Materials Science · Cross-listed from physics.optics
Quantum Dot Colloidosomes as Triggerable Microlasers
Cristian Gonzalez, Saranya Subramanian, Marco Reale et al. (+13 more)
Quantum dot (QD) supraparticle
lasers are promising platforms for microscale light sources and photonic labeling, yet their optical properties are set during assembly. Here we introduce QD colloidosomes,
liquid-core/solid-shell supraparticles that combine whispering-gallery-mode optical feedback with stimulus-triggered structural collapse. Intact QD colloidosomes show cavity-defined lasing with fluence thresholds of ~2.8 mJ/cm2 and linewidths of 2.2-3.7 nm, demonstrating efficient light trapping without a solid core. We identify shell continuity as a critical determinant for whispering-gallery feedback and lasing by exploring a morphological continuum of suprastructures comprising solid supraparticles, colloidosomes, and microporous hollow shells. Intact colloidosomes support narrow cavity modes, whereas porous shells remain broadband even at high pump fluence. We show that colloidosomes can be driven to rupture and release payload through well-defined pathways, including meniscus-driven capillary failure, uniform heating, and localized near-infrared activation, thereby reconfiguring their optical response from cavity-defined lasing to broadband emission. These results establish QD colloidosomes as reconfigurable microlasers that couple optical-state switching and triggered release within a single self-assembled platform.
Read the full abstract ▾
All authors Cristian Gonzalez, Saranya Subramanian, Marco Reale, Giuseppe Soligno, Ilia Geints, Siyuan Yin, Claire Y. Kang, Ricky Ronquillo, Gary Chen, Marco Cannas, Cherie R. Kagan, Alice Sciortino, Michael Engel, Fabrizio Messina, Christopher B. Murray, Emanuele Marino
Materials Science
Role of self-coherence in single-electron phase contrast imaging
Christian Kisielowski, Petra Specht, Joerg Jinschek et al. (+1 more)
The extension of coherent
lattice contrast into the energy loss region in high-resolution transmission electron microscopy (HRTEM) is described by a pulse-like electron-sample interaction in the energy/time uncertainty limit. It generates a wave packet by electron self-interference in any coherent-inelastic scattering event with energy loss. The width of this wave packet is characterized by a self-coherence length ls({\Delta}E) that is predictable because an intrinsic decoherence phase around one radian is set by the expectation value for phase fluctuations. In this case the visibility of interference contrast from a crystalline sample with
lattice parameter a is limited by a Rayleigh-like transfer factor P(ls, a) in the self-coherently illuminated sample area. The model is verified by energy-filtered HRTEM images of hexagonal BN and identifies energy-loss-induced phase noise as a single-electron visibility limit distinct from resolution limitations caused by ensemble-coherence or counting-statistical noise.
Read the full abstract ▾
All authors Christian Kisielowski, Petra Specht, Joerg Jinschek, Stig Helveg
Materials Science
Fine structure of the M-center in Si
Aurora Teien, David R. Gongora, Arnulf Johannes Snedker-Nielsen et al. (+6 more)
Color centers in silicon offer great possibilities for scalable
quantum technologies. The M-center, proposed to originate from a carbon-hydrogen complex, offers telecommunications-band emission and a paramagnetic ground state similar to the T-center. Here, we report on photoluminescence lines in the vicinity of the M-center and investigate their properties, including their dependence on temperature, implantation fluence, implantation isotope, and annealing temperature. Three emission lines are observed that are blue-shifted by 1.1, 2.8 and 3.6 meV relative to the 761 meV zero
phonon line of the M center, where the 2.8 meV line exhibits negative thermal quenching and is therefore proposed to originate from a second excited state of the M-center. The remaining blue-shifted emission lines, together with two additional red-shifted (4.7 and 6.4 meV) emission lines display normal thermal quenching, and are unaffected by an isotope shift of the implanted carbon atom ($^{12}$C versus $^{13}$C implantation) and implantation fluence. Thus, they likely arise either from other defects with similar emission energies or from a perturbed configuration of the M-center.
Read the full abstract ▾
All authors Aurora Teien, David R. Gongora, Arnulf Johannes Snedker-Nielsen, Viktor Bobal, Augustinas Galeckas, Peter Granum, Stefano Paesani, Marianne Etzelmüller Bathen, Lasse Vines
Materials Science
Universal unconventional responses controlled by ferroaxial order
Zhiren He, Guru Khalsa and Jagoda Slawinska
Ferroaxial materials are an emerging class of ferroic materials that, in contrast to ferromagnets and ferroelectrics, are fully robust against stray fields, making them ideally suited for data storage and other nonvolatile applications. However, detection of the ferroaxial state remains challenging, as ferroaxiality does not manifest directly through a measurable macroscopic electric polarization or magnetization, and probes are mostly limited to optical methods. Here, we theoretically establish that ferroaxial order universally generates unconventional components of responses to external stimuli, such as the
spin Hall effect, magneto-Seebeck effect, or Faraday effect, across a broad range of linear and nonlinear transport, optical and
equilibrium phenomena. These unconventional responses are always directly coupled to ferroaxial order and can distinguish ferroaxial domains, providing probes of ferroaxial order. This general connection also reveals a largely unexplored class of ferroaxial metals, in which unconventional transport provides a natural probe of ferroaxial order, as demonstrated by our first-principles calculations for representative materials. Our results reveal a fundamentally different way for ferroic order to manifest – ferroaxiality primarily shows unconventional material responses rather than the directly measurable order parameters, broadening the possibilities of nonvolatile ferroic control and flexible device design.
Read the full abstract ▾
Materials Science
Halide donors in monoclinic- and corundum-phase Ga$_2$O$_3$ and Al$_2$O$_3$
Sai Mu, Haochen Wang, Yongjoong Shin et al. (+2 more)
We present a systematic first-principles investigation of halide impurities (F and Cl) in Ga$_2$O$_3$ and Al$_2$O$_3$, considering both monoclinic and corundum phases. Our study of the structural properties, formation energies, and charge-state transition levels establishes the relative stability of different atomic configurations and charge states. We find that F and Cl on oxygen sites act as shallow donors in Ga$_2$O$_3$ in both the monoclinic and corundum phases. However, their behavior differs substantially as the band gap increases with greater Al compositions. Fluorine is prone to $DX$-center formation with increased Al composition, leading to self-compensation at 38% Al concentration in monoclinic (Al$_x$Ga$_{1-x}$)$_2$O$_3$ and 70% Al concentration in corundum (Al$_x$Ga$_{1-x}$)$_2$O$_3$. Chlorine is more resistant to $DX$-center formation: in monoclinic (Al$_x$Ga$_{1-x}$)$_2$O$_3$, Cl$_\mathrm{O}$ on the lowest-energy oxygen site shows an onset of $DX$ behavior at 50%
alloy composition, while in corundum (Al$_x$Ga$_{1-x}$)$_2$O$_3$ this onset for Cl$_\mathrm{O}$ occurs only at Al concentrations as high as 84%. We also study F and Cl interstitials, finding that they act as compensating centers but also exhibit migration barriers that are low enough for them to be removed by post-growth annealing. Surprisingly, in both monoclinic and corundum Al$_2$O$_3$, Cl$_\mathrm{O}$ exhibits a relatively shallow transition level located at $\sim$0.48 eV below the conduction-band minimum, much shallower than F$_\mathrm{O}$ and other donor candidates. These remarkable results identify Cl as an unusually promising donor candidate in (Al$_x$Ga$_{1-x}$)$_2$O$_3$
alloys and even pure Al$_2$O$_3$, although high formation energies and compensation will render observation of true $n$-type conductivity in Al$_2$O$_3$ difficult.
Read the full abstract ▾
All authors Sai Mu, Haochen Wang, Yongjoong Shin, Zhi-Hao Wang, Chris G. Van de Walle
Materials Science
Terahertz Control of Optical Second-Harmonic Generation in Displacive Ferroelectrics: Electronic Bloch-State Reconstruction
Hong-Kui Liu, Zi-Chen Qin, Jun-Song Wu et al. (+1 more)
Optical second-harmonic generation (SHG) is a powerful probe of ferroelectric order, yet its microscopic origin and dynamical control are often understood primarily from
symmetry considerations rather than from the underlying electronic processes. Here, we develop a microscopic theory of terahertz-controlled optical SHG in displacive ferroelectrics, establishing a direct connection between THz-driven polar
lattice distortions and the resulting electronic nonlinear optical response. Starting from a complete Bloch-band representation, we show that an inversion-breaking
lattice distortion reconstructs electronic Bloch wave functions, modifies optical dipole
matrix elements, and activates nonlinear optical pathways that are forbidden in the centrosymmetric structure. We derive the second-order susceptibility in terms of the distortion-induced reconstruction of electronic states and optical transition
matrix elements, and demonstrate that the electronic SHG susceptibility is linear in the polar distortion, $\chi^{(2)}({\bf Q})\propto{\bf Q}$, leading to an SHG intensity quadratic in the inversion-breaking order parameter. When the polar mode is coherently driven by a terahertz electric field, the resulting time-dependent
lattice distortion dynamically reconstructs the electronic states and thereby modulates the optical SHG response, with $I_{2\omega}(t)\propto|{\bf Q}(t)|^2$ to leading order. This framework distinguishes the THz-driven
lattice dynamics from the electronic interband processes responsible for optical SHG, which is particularly important in insulating ferroelectrics where low-energy carrier dynamics are absent. Our theory thus provides a microscopic bridge between nonequilibrium polar
lattice dynamics and ultrafast electronic nonlinear optics.
Read the full abstract ▾
All authors Hong-Kui Liu, Zi-Chen Qin, Jun-Song Wu, Yue Yuan
Materials Science
Emergence and suppression of phonon vortices in two-dimensional crystals: Interplay of lattice symmetry, heavy impurities, and shear
Yu-Tian Zhang, Deng Pan and Yuliang Jin
Phonon vortices are
vortex-like displacement fields that appear in the vibrational modes of two- dimensional materials. Here, we demonstrate that these
vortices arise as
symmetry-adapted linear combinations of degenerate planar
phonon modes, with the superposition coefficients uniquely de- termined by the
lattice point group. This
symmetry principle establishes that
vortices are intrinsic standing-wave solutions in perfect
crystals, requiring neither impurities nor disorder. A heavy mass impurity favors
vortex modes over planar modes through stronger resonance-induced frequency soft- ening, whereas shear deformation suppresses
vortex modes by breaking rotational
symmetry. The competition between these two effects gives rise to a precisely predictable strain threshold. The proposed framework, grounded in
symmetry and energy-minimization, provides a useful basis for understanding vibrational topological defects induced by other types of impurities or defects. This study further suggests that defect and shear engineering constitutes an effective tuning strategy for controlling vibrational modes and the associated thermal and mechanical properties of
crystals.
Read the full abstract ▾
Materials Science
Topological and spin-orbit effects on orbital moments in ultra-thin magnetic films
Felix Nickel, Soumyajyoti Haldar, Mara Gutzeit et al. (+1 more)
Topological orbital moments (TOMs) are a direct hallmark of a
magnetic texture with a non-trivial
spin topology. In addition to giving insight into the
topology of the
magnetic texture, TOMs could also be used to manipulate
magnetic structures with a compensated total
spin moment. Experimental evidence of TOMs has been provided via transport measurements of the Hall effect in intercalated van-der-Waals materials. However, a direct observation of TOMs is still missing. Another complication arises for the unambiguous proof of the topological origin since orbital moments can also occur due to
spin-orbit coupling. Here, we use first-principles electronic structure theory to investigate the origin of orbital moments in different compensated
spin structures with a non-trivial
topology. We focus on ultrathin
magnetic films at surfaces such as Pd/Mn bilayers on Re(0001) which represent ideal model systems for the detection of TOMs since it is possible to apply experimental techniques with local resolution of
magnetic properties such as
spin-polarized scanning tunneling microscopy. Due to its trivial
topology we use the row-wise antiferromagnetic (RW-AFM) state in a hexagonal monolayer to analyze the
spin-orbit induced contributions. The triple-Q (3Q) state is a superposition state of three RW-AFM (1Q) states and thus electronically similar, however, due to its non-trivial
spin topology it exhibits TOMs. The comparison between these two
spin states allows us to disentangle the topological and
spin-orbit contributions to the orbital moments. We find that TOMs have an important contribution in
spin-compensated systems, since the
spin-orbit coupling induced orbital moments are nearly compensated. First-principles calculations for atomic-scale skyrmion
lattices in Fe monolayers on different surfaces exhibit the same general trend found for the 3Q state.
Read the full abstract ▾
All authors Felix Nickel, Soumyajyoti Haldar, Mara Gutzeit, Stefan Heinze
Materials Science
Layer Axial Phonons and Dipolar Thermal Response in Centrosymmetric Thin Films
Madhubanti Mukherjee, Kapil Gope and Barun Ghosh
In nonmagnetic centrosymmetric materials, $\mathcal{PT}$
symmetry enforces vanishing total
phonon angular momentum (
phonon AM) at every wave vector, making them appear unsuitable as hosts of axial
phonons. Here, using first-principles calculations for BaAgAs and representative van der Waal's layered materials, we show that centrosymmetric slabs can still host large hidden layer-resolved
phonon AM with both chiral and cycloidal modes. This hidden
phonon AM texture produces layer resolved
phonon thermal Edelstein-like responses and a real-space
phonon AM dipole response, both tunable by strain. Our results establish centrosymmetric layered materials as an exciting platform for hidden axial
phonon and multipolar
phonon thermal response.
Read the full abstract ▾
Materials Science
Freezing of a deformable water-saturated porous medium. Part I: THM formulation, OpenGeoSys-6 implementation and benchmarking
Tymofiy Gerasimov, Christian B. Silbermann, Dmitri Naumov et al. (+3 more)
In this contribution, Part I, we present a coupled thermo-hydro-mechanical formulation for modeling and analyzing water-to-ice phase change in a deformable fully-saturated porous medium. It is implemented in the multi-physics computational platform OpenGeoSys-6. We compute a series of carefully designed
benchmark problems which critically examine the corresponding formulation components and the overall implementation. Several ingredients that have a qualitative and quantitative impact on the numerical results are identified, particularly dissected and commented on. Simulations also account for soil deformation induced by freezing (as a result of 9% volumetric expansion caused by water-to-ice phase transition). The forthcoming Part II will complete the code verification and validation campaign by considering a real full-scale three-dimensional case study of shallow subsurface ice storage. More specifically, we simulate the ice growth process in a fully saturated soil specimen surrounding a group of borehole heat exchangers (BHEs) that contain subzero temperature coolant fluid. A snapshot of the numerical results of this task is already depicted here in Part I as a teaser.
Read the full abstract ▾
All authors Tymofiy Gerasimov, Christian B. Silbermann, Dmitri Naumov, Olaf Kolditz, Haibing Shao, Thomas Nagel
Materials Science
Heterogeneous ferroelectricity and conductivity of oxidized BaTiO$_3$ crystals: the role of nanoscale phase segregation in the surface region
Christian Rodenbücher, Gustav Bihlmayer, Susan Trolier-McKinstry et al. (+3 more)
We investigate the effect of thermal oxidation on BaTiO$_3$ single
crystals. Our results reveal that, even at moderate temperatures of up to 1000 {\deg}C, complex segregation mechanisms occur involving the movement of Ba-rich compounds to the upper surface, where they form inhomogeneously distributed BaO nanocrystals. As a result, deeper regions of the surface layer become depleted in Ba and become TiO$_2$-rich. A sandwich-like structure evolves in the surface layer, exhibiting a measurable electromotive force and self-polarization. This, in turn, screens the polarization and diminishes the global ferroelectric response. The conductivity is also strongly influenced by the irreversible segregation effects in the surface region. An as-received
crystal can be transformed into a metallic state, while oxidation induces semiconducting properties and prevents a return to the metallic state upon subsequent reduction. Nanoscale analysis demonstrates that the conductivity is channeled to filaments forming along dislocations, whose local chemical composition changes upon reduction and oxidation even at moderate temperatures due to preferential Ba and O pipe
diffusion thus determining the electric behavior of the whole sample.
Read the full abstract ▾
All authors Christian Rodenbücher, Gustav Bihlmayer, Susan Trolier-McKinstry, Jacek Szade, Franciszek Krok, Kristof Szot
Materials Science · Cross-listed from cond-mat.mes-hall
Moiré-induced lattice reconstruction at buried atomic interfaces
Nicholas Clark, Frederick Allars, Isaac Soltero et al. (+18 more)
Atomic reconstruction at twisted two-dimensional interfaces governs many of their emergent optical, electronic, and mechanical properties, including sliding ferroelectricity. Despite recent progress in understanding
lattice reconstruction in suspended twisted bilayers, structural changes at van der Waals heterointerfaces between multilayer
crystals remain largely unexplored. Here we use multi-slice electron ptychography to non-invasively recover the three-dimensional atomic structure at marginally twisted rhombohedral interfaces between thick transition-metal dichalcogenide
crystals. With a position precision of ~3 pm and a depth resolution ~1 nm, we resolve the twist-induced
lattice reconstruction field per layer, and the resulting dislocation network at the buried interface. Despite the bulk nature, we observe markedly strong in-plane interfacial reconstruction due to suppression of the out-of-plane bending by outer layers, exceeding predictions from our three-dimensional modelling. Furthermore, we extract the strain tensor
evolution during the decay of the reconstruction into the bulk, providing a structural foundation for understanding multi-layer moiré systems.
Read the full abstract ▾
All authors Nicholas Clark, Frederick Allars, Isaac Soltero, Wendong Wang, David Hopkinson, Hugo de Latour, James G. McHugh, William Talbott, Sam Sullivan-Allsop, Rongsheng Cai, Astrid Weston, Xiao Li, Gareth Tainton, Casey K. Cheung, Francisco Selles, Alex Summerfield, Andrey Kretinin, Christopher S. Allen, Vladimir Falko, Sarah J. Haigh, Roman Gorbachev
Materials Science
Chemically Resolved Topological Coordinates Link Structural Dynamics and Configurational Thermodynamics
Ayush Kumar Pandey and Abhishek Tewari
Atomic coordinates specify a structure, but they do not reveal how chemical connectivity across several length scales relates to atomic motion and configurational energy ordering. We formulate chemically directed persistent homology at four resolutions—complete networks, individual sites, spatial fields, and substitutional arrangements—while retaining the chemical identity and length scale of each connectivity feature. In ab initio molecular dynamics (AIMD) trajectories of $\delta$- and $\gamma$-CsPbI$_3$ at five temperatures spanning 500–700 K, the corner-sharing $\gamma$ network has a lower Pb–I restoring stiffness and permits larger iodide excursions, yet iodide positional correlations decay 2.27 times more slowly and Pb-network
topology retains
memory 1.63 times longer than in the edge-sharing $\delta$ phase. Local softness and loss of network
memory are therefore distinct. At individual sites, rare $\gamma$-phase Pb environments with a $\delta$-like Cs-cage connectivity precede 0.17 $\mathring{\mathrm{A}}$ greater Pb displacement over the subsequent 0.5 ps. The same Pb-network coordinate resolves disruption of corner-sharing connectivity across a 2560-atom $\delta|\gamma$ boundary. In substituted CsPbI$_3$, compact dopant arrangements undergo greater cooperative host relaxation and lie lower in density-functional-theory (DFT) energy than dispersed arrangements of the same composition. SchNet and Allegro model families with comparable energy errors encode opposite ordering along this coordinate, and 61 of 247 supplied models with errors below 1 meV atom$^{-1}$ on separate test structures reverse the DFT relation. Because relative configurational energies set Boltzmann populations, chemical network
topology links structure to physical response and tests whether learned energy models preserve DFT configurational ordering even when their average errors are small.
Read the full abstract ▾
Materials Science
Dark exciton signatures in the infrared transient absorption of MoS$_2$ monolayer
Tian-Xiang Qian, Marco D'Alessandro, Claudio Attaccalite et al. (+3 more)
Dark
excitons play a central role in the nonequilibrium dynamics of two-dimensional
semiconductors, but remain difficult to characterize. Transient-absorption experiments, with probes tuned in
exciton-
exciton transitions energy range (exc-tr-abs), can detect excitations from any populated dark
excitons, including
symmetry-forbidden,
spin-forbidden, and finite-momentum ones. In this work, we develop a $GW$+BSE scheme for computing exc-tr-abs spectra from arbitrary populated
exciton distributions. These dark
excitons are included equally by evaluating
exciton-
exciton dipoles in a locally smooth gauge, including intra- and inter-band contributions. For monolayer MoS$_2$, the exc-tr-abs signal arises from the $\Gamma$, $K$, $M$, and $Q$ valleys, differing substantially from the $\Gamma$-only interpretation.
Exciton-
exciton dipoles show similar intensities across these valleys, while their weights are dictated by initial excitonic populations. State- and
spin-resolved analyses assign the peaks to $1s \rightarrow 2p$ and $1s \rightarrow 3p$ transitions from both
spin-flip and
spin-conserving A and B
excitons across valleys and momenta.
Read the full abstract ▾
All authors Tian-Xiang Qian, Marco D'Alessandro, Claudio Attaccalite, Tian-Yi Cai, Sheng Ju, Davide Sangalli
Materials Science · Cross-listed from cond-mat.soft
A multi-scale study to unravel the dehydration mechanism of hydrated salts
A. C. Claude, H. Derluyn, J. van de Groep et al. (+1 more)
Understanding the dehydration mechanism of hydrated salts remains fundamentally important in solid state chemistry, as their behavior affect fields ranging from heat storage to heritage conservation and pharmaceutical crystallization. Combining Raman confocal microscopy, dynamic weight loss measurements, SEM, and micro CT, we show that dehydration kinetics of sodium sulfate decahydrate (mirabilite) unfold through two regimes: an initial nucleation controlled phase, where atomic rearrangement drives two dimensional lateral growth following an exponential law, and a subsequent phase boundary controlled regime, where growth advances into the
crystal depth, limited by water vacancy formation at the hydrated dehydrated interface. The resulting thenardite product shows around 35 percent shrinkage and forms a porous, layered dual porosity nanocrystalline structure, with relative humidity directly governing
crystal size. Extending this analysis to other sulfate hydrates reveals that crystallographic
symmetry changes between hydrate and anhydrous phases dictate surface morphology, linking microstructure to mechanism. This multiscale framework uncovers dynamics hidden from bulk measurements and suggests structural indicators could predict dehydration pathways in other hydrated salt families, and opening route toward designing thermal energy storage materials without exhaustive experimental screening.
Read the full abstract ▾
All authors A. C. Claude, H. Derluyn, J. van de Groep, N. Shahidzadeh
Materials Science
Coupling of two individual magnon resonators via a superconducting microwave resonator operating in the strong coupling regime
Anoop Kamalasanan, Georg Schmidt and Seth W. Kurfman
We demonstrate coherent coupling of ferromagnetic resonance in two individual permalloy stripes via a superconducting coplanar waveguide resonator. The two stripes are placed on top of the resonator with an angle of 50$^{\circ}$ between their respective long axes. This
alignment enables us to separately tune their ferromagnetic resonance frequency by exploiting their shape anisotropy by simply rotating the external bias
magnetic field in the sample plane. Both individual ferromagnets exhibit strong coupling with the microwave resonator. This method avoids the use of local individual bias coils and facilitates the integration of similar experiments into planar device infrastructures.
Read the full abstract ▾
Materials Science
Extending the Pnictide Chemical Space for Photovoltaics
Avaneesh Balasubramanian and Gopalakrishnan Sai Gautam
Developing novel and efficient materials that are beyond silicon for photovoltaic (PV) applications is required to meet the upcoming energy needs of our societies. To identify novel candidate materials that can act as PVs, we use first principles calculations to perform a systematic screening of the pnictide chemical space (i.e., nitrides and phosphides). Specifically, we explore three different ternary and quaternary pnictide classes, namely, ABCX$_2$, BB'B"X$_2$, and A$_4$BX$_2$ (A = Li, Na, or K; B, B', B" = Ca, Sr, Mg, or Zn; C = Al, Ga, or In; X = N or P), leading to a set of 104 possible pnictide compositions. Based on our evaluations of ground state structures, 0 K thermodynamic stabilities, electronic structures, carrier effective masses, dynamic stabilities, and intrinsic point defect formation energies, we arrive at three promising candidates, namely, NaCaInN$_2$, NaSrInN$_2$, and K$_4$ZnP$_2$. Notably, all the identified candidates are thermodynamically (meta)stable, exhibit direct (or nearest direct) band gaps that are optimal for PV applications, and are resistant to forming several types of point defects. We hope that our first principles driven workflow and the identified candidates will advance the development of novel PV materials and reinvigorate interest in the exploration of pnictides.
Read the full abstract ▾
Materials Science · Cross-listed from physics.app-ph
Towards an effective medium theory for in-vivo Magnetic Resonance: Characterizing Admissible Magnetization Dynamics
Alessandro Sbrizzi, Miha Fuderer and Ray Sheombarsing
The classical Bloch equation forms the foundation of
magnetic resonance theory but may be insufficient to capture the complex effective dynamics observed in heterogeneous materials such as biological tissue. Here an effective-medium strategy is proposed to describe
magnetic resonance dynamics from observations at macro-scale (order 1 mm$^3$). In this framework, the classical Larmor torque is retained while the relaxation term is replaced by a general nonlinear field (i.e. the effective medium term). This field is required to preserve key physical properties, including rotational
symmetry, global stability of thermal
equilibrium, and dissipativity. These requirements lead to a complete characterization of admissible relaxation fields and provide a constructive framework for generating nonlinear relaxation models. The resulting theory recovers classical Bloch dynamics as a special case and provides a principled foundation for effective-medium descriptions of
magnetic resonance phenomena.
Read the full abstract ▾
Materials Science
Real-space overlap is not enough: ambiguity in nanobeam iterative ptychography
Stephanie M. Ribet, Mohsen Danaie, Willem P.M. de Kleijne et al. (+5 more)
High-resolution iterative ptychography typically relies on a well-aligned, high-convergence-angle electron probe. Here we explore whether it can instead be performed at small convergence angles, relaxing the need for probe correctors and enabling experiments at low accelerating voltages or with a de-excited objective lens, as in Lorentz mode. Through experiments and simulations, we show that once the convergence angle is small enough that no diffracted disks overlap, the resulting reconstruction is ambiguous, posing a significant challenge for robust interpretation of results. This challenge arises because of the lack of interference between Bragg disks in the recorded diffraction pattern intensity, leading to no phase information for each reflection. Reconstructions with these data lead to degenerate objects in which rigid translations of the
lattice and reversals of contrast of the object produce the same error between experimental data and the ptychography forward model. Increasing the real-space overlap between probe positions does not lift this degeneracy. An amorphous substrate can supply the missing phase relationships by giving the Bragg beams support in the gaps between disks. This phasing is fragile, however, and survives only where the forward model matches the experiment. At fixed dose, either constraining the object to be a pure phase object or introducing thermal motion into the forward model is enough on its own to make the solution non-unique, highlighting why our experimental reconstructions below the overlap threshold are ambiguous despite ample dose and real-space redundancy. Most troublingly, the
lattice spacing and orientation are always recovered correctly, so a non-unique reconstruction looks convincing and can be diagnosed only by repeating the reconstruction from different starting points.
Read the full abstract ▾
All authors Stephanie M. Ribet, Mohsen Danaie, Willem P.M. de Kleijne, Arthur R. C. McCray, Frederick Allars, Christopher S. Allen, Colin Ophus, Georgios Varnavides
Materials Science
Covariant formula for the driving force for interface migration
Adam Morawiec
Interfaces of crystalline materials are strongly affected by the anisotropy of interface energy. A key quantity in this context is the interface stiffness tensor, which characterizes the response of the interface energy to changes in interface orientation and plays a role in determining the driving force for interface migration. The latter is expressible via contraction of the stiffness tensor and interface
curvature tensor. Practical computations involving tensors necessarily rely on their individual components. In this work, an explicit component-wise expression is derived for the contraction of the stiffness and
curvature tensors, valid in arbitrary coordinate systems. Within this formulation, to get the driving force, the
curvature tensor is contracted with the pullback of a stiffness-related tensor - originally defined in three-dimensional Euclidean space - onto the interface
manifold. This covariant treatment establishes a physically consistent foundation for three-dimensional computational models involving interface stiffness.
Read the full abstract ▾
Materials Science
Coexisting Large and Small Polarons in Photoexcited CeO$_2$
Valentina Mazzotti, Eleonora Spurio, Nicolas Delnour et al. (+5 more)
Time-resolved terahertz (THz) spectroscopy is used to probe polaron formation in CeO$_2$. The ultrafast THz photoconductivity is dominated by contributions from large hole and small electron polarons. Delocalized large hole polarons are formed on a $820 \pm 50$ fs time scale and are of Fröhlich type, with optical conductivity well described by a simple Drude model and a transient hole mobility of $100$ cm$^2$/Vs. Small electron polarons form via localized coupling to Ce
lattice sites, revealed by reduction in the
lattice Born effective charge causing a transient
phonon softening. These results establish the dual polaron nature of CeO$_2$ and provide a basis for understanding charge transfer dynamics in metal oxide photocatalysts.
Read the full abstract ▾
All authors Valentina Mazzotti, Eleonora Spurio, Nicolas Delnour, Michael Hilke, Kirk H. Bevan, Alexander Shluger, Paola Luches, David G. Cooke
Materials Science · Cross-listed from cond-mat.supr-con
Superconductivity of Tellurium Polyhydride with Tc above 90K
Jinfu Zhu, Guiqi Liu, Yuanhao Su et al. (+15 more)
We report experimental diacovery of superconductivity (SC) in tellurium (Te) polyhydride. The compound was synthesized at high pressure and high temperature conditions using a diamond anvil
cell combined with a
laser heating system. Subsequent in situ transport measurements at high pressures, performed as a function of temperature and applied
magnetic field, revealed a superconducting transition with a critical temperature Tc about 91 K at 263 GPa. The superconducting phase is assigned to TeH4 with characterized face shared TeH12 cage forming quasi molecular H2 units based on synchrotron x-ray diffraction experiments. Analysis of the SC behavior at
magnetic fields yielded a Ginzburg Landau (GL) coherence length of approximately 54 angstroms. Tellurium polyhydride thus becomes another chalcogen polyhydride
superconductor in addition to the landmark discovery of the first polyhydride high Tc SC SH3.
Read the full abstract ▾
All authors Jinfu Zhu, Guiqi Liu, Yuanhao Su, Hongyu Liu, Sijia Zhang, Panpan Kong, Qingqing Liu, Jianfa Zhao, Shaomin Feng, Jun Zhang, Haoyu Zheng, Jing Song, Luhong Wang, Fuyang Liu, Haozhe Liu, M. Bykov, Xiancheng Wang, Changqing Jin
Materials Science
Attosecond Reconstruction of Strain Tensors via Electronic Fingerprints
Jing Li, Jiayu Yan, Guoyong Yuan et al. (+3 more)
We demonstrate an attosecond transient absorption spectroscopy (ATAS) scheme for reconstructing strain tensors in two-dimensional materials. Using strained
graphene as a prototype system, we show that the fishbone structures in ATAS serve as distinctive spectral fingerprints of strain, where strain-induced shifts and splittings of van Hove singularities encode the magnitude and orientation of the strain tensor, respectively. By combining density-
matrix simulations with analytical modeling, we establish a direct mapping between transient absorption spectra and strain tensors, enabling accurate
retrieval of
lattice deformation from ultrafast electronic responses. Our work introduces an attosecond spectroscopic paradigm for ultrafast strain metrology, where electronic fingerprints replace conventional structural probes for sensing
lattice deformation in
quantum materials.
Read the full abstract ▾
All authors Jing Li, Jiayu Yan, Guoyong Yuan, Chao Chen, Shang Wang, Fulong Dong
Materials Science
Two-step transient liquid phase bonding of NiTi to Ti-6Al-4V through a NbZrW barrier
Zhaoxi Cao, Samuel Price, John P. Reidy et al. (+1 more)
Dissimilar joining of NiTi to Ti-6Al-4V (Ti-64) is limited by brittle Ti2Ni formation and degradation of NiTi functionality. A two-step transient
liquid phase (TLP) route was developed in which a refractory NbZrW
diffusion barrier converts the incompatible couple into two independently bondable interfaces. The barrier plays a different role for each
alloy: a reactive substrate for NiTi, dissolving to form a Ti-rich Ni-Ti-Nb
liquid that infiltrates its own grain boundaries and is terminated by selective Ti absorption into the barrier; and an inert substrate for Ti-64, joined through contact melting of a sacrificial Cu foil. Both interfaces are fully dense and free of continuous intermetallic layers. In tension, joints spanning both interfaces began transforming at 350 MPa, exhibited a stress plateau to 2.5 global strain (consistent with stress-induced transformation of the NiTi half of the gauge) and failed beyond the plateau at 380-410 MPa. Five load-unload cycles to 460 MPa showed stable superelastic loops with minor ratcheting. These results demonstrate that a
diffusion barrier enables dissimilar TLP joining of otherwise incompatible
alloys.
Read the full abstract ▾
All authors Zhaoxi Cao, Samuel Price, John P. Reidy, Ian McCue
Materials Science · Cross-listed from cond-mat.soft
Experimental Observation of Mesoscopic Dynamic Fluctuations in Water-Alcohol Mixtures
Yukio Kajihara, Nanako Shibata and Masanori Inui
We applied a dynamic fluctuation measurement method to
liquid water-methanol mixtures over a wide range of compositions and temperatures. This method, which we developed in recent years, combines ultrasonic and inelastic X-ray scattering techniques to detect mesoscopic-level fluctuations - that is, the degree of heterogeneity - in
liquids using sound waves. As a result, it was found that dynamic fluctuations exist across a wide range of compositions and temperatures, including pure substances (water and methanol). Furthermore, in the low-methanol composition range (approximately 20% mol or less), the strength of dynamic fluctuation increased toward lower compositions and lower temperatures, suggesting that the origin of the fluctuation lies in the low temperature (supercooled) region of water alone. Conversely, this indicates that in the range below 20% methanol, fluctuations in water alone are dominant rather than the mixed effects of water and methanol. We performed similar dynamic fluctuation measurements on water-ethanol and water-glycerol mixtures at room temperature. We found that dynamic fluctuations exist universally across the entire composition range, and confirmed an increase in the strength of dynamic fluctuations toward lower compositions in the regions approximately below 15% and below 20%, respectively. This revealed that the phenomenon is not unique to methanol systems but is a common behavior shared by water-alcohol mixtures. It has long been known that water-alcohol mixtures exhibit various thermodynamic anomalies, but the mechanisms behind them have not yet been fully elucidated. The present results are expected to provide a new direction for discussion on this issue.
Read the full abstract ▾