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Physics Condensed Matter Mesoscale and Nanoscale Physics

cond-mat.mes-hall Watch Mesoscale and Nanoscale Physics

Sunday 30 August

Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

Controlling the Coupling Strengths in Nanophotonic Networks using Modified Yagi-Uda Nanoplasmonic Antennas

Vidar Flodgren and Anders Mikkelsen

On-chip communication in optical neural networks is commonly done via waveguides which results in large system footprints. A compact alternative is to broadcast light signals between nano-optoelectronic components in free space and tailor the light field distribution using sub-wavelength nanophotonics. We propose and simulate nanoplasmonic metal structures in combination with III-V nanowire emitters and receivers to create an optical network in which the shape and position of these nanostructures create varying weights between the nano-optoelectronic nodes. Using Finite Difference Time Domain modelling, we investigate systems of experimentally verified nanowire optoelectronics combined with nanoplasmonic structures that can be made in the same fabrication step as electrical contacts powering the nanowires. We investigate both individual nanowire/antenna devices as well as networks corresponding to two layers in a neural network. We show that directed communication from a nanowire node can be significantly altered using Yagi-Uda antennas. Modifying the antenna with an asymmetric director component enables the directing of light several different angular directions simultaneously. We find that highly variable complex weight distribution between the connections in two seven node layers can be achieved depending on the combined geometry of the antenna components. The possible weight distributions in compact layers of nanowire nodes could be used for creating a variety of neural networks with complex connectivity. The concepts can be generalized to other types of nanoscale emitter/receiver systems.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.supr-con

Ballistic-to-Localized Dynamics as Signature of Quantum Phase Transition in Josephson Junction

F. G. Capone, A. de Candia, G. Di Bello et al. (+5 more)

Using state-of-the-art numerical techniques, we investigate how quantum phase fluctuations and quasiparticle tunneling shape the behavior of a small-capacitance Josephson junction across Ohmic, sub-Ohmic, and super-Ohmic dissipation regimes. We show that increasing the Ohmic dissipation strength drives a Berezinskii-Kosterlitz-Thouless quantum phase transition at thermodynamic equilibrium. Deviations from Ohmic behavior profoundly alter this scenario: the super-Ohmic regime exhibits no phase transition, whereas the sub-Ohmic regime displays a continuous second-order transition, consistent with the universality classes of the spin-boson model. Within the Ohmic regime, real-frequency linear-response calculations reveal that the phase particle does not undergo the commonly assumed diffusive-to-localized crossover. Instead, finite resistance progressively suppresses the singular zero-frequency response, producing a ballistic-to-localized change in the dynamics. At finite frequencies, coupling to the environment generates a long-lived excitation in the charge response, which evolves into a resonance as the subgap and shunt resistances are reduced.
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All authors F. G. Capone, A. de Candia, G. Di Bello, V. Cataudella, R. Fazio, N. Nagaosa, C. A. Perroni, G. De Filippis

Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

Localization in microcavities revealed by phase-space non-Hermitian skin effect

Jung-Wan Ryu, Yong-Hoon Lee, Muhan Choi et al. (+2 more)

Contrary to the semiclassical expectation for fully chaotic systems, localization of resonances is found to be a common feature in open microcavities. In spiral-shaped dielectric microcavities, a substantial fraction of resonances localize on polygonal patterns in real space, are chiral, and their momentum distributions accumulate near the critical line for total internal reflection. Despite the extensive investigation, the physical mechanism responsible for their remarkable abundance has remained a long-standing question. Addressing this, we reveal a physical correspondence between an inhomogeneous-loss Hatano-Nelson model and the dielectric phase space of a spiral microcavity. We show that the combination of geometry-induced momentum drift and refractive escape yields a generalized non-Hermitian skin effect in the phase space momentum. We identify this mechanism as the origin of the critical-line localization of resonances in open chaotic spiral microcavities, extending the skin-effect concept beyond nonreciprocal lattices to phase space and to open chaotic wave systems.
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All authors Jung-Wan Ryu, Yong-Hoon Lee, Muhan Choi, Chang-Hwan Yi, Martina Hentschel

Mesoscale and Nanoscale Physics

Josephson-Phase Reversal of Non-Bloch Andreev Propagation

X. Z. Zhang and Hechen Ren

Non-Hermitian control is difficult in solid-state systems due to fixed dissipation. Here, we show that in a spin-orbit-coupled planar Josephson junction, changing only the Josephson phase reverses the non-Bloch propagation of a low-energy Andreev band and switches its boundary accumulation between junction edges. The phase reshapes the band's spin and electron-hole composition, causing a fixed reservoir to unequally attenuate counterpropagating modes. Weak-loss theory links this phase-controlled loss imbalance to boundary-selected complex momenta, offering an in situ route to reconfigurable non-Hermitian transport in superconducting platforms.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.supr-con

Magnetic contacts on freestanding superconducting LaAlO$_3$/SrTiO$_3$ micromembranes

Thies Jansen, Pinelopi Konstantinopoulou, Niklas Martin et al. (+5 more)

The superconducting two-dimensional electron gas (2DEG) at the LaAlO$_3$/SrTiO$_3$ (LAO-STO) interface is a promising platform for superconducting spintronics, however, integrating ferromagnetic contacts with the superconducting 2DEG remains challenging. Here, we realize superconducting LAO-STO micromembrane devices contacted by ferromagnetic nickel contacts through a side-contact geometry. Low-temperature transport measurements demonstrate that superconductivity is preserved in the presence of the ferromagnetic contacts. We show that the superconducting state is strongly influenced by the magnetic history of the nickel contacts, which generates a tunable effective magnetic field in the 2DEG. Through an effective field model, the magnetization of the contacts can be inferred from the maximum superconducting response. Our results establish ferromagnetically contacted LAO-STO as a platform for future investigations of spin injection into oxide superconductors and provide a route towards superconducting spintronic devices based on complex oxide interfaces.
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All authors Thies Jansen, Pinelopi Konstantinopoulou, Niklas Martin, Fabio Miletto Granozio, Alessia Sambri, Rasmus Bjørk, Felix Trier, Thomas S. Jespersen

Mesoscale and Nanoscale Physics

Localized orbitals and tunnel couplings from general confinement potentials in gate-defined quantum-dot arrays

Bohdan Khromets, William Chow and Jonathan Baugh

Efficient simulation of dense gate-defined multi-quantum-dot arrays requires accurate and scalable modeling methods, compatible with asymmetries and imperfections of realistic voltage-controlled confinement potentials. We present a numerical localization procedure that rotates the eigenbasis of a general one-particle effective orbital Hamiltonian into $s$-, $p$-, $d$-, $\ldots$-shells of localized orbital wavefunctions associated with individual quantum dots. The pairwise tunnel couplings between such states are computed directly as matrix elements of the Hamiltonian. We demonstrate this procedure on a 2D triangular Si-MOS triple-quantum-dot array by obtaining the voltage dependencies of the tunnel couplings and their distributions in the presence of disorder. We discuss the implications of this evaluation method on the many-body calculations, and relate it to the experimental tunnel coupling measurements.
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Mesoscale and Nanoscale Physics

Harnessing the skyrmion Hall effect for low-power skyrmion transport in a tubular synthetic antiferromagnet

Ivan P. Miranda, Grzegorz J. Kwiatkowski, Jacob J. Mankenberg et al. (+4 more)

We show that optimal control can turn the skyrmion Hall effect from a source of typically unwanted transverse motion into a mechanism for reducing Ohmic losses in skyrmion transport. We consider a pair of antiferromagnetically coupled skyrmions confined to a tubular geometry, where their relative transverse displacement becomes a periodic internal coordinate. The skyrmion Hall effect drives this coordinate, while finite interlayer coupling makes the resulting relation between applied current and longitudinal velocity nonlinear, allowing different current protocols to produce the same prescribed average velocity. We determine which of these protocols minimizes Joule heating. Depending on the interlayer coupling and spin-transfer-torque parameters, the optimal current is either constant, with the skyrmion pair maintaining a fixed relative position, or time dependent, with the pair undergoing periodic relative motion around the tube. In either case, the additional internal degree of freedom created by the skyrmion Hall effect and interlayer coupling enables skyrmion transport at a lower power than in the uncoupled limit.
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All authors Ivan P. Miranda, Grzegorz J. Kwiatkowski, Jacob J. Mankenberg, Cecilia M. Holmqvist, Igor S. Lobanov, Valery M. Uzdin, Pavel F. Bessarab

Mesoscale and Nanoscale Physics

Extreme Polarization of the Optical Gap and High-Energy Exciton Landscape in CrSBr

Sayantan Patra, Sourabh Jain, Bhumika Chauhan et al. (+8 more)

We reveal a strongly anisotropic excitonic landscape in monolayer and bulk-like CrSBr using optical absorption spectroscopy and $GW$-Bethe-Salpeter equation $\textit{ab initio}$ calculations. The direct absorptive determination of the lowest bright optical onsets i.e. $X_0^a$ and $X_0^b$ excitons for the two in-plane polarization eigenaxes yield an in-plane optical gap anisotropy of $470 \pm 15$ meV. This is the highest observed value for any material in the near-infrared-to-visible spectral region to the best of our knowledge. Energetically above, we identify multiple strongly polarized excitons spanning $1.25$ eV to $3.1$ eV selectively aligned along the two orthogonal axes. A resonance $X^-$, located $24$ meV below the $X_0^b$ progressively transfers oscillator strength to $X_b^0$, a behavior consistent with a coupled trion (Fermi-polarion)/exciton pair. Our experiments also provide polarization-resolved broadband dielectric functions of CrSBr. These results establish CrSBr as a strongly polarization-selective excitonic system and highlight its potential for polarization-selective optoelectronics enabled with its large optical-gap anisotropy.
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All authors Sayantan Patra, Sourabh Jain, Bhumika Chauhan, Marie-Christin Heißenbüttel, Abhisek Saidarsan, Ranjuna M. K., Kseniia Mosina, Zdeněk Sofer, Michael Rohlfing, Thorsten Deilmann, Ashish Arora

Saturday 29 August

Mesoscale and Nanoscale Physics

Heavy-Hole–Light-Hole Mixing and Spin–Photon Coupling in Germanium Flopping-Mode Qubits

Jose Reina-Gálvez and Guido Burkard

Intrinsic spin–orbit interaction in germanium provides electrically active flopping-mode qubits without requiring magnetic-field gradients to generate spin–charge hybridization. We study double quantum dots (DQDs) with a multiband Luttinger–Kohn framework that retains heavy-hole (HH) and light-hole (LH) states on equal footing. Modeling vertical confinement with a finite confinement potential along the growth direction brings selected subbands into a regime of appreciable HH–LH mixing. This admixture activates electric-dipole spin-coupling through LH–LH and LH–HH transitions, complementing the conventional HH–HH pseudospin-flip resonance. For the parameter sets considered, these additional channels can produce larger spin–photon figures of merit than the HH–HH transition. HH–LH mixing thus supplies a tunable ingredient for qubit–cavity coupling in germanium hole-spin qubits and extends the operating regimes available to circuit-QED architectures.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci

Single-pulse strain-induced precessional dynamics of magnetization in Co-doped iron garnet

Héloïse Damas, Carl S. Davies, Tomasz Zalewski et al. (+4 more)

Ultrafast control of magnetization through lattice excitation provides a route to manipulating magnetic order on short timescales, yet the role of transient strain in driving magnetization dynamics remains poorly understood. Here, single-shot pump-probe magneto-optical microscopy is used to resolve the structural and magnetic responses of cobalt-doped yttrium iron garnet to individual 5-ps mid-infrared pulses. The excitation generates a localized strain field together with an outward-propagating elastic wave. Concurrently, the magnetic contrast decreases following excitation and subsequently reverses on a timescale of approximately 1.5-2 ns before recovering to its initial state. The structural and magnetic responses exhibit closely correlated wavelength and pulse-energy dependences, indicating a common excitation pathway. Micromagnetic simulations incorporating transient strain reproduce the precessional reorientation of the magnetization within individual domains while largely preserving the labyrinthine domain morphology. These results identify transient lattice deformation as the link between single-pulse mid-infrared excitation and reversible precessional magnetization dynamics in Co-doped yttrium iron garnet.
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All authors Héloïse Damas, Carl S. Davies, Tomasz Zalewski, Petr M. Vetoshko, Vladimir I. Belotelov, Andrzej Stupakiewicz, Andrei Kirilyuk

Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Probabilistic generation of two-mode binomial cat states using cross-Kerr interactions

S. Zhao, A. Metelmann and S. Qvarfort

Superpositions of macroscopically distinct coherent states, or cat states, are a key resource for quantum technologies. In particular, two-mode binomial cat states can give rise to exact quantum error correction in continuous-variable quantum computing. However, their preparation typically requires non-Gaussian initial states, such as Fock or NOON states, which are challenging to realize experimentally. Here, we propose a protocol to generate two-mode binomial cat states where the only requirements are Gaussian initial states in combination with heralded heterodyne measurements. Our approach utilizes cross-Kerr interactions between bosonic modes commonly realizable in superconducting circuit architectures. We show that by adjusting the input state parameters, our protocol remains robust to dissipation under realistic experimental conditions. Our work provides a practical route to realizing multinomial cat states in current experimental platforms without requiring non-Gaussian initial resources, overcoming a key limitation of existing preparation schemes.
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Mesoscale and Nanoscale Physics

Quantitative Disentanglement of Terahertz Spin and Orbital Pumping in 3d Ferromagnetic Heterostructures

Tongyang Guan, Jiahao Liu, Yuxiao Mo et al. (+3 more)

Spin and orbital pumping - the injection of spin and orbital angular momentum from a driven ferromagnet into an adjacent nonmagnetic layer - are fundamental processes underlying angular-momentum generation and transport in magnetic heterostructures. Femtosecond optical excitation extends these phenomena into the ultrafast regime, where spintronic terahertz emission spectroscopy (STES) detects picosecond angular-momentum currents in a contact-free manner through spin-to-charge and orbital-to-charge conversion. Microscopic theory predicts that orbital-pumping efficiency increases from Fe to Ni across the 3d series, yet whether these predictions hold under ultrafast excitation remains unclear. A central challenge is that spin and orbital currents are generated simultaneously and contribute additively to the same terahertz emission, preventing their quantitative separation. Here, we overcome this limitation by combining STES with wedge-sample thickness control in heterostructures whose nonmagnetic layers (Ta, W, and Nb) have spin Hall and orbital Hall angles of opposite signs. The two angular-momentum channels therefore exhibit distinct emission polarities and thickness dependences, enabling their quantitative decomposition. Systematic measurements on Fe, Co, and Ni heterostructures reveal that the orbital-pumping contribution increases progressively toward Ni, reaching several tens of percent of the spin-current contribution - far exceeding theoretical predictions. Even Fe generates a non-negligible orbital current that becomes essential in the thin-nonmagnetic-layer regime. The extracted orbital diffusion lengths are consistently shorter than spin diffusion lengths and increase with decreasing spin-orbit coupling strength of the nonmagnetic layer. These results establish a quantitative framework for ultrafast spin and orbital pumping in magnetic heterostructures.
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All authors Tongyang Guan, Jiahao Liu, Yuxiao Mo, Liangliang Zhu, Yizheng Wu, Zhensheng Tao

Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci

Directional commensurability stabilizes structural superlubricity in patterned mesoscale interfaces

Viet Hung Ho, Ge Li, Melisa M. Gianetti et al. (+3 more)

Structural superlubricity, arising from lattice incommensurability, offers a promising route to eliminate friction and associated energy losses in mechanical systems. In real-world systems, roughness and wear currently pose severe limitations on its robustness and especially the contact size. Here, we consider patterned surfaces as a possible route to overcome some of these limitations. We show that the simplest choice of patterning, contacts made up of two incommensurate triangular-triangular patterns, fails at elevated loads because of the small number of load-bearing contacts, causing the maximum local contact pressure to exceed the strength of the superlubric coating. We introduce a square-triangular patterned interface that increases the number of load-bearing contacts and organizes them into continuous contact lines. When sliding along specific directions relative to these lines, superlubricity is maintained at significantly higher loads by reducing pressure-induced coating failure while also remaining somewhat tolerant to surface imperfections. These findings establish a mechanism for stabilizing structural superlubricity against coating failure and a design principle for engineering low-friction interfaces with enhanced load-bearing capacity and defect tolerance.
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All authors Viet Hung Ho, Ge Li, Melisa M. Gianetti, Bjørn Haugen, Graham L. W. Cross, Astrid S. de Wijn

Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.stat-mech

Light-induced nonconservative static forces in many-body systems

Jinze Li, Xuemei Yang and Zhiyuan Sun

In a quantum many-body system, a periodic drive can often generate effective static forces on the slow collective degrees of freedom. We study the static forces generated by light on electronic order parameters in solid-state systems. We show that the forces can have nonconservative components that originate from dissipation, i.e., optical absorption. This effect is demonstrated in two nontrivial examples. In excitonic insulators, via interband excitations, the light field generates a nonconservative force on the phase of the excitonic order parameter. This force leads to an acceleration of the phase, which manifests as a shift of the photon emission peak from an exciton condensate. In materials with an incommensurate charge density wave, a propagating light field generates a nonconservative force on the phase of its order parameter. It drives the charge density wave into sliding motion, leading to a DC electric current via topological Thouless pumping.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el

Real-space manifestation of ferroic multipoles in altermagnetic MnF$_2$

Iurii Kibalin, Dalila Bounoua, José A. Rodriguez Velamazán et al. (+9 more)

Altermagnets are unconventional spin split magnets arising from the zero spin-orbit coupled limit. They host a magnetic multipolar order parameter yet direct real-space observation of these multipoles has remained elusive. Here we use polarized-neutron diffraction to reconstruct the three-dimensional magnetization density of the prototypical altermagnet MnF$_2$. By exploiting symmetry-selective magnetic reflections, we separate the dominant spherical Mn$^{2+}$ contribution from the much weaker anisotropic Mn magnetization and the covalent spin polarization of the fluorine ligands. The reconstructed spin density reveals a finite fluorine ion moment together with an anisotropic Mn magnetization consistent with the symmetry-allowed altermagnetic rank-5 magnetic multipole $O_{52}$(magnetic triacontadipole). These results provide direct real-space evidence of ferroic multipolar order in an altermagnet and establish polarized-neutron diffraction as a powerful probe of hidden magnetic multipoles in quantum materials.
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All authors Iurii Kibalin, Dalila Bounoua, José A. Rodriguez Velamazán, Oscar Fabelo, Navid Qureshi, Quentin Faure, Philippe Bourges, Victor Balédent, Jian-Rui Soh, Jeffrey Rau, Paul McClarty, Arsen Gukasov

Mesoscale and Nanoscale Physics

Probing spin order via magnon transmission across quantum Hall ferromagnet heterojunctions

Seung Hwan Lee, Shaowen Chen, Andrew T. Pierce et al. (+4 more)

Two-dimensional material platforms now host a remarkable array of exotic correlated phases, from unconventional superconductivity to fractional Chern insulators. Probing magnetic order in these systems is essential for understanding their underlying physics, yet dilute spin densities render conventional magnetic probes ineffective. Spin waves, or magnons, in quantum Hall ferromagnets (QHFM) have proven effective for probing the magnetic order in various symmetry-broken quantum Hall (QH) phases in graphene systems, but previous works have been limited to homojunction configurations within a single material. Here, we demonstrate magnon transmission across a monolayer-bilayer graphene quantum Hall ferromagnet heterojunction - the first magnon transmission across quantum Hall ferromagnet heterojunctions, using one material as a magnon source to probe magnetic order in a distinct material. Generating magnons in monolayer graphene (MLG) at $\nu$ = 1, we detect their transmission through bilayer graphene (BLG) via nonlocal voltage measurements, revealing spin order in BLG symmetry-broken quantum Hall states. The transmission exhibits hallmark magnon signatures: a sharp onset at the Zeeman energy and systematic variation with Landau level filling, including suppression at $\nu$ = 4 and 8 where spin polarization vanishes. Our findings establish heterojunction magnon transmission as a powerful, modular probe of magnetic order, opening new avenues for investigating exotic quantum states across the rapidly expanding family of two-dimensional materials.
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All authors Seung Hwan Lee, Shaowen Chen, Andrew T. Pierce, Patrick R. Forrester, Kenji Watanabe, Takashi Taniguchi, Amir Yacoby

Mesoscale and Nanoscale Physics

Fractional Impurity Entropy from Potential Scattering in a Free Electron Gas

Syeda Neha Zaidi and Jukka I. Väyrynen

Fractional changes in entropy are often associated with strong electron correlations or non-Abelian anyons in topological systems. We show that neither condition is necessary – a system of free electrons on a ring scattering off a repulsive point-like impurity undergoes a $k_B\ln\sqrt 2$ entropy change as the impurity strength is increased. This effect arises from a shift of allowed single-particle momenta from integer quantization to half-integer quantization, induced by the impurity. We show that this fractional entropy change is universal across a broad class of single-particle dispersions, demonstrating that such signatures can arise without strong correlations or topological order.
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Mesoscale and Nanoscale Physics

Surface-mediated frequency aging beyond quality-factor saturation in an AlScN-on-silicon resonator

S M Enamul Hoque Yousuf, Mahmudul Hasan, Shruti Mishra et al. (+3 more)

Vacuum package integrity in micro- and nanoelectromechanical resonators is commonly assessed through the quality factor Q, although Q probes residual-gas damping rather than the surface-state evolution that can govern frequency aging. Here, we disentangle the pressure responses of Q and the resonance frequency f0 in a 64.21 MHz Al0.7Sc0.3N-on-silicon cross-sectional Lamé-mode resonator between 0.01 to 760 Torr. Measurements at 25 {\deg}C and at the 68.8{\deg}C frequency turnover, where first-order thermal sensitivity is suppressed, reveal widely separated equilibration timescales. Following each pressure step, Q reaches a reversible, history-independent steady value on the pressure-control timescale and approaches a fitted pressure-independent ceiling of 8.5e4 below approximately 1 Torr. By contrast, f0 responds measurably down to 1e-5 Torr and remains history-dependent, relaxing for hours at fixed pressure. The transients follow stretched-exponential kinetics, consistent with a broad distribution of surface relaxation rates, and individual pressure steps produce fractional frequency shifts as large as 1.9 ppm. Ten-hour phase-locked measurements show a common short-term time-deviation floor near 1e-10 s from 0.01 to 100 Torr, whereas residual deterministic relaxation dominates at long averaging times; at 760 Torr, gas damping degrades short-term tracking through the reduced Q. These results establish gas-damping equilibrium and frequency equilibrium as distinct states. Quality-factor saturation alone is therefore insufficient to qualify vacuum packaging for precision mechanical frequency references; package specifications must also constrain surface-mediated frequency aging.
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All authors S M Enamul Hoque Yousuf, Mahmudul Hasan, Shruti Mishra, Sourav Mukherjee, Jinghan Gao, Roozbeh Tabrizian

Friday 28 August

Mesoscale and Nanoscale Physics

Graphene-enabled dynamic H-J switching of dipole-dipole coupling

Michael McFadden and Robert Bennett

Environmental modification of dipole interactions has long been explored in energy transport. Here we consider the effects of a tunable graphene monolayer upon nearly H-type or J-type molecular aggregates, concentrating on the inversion of one type of coupling to the other. Modelling the graphene as being deposited on a metallic substrate, we find that as the surface conductivity of the graphene is varied, there is a corresponding change in the parameter region over which coupling inversion is predicted. This provides a route towards observing the predicted coupling inversion in a real system by dynamically changing the surface conductivity during a single run of an experiment.
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Mesoscale and Nanoscale Physics

Coherent phononic frequency combs in ferroelectric CMOS oxides

Jinghan Gao, Shruti Mishra, Yilin Kou et al. (+3 more)

Modern electronic systems require tens of clock and carrier frequencies, each synthesized by a dedicated phase-locked loop from a shared reference, imposing routing, power and synchronization burdens that grow with every domain. Optical frequency combs solved this problem in photonics, whereas electronics has lacked an equivalent source in its native radiofrequency domain. Here we report broadband phononic frequency combs in ferroelectric hafnia-zirconia nanoelectromechanical resonators built from complementary metal-oxide-semiconductor (CMOS) oxides. Lithographically defined detuning of a 2:1 internal resonance selects the generation mechanism: two-tone-seeded wave mixing yields more than 170 lines distributed over two octaves, with mutual coherence verified for representative pump and generated lines, whereas an autonomous Hopf route yields hierarchical combs of more than 200 lines through torus and period-doubling dynamics, in agreement with slow-flow bifurcation theory. Geometric scaling extends comb generation across 0.44 GHz to 2.1 GHz. Heterodyne measurements, analyzed using the modified Allan deviation (MDEV), establish a two-timescale law. The mechanism governs short-term stability: seeded combs inherit the white-phase-noise scaling of their pumps, whereas autonomous combs acquire the phase diffusion of a free-running oscillator, with the one-second MDEV increasing from 1e-11 to 1e-8. The material governs long-term stability: in air and without active thermal control, the temperature-compensated stack suppresses the random-walk drift that dominates uncompensated resonators. These results establish mechanism- and material-level design rules for operating a single resonator as chip-scale frequency infrastructure, from multi-clock generation to radiofrequency parallel processing.
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All authors Jinghan Gao, Shruti Mishra, Yilin Kou, S M Enamul Hoque Yousuf, Hanna Cho, Roozbeh Tabrizian

Mesoscale and Nanoscale Physics

Chiral Tubular Magnonic Crystals with Periodic Dzyaloshinskii–Moriya Interaction

P. Contreras-Gallardo, J. Flores-Farias, B. Mimica-Figari et al. (+3 more)

We introduce a chiral tubular magnonic crystal formed by a ferromagnetic nanotube with a periodically modulated interfacial Dzyaloshinskii–Moriya interaction (DMI). Using a plane-wave formalism adapted to the cylindrical geometry, we calculate the spin-wave band structure including exchange, nonlocal dipolar coupling, and interfacial DMI. We show that the tubular geometry qualitatively modifies the role of periodic DMI compared with planar chiral magnonic crystals. Besides producing the usual nonreciprocal frequency shift, curvature converts part of the interfacial DMI into an effective anisotropy-like internal field. This creates a sign-dependent frequency landscape along the tube, so that DMI-covered regions can act either as potential wells or barriers for the lowest-frequency modes. As a result, flat and weakly dispersive bands appear in both Damon–Eshbach-like and backward-volume-like configurations, with the latter having no direct counterpart in planar systems. Our results identify periodically engineered DMI in nanotubes as a route for controlling nonreciprocal spin waves, localized modes, and flat magnonic bands in curved architectures.
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All authors P. Contreras-Gallardo, J. Flores-Farias, B. Mimica-Figari, V. Puliafito, P. Landeros, R. A. Gallardo

Mesoscale and Nanoscale Physics

Design and Modeling of the Charge Readout of a SiMOS Quantum Dot with a Single Electron Transistor and CryoCMOS

Adam Quinn, Troy England, Andrew Li et al. (+1 more)

Single electron spin qubits trapped in SiMOS quantum dots are a promising technology for scaling to thousand- or million-qubit systems due to their compatibility with mature CMOS manufacturing processes. A readout system that combines a single electron transistor with a custom cryogenic CMOS amplification and digitization chain offers key advantages by avoiding the use of bulky RF components or room-temperature interconnects. We present design techniques and simulation results for an optimized qubit-SET cryoCMOS interface, culminating in the design of the QNDR1 ASIC, the first cryogenic readout ASIC designed under the Quandarum project, which targets the development of a many-channel spin qubit based detector for use in high energy physics.
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All authors Adam Quinn, Troy England, Andrew Li, Sharmila Mustari Nandita

Mesoscale and Nanoscale Physics

Electrochemical impedance spectroscopy of graphene nanogaps

Patrick A. McKee, Chris S. DeMellier, Robin N. Schipper et al. (+1 more)

Graphene nanogaps represent an emerging platform for nanoscale electrochemical and sensing devices, with potential applications in next-generation biomolecular sequencing. However, their interfacial behavior in aqueous environments remains poorly characterized, particularly with respect to frequency-dependent impedance and charge transport mechanisms at the graphene edge. We fabricate graphene nanogaps by controlled electrical breakdown in an inert atmosphere and study their electrochemical response. Upon exposure to ambient conditions, a surface contamination layer supports electrochemical activity within an adsorbed ultrathin conductive film between the graphene edges. Electrochemical impedance spectroscopy reveals distinct frequency-dependent responses consistent with a Warburg element associated with diffusion in this confined interfacial film. The impedance evolves systematically with liquid $\mathrm{p}H$, reflecting changes in electrochemical reaction-diffusion processes at the graphene edges. A quantitative equivalent-circuit model captures these effects and enables extraction of an effective nanogap length scale from impedance spectra, providing information complementary to that obtained from tunneling measurements.
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All authors Patrick A. McKee, Chris S. DeMellier, Robin N. Schipper, Henk W.Ch. Postma

Mesoscale and Nanoscale Physics

Domain walls with alternating magnetic order in a model with dipolar coupling

G. M. Wysin

A model for a one-dimensional chain of elongated nano-scale magnetic islands with dipole interactions is analyzed here for the properties of its static domain walls with site-by-site alternating order. The anisotropic magnetic islands on a nonmagnetic substrate have their longer axes oriented transverse ($y$-direction) to the chain direction ($x$-direction), in a transverse applied magnetic field. The islands' magnetic dipoles $\vec{\mu}_n$ are represented as macrospins of fixed length $\mu$. The nearest-neighbor (NN) dipole interactions drive transverse alternating order, allowing for doubly-degenerate, uniform, static, $y$-alternating states, where the dipoles alternately point transverse to the chain direction, as in $\vec{\mu}_n = \pm(-1)^n \mu \hat{y}$. Assuming only NN interactions, the domain walls connecting these two alternating states are found with numerical relaxation simulations and analyzed in a two-sublattice continuum theory. As the uniaxial anisotropy constant $K_1$ descends from larger values until it closely approaches the NN dipolar coupling constant $D$, the domain wall width grows indefinitely, and the large-$x$ continuum solutions closely approach the lattice numerical solutions. The applied field produces a very slight canting of the dipoles towards the field, maximum in the center of the domain wall. The dipoles on the two sublattices are found to rotate in opposite senses as one scans along the lattice, resulting in a large longitudinal magnetic moment of the domain wall. A much smaller transverse magnetic moment has a topological contribution that depends on whether the chain length is odd or even.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

Dissipation across the ultrastrong-coupling regime of nanomechanical quantum Rabi systems

Janine C. Franz and Fabio Pistolesi

Mechanical resonators ultrastrongly coupled to quantum two-level systems provide a promising route towards mechanical qubits by introducing significant anharmonicity to the mechanical modes, particularly in the slow-oscillator regime. Although the resulting hybrid system is well described by the quantum Rabi model, a consistent treatment of dissipation remains challenging across the broad parameter space routinely probed in current nanotube electromechanical devices. Here, we investigate dissipation in the open quantum Rabi model using a Born-Markov framework based on the slowly varying bath spectrum approximation, yielding a Lindblad master equation applicable far beyond conventional descriptions while recovering them in their respective limits. Using this framework, we analyze experimentally accessible observables across this parameter space. As the secular approximation breaks down, phonon blockade progressively washes out. Our approach remains valid in this regime, enabling a quantitative description of the continuous evolution of phonon blockade with coupling strength and dissipation. At finite temperature, we find a suppression of the temperature-induced increase of coherence decay rate for weak anharmonicity. Under driving, our approach remains applicable to substantially stronger perturbations than conventional dressed-state master equations and shows that an apparently classical observable can coexist with Wigner negativity. We further capture the weakly anharmonic regime arising from finite detuning in the double-quantum dot. These results establish a unified description of dissipation from weakly anharmonic operating regimes to the strongly anharmonic mechanical-qubit regime and provide experimentally relevant predictions for ultrastrong electromechanical systems.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.dis-nn

Fractal Confinement and Magnetic Self-sabotage of Current Flow: Electrons Near the Metal-insulator Crossover in a 2D $\delta$-layer

Xinghai Zhang, Matthew S. Foster and Markus Mueller

We study low-$T$ transport and itinerant magnetism in 2D $\delta$-doped semiconductors. Large-scale Hartree-Fock calculations with random hoppings and repulsion $U_0$ reveal two transport regimes near a critical density. The conductivity $\sigma(T)$ initially increases as $T$ drops below $U_0 / 10$. However, at $T \sim U_0/100$, a tiny density of magnetic moments forms, driving an insulating downturn. Fractal wavefunctions locally amplify magnetic interactions, initially concentrating currents into branched filaments, but ultimately choking them off via dynamic SU(2) symmetry breaking.
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Mesoscale and Nanoscale Physics

Statistical Properties of a Fluctuation-Driven Nanomechanical Duffing Resonator

Monan Ma, Nathan Welles, Johnathon Barbish et al. (+5 more)

We investigate the fluctuating nonlinear dynamics of multiple modes of a nanomechanical doubly clamped beam resonator. Each mode is driven by Gaussian force noise centered around the resonance; the mode response is monitored while the force magnitude is increased, inducing a transition from harmonic to the nonlinear Duffing regime. To characterize the dynamics, we introduce an effective temperature based on the mode fluctuation amplitude. As the nonlinearity becomes prominent at large amplitudes, we observe a reduction in the effective thermal energy and a crossover in response statistics from Gaussian to platykurtic, consistent with the dynamics expected in a Duffing potential.
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All authors Monan Ma, Nathan Welles, Johnathon Barbish, Ismet I. Kaya, M. Selim Hanay, Oleksiy Svitelskiy, Mark R. Paul, Kamil L. Ekinci

Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci

Layer-Controlled Intermolecular Coupling and Many-Body Effects in C$_{60}$ Films

Hai-Lan Luo, Weitang Li, Luca Moreschini et al. (+4 more)

Crystalline C$_{60}$ is a molecular solid whose electronic properties emerge from the interplay of intermolecular hopping, electron correlations, and electron-vibration coupling. Unlike moir$\rm\acute{e}$ van der Waals heterostructures, where interaction strength is commonly tuned by twist angle, molecular materials offer a complementary route in which layer number, molecular orientation, and substrate registry provide experimentally accessible control parameters. Here we present a systematic thickness-dependent angle-resolved photoemission study of C$_{60}$ films, spanning the monolayer to the bulk limit. The HOMO-derived band exhibits a non-monotonic evolution: the intermediate-thickness film shows larger bandwidth, reduced effective mass, and pronounced gap-like and sub-band features. The experimental trends, together with Holstein-model simulations, point to strengthened effective intermolecular electronic coupling and enhanced electron-phonon-induced spectral renormalization in the intermediate-thickness regime. These results identify a dimensional crossover in C$_{60}$ films and establish layer number as an effective knob for engineering electronic structure and many-body interactions in molecular thin films.
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All authors Hai-Lan Luo, Weitang Li, Luca Moreschini, Jonathan Denlinger, Zhigang Shuai, Claudia Ojeda-Aristizabal, Alessandra Lanzara

Mesoscale and Nanoscale Physics · Cross-listed from quant-ph

How Long-Range Tails Reshape Non-Hermitian Spectra

Ding Gu, Zhanpeng Fu, Yu-Min Hu et al. (+1 more)

Exponentially decaying long-range hoppings are ubiquitous in realistic tight-binding models and are often truncated to obtain a finite-range description. We show that this approximation can fail dramatically in non-Hermitian systems under open boundary conditions: an infinitesimal long-range hopping can nonperturbatively reconstruct the spectrum and eigenstates of a short-range non-Hermitian system. The mechanism is controlled by a competition between the decay length of infinitesimal long-range hoppings and the localization length of non-Hermitian skin modes, leading to a sharp transition as the decay rate is tuned. In one dimension, we show that a squeezed generalized Brillouin zone (GBZ) replaces the original GBZ of the short-ranged Hamiltonian, yielding the reconstructed open-boundary spectrum. In two or higher dimensions, we formulate a squeezed amoeba formulation describing the reconstructed spectral density. We further show that long-range hoppings can qualitatively reshape Green's function, which can be readily detected in experiments.
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All authors Ding Gu, Zhanpeng Fu, Yu-Min Hu, Zhong Wang

Mesoscale and Nanoscale Physics

Super-resolution Control of Individual Two-dimensional Quantum Emitters

Bosai Lyu, Valeria Vento, Ludivine Fausten et al. (+8 more)

Localized interlayer excitons in semiconducting transition-metal dichalcogenide heterobilayers are quantum emitters with a static electric dipole moment, making them excellent nanoscale charge sensors to probe correlated quantum phases in a proximal layer. These emitters are electrically tunable and inherit spin-valley selection rules, yet their deterministic spatial control remains challenging due to subwavelength confinement. Here, we present a platform that combines cryogenic optical spectroscopy with scanning probe microscopy to investigate trapped interlayer excitons in MoSe$_2$/WSe$_2$ bilayers. By exploiting tip-induced local Stark shift, we achieve super-resolution of emitters separated by a few tens of nanometers and demonstrate deterministic control of individual charge states, including trion formation. Time-resolved measurements reveal tip-induced modification of the electromagnetic vacuum around individual emitters, and thus control of their radiative emission. Our multi-point charge sensing platform with optical readout is particularly well-suited for future study of fractionalization and anyon dynamics in semiconducting fractional Chern insulators.
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All authors Bosai Lyu, Valeria Vento, Ludivine Fausten, Daniel Suarez-Forero, Klevis Domi, Kenji Watanabe, Takashi Taniguchi, Alberto Morpurgo, Iaroslav Gaponenko, Patrycja Paruch, Ajit Srivastava