical applications require fast operation. Here, we demonstrate fast, gate-based switching of an Al nanowire-based superconducting switch in time-domain experiments. We apply voltage pulses on the gate while monitoring the microwave transmission of the device. Utilizing the usual leakage-based operation these measurements yield a fast, 1--2~ns switching time to the normal state, possibly limited by the bandwidth of our setup, and a 10--20~ns delay in the normal to superconducting transition. However, having a significant capacitance between the gate and the device allows for a novel operation, where the displacement current, induced by the fast gate pulses, drives the transition. The switching from superconducting to the normal state yields a similar fast timescale, while in the opposite direction the switching is significantly faster (4--6~ns) than the leakage based operation, which may be further improved by better thermal design. The measured short timescales and novel switching operation open the way for future fast and low-power-consumption applications.

cond-mat.mes-hall↗

arXiv2025

Microwave dynamics of gated Al/InAs superconducting nanowires

Several experiments have recently reported on gate-tunable superconducting properties in metallic devices, holding promise for the realization of cryogenic switches, tunable resonators, and superconducting logic. In particular, the suppression of the critical current as a function of the gate voltage has been widely investigated. However, time-domain studies are discussed only in a few cases. In this paper, we present a microwave characterization of a gate-controlled Al-capped InAs nanowire embedded in a $λ/4$ coplanar waveguide resonator. We observe a shift in the resonator frequency and an increase in its internal losses as a function of the gate voltage, which we relate to a change in the imaginary and real components of the nanowire impedance, respectively. We demonstrate that these changes are described by the Mattis-Bardeen model with an effective temperature. We further study the resonator response to fast gate signals and measure characteristic response times of the order of 40 ns, both in time-domain and parametric modulation experiments. Our study elucidates the impact of the gate on the complex impedance of the nanowire in the superconducting state, as well as its dynamic performance, providing a foundation for the design of gate-controlled superconducting devices.

quant-ph↗

arXiv2024

Signature of pressure-induced topological phase transition in ZrTe$_5$

The layered van der Waals material ZrTe$_5$ is known as a candidate topological insulator (TI), however its topological phase and the relation with other properties such as an apparent Dirac semimetallic state is still a subject of debate. We employ a semiclassical multicarrier transport (MCT) model to analyze the magnetotransport of ZrTe$_5$ nanodevices at hydrostatic pressures up to 2 GPa. The temperature dependence of the MCT results between 10 and 300 K is assessed in the context of thermal activation, and we obtain the positions of conduction and valence band edges in the vicinity of the chemical potential. We find evidence of the closing and re-opening of the band gap with increasing pressure, which is consistent with a phase transition from weak to strong TI. This matches expectations from ab initio band structure calculations, as well as previous observations that CVT-grown ZrTe$_5$ is a weak TI in ambient conditions.

cond-mat.mes-hall↗

arXiv2024

Stabilizing the inverted phase of a WSe$_2$/BLG/WSe$_2$ heterostructure via hydrostatic pressure

Bilayer graphene (BLG) was recently shown to host a band-inverted phase with unconventional topology emerging from the Ising-type spin--orbit interaction (SOI) induced by the proximity of transition metal dichalcogenides with large intrinsic SOI. Here, we report the stabilization of this band-inverted phase in BLG symmetrically encapsulated in tungsten-diselenide (WSe$_2$) via hydrostatic pressure. Our observations from low temperature transport measurements are consistent with a single particle model with induced Ising SOI of opposite sign on the two graphene layers. To confirm the strengthening of the inverted phase, we present thermal activation measurements and show that the SOI-induced band gap increases by more than 100% due to the applied pressure. Finally, the investigation of Landau level spectra reveals the dependence of the level-crossings on the applied magnetic field, which further confirms the enhancement of SOI with pressure.

cond-mat.mes-hall↗

arXiv2024

Self-heating effects and switching dynamics in graphene multiterminal Josephson junctions

We experimentally investigate the electronic transport properties of a three-terminal graphene Josephson junction. We find that self-heating effects strongly influence the behaviour of this multiterminal Josephson junction (MTJJ) system. We show that existing simulation methods based on resistively and capacitively shunted Josephson junction networks can be significantly improved by taking into account these heating effects. We also investigate the phase dynamics in our MTJJ by measuring its switching current distribution and find correlated switching events in different junctions. We show that the switching dynamics is governed by phase diffusion at low temperatures. Furthermore, we find that self-heating introduces additional damping which results in overdamped I-V characteristics when normal and supercurrents coexist in the device.

cond-mat.mes-hall↗

arXiv2024

Heteroatomic Andreev molecule in a superconducting island-double quantum dot hybrid

Topological superconductors (SCs) hold great promise for fault-tolerant quantum hardware, however, their experimental realization is very challenging. Recently, superconducting artificial molecules (Andreev molecules) have opened new avenues to engineer topological superconducting materials. In this work, we demonstrate a heteroatomic Andreev molecule, where two normal artificial atoms realized by quantum dots (QDs) are coupled by a superconducting island (SCI). We show that the two normal atoms strongly hybridize and form a 3-electron-based molecular state. Our density matrix renormalization group (DMRG) calculations explain quantitatively the robust binding of electrons. The tunability of the structure allows us to drive a quantum phase transition from an antiferromagnetic Andreev molecular state to a heteroatomic Andreev molecule with ferromagnetically coupled QDs using simple electrical gating.

cond-mat.mes-hall↗

arXiv2024

Determination of the current-phase relation of an InAs 2DEG Josephson junction with a microwave resonator

Semiconductor-superconductor hybrid nanocircuits are of high interest due to their potential applications in quantum computing. Semiconductors with a strong spin-orbit coupling and large $g$-factor are particularly attractive since they are the basic building blocks of novel qubit architectures. However, for the engineering of these complex circuits, the building blocks must be characterized in detail. We have investigated a Josephson junction where the weak link is a two-dimensional electron gas (2DEG) hosted in an InAs/InGaAs heterostructure grown on a GaAs substrate. We employed the in-situ epitaxially grown Al layer as superconducting contacts to form an rf SQUID, and also to create a microwave resonator for sensing the Josephson inductance. We determined the gate-dependent current-phase relation, and observed supercurrent interference in out-of-plane magnetic fields. With the application of an in-plane magnetic field, we induced asymmetry in the interference pattern, which was found to be anisotropic in the device plane.

cond-mat.mes-hall↗

arXiv2024

Switching dynamics in Al/InAs nanowire-based gate-controlled superconducting switch

The observation of the gate-controlled supercurrent (GCS) effect in superconducting nanostructures increased the hopes for realizing a superconducting equivalent of semiconductor field-effect transistors. However, recent works attribute this effect to various leakage-based scenarios, giving rise to a debate on its origin. A proper understanding of the microscopic process underlying the GCS effect and the relevant time scales would be beneficial to evaluate the possible applications. In this work, we observed gate-induced two-level fluctuations between the superconducting state and normal state in Al/InAs nanowires (NWs). Noise correlation measurements show a strong correlation with leakage current fluctuations. The time-domain measurements show that these fluctuations have Poissonian statistics. Our detailed analysis of the leakage current measurements reveals that it is consistent with the stress-induced leakage current (SILC), in which inelastic tunneling with phonon generation is the predominant transport mechanism. Our findings shed light on the microscopic origin of the GCS effect and give deeper insight into the switching dynamics of the superconducting NW under the influence of the strong gate voltage.

cond-mat.mes-hall↗

arXiv2024

Strong nonlocal tuning of the current-phase relation of a quantum dot based Andreev molecule

Multiple systems hosting Andreev molecular states have been proposed and studied, consisting of closely spaced Josephson junctions modeled as ballistic channels. We show that replacing the ballistic channels in the weak link of the Josephson junctions with quantum dots (QD), leads to a very exciting, rich phase diagram. It shows a strong nonlocal Josephson effect: as one junction is tuned the current-phase relation of the other junction is modified. This architecture hosts $0 - π$ transitions and shows a tunable anomalous phase-shift $ϕ_0$ , nonlocally controlled in both cases, without relying on spin-orbit interaction or Zeeman fields. In addition significant superconducting diode effect can also be observed. The presented non-local current-phase relation can be used as a signature of the formation of an Andreev molecular state, as well as to introduce new ways to tune quantum architectures.

cond-mat.mes-hall↗

arXiv2024

Electron quantum optics in graphene

In the last decade, graphene has become an exciting platform for electron optical experiments, in many aspects superior to conventional two-dimensional electron gases (2DEGs). A major advantage, besides the ultra-large mobilities, is the fine control over the electrostatics, which gives the possibility of realising gap-less and compact p-n interfaces with high precision. The latter host non-trivial states, \eg, snake states in moderate magnetic fields, and serve as building blocks of complex electron interferometers. Thanks to the Dirac spectrum and its non-trivial Berry phase, the internal (valley and sublattice) degrees of freedom, and the possibility to tailor the band structure using proximity effects, such interferometers open up a completely new playground based on novel device architectures. In this review, we introduce the theoretical background of graphene electron optics, fabrication methods used to realise electron-optical devices, and techniques for corresponding numerical simulations. Based on this, we give a comprehensive review of ballistic transport experiments and simple building blocks of electron optical devices both in single and bilayer graphene, highlighting the novel physics that is brought in compared to conventional 2DEGs. After describing the different magnetic field regimes in graphene p-n junctions and nanostructures, we conclude by discussing the state of the art in graphene-based Mach-Zender and Fabry-Perot interferometers.

cond-mat.mes-hall↗