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Physics Condensed Matter Mesoscale and Nanoscale Physics

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

Tuesday 8 September

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

Study on Thickness and Temperature Dependence of Thermoelectric Properties in SnS Nanofilms

Liqi Chen, Ziyang Wang, Donghao Li et al. (+5 more)

SnS as an environmentally friendly, cost-effective, and earth-abundant narrow-bandgap semiconductor material, has demonstrated significant application potential in the field of medium-temperature thermoelectric conversion. However, the thermoelectric performance of its bulk counterpart is inherently constrained by intrinsic point defects (e.g., vacancies) and the material's specific band structure. Low-dimensional engineering has emerged as a pivotal strategy for overcoming these limitations and enhancing thermoelectric performance. In this work, we systematically investigate the thermoelectric properties of SnS nanofilms with distinct thicknesses (82 nm, 199 nm, 616 nm, and 813 nm) across a temperature range of 300-600 K. Measurements were conducted using time-domain thermoreflectance (TDTR) and a dedicated thin-film thermoelectric parameter test system (ZEM-3). Our results confirm that low-dimensionalization effectively boosts the thermoelectric performance of SnS, with the thermoelectric figure of merit (ZT) displaying a pronounced dependence on both film thickness and temperature. All four SnS thin films exhibit thermoelectric performance that is markedly superior to that of bulk SnS. This enhancement is primarily attributed to the quantum confinement effect, energy filtering effect, and intensified phonon scattering, all of which are induced by the low-dimensional structural characteristics. This work provides not only experimental evidence and theoretical insights for the performance optimization of SnS nanofilms but also establishes a foundational framework for the development of high-efficiency, eco-friendly medium-temperature thermoelectric materials, thereby holding significant scientific value and practical implications.
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All authors Liqi Chen, Ziyang Wang, Donghao Li, Jingye Wang, Ning Zhao, Jun Zhou, Jie Zhu, Dawei Tang

Mesoscale and Nanoscale Physics

Observation of linear magnetoresistance and planar Hall effect in the Dirac semimetal PdTe

Bhawana Mehra, Bibek Ranjan Satapathy, V S Abhishek et al. (+5 more)

PdTe is a Dirac semimetal that also exhibits superconductivity, providing an intriguing platform to explore topological superconductivity and unconventional magnetotransport phenomena. While the superconducting properties of PdTe have been extensively studied in recent years, the detailed magnetotransport phenomena have remained unexplored. Here, we present the first observation of linear magnetoresistance (LMR) and the planar Hall effect (PHE) in a high-quality single crystal of PdTe. We observe temperature-dependent unsaturated LMR in both in-plane ($B \parallel I$) and out-of-plane ($B \perp I$) configurations. The magnetoresistance (MR) shows a crossover from parabolic to linear dependence at the critical field Bc, and detailed analysis indicates that disorder-driven mobility fluctuations are the origin rather than the Abrikosov quantum-limit mechanism. Furthermore, prominent PHE has been observed by rotating the magnetic field within the plane of the sample. The detailed analysis of the field and temperature dependence of PHE-amplitude, along with the parametric plot, suggests that PHE originates predominantly from the anisotropic orbital magnetoresistance rather than the chiral anomaly. Our results demonstrate that although the Dirac point is close to the Fermi level, the observed LMR and PHE in the Dirac semimetal PdTe can be understood within a semiclassical transport framework, highlighting the importance of distinguishing between topological and conventional classical transport mechanisms in topological materials
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All authors Bhawana Mehra, Bibek Ranjan Satapathy, V S Abhishek, Reena, Ritu Gupta, Yogesh Singh, S. Chakraverty, Amit Vashist

Mesoscale and Nanoscale Physics

Wafer-Level 1/f Noise Characterization of Scaled P-Type Nanosheets and Comparison with Planar HKMG Transistors

Ruben Asanovski, Anabela Veloso, Ben Kaczer et al. (+2 more)

We present a comprehensive wafer-level 1/f noise study of scaled Gate-All-Around (GAA) p-type nanosheet transistors and benchmark them against large-area planar High- ąppa} Metal Gate (HKMG) devices to assess the impact of device architecture on reliability. By statistically analyzing noise data from 188 nanosheets, we extract the effective trap density in the dielectric and compare it to that of planar transistors with identical gate stack, comparable processing thermal budgets, and no specific reliability anneals. The effective trap density extracted from 1/f noise is comparable in planar and nanosheet architectures. This indicates that transitioning to GAA nanosheets does not increase noise, which remains governed by gate stack quality.
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All authors Ruben Asanovski, Anabela Veloso, Ben Kaczer, Naoto Horiguchi, Jacopo Franco

Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.quant-gas

Exciton-polariton condensates in epsilon-near-zero cavities

Ege Özgün

We propose an epsilon-near-zero (ENZ) artificial cavity that can enhance light-matter coupling around the ENZ frequency and theoretically show the possibility of exciton-polariton condensation in the suggested platform. By using a rate equation model based on the driven-dissipative reservoir approach, we calculate the pump threshold for condensation and then compare the suggested platform's advantages/disadvantages with distributed Bragg reflector cavities. We also discuss the validity of the mean field theory within our model.
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Mesoscale and Nanoscale Physics

Equivalent Circuit Representation and Thermodynamic Limitations of Non-Adiabatic Spin-Transfer Torque effect

Wataru Koshibae

We present an equivalent circuit representation of the Thiele equation for the current-driven domain walls. We show that the non-adiabatic spin-transfer torque (\beta-term) cannot be represented by passive elements alone (such as resistors, inductors, and capacitors) and necessarily requires active elements, corresponding to negative dissipation. Consequently, assuming that the driving current is the only power source for the texture dynamics, directly incorporating the \beta-term introduces a fundamental contradiction with thermodynamic principles. This equivalent circuit theory indicates that the interpretation of experiments solely through the \beta-term does not fully capture the underlying physics, highlighting the need to account for effects distinct from the spin dynamics.
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Mesoscale and Nanoscale Physics

Memory Control of Ice Growth During Non-Equilibrium Freezing of Water

Abhigyan Hazarika, Sudeep N. Punnathanam, Biman Bagchi et al. (+1 more)

Freezing of supercooled water is a classic non-equilibrium problem, yet the influence of thermal history on crystallization remains unclear. Using molecular dynamics simulations with the TIP4P/Ice model, we investigate how the initial temperature $T_i$ shapes freezing following rapid quenching to 250 K. By monitoring the evolution of hydrogen-bonded ring structures, we find a non-monotonic dependence of the freezing time $t_F$ on $T_i$, with the slowest crystallization occurring near 300 K. Remarkably, this means that initially hotter water can freeze faster than cooler water, a molecular-scale analogue of the Mpemba effect. A non-stationary generalized Langevin equation framework shows that two-time memory kernels retain information about the system's thermal past, directly influencing crystallization dynamics. Structural analysis further reveals that five-membered rings act as kinetic traps, while correlations among ring types regulate the accessibility of ice-like motifs. These results uncover a molecular origin of memory-driven freezing and establish structural memory as a key driver of non-equilibrium phase transitions.
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All authors Abhigyan Hazarika, Sudeep N. Punnathanam, Biman Bagchi, Prabal K. Maiti

Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.supr-con

Thomas-Fermi screening of electrostatic fields in a type-I superconductor

Nikhil Seeja Sivakumar, Tyler James, Frederick Carlisle et al. (+2 more)

The empirical London equations make distinct predictions for a superconductor's longitudinal and transverse electrodynamic response. Conventionally, this framework attributes the Meissner effect to the transverse component, with the longitudinal response predicted to remain unchanged on entering the superconducting state, i.e. a static electric field is screened over the Thomas-Fermi length ($\lambda_{\mathrm{TF}} \sim 1$~Å), just as in the nonsupercondcuting metal. J.~E.~Hirsch~[Phys.~ Rev.~B~69,~214515~(2004)] has developed an alternative formalism, which predicts that the longitudinal screening length should instead be governed by the London penetration depth as the system is cooled below the superconducting transition temperature ($T_{\mathrm{c}}$). Here we use a combination of qPlus atomic force microscopy and scanning tunneling microscopy/spectroscopy of single-crystal Pb(111) at $\sim$~340~mK~ \mbox{($T/T_{\mathrm{c}}\sim0.05$)} in an attempt to detect any modifications in electrostatic screening of the longitudinal tip field upon entering the superconducting phase. We quench superconductivity using a magnetic field of 200 mT normal to the Pb(111) surface. By measuring force-distance curves and local field-emission resonance spectra at the same sample position in the presence and absence of the magnetic field, we constrain the change in screening between the normal and superconducting state to less than $\sim 1 \%$. This is between two to three orders of magnitude smaller than that predicted by Hirsch's theory, and entirely consistent with unmodified Thomas-Fermi screening across the superconducting transition.
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All authors Nikhil Seeja Sivakumar, Tyler James, Frederick Carlisle, Philip Moriarty, Brian Kiraly

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

Magic-free coexisting photonic and phononic moiré flat bands

Ziming Chen, Kaiyu Cui, Ning Wu et al. (+8 more)

Moiré flat bands enhance localization and interactions through suppressed group velocity, but existing approaches largely target a single physical field because distinct excitations generally require different, finely tuned magic configurations. Here we introduce a flat-band mechanism based on strong diffractive hybridization among moiré-folded bands. Period-mismatched modulations open distinct coupling channels whose hybridization renormalizes the band dispersion. An effective Hamiltonian shows that increasing the diffractive coupling progressively suppresses the group velocity, driving the system toward a flat-band regime without field-specific magic configurations. This coupling-induced mechanism enables band flattening across distinct physical excitations. We demonstrate this mechanism in a single-layer moiré optomechanical crystal, where photonic and phononic flat bands are simultaneously realized, and their localized modes and optomechanical interaction are experimentally observed. Beyond photonic and phononic systems, this mechanism may extend to other wave and quasiparticle platforms, providing a general route to co-localizing and coupling distinct physical fields in moiré systems.
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All authors Ziming Chen, Kaiyu Cui, Ning Wu, Shuyuan Li, Chenxuan Wang, Xue Feng, Fang Liu, Wei Zhang, Hao Sun, Yongzhuo Li, Yidong Huang

Mesoscale and Nanoscale Physics

Impurity as a probe of Berry curvature and wavefunction winding in gapped two-band models

Reda Nabil, Pascal Simon and Andrej Mesaros

We explore the possibility of using quasiparticle interference near impurities to extract non-local properties of bands. Focusing on the minimal two-band description of a system with multiple valleys, we show that the local density of states (LDOS) induced by non-magnetic impurities can effectively probe both the Berry curvature and the wavefunction winding, locally in each valley. We analyze gapped models based on Dirac, semi-Dirac, quadratic touching, and higher-order touching energy dispersions, in presence of a point-like potential scatterer. We find that for strong enough impurity potentials the LDOS along a contour around the impurity unambiguously shows the wavefunction winding number, in contrast to the case of gapless Dirac-like dispersions where the winding can be precluded by LDOS oscillations in the radial direction. We also establish a general connection between, on the one hand, the Berry curvature as a function of momentum locally in a valley, and on the other hand, the wavefunction winding number and the energy dispersion parameters, making hence the local Berry curvature directly observable from spectroscopic LDOS information.
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Mesoscale and Nanoscale Physics

From London to Morse via Binnig, Quate, and Gerber

Sofia Alonso Perez, Matthew O. Blunt, Frederick Carlisle et al. (+30 more)

In their landmark paper introducing the atomic force microscope [Phys. Rev. Lett. 56, 930 (1986)], Binnig, Quate, and Gerber presciently anticipated that the technique would ultimately be capable of probing interactions running the gamut from weak van der Waals interactions to strong covalent bonding. They also highlighted that the tip-sample forces central to AFM are present, and often highly influential, in scanning tunnelling microscopy; indeed, this realisation directly inspired the invention of the force microscope. In this perspective for the Forty Years of AFM special issue, we review selected aspects of two decades of work from our group at the University of Nottingham that span the force range highlighted by BQG and are united by a common, central theme: the probe as active participant rather than passive observer. Our selection of results also covers length- and correlation-scales from the microscopic right down to the single chemical bond limit, tracking a spectrum of interactions from van der Waals/Hamaker forces, through hydrogen bonding, to covalent bonds and, finally, atom-by-atom assembly of metal clusters via vertical tip-sample transfer. Echoing BQG's own observations on the prevalence of probe-sample forces in STM, we also discuss recent evidence that tip-induced heterogeneity underpins first-passage dynamics in molecular diffusion and highlight the challenges in acquiring non-invasive measurements of diffusion barriers for adsorbed molecules that are readily perturbed by the probe. We close with a perspective on machine learning's growing role in automating tip-driven atomic and molecular manipulation.
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All authors Sofia Alonso Perez, Matthew O. Blunt, Frederick Carlisle, Neil R. Champness, Janette L. Dunn, Matthew Edmondson, Rowan Evers, Connor Fields, Subhashis Gangopadhyay, James Hayton, Samuel P. Jarvis, Filipe Junqueira, Lev Kantorovich, Brian Kiraly, Natalio Krasnogor, Ioannis Lekkas, Morten Møller, Philip Moriarty, Chris Pakes, Emmanuelle Pauliac-Vaujour, Oliver Phillips, Adrian Radocea, Philipp Rahe, Mohammad Abdur Rashid, Hongqian Sang, Alex Saywell, Nikhil Seeja Sivakumar, Peter Sharp, Andrew Stannard, Julian Stirling, Adam Sweetman, Simon Taylor, Richard A.J. Woolley

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

Non-Markovian dynamics of a qubit on the zigzag edge of photonic graphene

Enrico Di Benedetto

We present an analytical study of the dynamics of a qubit coupled to the zigzag edge of a photonic honeycomb lattice. Leveraging a resolvent operator approach and exact lattice Green's functions, we map the spectrum of qubit-photon bound states and complex poles to uncover the long-time scaling laws of the qubit population. Unlike a qubit coupled to the bulk of graphene, the presence of a zero-energy flat band connecting the Dirac points suppresses long-time branch-cut-induced tails, instead driving damped Rabi oscillations. Potential experimental platforms are briefly discussed.
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Mesoscale and Nanoscale Physics

The First Magic Angle Beyond the Chiral Limit in Twisted Bilayer Graphene

Leonardo A. Navarro-Labastida, Pierre A. Pantaleon, Francisco Guinea et al. (+1 more)

We develop a squared-Hamiltonian description of twisted bilayer graphene beyond the chiral limit to explain why the first magic angle remains robust under lattice relaxation, while higher-order magic angles are strongly destabilized. Starting from the non-chiral Bistritzer–MacDonald model with finite same-sublattice tunneling, we show that lattice relaxation reshapes the effective confinement landscape rather than acting as a simple perturbation of the chiral theory. A central result is that the realistic relaxation-renormalized tunneling ratio lies close to a special confinement point where the oscillatory part of the symmetric confinement potential nearly cancels. This places realistic twisted bilayer graphene near a nearly uniform confinement regime. At the same time, finite same-sublattice tunneling activates an additional inter-sublattice current-like channel that competes with the chiral orbital channel. The first magic angle survives because these confinement and current-like contributions remain balanced, whereas higher-order magic angles lose this balance through stronger remote-band hybridization and enhanced real-space localization around AA regions. Our results provide a single-particle mechanism for the breakdown of the chiral magic-angle hierarchy and clarify why the experimentally relevant first magic angle remains the most stable remnant of the chiral flat-band structure.
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All authors Leonardo A. Navarro-Labastida, Pierre A. Pantaleon, Francisco Guinea, Gerardo G. Naumis

Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.supr-con

$1/3$-Flux Bound States in Multicomponent Superconductor Exhibiting Non-Abelian Statistics of $\mathbb {Z}_3$ Parafermions

Xing-Yu Wu, Y. H. Wang, X. C. Xie et al. (+1 more)

Multicomponent superconductors (MSCs) are predicted to host magnetic flux quanta carrying arbitrary fractions of the superconducting flux quantum. Recent advances have raised the expectation that $1/3$ flux quanta may emerge in MSCs with $C_3$ rotational symmetry. Electrons bound to such fractional flux are long regarded to form anyons, yet their explicit braiding statistics remain unexplored. We propose that these $1/3$-flux bound states ($1/3$-FBSs) exhibit the intriguing non-Abelian statistics of $\mathbb{Z}_3$ parafermions. Under no-double-occupancy constraint, two successive braiding operations of $1/3$-FBSs are equivalent to a single $\mathbb Z_3$ parafermion braiding operation. The parafermion parity encoding the braiding outcome can be read out via the fermionic occupation number of the $1/3$-FBSs. Combined with a crossed-Andreev-reflection-induced Hadamard gate, one can realize the complete set of $\mathbb{Z}_3$ parafermion braiding operations.
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All authors Xing-Yu Wu, Y. H. Wang, X. C. Xie, Yijia Wu

Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.supr-con

Signatures of nodal superconductivity in stoichiometric FeTe

Cequn Li, Zi-Jie Yan, Yang Ge et al. (+13 more)

Superconductivity in stoichiometric FeTe opens access to the FeTe endpoint of the Fe(Se,Te) phase diagram, yet the nature of its superconducting pairing state remains unresolved. In this work, we combine scanning superconducting quantum interference device (SQUID) microscopy, electrical transport, scanning tunneling microscopy and spectroscopy (STM/S), and mean-field calculations to investigate the local superfluid response and pairing state of FeTe thin films with tunable stoichiometry. Even in stoichiometric FeTe, we observe micrometer-scale spatial variations in both superfluid stiffness and superconducting transition temperature $T_c$, while the London penetration depth remains non-saturating down to 0.02$T_c$ and follows a power-law temperature dependence with an exponent of approximately 1-1.5. Together with a V-shaped low-energy density of states and two-gap modeling, these results indicate a superconducting state with gap nodes or deep minima, consistent with either a $d$-wave or nodal $s$-wave superconducting state. Our findings establish stoichiometric FeTe as a distinct superconducting regime that departs from the trend toward more isotropic gaps at intermediate Se/Te compositions, providing a new benchmark for modern microscopic theories of iron-chalcogenide superconductivity. Our work also reveals a crossover from weak to rapid suppression of $T_c$ as superfluid stiffness decreases, connecting FeTe to the broader phenomenology observed in unconventional superconductors.
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All authors Cequn Li, Zi-Jie Yan, Yang Ge, Zihao Wang, Bing Xia, Stephen Paolini, Pu Xiao, Lok-Kan Lai, Jiatao Song, Austin R. Kaczmarek, Lujin Min, Kenji Yasuda, Peter J. Hirschfeld, Jiabin Yu, Cui-Zu Chang, Katja C. Nowack

Mesoscale and Nanoscale Physics

Tunable topological narrow bands in twisted bilayer-trilayer graphene

Dong Wang, Federico Escudero, Zhen Zhan et al. (+1 more)

We investigate the low-energy band structure and topology of twisted bilayer–trilayer graphene with four stacking configurations: AB–ABC, BA–ABC, AB–ABA, and BA–ABA. Using both tight-binding and continuum models, we first establish that the two approaches show good agreement in the band structure in low-energy regime. We then study the evolution of the flat bands and their valley Chern numbers as functions of twist angle, perpendicular electric field, and the self-consistent Hartree potential. At relatively large twist angles and under electric field, we find a topological transition between the narrow bands, with the total Chern number of the flat bands following the Chern number sum rules derived from the chiral-limit description. We also observe another type of topological transition when the flat bands hybridize with adjacent remote bands, where gap closing and reopening processes lead to Chern number and charge density transfer. By constructing topological phase diagrams in the space of twist angle and electric field, we show that the perpendicular electric field provides an efficient tuning knob for controlling the stability and transitions of the Chern bands. Finally, we find that the Hartree potential mainly induce weak band shifts and reshaping in the narrow bands. However, with a combination of Hartree potential and the electric fields, the narrow bands show rich topological phase diagram. Our results clarify the interplay between the stacking, twist angle and electric field in manipulating the narrow bands and their topology in twisted bilayer–trilayer graphene, and provide guidance for engineering topological narrow bands with tunable Chern numbers in realistic twisted multilayer graphene systems.
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All authors Dong Wang, Federico Escudero, Zhen Zhan, Shengjun Yuan

Mesoscale and Nanoscale Physics

Electronic Orbital Angular Momentum Driven by Finite-Momentum Phonons: Beyond Chiral and Axial Phonons

Yongho Park, Jeonghun Sohn, Sejoong Kim et al. (+1 more)

We show that finite-momentum phonons generate electronic orbital angular momentum (OAM) even without phonon axiality or chirality, with the response controlled by the phonon wave vector $q$ and frequency $\omega$. We develop a general gauge-field theory in which a unitary transformation absorbs the phonon displacement into emergent vector and scalar potentials acting on the electrons, providing a perturbative classification of the OAM response in $q$ and $\omega$. We derive $q$- and $\omega$-scaling laws for AC and DC responses. Notably, AC OAM arises even for linearly polarized phonons, with its magnitude and sign tunable by $q$. Its generation is governed by the matching between the phonon geometry and the electronic orbital texture rather than solely by the phonon angular momentum. The connection of the DC response to the electronic Berry curvature further supports that phonon angular momentum is not the only degree of freedom governing electronic OAM generation. Time-dependent tight-binding simulations under acoustic-phonon driving independently confirm the core predictions. Our results extend phonon-driven OAM beyond chiral and axial phonons and establish a wave-vector-tunable route to orbitronics, accessible with surface acoustic waves.
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All authors Yongho Park, Jeonghun Sohn, Sejoong Kim, Kyoung-Whan Kim

Mesoscale and Nanoscale Physics

Edge energy fluctuation: A unified theory of friction scaling laws in twisted layered material interfaces

Ze Liu

Interlayer twisting in van der Waals (vdW) layered materials generates moire superlattices, unlocking unique opportunities for engineering their electronic and mechanical functionalities. Here, building on two key insights - the invariance of the potential energy of complete moire tiles during sliding, and the symmetry-breaking effect induced by the slider edge - we propose the concept of edge energy fluctuation (EEF) and demonstrate that the EEF governs the sliding energy barrier of finite-sized sliders. Interestingly, we found that even at a fixed twist angle and sliding direction, significant frictional anisotropy emerges when the slider edge is cut along different directions, resulting in distinct friction scaling laws. Furthermore, we present a friction engineering paradigm for twisted layered material interfaces through the deliberate introduction of hierarchical edges, offering a promising route for friction control in superlubric devices.
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Monday 7 September

Mesoscale and Nanoscale Physics

Nonlinear Topological Orbital Responses of Antiferromagnetic Skyrmions

Amir N. Zarezad, Arne Brataas and Alireza Qaiumzadeh

Antiferromagnetic skyrmions evade the skyrmion Hall effect, but compensation suppresses their conventional topological charge Hall signal. We predict a semiclassical nonlinear topological orbital response of an isolated skyrmion in a $\mathcal{PT}$-symmetric hexagonal antiferromagnet without spin-orbit coupling. In the diffusive, weak-emergent-field regime, the spin-dependent emergent Lorentz force reshapes the carrier distribution, generating a local orbital Hall-current correction and a local orbital accumulation, both quadratic in the applied electric field. The current correction requires spin-asymmetric longitudinal scattering, whereas the accumulation survives spin-symmetric scattering. When the spin-diffusion length greatly exceeds the strip width, the current correction persists while the accumulation approaches zero. Both signals are even under electric-field reversal, odd under reversal of the skyrmion topological charge $Q$, and helicity independent within this model. These symmetries enable rectified detection and distinguish this mechanism from the $Q$-even quantum-regime topological orbital Hall effect.
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Mesoscale and Nanoscale Physics

Steady reservoir-mediated self-trapping of polariton condensates

Pavel N. Kozhevin, Oleg I. Utesov, Igor S. Aranson et al. (+2 more)

Nonequilibrium bosonic condensates of exciton-polaritons generated by tightly focused incoherent optical beams are typically expected to form a stationary ballistically expanding state with the notable exception of experimentally observed compact self-trapped states [Phys. Rev. Lett. 123, 047401 (2019)]. We show that the back-action of the condensate on the optically pumped excitonic reservoir via bosonic stimulated scattering can cause local reservoir depletion, producing a steady condensate confined in a self-induced potential trap. Notably, this self-trapped state is formed by persistent converging rather than radially expanding polariton currents and exists even below the conventionally defined condensation threshold. This state remains steady over nanosecond-scale times and is eventually ejected from the self-induced trap due to a bullet-type instability, enabling spiking neuromorphic dynamics in networks of polariton condensates.
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All authors Pavel N. Kozhevin, Oleg I. Utesov, Igor S. Aranson, Sergey V. Koniakhin, Anton V. Nalitov

Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el

Vertical quantum confinement in bulk MoS$_2$

Jairo Obando-Guevara, Álvaro González-García, Marcin Rosmus et al. (+5 more)

We experimentally observe quantum confinement states in bulk MoS$_2$ using Angle-Resolved Photoemission Spectroscopy (ARPES). The band structure at the $\overline{\Gamma}$ point reveals quantum well states (QWSs) linked to vertical quantum confinement of the electrons, confirmed by the absence of dispersion in k$_z$ and a strong intensity modulation with photon energy. Notably, the binding energy dependence of the QWSs vs $n$ does not follow the quadratic dependence of a two-dimensional electron gas. Instead, a linear behaviour is observed that is consistent with a parabolic-like quantum well. This confinement arises from the mechanical exfoliation preparation method, which leads to the detachment of a multilayer stack from the underlying bulk. This is confirmed by Density Functional Theory (DFT) calculations. The quantum confinement in bulk-like MoS$_2$ not only offers the opportunity to explore intersubband transitions to exploit optical properties but also provides a means to study fundamental quantum phenomena in multilayer stacks of different thicknesses.
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All authors Jairo Obando-Guevara, Álvaro González-García, Marcin Rosmus, Natalia Olszowska, César González, Miguel Ángel González-Barrio, Antonio Tejeda, Arantzazu Mascaraque

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

Tensor network investigation of the monomer-dimer model on the honeycomb lattice

De-Zhang Li, Jie Liu and Xin Wang

The monomer-dimer model is one of the most well-known unsolved lattice models. In this paper we study the monomer-dimer model on the honeycomb lattice using the tensor network method, in the case that the dimer and monomer activities are 1. The monomer-dimer configurations are exactly mapped into the ground states of the antiferromagnetic Ising model on the Kagomé lattice in the critical field $H_{\rm{ex}}=4J$, and the tensor network is constructed based on the local ground states of each Ising triangle. The VUMPS approach is employed to contract the tensor network, providing a high-precision result of the monomer-dimer problem. We also revisit the edge coloring problem on the honeycomb lattice and discuss its relationship to the monomer-dimer model. Finally we formulate the monomer-dimer problem in the language of the sixteen-vertex model, and discuss the non-integrability of the general monomer-dimer model and the integrability of the pure dimer model.
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Mesoscale and Nanoscale Physics

Creation and characterization of leviton excitations in tight-binding chains

Stephen R. McMillan, Thomas Frederiksen and Géza Giedke

Levitons are minimal-excitation electronic wave packets generated by Lorentzian voltage pulses and constitute a central resource for electron quantum optics. Their creation and defining properties are usually formulated in continuum scattering descriptions, whereas many candidate platforms for integrated electronic quantum circuits are finite, discrete, and strongly shaped by lattice dispersion. We study leviton generation in finite one-dimensional tight-binding chains of non-interacting fermions driven by time-dependent voltage pulses. Using the single-particle density matrix, we resolve the excitation above the initial Fermi sea and quantify its quality through the average excitation number and its fluctuations. We find that clean leviton-like states emerge only in an intermediate regime where the pulse is slow enough to be resolved by the dynamics on the lattice, but not so slow that truncation and finite-size effects distort the Lorentzian profile in the time domain. Lorentzian pulses (even if truncated) systematically outperform non-Lorentzian pulse shapes in approaching the low-noise limit with increasing system size. We further identify finite-lattice signatures associated with band filling, pulse amplitude, linear voltage-drop geometry, and residual deviations from the continuum integer-charge condition. These results establish a microscopic framework for understanding leviton formation beyond the ideal continuum limit and for evaluating lattice-based platforms for coherent few-electron transport.
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Mesoscale and Nanoscale Physics

Simple invariants for band topology

Adam Yanis Chaou, Adolfo G. Grushin and Peru d'Ornellas

Despite the exhaustive understanding gathered around non-interacting topological states of matter, there is no single method capable of systematically delivering simple, numerically efficient topological invariants that is applicable to all crystalline and non-crystalline systems alike. Here we revisit the spectral localizer operator, constructed from the Hamiltonian and position operators, and show how it can be treated it as an auxiliary zero-dimensional Hamiltonian whose topology encodes the higher dimensional phases of the parent Hamiltonian. Its classification reduces every topological invariant to a matrix signature or the sign of a Pfaffian for an appropriate localizer, both of which are simple to interpret and efficient to compute in real space. We validate this approach by deriving simple real-space invariants for weak and rotationally invariant crystalline phases that were previously beyond the grasp of the spectral localizer formalism, atomic limits that escape scattering invariants, phases that evade symmetry-based indicator methods, as well as phases that had no previously known invariant. Our work provides a systematic way to construct any non-interacting topological invariant for a crystalline or non-crystalline systems, opening avenues to classify and predict the topology of previously unexplored classes of materials.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci

High-Field Electron Transport in AlGaN alloys: A Full-Band Monte Carlo Study Based on Ab Initio Supercell Calculations

Animesh Datta, Matinehsadat Hosseinigheidari and Uttam Singisetti

AlGaN alloys are promising wide and ultra-wide-bandgap semiconductors for next-generation power and RF electronics applications. To realize the full potential of AlGaN based devices, it is important to understand the electron transport to accurately predict device performance and identify material limits under various operating conditions. In this work, the high-field electron transport properties of AlxGa1-xN are investigated using a supercell based full band Monte Carlo method. The supercell approach is employed to explicitly capture the true disorder of the alloy system, enabling a more realistic description of carrier transport. The velocity field characteristics are calculated across a range of Al compositions to evaluate key transport metrics, including peak velocity, saturation velocity, and critical electric field. The role of different scattering mechanisms is studied in detail to understand the high field transport mechanism in the AlGaN alloy system. In addition to steady state transport, transient electron dynamics are examined for various Al fractions to study velocity-overshoot behavior, which is especially important for improving the performance of scaled RF devices. Finally, the temperature dependence of the velocity field characteristics in ultra-wide-bandgap Al0.75Ga0.25N is investigated to assess its transport performance under high temperature conditions. These results provide a detailed understanding of high-field transport in AlGaN alloys and offer guidance for the design of AlGaN-based RF and power electronic devices.
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Mesoscale and Nanoscale Physics

Metal-Insulator Coexistence and Gap-Crossing Domain-Wall Modes in an Aubry-André Model with Nonlocal Hopping

Xiarui Zhan, Mingsheng Tian, Qiongyi He et al. (+2 more)

Nonequilibrium transport remains a central theme in modern physics, spanning from condensed matter to synthetic systems. Here, we investigate particle transport in an extended Aubry-André model with system-scale hopping, namely nonlocal hopping with a range proportional to the system size, and uncover a metal-insulator coexistence regime in real space, where metallic and insulating spatial domains coexist within the same system and are separated by sharp spatial boundaries. In the insulating region, particles exhibit flat-band-like localization in the absence of quasiperiodic potentials, while a quasiperiodic potential induces distinct multi-point localization, different from conventional exponential localization. Meanwhile, particles can freely propagate and tunnel across spatially disconnected metallic domains separated by the insulating region. Beyond this coexistence phase, we identify unconventional gap-crossing domain-wall modes with comb-like spatial profiles that mediate nonlocal, multi-point transport across separated metallic domains. Our findings reveal a rich interplay between localization, nonlocality, and transport in systems with nonlocal hopping.
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All authors Xiarui Zhan, Mingsheng Tian, Qiongyi He, Kaiye Shi, Wei Zhang

Mesoscale and Nanoscale Physics

Encapsulated macroscopic WS$_2$ monolayers enable room-temperature exciton-polariton lattices

Shiyu Huang, Sander Scheel, Jiang Qu et al. (+11 more)

Large-area, optically homogeneous monolayer semiconductors are a critical prerequisite for scalable room-temperature polaritonics and for realizing polariton lattices extending across many unit cells. Yet, the small size, optical inhomogeneity, and device-to-device variability of conventional exfoliated flakes have remained major obstacles. Here, we overcome these limitations using 1-dodecanol-encapsulated WS$_2$ monolayers that combine millimeter-scale coverage with remarkably uniform optical properties over lateral distances approaching $300\,$$\mu \mathrm{m}$. Integrated into a tunable open microcavity, these monolayers exhibit robust room-temperature exciton-photon strong coupling, evidenced by a pronounced anti-crossing and a Rabi splitting of $\hbar \Omega_{\mathrm{R}} \approx 31\,\mathrm{meV}$. Leveraging the exceptional uniformity of this platform, we realize a two-dimensional polaritonic kagome lattice and directly resolve its characteristic band structure. Angle-resolved spectroscopy reveals Dirac dispersive bands together with a weakly dispersive flat-band-like branch within the $s$-band, in good agreement with a linear non-interacting model. Complementary momentum- and real-space imaging further identifies the associated bond-centered and site-centered mode profiles. These results establish large-area WS$_2$ monolayers in open microcavities as a scalable platform for engineering polariton band structures and exploring synthetic quantum materials under ambient conditions.
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All authors Shiyu Huang, Sander Scheel, Jiang Qu, Johannes Düreth, Dominik Horneber, Edith Wietek, Simon Widmann, Libo Ma, Monika Emmerling, Martin Kamp, Simon Betzold, Alexey Chernikov, Sven Höfling, Sebastian Klembt

Mesoscale and Nanoscale Physics

Direct Realization of Near-Ideal Carbyne in Ultrathin Boron Nitride Nanotubes

Iryna Ivanenko, Pietro Marabotti, Yifan Zhang et al. (+8 more)

Carbyne, the sp-hybridized one-dimensional allotrope of carbon, is predicted to be the stiffest known material, with electronic and optical properties set by a single structural parameter, the bond length alternation. However, its intrinsic properties have never been measured: chains synthesized through molecular chemistry carry endgroup and finite-length perturbations that persist even in the longest molecules available, while chains grown inside carbon nanotubes strongly couple to the host, which renormalizes their vibrational frequency by up to 110 cm$^{-1}$ in a diameter-dependent manner. Here, we show that encapsulating and thermally converting hydrogen-capped polyynes inside ultrathin boron nitride nanotubes, structural analogues of carbon nanotubes but electrically insulating, yields carbyne chains in a near-ideal regime, where endgroup, finite length, and host-guest perturbations are reduced to secondary effects. Statistical Raman spectroscopy across 245 locations returns a vibrational frequency distribution an order of magnitude narrower than in carbon nanotubes, an anharmonicity consistent with the universal law for carbyne-like materials, and a bond length alternation matching correlated calculations for the free chain. No photoluminescence is detected, despite the transparent host, as expected for the dipole-forbidden emission of an unperturbed carbyne chain. Boron nitride nanotubes give experimental access to carbyne in its near-ideal form.
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All authors Iryna Ivanenko, Pietro Marabotti, Yifan Zhang, Getulio Silva e Souza Júnior, Johannes M. A. Lechner, Pablo Hernández López, Martin Magg, Shivani Shivaprakash, Carlo Spartaco Casari, Sebastian Heeg, Benjamin S. Flavel

Mesoscale and Nanoscale Physics

Charge-spin conversion in altermagnets: electronic anisotropy versus magnon-mediated spin drag

Koki Mizuno

Altermagnets acquire a momentum-dependent spin splitting without net magnetization or spin-orbit coupling. This raises the question of whether the transport anisotropy originates in the electrons or the magnons, and whether the magnon-mediated channel distinguishes an altermagnet from a conventional antiferromagnet. We compute the spin-resolved conductivity of a metallic ferromagnet, antiferromagnet, and altermagnet within a common model, treating the spin-diagonal channel with the magnon self-energy and the spin-flip channel to leading order in the electron-magnon coupling. The anisotropy of the charge-spin conversion is dominated by the electronic spin splitting, the magnon branches contributing only marginally. The magnon-mediated spin-flip channel is even under $C_{4}$, so it carries no signature at first order in the anisotropy and cannot on its own distinguish an altermagnet from a conventional antiferromagnet. It does, however, respond linearly to a sublattice-selective perturbation that lowers the bulk $B_{1g}$ symmetry. The resulting susceptibility vanishes identically in the antiferromagnet, is small in the ferromagnet, and is finite in the altermagnet, where the electronic anisotropy ties spin and sublattice together, so that among magnets with no net magnetization it is unique to altermagnetic order. Being even in the magnetic domain index, this response can be measured without preparing a single magnetic-domain sample.
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Mesoscale and Nanoscale Physics

Layer-Dependent Phonons, Excitons, and Magneto-Optical Phenomena in CrSBr: A Mini Review

Muhammad Aftab, Chinmay Kumar Mohanty, Zain Ashfaq et al. (+5 more)

Two-dimensional layered magnetic materials offer a versatile platform for exploring low-dimensional magnetism and coupled many-body interactions in these materials. Chromium sulfur bromide (CrSBr) is a promising candidate for advanced spintronic and optoelectronic applications because of its intrinsic air stability, semiconducting nature, strong in-plane anisotropy, and A-type antiferromagnetic ordering. This review summarizes recent advances in the understanding of the layer-dependent vibrational and excitonic properties of CrSBr, as well as its magneto-optical response, from bulk crystals to the monolayer limit. We examined its crystal structure, magnetic anisotropy, and interlayer spin reorientation, followed by insights into vibrational dynamics and spin-phonon coupling. Particular emphasis is placed on the excitonic landscape, including magnetic-field-sensitive photoluminescence, localized excitonic states, and the coexistence of Frenkel- and Wannier-Mott excitons in the bandgap. Finally, we discuss the challenges and prospects of harnessing the unique layer-dependent properties of CrSBr in spintronic, magneto-optical, and quantum photonic technologies.
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All authors Muhammad Aftab, Chinmay Kumar Mohanty, Zain Ashfaq, Warisha Mehmood, Xiaoli Wang, Clément Faugeras, Wajid Ali, Maciej R. Molas

Mesoscale and Nanoscale Physics

Static-Dynamic Correlations and Complex Spin-Wave Eigenmodes in Single- and Multilayer Diamond-Shaped Nanomagnets Without Bias Field

Krishna Begari

Diamond-shaped nanomagnets provide a suitable platform for developing microwave devices with reconfigurable characteristics. In this study, the static and dynamic magnetic behaviour of single layer and multilayer diamond-shaped nanomagnets was systematically investigated using micromagnetic simulations. Two distinct remanent magnetic configurations were obtained through a simple magnetic field initialization process. These configurations exhibited different magnetization patterns and dynamic responses. Their resonance characteristics could be modified by applying a nanosecond-scale magnetic field pulse, enabling reconfigurable microwave operation. A clear resonance frequency shift in the sub-GHz (0.9 GHz) range was observed for the single-layer structure, while the multilayer structure exhibited a significantly larger frequency shift in the GHz range (3 GHz). The larger frequency tunability observed in the multilayer configuration arises primarily from the enhanced dipolar coupling between the vertically coupled magnetic layers, which modifies the local effective magnetic field and consequently influences the magnetization dynamics. These findings demonstrate that diamond-shaped nanomagnets can provide a simple and effective route toward reconfigurable microwave functionality, with potential applications in ultralow-power, ultrafast, and frequency tunable microwave devices.
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