Mesoscale and Nanoscale Physics
Fluctuation-induced magnetoresistance in graphene Hall bars at charge neutrality
Anna Grigoreva, Alex Levchenko, Eleftherios Kirkinis et al. (+1 more)
In the temperature interval $T\sim 50 - 100 K$, the rate of electron-electron collisions in
graphene devices may exceed the momentum relaxation rate due to disorder and electron-
phonon scattering. In this regime, the motion of the electron
liquid may be described by the hydrodynamic equations. In the hydrodynamic approximation, at the charge neutrality point the electric current is decoupled from the hydrodynamic flow, and the conductivity of the system is equal to the intrinsic conductivity of the electron
liquid, $\sigma_0$. It was recently shown that the coupling of charge transport and hydrodynamic flow induced by the thermal fluctuations enhances the macroscopic conductivity of the system and results in very strong positive magnetoresistance (MR) at relatively weak fields. Here we develop a quantitative theory of the fluctuation mechanism of MR at charge neutrality and obtain analytic expressions for MR in
graphene Hall bars. The functional dependence of MR on the
magnetic field $H$ is sensitive to the Hall bar geometry and orientation relative to the current. We also account for the effect of momentum relaxation on MR.
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All authors Anna Grigoreva, Alex Levchenko, Eleftherios Kirkinis, Anton Andreev
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Intrinsic electromagnetic properties
Eduardo Barredo-Alamilla, Timur Z. Seidov, Daniel A. Bobylev et al. (+1 more)
Electromagnetic properties of materials are commonly inferred from how they scatter light. Here we show that this diagnostic is fundamentally incomplete. We predict the existence of an intrinsic electromagnetic property that remains invisible in any scattering experiment independently of geometry, polarization, far-field or near-field excitation. Still, this property affects the radiation emitted by the sources embedded inside the material. We reveal this phenomenon for a specially designed nonreciprocal magnetoelectric material combining
axion and dual
axion responses. Our results establish intrinsic electromagnetic properties as a distinct class of material responses and show that scattering experiments alone are insufficient to characterize matter.
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All authors Eduardo Barredo-Alamilla, Timur Z. Seidov, Daniel A. Bobylev, Maxim A. Gorlach
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.dis-nn
Hyperbolic lattices with mass disorder: Phases and phase transitions
Sheersh Sen, Christopher A. Leong and Bitan Roy
Nearest-neighbor (NN) tight-binding models (TBMs) on plaquette-centered $\{ 10,3\}$ (Schläfli symbol), $\{ 8,3\}$, and $\{ 8,4\}$
hyperbolic lattices on a Poincaré disk with open boundary conditions display a vanishing, a finite, and a diverging density of states (DOS) near zero energy (band center), respectively, yielding a Dirac
liquid, a Fermi
liquid, and a flat band. Emergent bipartite nature of these
lattices within the framework of NN-TBMs, allows us to scrutinize the impact of mass disorder on the electronic states and DOS therein. From extensive numerical calculations of the average and typical DOS using the kernel
polynomial method, we show that
hyperbolic Dirac
liquid remains stable against weak mass disorder, undergoing a semimetal-to-metal
quantum phase transition at moderate disorder, followed by an Anderson metal-to-
insulator transition at even stronger disorder. The remaining two systems display only the latter transition. Critical exponents near all these transitions are found to be close to the ones mediated by on-site potential disorder.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Thin-capping layer epitaxial quantum dots for near-field quantum photonics
Yuting Guo, Jonathan Bar-David, Pasquale Cilibrizzi et al. (+3 more)
Epitaxial
quantum dots (QDs) are widely recognised as one of the best
quantum light sources, given their good stability, brightness,
quantum efficiency and coherence. To reach such properties, QDs are protected from potentially detrimental surface states by a relatively thick capping layer, typically exceeding 50nm. This prevents the implementation of near-field effects, like plasmonic-based ones, that can dramatically increase the light-matter interaction, since the control of the spontaneous emission dynamics and directionality of the emission can only occur if the emitter is in close proximity (typically tens of nanometers or less) from the metallic structures. In this work, we report the growth and optical characterisation of InAs/GaAs QDs with GaAs capping layer thickness of 10nm, 20nm, and a more standard 95nm. Remarkably, we observe emission linewidths up to 5 times smaller than previously reported, with unperturbed excitonic lifetimes. These results demonstrate that the epitaxial QD's high optical quality can be maintained even when the emitters are at reduced distances from the surface, opening the path for the exploration of near-field light-matter interactions with coherent and stable emitters, suitable for
quantum technology applications.
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All authors Yuting Guo, Jonathan Bar-David, Pasquale Cilibrizzi, Sung-Yul L. Park, Jin Dong Song, Luca Sapienza
Mesoscale and Nanoscale Physics
Symmetry considerations in chirality-induced spin selectivity
Dmitry Budker and Angela Wittmann
The chirality-induced
spin selectivity (CISS) effect, the coupling between structural chirality and electron
spin polarization, has been experimentally observed across many diverse systems. However, despite extensive theoretical effort, a unified mechanistic understanding remains elusive. In this perspective, we demonstrate how some of the basic properties of the fascinating effects of CISS can be understood based on straightforward
symmetry considerations commonly employed in fundamental particle physics. In particular, we show that CISS does not violate any fundamental
symmetries including parity and time-reversal. By anchoring CISS within the universal
language of
symmetry, we offer a robust conceptual foundation for interpreting experiments and guiding future theoretical and experimental designs.
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Mesoscale and Nanoscale Physics
Flux- and tunnel-parity-controlled Josephson nonreciprocity from singlet-triplet competition in a parallel double quantum dot
Debika Debnath, Fernando Dominguez and Patrik Recher
Nonreciprocal supercurrents in interacting nanostructures can arise when the positive and negative critical currents probe inequivalent portions of a phase-dependent many-body spectrum. We study this mechanism in a parallel double-
quantum-dot Josephson junction with strong intradot Coulomb repulsion, where local and non-local Cooper-pair transfer coexist. Using exact diagonalization of a zero-bandwidth
Hamiltonian with explicit superconducting orbitals, we show that orbital flux and the gauge-invariant tunnel-sign parity control the interference between local Josephson processes and non-local exchange. For detuned dots, this produces flux-tunable singlet, triplet, and doublet ground-state spectral branches and two rectification regimes. Near the boundaries of the charge sector with singly occupied dots [(1,1) sector], doublet branches compete with singlet or triplet branches, yielding diode efficiencies approaching 40%. Within the triplet-dominated (1,1) sector, nearby singlet crossings asymmetrically reshape the ground-state envelope even when both critical-current extrema lie on the triplet-like branch, producing a broader response of order 10-15%. Finite temperature generally suppresses charge-crossover rectification, however, for intermediate temperatures we find an enhancement of both the normalized efficiency and the absolute critical-current asymmetry in the triplet regime. These results establish phase-dependent many-body branch competition as a gate-, flux-, and tunnel-parity-sensitive source of Josephson nonreciprocity.
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Mesoscale and Nanoscale Physics
Single-Pulse Optical Switching combined with Current-Induced Motion of Skyrmionic Spin Textures
Edoardo Mangini, Duc Minh Tran, Boonthum Kunyangyuen et al. (+5 more)
Magnetic skyrmions are promising nanoscale information carriers because their position can be manipulated by electrical currents. The additional ability of deterministic control of the
spin structure would allow the use of
magnetic skyrmions as multi-state bits, expanding the capabilities of skyrmion devices further. Such control could be realized by coupling all-optical helicity independent switching of magnetization (AO-HIS) to
magnetic skyrmions. This is realized in a Pt/Ir/CoB/Gd/Pt multilayer that is engineered to stabilize
magnetic skyrmions and, at the same time, enable AO-HIS by single ultrafast
laser pulse.
Laser excitation is used to write skyrmionic textures, whose polarity is selected by a small applied out-of-plane field. A single 30 fs
laser pulse is then used to toggle the magnetization of an illuminated region containing skyrmionic textures, reversing their polarities without requiring any
magnetic field or current pulses. This establishes deterministic optical switching of the skyrmion
spin structure as a new manipulation channel, distinct from previously reported optical nucleation and annihilation. The material is then patterned into a wire, to combine the optical manipulation with current-induced skyrmion motion. These results establish a route toward opto-spintronic skyrmion devices in which light programs the internal state of a skyrmion and electrical currents control its position.
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All authors Edoardo Mangini, Duc Minh Tran, Boonthum Kunyangyuen, Jun Xiao Lin, Raphael Gruber, Michel Hehn, Stéphane Mangin, Mathias Kläui
Mesoscale and Nanoscale Physics
Aaron Amire
Most proposals for $Z_3$ parafermions in fractional
quantum Hall-
superconductor structures used the
spin-unpolarized $\nu = 2/3$ Halperin $(1,1,2)$ state. The fractional
quantum anomalous Hall (FQAH) states of twisted MoTe$_2$ and rhombohedral
graphene are believed to be
spin- and valley-polarized Jain states, with the same topological order but a different
spin structure. We analyze a trench between two polarized $\nu = 2/3$ edges. Among the pairing and tunneling bilinears of the edge-mode electrons, exactly two of each have zero conformal
spin. Pairing is compatible only with the neutral-mode superconductivity channel and tunneling only with neutral-mode backscattering, whereas in the unpolarized state singlet pairing and tunneling select the same channel. Since the two channels condense the same neutral anyon up to a local operator, the domain walls carry $Z_3$ parafermions, with 3 protected states per pair, whether or not the neutral channel changes between regions; fixing the
fermion parity does not enlarge this count. Before the neutral gap forms, pairing is at best marginal for repulsive inter-edge coupling unless an attractive neutral coupling favors its channel; once the gap has formed, both charge terms are relevant for an inter-edge Coulomb coupling below 7/25 of the intra-edge one. The
superconductor must supply even-frequency, equal-
spin, intravalley pairing, which an s-wave singlet
superconductor with only Ising
spin-orbit coupling does not provide at leading order, whereas chiral $p+ip$ and $f+if$ states do. The $Z_3$ label is carried by a quasiparticle of the FQAH state, so no process confined to a junction whose tunneling segments are not FQAH can change it, and we expect a $6\pi$-periodic Josephson current with or without fixed
fermion parity.
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Mesoscale and Nanoscale Physics
Sector-Resolved Winding Selection Rules for Structured-Light-Driven dc Currents
Tomohiro Tamaya and Kenichi L. Ishikawa
Structured light can generate electronic dc currents with azimuthal winding, yet the rules governing their winding order $m$ remain unclear. Here we identify sector-resolved winding selection rules using
graphene as a clean two-dimensional platform. By decomposing the current response into local and gradient sectors at the current-operator level, we show that the winding order is determined not by the optical orbital angular momentum $\ell$ alone, but by the angular structure of the corresponding current operators together with projection onto the azimuthal direction. For scalar Laguerre-Gaussian beams, linear polarization yields $m=|\ell\pm1|$ in the local sector and $m=|\ell|,|\ell\pm2|$ in the gradient sector, whereas circular polarization with helicity $\sigma=\pm1$ selects $m=|\ell-\sigma|$ in the local sector and $m=|\ell+2\sigma|$ in the gradient sector. Numerical time-
evolution calculations verify these rules and further show that helicity can select an $m=0$ branch, producing an azimuthally uniform circulating current whose radial profile determines the axial
magnetic field $B_z(z)$. Our results provide a sector-resolved organizing principle for classifying and controlling structured-light-driven dc currents with tailored winding structures.
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Mesoscale and Nanoscale Physics
Transport theory for a generic two-arm co-propagating Majorana interferometer with Majorana fermion and edge vortex tunneling
Domenico Giuliano, Andrea Nava, Fabian Hassler et al. (+1 more)
Co-propagating chiral Majorana edge modes are predicted to exist in proximity-coupled
quantum anomalous Hall systems. They combine the exciting prospects of edge
vortices as flying non-Abelian Ising anyons, with their fully electrical detection through anyon fusion processes. In this setup, electrical transport arises from the interference of a pair of Majorana edge states. By bosonizing the model with an additional replica sector, we generalize previous treatments to fully asymmetric configurations. We analyze a Mach-Zehnder interferometer and show that while the DC conductance does not exhibit signatures of edge-
vortex interference, at low frequencies, this interference manifests as an effective capacitance. This quantity is sensitive to the non-Abelian anyon statistics of edge
vortices and, in particular, carries signatures of their topological
spin and nontrivial conformal dimension. We demonstrate that the thermal length $l_T = \hbar v/(\pi k_B T)$ is the relevant scale at low temperatures $T$, analogous to quasiparticle transport in conventional
quantum Hall edge states with velocity $v$. As long as the interferometer arm lengths match within this length scale, transport signatures of the non-Abelian statistics of edge
vortices remain visible.
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All authors Domenico Giuliano, Andrea Nava, Fabian Hassler, Reinhold Egger
Mesoscale and Nanoscale Physics
Inertial Dynamics of a Skymeron
Mona Bhukta, Duc Minh Tran, Kilian Leutner et al. (+19 more)
Topological
spin textures in antiferromagnets inherit the compensated
magnetic order of the host material, resulting for skyrmions in the suppression of the skyrmion Hall effect and enabling ultrafast dynamics that make them attractive for low-power spintronic devices. In intrinsic antiferromagnets, the two sublattices are identical, but synthetic antiferromagnets offer additional control mechanisms by enabling independent tuning of the properties of two ferromagnetic layers. Analogous to a ferrimagnet, the total
magnetic moment can be adjusted by compensating the two-layer moments. Here, we demonstrate that tuning the effective
magnetic anisotropy difference between the two layers drives a
spin-flop transition where one layer reorients and thus stabilizes an orthogonal configuration with one layer oriented along the out-of-plane direction and the other in-plane. In this transition, an antiferromagnetic skyrmion undergoes a homotopic reconfiguration into a complex
spin texture comprising a skyrmion coupled to an in-plane bimeron. Element-specific X-ray microscopy resolves this texture layer by layer: one hosts an out-of-plane skyrmion coupled to an in-plane bimeron in the other. We refer to this previously unexplored three-dimensional
spin texture as a skymeron. By using time-resolved pump-probe X-ray microscopy, we discover unique polarity ,dependent dynamics during current pulses: a short post-pulse inertia-like continuation of the motion, and a slower return towards the pinned initial state. Micromagnetic simulations reveal that the inertia-like propagation originates from the finite-time relaxation of reorientation of the skymeron. Our results establish layer-selective anisotropy engineering as a route to uncharted composite
spin textures with internal dynamical degrees of freedom, not possible in conventional antiferromagnets with identical sublattices.
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All authors Mona Bhukta, Duc Minh Tran, Kilian Leutner, Takaaki Dohi, Nikolai S. Kiselev, Filipp N. Rybakov, Olle Eriksson, Fabian Kammerbauer, Sebastian Wintz, Markus Weigand, Hendrik Ohldag, Maria-Andromachi Syskaki, Robin Tietgen, Edoardo Mangini, Sabrina Kerber, Thibaud Denneulin, Joseph Vimal Vas, Rafal E. Dunin-Borkowski, Bastian Pfau, Oleg A. Tretiakov, Robert Frömter, Mathias Kläui
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Achieving Identical Stored Energy in Cascaded Collisional Quantum Battery Charging: Analytical Result
Longyan Gong, Jing Zhang and Yongtao Li
Charging uniformity across distinct trials is an essential requirement for reliable
quantum batteries. Nevertheless, intrinsic
quantum stochasticity poses a fundamental challenge to this goal. This work investigates a two-
qubit quantum battery within the framework of cascaded collision models. We propose an adaptive measurement on the charger after each collision, yielding two conditional battery states of equal expected stored energy. For chargers prepared in the excited state, we analytically prove that complete suppression of trajectory-dependent stored-energy fluctuations is attainable; for chargers prepared in general superposition states, our theory reveals that full suppression is fundamentally prohibited owing to battery-phase-dependent recursive dynamics. Numerical simulations are in excellent quantitative agreement with theoretical predictions. These findings provide a feasible pathway toward high-uniformity
quantum-battery charging.
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Mesoscale and Nanoscale Physics
Composite fermions in ideal Chern bands
Songyang Pu, Liangtao Peng and Shaffique Adam
The composite-
fermion framework maps the strongly correlated fractional
quantum Hall state onto a weakly interacting integer
quantum Hall state in a reduced effective
magnetic field. We ask how this framework is modified for fractional Chern
insulators, where the role of a uniform
magnetic field is replaced by the nonuniform Berry
curvature of a Chern band. Specifically, we construct composite-
fermion wave functions for Jain states and their quasiparticles and quasiholes in Aharonov-Casher bands, a widely used model for ideal Chern bands. We find that these states overlap closely with exact eigenstates over a broad range of field modulation. Using these wave functions, we demonstrate that the emergent composite-
fermion band structure goes beyond the conventional picture of effective Landau levels, correctly capturing the quasiparticle dispersion. Remarkably, we find that an isolated quasiparticle band carries a total Berry flux that is different from a Landau level. These results establish a composite-
fermion description for mobile fractional Chern
insulator anyons and provide a framework to understand their stability.
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Mesoscale and Nanoscale Physics
Phonon interference induced by defect pairs
Ran-Bo Yang, Ming-Hao Li, Chun-Yu Cai et al. (+4 more)
The coherent dynamics of
lattice waves is of significant importance for exploring the nonadiabatic phenomena of the electron-
phonon coupling under nonequilibrium conditions. Here, we propose a theoretical model for
phonon interference induced by a defect pair, in which
lattice waves with the selective modes are launched independently by each of defects due to the strongly local electron-
phonon coupling. We find that the intensities of
phonon interference fringes could be directly evaluated by a measurable quantity in experiments–Huang-Rhys factor, and the geometry of interference patterns could be modified by the internal parameters of defect pair, including the charge states, spatial distance, energy-level depth and localization strength. In particular, several novel
quantum states, such as the Dirac-like and nodal-line topological states are emerged for the appropriate internal parameters. Furthermore, using Huang-Rhys model, we simulate the ultrafast optical spectroscopy in the
phonon interference duration when defect pairs are excited as the color centers, where interference fringes are perfectly matched by intensities of spectrum, similar to the $\textit{lock-key}$ pattern. These results show that defect pair, serving as the driven force for the coherent dynamical processes for multidegrees of freedom, offers an ideal platform to explore fundamental
quantum phenomena in nonequilibrium and ultrafast physics.
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All authors Ran-Bo Yang, Ming-Hao Li, Chun-Yu Cai, Yue-Wen Wang, Zhi-Qing Li, Li-Xia Zhao, Zi-Wu Wang
Mesoscale and Nanoscale Physics
Synthesis of Metal-Semiconductor Heterojunctions in Single Graphene Nanoribbons
Ziyi Wang, Kaitlin Slicker, Weichen Tang et al. (+9 more)
Graphene nanoribbons (GNRs) are a highly tunable class of one-dimensional (1D)
quantum materials that can be fabricated through bottom-up synthesis. Precise control over GNR band gaps and band-edge
alignments has established them as a promising nanoelectronics platform, but forming high-quality electronic interfaces remains challenging. Here we combine sequential on-surface synthesis and scanning tunneling microscopy (STM)-induced dehydrogenation to directly write metallic 7-iGNR segments into otherwise semiconducting H$_2$-7-iGNRs without changing the GNR width or carbon backbone connectivity. The resulting metallic segments exhibit nonzero spectral weight at the Fermi level ($E_\mathrm{F}$) and spatially extended electronic states, consistent with two dispersive bands crossing $E_\mathrm{F}$. The new metallic states are well described by an extended Su–Schrieffer–Heeger zigzag-ladder
Hamiltonian. Scanning tunnelling spectroscopy (STS) and first-principles calculations show that the valence band edge of adjacent, connected semiconducting GNR segments lies close to $E_\mathrm{F}$ for the metallic segments. STS spectra recover bulk GNR properties within $\sim$1 nm on either side of the metal-
semiconductor GNR interface, with no discernible depletion region. The observed GNR band edge
alignment is consistent with a small energy barrier for hole injection, thus suggesting a possible route towards atomically precise, low-barrier p-type contacts for future GNR-based electronic devices.
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All authors Ziyi Wang, Kaitlin Slicker, Weichen Tang, Boyu Qie, Rafal Zuzak, Haowen Pang, Yudi Huang, Xinheng Li, Peter H. Jacobse, Steven G. Louie, Felix R. Fischer, Michael F. Crommie
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Vector chiral order and dynamical quantum phase transitions in an Ising chain with dimerized anisotropic Gamma interaction
Yu-Hong Yan, Shi-Qiao Wu and Kun-Liang Zhang
We investigate a transverse-field Ising chain with dimerized anisotropic Gamma interactions and demonstrate that, both in the absence and presence of Ising interactions, the competition between Gamma anisotropy and the transverse field gives rise to vector chiral order and dynamical
quantum phase transitions. The phase diagram comprises positive and negative vector chiral phases and a paramagnetic phase, characterized by the vector
spin chirality and the vector chiral order parameter. In the absence of Ising interactions, we identify a gapless critical line that exhibits no finite-size drift, along which the
spin-
spin correlations and subsystem
entanglement entropy display behavior distinct from that of Ising criticality. Furthermore, we find that the critical times of dynamical
quantum phase transitions form periodic or aperiodic sequences, depending on the quench path. Our findings highlight how dimerized off-diagonal exchange enriches both
equilibrium ordering and dynamical critical behavior in a
quantum Ising chain.
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Mesoscale and Nanoscale Physics
Nutational Spin Pumping and Dissipation
Hans Gløckner Giil and Arne Brataas
At terahertz drive frequencies, magnetization dynamics enter an inertial regime beyond the scope of standard Landau-Lifshitz-Gilbert (LLG) theory. We reveal a nutational damping torque comprising a bulk term and an interfacial contribution that describes
spin emission into adjacent metals. The interfacial term generates nutational
spin pumping: a dc
spin current that scales quadratically with the drive frequency. Using a scattering approach, we relate this effect to microscopic material parameters and predict pronounced enhancements in ultrathin films and low-Fermi-energy conductors. Nutational
spin pumping can be detected directly via the inverse
spin Hall effect or indirectly via thickness-dependent renormalization of nutational damping.
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Mesoscale and Nanoscale Physics
Gate Dispersive Charge Detection in Ge/SiGe Quantum Dots
M.R. Tanvir, E. Sajadi, M. Veldhorst et al. (+2 more)
Spin qubits are an attractive platform for scalable
quantum information processing, and recently, laterally gated
quantum dots (QDs) in Ge
heterostructures have emerged as a leading implementation of
spin qubits. To date, RF single-hole transistors (SHT) and integrated superconducting resonators have been used for
spin and charge readout, but their size can pose challenges. Here we demonstrate compact RF gate-dispersive charge readout of a Ge double QD (DQD), and a single hole box (SHB)-DQD system. We resolve QD loading and interdot transitions with both techniques. We find that the SHB enhances the interdot signal-to-noise ratio (SNR) of our 540 MHz
circuit by a factor of 20 for a DQD coupling $t_c \approx 5$ GHz, providing a unity-SNR at 135 microseconds, c.f. for 2.7 miliseconds for the direct detection. Power- and temperature-dependent measurements verify that SNR is limited by dielectric loss which compromises impedance matching. These results establish a compact readout approach based on gate-dispersive detection for Ge/SiGe
heterostructure QDs.
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All authors M.R. Tanvir, E. Sajadi, M. Veldhorst, G. Scappucci, J. Salfi
Mesoscale and Nanoscale Physics
Charge and spin dynamics in spintronic THz emitters from Time-Dependent Density Functional Theory
Ali Kefayati
Spintronic terahertz (THz) emitters based on ferromagnet/heavy-metal
heterostructures provide efficient broadband sources of THz radiation, yet the microscopic relation between ultrafast
spin transport and charge redistribution remains incompletely understood. Here, we employ time-dependent density functional theory to resolve the coupled charge,
spin, and magnetization dynamics of Co/Pt and Co/W bilayers in real time and space. Despite qualitatively similar interlayer
spin-current dynamics, the two
heterostructures exhibit markedly different interlayer charge transfer: Co/Pt shows a relatively small and partially reversed transfer from Pt to Co, whereas Co/W exhibits a larger and persistent transfer from Co to W. We trace these differences to the material-dependent ground-state electronic structure and the
spin- and orbital-resolved phase space accessible to photoexcited carriers.
Spin-resolved dynamics further reveal coexisting
spin-orbit-mediated redistribution and optically induced intersite
spin transfer, including a delayed minority-
spin transfer from the heavy metal to Co common to both systems. While net electronic
spin angular momentum is transferred between the layers, we find no corresponding net transfer of electronic orbital angular momentum. In Co/W, the persistent redistribution of electronic density from interstitial to atom-centered states additionally provides strong evidence for light-induced electronic localization. These results demonstrate that ultrafast
spin transport does not uniquely determine charge or angular-momentum redistribution in spintronic THz emitters, which instead depends critically on the material-specific electronic phase space.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
Topological robustness of thermally disordered lattices: From average structures to ensemble electronic properties
Oleg Rubel and Karekin Sadikian
Band
topology is usually assigned to a single
crystal structure, yet at finite temperature a
crystal is an ensemble of thermally disordered configurations with a fluctuating band gap. We ask whether the thermally averaged structure is a faithful proxy for this ensemble, taking Bi$_2$Se$_3$ as a representative topological
insulator and classifying band ordering in each ab initio molecular dynamics snapshot by scaling the
spin-orbit coupling. The averaged structure fails in two ways: it misses the Rashba-like
spin splitting that instantaneous
symmetry breaking produces in individual configurations, and it substantially underestimates the band-gap renormalization, whereas a small ensemble of harmonic Monte Carlo configurations reproduces both the mean and the spread of the gap. Using a band-inversion survival probability, we find that the band inversion of Bi$_2$Se$_3$ holds in every sampled configuration up to 600 K, above which individual configurations cross into normal band ordering well before the average gap closes. Topological robustness at finite temperature is thus a property of the distribution over configurations rather than of any single structure.
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Mesoscale and Nanoscale Physics
Hydrogen plasma-assisted atomic layer epitaxy of superconducting titanium nitride
Yi-Hsun Chen, Yin-Chun Huang, Zachary Degnan et al. (+10 more)
Atomic layer deposition (ALD) offers precise, conformal control of thin-film growth and is a workhorse for
semiconductor manufacturing, but its use in superconducting
quantum circuits is constrained by the need to simultaneously control crystallinity, stoichiometry and interfacial disorder at cryogenic temperatures. Here we develop hydrogen
plasma assisted ALD to epitaxially grow superconducting titanium nitride (TiN) thin films, using a hydrogen
plasma step to modify the surface chemistry to suppress precursor-derived impurities during each deposition cycle. Synchrotron X-ray scattering reveals semi-coherent epitaxy of TiN on c-plane sapphire, with discrete crystallographic domains and minimal long-range structural disorder. Complementary X-ray spectroscopy and
neutron reflectometry show negligible oxygen-related disorder throughout the film and no substantial hydrogen incorporation. The resulting TiN films exhibit a superconducting transition at 2.2 K, a kinetic inductance of 15 pH/sq and a superconducting coherence length of 14.6 nm, comparable to the measured
crystal coherence length. These results establish hydrogen
plasma assisted ALD as a route to structurally ordered superconducting TiN thin film epitaxy and demonstrate that the nanoscale control of ALD can be extended to materials suitable for cryogenic
quantum technologies.
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All authors Yi-Hsun Chen, Yin-Chun Huang, Zachary Degnan, David Sommers, Kaijian Xing, Manjith Bose, Eduardo Solano, David Cortie, Michael Fuhrer, Julian A. Steele, Peter Jacobson, Miin-Jang Chen, Arkady Fedorov
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Telecom-Band Optical Transitions of Erbium Atoms in Rare-Gas Solids
Evgenii Zaitsev, Alec Dinerstein, Shan Zou et al. (+6 more)
Rare-earth (RE) atoms, such as erbium (Er), have inner-shell optical transitions in the near-infrared, some of which are in the telecom bands. These transitions are largely insensitive to the host environment due to effective shielding by the filled outer shells. Cryogenic rare-gas (RG) solids, such as solid neon (Ne) and argon (Ar), combine high chemical purity with a nearly nuclear-
spin-free environment, making them attractive solid hosts for preserving optical and
spin coherence. In this work, we isolate neutral Er atoms in solid Ne and Ar at 6 K and characterize their emission by steady-state and time-resolved photoluminescence (PL) spectroscopy. In both hosts, we observe several near-infrared transitions between 1000–1500 nm, including inner-shell emission in the telecom O and E bands. The $4f \rightarrow 5d$ transition near 1299 nm forms a multiplet of narrow components, consistent with
crystal-field splitting, and decays on a microsecond timescale. The $4f \rightarrow 4f$ transition near 1437 nm shows a
matrix shift below 1 cm$^{-1}$ in both hosts. In solid Ne, its inhomogeneous linewidth is bounded by the spectrometer resolution to < 22 GHz, and its PL lifetime reaches up to 78.9 ms, close to the estimated radiative limit. Thermal annealing extends the 1437 nm lifetime in Ne and suppresses the
phonon sidebands relative to the zero-
phonon lines in Ar. These results identify RG solids as promising hosts for long-lived telecom-band Er emission and provide a foundation for future
spin-
photon interfaces and hybrid
quantum architectures.
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All authors Evgenii Zaitsev, Alec Dinerstein, Shan Zou, Charles Peretti, Yutian Wen, Wei Guo, Gregory V. Hartland, Yizhong Huang, Dafei Jin
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
Complex Magnetic Phases and Unconventional Skyrmion Thermodynamics in Magnetically Intercalated Cr$_{1+x}$Te$_2$Compounds
Clayton Conner, Santosh Karki Chhetri, Avinash Sah et al. (+13 more)
Chemical intercalation provides a powerful route for tuning the electronic and
magnetic properties of transition metal dichalcogenides (TMDs), enabling the emergence of
magnetic phases and phenomena that are otherwise inaccessible in their pristine forms. Here, we investigate the structural, electronic, and
magnetic properties of magnetically intercalated Cr$_{1+x}$Te$_2$ through a combination of scanning tunneling microscopy, angle-resolved photoemission spectroscopy, magnetization, electrical transport, and Lorentz transmission electron microscopy measurements. We uncover a rich
magnetic phase diagram comprising paramagnetic, in-plane
spin-fluctuation, out-of-plane ferromagnetic, and field-induced Néel-type skyrmion phases. In particular, Lorentz transmission electron microscopy directly reveals the formation of Néel-type skyrmion textures slightly below the Curie temperature, with their configurations evolving strongly with temperature and
magnetic field. The skyrmions exhibit pronounced thermal hysteresis and coexist with stripe domains, indicative of a complex
magnetic energy landscape arising from the competition among disorder-induced local Dzyaloshinskii-Moriya interactions, perpendicular
magnetic anisotropy, and dipolar interactions. Our results demonstrate that chemical intercalation can profoundly reshape the
magnetic interactions and phase behavior of TMDs, establishing Cr$_{1+x}$Te$_2$ as a versatile platform for exploring tunable magnetism, skyrmion physics, and unconventional thermodynamic phenomena in low-dimensional
quantum materials.
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All authors Clayton Conner, Santosh Karki Chhetri, Avinash Sah, Manoj Gadtoula, Dilan M. Gamachchi, Indeewari M. Karunarathne, Steven Kelley, Andrew C. Meng, Jacob Cook, Cheng Zhang, Jin Hu, Yue Li, Hoyeon Jeon, An-Ping Li, Zheng Gai, Guang Bian