arXiv subjects

Matthijs Rog

Publications and source records attributed to Matthijs Rog.

5 recordsLinked to original sources

arXiv2026

Direct Observation of Channelised Supercurrents in a Kagome Superconductor

Superconductors are many-body quantum states in which current flows without dissipation. Theory predicts that supercurrents follow a relatively simple spatial pattern in both conventional and unconventional superconductors. Recent studies into the AV3Sb5 (A = Cs, K, Rb) family of Kagome superconductors indicate that CsV3Sb5 has unconventional transport properties that cannot be accounted for with these simple theories, including reports of intrinsic Josephson junctions, higher order Cooper pairing and the zero field diode effect. Attempts to interpret these findings have focused on the interplay of superconductivity with the unconventional charge density wave (CDW) order in these materials, with which superconductivity competes. A current roadblock to understanding how these kagome superconductors give rise to their intriguing properties is the lack of spatially resolved information about transport. Here we show, using a recently developed superconducting quantum interference device (SQUID) microscope, that flakes of CsV3Sb5-xSnx host a network of narrow supercurrent channels. These supercurrent channels emerge at the critical temperature and remain stable for all temperatures and currents. Their non-linear behaviour is consistent with a network of Josephson junctions linked by narrow supercurrent filaments, which naturally leads to the observed transport anomalies. Intriguingly, these observations are much weaker in undoped samples, which suggests links to the physics of charge density waves, disorder, and electronic correlations, all of which are greatly influenced by the doping strength. These results establish new frontiers for the local investigation of charge transport and competing orders in strongly correlated electron systems, and shine a new light on the anomalous transport properties of the AV3Sb5 kagome superconductors.

cond-mat.supr-con↗

arXiv2025

Emergent Network of Josephson Junctions in a Kagome Superconductor

Materials with a Kagome lattice are intensely studied because they host exotic states that combine strong correlations and topology. Recently, critical current oscillations were observed in an unstructured flake of CsV3Sb5 . In this work, we show that the origin of these oscillations is a network of Josephson junctions intrinsic to the flake that emerges below its critical temperature. Under radio-frequency radiation, we observe quantized Shapiro steps. The sensitivity of the step height to the contact placement indicates a complex network of junctions. By performing interference studies along multiple field directions, we demonstrate that the interference effects are a result of small junctions and filamentary supercurrent flow. Upon nanostructuring the flake, prominent features of the interference pattern are preserved, illustrating the localized nature of these junctions and their stability to thermal cycles. These results pave the way for determining the exact nature of superconductivity in the AV3Sb5 family.

cond-mat.supr-con↗

arXiv2025

Tapping-mode SQUID-on-tip Microscopy with Proximity Josephson Junctions

Studying nanoscale dynamics is essential for understanding quantum materials and advancing quantum chip manufacturing. Still, it remains a major challenge to measure non-equilibrium properties such as current and dissipation, and their relation to structure. Scanning nanoprobes utilizing superconducting quantum interference devices (SQUIDs) are uniquely suited here, due to their unparalleled magnetic and thermal sensitivity. Here, we introduce tapping-mode SQUID-on-tip, which combines atomic force microscopy (AFM) with nanoSQUID sensing. Our probes minimize nanoSQUID-sample distance, provide in-plane magnetic sensitivity, and operate without lasers. Frequency multiplexing enables simultaneous imaging of currents, magnetism, dissipation and topography. The large voltage output of our proximity-junction nanoSQUIDs allows us to resolve nanoscale currents as small as 100 nA using a simple four-probe electronic readout without cryogenic amplification. By capturing local magnetic, thermal, and electronic response without external radiation, our technique offers a powerful non-invasive route to study dynamic phenomena in exotic materials and delicate quantum circuits.

cond-mat.mes-hall↗

arXiv2025

Young's double-slit experiment with anisotropic GHz surface acoustic waves on gallium arsenide

We demonstrate Young's double-slit experiment with GHz surface acoustic waves (SAWs) on gallium arsenide (GaAs). This experiment differs from the well-known optical case due to the anisotropy of SAW propagation on GaAs. We generate SAWs using an interdigital transducer (IDT), and the double-slit is realized by focused ion beam milled grooves which block the SAWs. We measure the out-of-plane SAW displacement with an optical scanning interferometer and apply a spatial Fourier filtering technique, enabling the observation of the two-slit interference pattern, as well as higher order diffraction and near field interference effects. We find reasonable agreement between the measured far-field interference pattern and anisotropic Huygens-Fresnel simulations based on previously reported angle-dependent SAW velocities on GaAs.

physics.optics↗

arXiv2025

Time-reversal symmetry breaking in microscopic single-crystal Sr$_2$RuO$_4$ devices

Time-reversal symmetry breaking superconductivity is a quintessential unconventional quantum state. In Josephson junctions, time-reversal symmetry breaking manifests itself in the supercurrent interference pattern as the invariance of the critical current under the reversal of both transport and magnetic field directions, i.e., $I_\text{c+}(H) = I_\text{c-}(-H)$. So far, such systems have been realized in devices where superconductivity is injected into a deliberately constructed weak link medium, usually carefully tuned by external magnetic fields and electrostatic gating. In this work, we report time-reversal symmetry breaking in spontaneously emerging Josephson junctions without intentionally constructed weak links. This is realized in ultra-pure single-crystal microstructures of Sr$_2$RuO$_4$, an unconventional superconductor with a multi-component order parameter. Here, the Josephson effect emerges intrinsically at the superconducting domain wall, where the degenerate states partially overlap. In addition to violating $I_\text{c+}(H) = I_\text{c-}(-H)$, we find a rich variety of exotic transport phenomena, including a supercurrent diode effect present in the entire interference pattern, two-channel critical current oscillations with a period that deviates from $\Phi_0$, fractional Shapiro steps, and current-switchable bistable states with highly asymmetric critical currents. Our findings provide direct evidence of TRSB in unstrained Sr$_2$RuO$_4$ and reveal the potential of domain wall Josephson junctions, which can emerge in any superconductor where the pairing symmetry is described by a multi-component order parameter.

cond-mat.supr-con↗