Local Broadband Gigahertz Spectroscopy via SQUID-on-Tip DC Readout

Senne Vervoort; Lukas Nulens; Julia Baumgarten; Daan B. Boltje; Jessalyn DeVine; Alejandro V. Silhanek; Joris Van de Vondel; Kaveh Lahabi

arXiv · 2610.35737

Local Broadband Gigahertz Spectroscopy via SQUID-on-Tip DC Readout

Senne Vervoort·Lukas Nulens·Julia Baumgarten·Daan B. Boltje·Jessalyn DeVine·Alejandro V. Silhanek·Joris Van de Vondel·Kaveh Lahabi

View original source ↗Read source document ↗Export metadata ↓

Abstract

Superconducting microwave circuits are shaped by their local electromagnetic environment, yet standard microwave measurements do not resolve the local fields and device features that govern their behavior. Here, we combine microwave spectroscopy, nanoscale magnetic sensing, and topographic imaging in a single tapping-mode SQUID-on-tip microscope. The nonlinear Josephson response converts local GHz excitations into Shapiro steps, enabling quantitative measurements of microwave frequency signals and their excitation strength using only DC readout. Applied to a superconducting coplanar waveguide resonator, local spectroscopy reproduces the power-dependent resonance and nonlinear bifurcation observed in microwave transmission measurements. Spatially resolved measurements map the microwave response while simultaneously recording topography and static magnetic features, including vortices and Meissner screening currents. Electromagnetic simulations reveal how coupling through the superconducting probe leads limits spatial resolution and guides localized detector designs. Together, these capabilities establish a platform for correlating microwave circuit dynamics with the local structural and magnetic environment of superconducting devices.

Explore related subjects

cond-mat.supr-con

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Senne Vervoort, Lukas Nulens, Julia Baumgarten, Daan B. Boltje, Jessalyn DeVine, Alejandro V. Silhanek, Joris Van de Vondel, Kaveh Lahabi. 2026-10-26. Local Broadband Gigahertz Spectroscopy via SQUID-on-Tip DC Readout. https://arxiv.org/abs/2610.35737

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Interlayer Phase Locking and Sliding Select Topological Melting Channels in Superconducting Bilayers

Topological transitions in coupled superconducting layers are intertwined: an elementary vortex in one layer carries both common and relative phase winding. We study a Josephson-coupled bilayer in an in-plane magnetic field using renormalization-group analysis and Monte Carlo simulations of the compact layer phases. The field drives Pokrovsky--Talapov (PT) entry of interlayer solitons, and free-energy calculations in fixed soliton sectors show PT square-root scaling over the sampled densities at finite temperature. Interlayer phase locking and sliding then select distinct Berezinskii--Kosterlitz--Thouless (BKT)-like melting channels. The locked commensurate phase melts through same-vorticity layer pairs when the geometric-mean common helicity modulus $Υ_{+,g}$ reaches $T/(2π)$, with layer correlation exponent $η_l=1/4$. A stable sliding incommensurate phase melts through elementary layer vortices on a line of BKT fixed points, where $Υ_{+,g}+Υ_{-,g}=2T/π$ and $η_l$ is set by the ratio of the relative and common moduli. When the relative helicity modulus is identified with the relative-phase stiffness, our simulations agree with this prediction, and the common superfluid stiffness at incommensurate melting is nearly twice its value at commensurate melting. Near soliton entry, however, the dilute sliding state is unstable to opposite-vorticity layer pairs. Our results connect PT soliton entry with field-tunable BKT-like melting and identify the pair-stability condition that links them.

cond-mat.supr-con↗

arXiv2026

Time-Reversal Symmetry Breaking in the Centrosymmetric Nonsymmorphic Superconductor RuB2

Centrosymmetric nonsymmorphic AB2 (A = Ru, Os) borides exhibit anomalous superconducting properties, but the microscopic nature of their superconducting ground state remains unresolved. Here, we investigate RuB2 using zero- and transverse-field muon spin relaxation (muSR), first-principles electronic-structure calculations, and Ginzburg-Landau symmetry analysis. Zero-field muSR reveals spontaneous internal magnetic fields below Tc = 1.6 K, providing direct evidence for time-reversal symmetry breaking (TRSB). Transverse-field measurements establish a fully gapped superconducting state, with a gap magnitude close to the BCS weak-coupling limit. Density-functional calculations show that RuB2 is a multiband Z2 topological metal with appreciable spin-orbit coupling. Guided by the experimental observations and the symmetry of the orthorhombic crystal structure, our Ginzburg-Landau analysis suggests that an internally antisymmetric, nonunitary spin-triplet state is a promising candidate for the superconducting order parameter. This candidate is consistent with both the observed TRSB and the fully gapped superconducting state. These results establish RuB2 as a promising platform for investigating unconventional superconductivity arising from the interplay of crystal symmetry, multiband electronic structure, and spin-orbit coupling, and motivate further studies of related nonsymmorphic borides. The two muSR measurements provide complementary constraints: zero-field data probe spontaneous magnetism associated with TRSB, while transverse-field data characterize superconducting field distribution and support a full gap. The topological electronic structure and spin-orbit coupling provide context for unconventional pairing. Although these results do not uniquely determine the order parameter, they narrow candidates and highlight that nonsymmorphic symmetry may shape superconductivity in RuB2.

cond-mat.supr-con↗

arXiv2026

Magnetic susceptibility and superfluid density of inhomogeneous superconducting films: the Tc-mosaic model

Whole-sample and mutual-inductance part-sample measurements of the linear magnetic susceptibility, $χ$, of superconducting films are routinely used to obtain the London penetration depth, $λ(T)$, assuming uniform superconductivity. However, spatially resolved probes show that many films of current interest are inhomogeneous on micrometer scales. Here we ask whether a distribution of local transition temperatures in a fully gapped film can produce an apparent line-nodal, $T$-linear $λ(T)$. The film is modeled as a random Voronoi mosaic of domains with $T_c$ distributed between $T_{c,\min}$ and $T_{c,\max}$ with s-wave (also d-wave, for comparison) London response inside each domain. We show that detectable screening appears only below the percolation temperature, $T_p$, and the transition broadens with the spread of $T_c$. For s-wave domains, $λ(T)$ remains activated for any $T_{c,\min}>0$. Only for $T_{c,\min}=0$ does it become a power law, $Δλ\propto T^n$ with $n\approx1.7$, but then the onset of screening drops to $T_p=T_{c,\max}/2$. Weighting the $T_{c}$ distribution towards $T_c\to0$ (more low-$T_{c}$ domains) can bring $n$ closer to 1 ($n\approx1.2$), but simultaneously pushes the apparent transition, $T_p$, more than an order of magnitude below $T_{c,\max}$. For d-wave domains, the linear term survives, and its relative slope is enhanced almost fourfold for $T_{c,\min}=0$. Hence, a $T$-linear $λ(T)$ measured in a film with screening onset within a factor of a few of $T_{c,\max}$ by whole-sample or mutual-inductance part-sample measurements cannot originate from $T_c$ mosaicity in a fully gapped superconductor.

cond-mat.supr-con↗