Materials Science · Cross-listed from physics.geo-ph
Quantifying the effects of nickel on Earth's inner-core nucleation
Jiahui Zhai, Liangrui Wei, Chen Gao et al. (+1 more)
The formation of Earth's solid inner core marks a major transition in the thermal and chemical
evolution of the deep Earth, yet its origin remains paradoxical, as initial nucleation appears to require unrealistically large undercooling in the outer core. Here, we use atomistic simulations to quantify how Ni affects this process under inner-core conditions. While Fe-Ni
alloys preserve strong thermodynamic competition between the hcp and bcc phases, the bcc phase consistently forms smaller critical
nuclei and has lower nucleation barriers than hcp. Increasing Ni content in the melts further lowers the nucleation barrier and shortens the nucleation waiting time. Local chemical fluctuations also strongly affect the macroscopic nucleation rate. Combining these effects, bcc nucleation in Fe80Ni20 reaches about 250 K of undercooling, approaching geophysical constraints. We demonstrate that Ni enrichment, bcc nucleation, and chemical heterogeneity substantially narrow the inner-core nucleation paradox.
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All authors Jiahui Zhai, Liangrui Wei, Chen Gao, Yang Sun
Strongly Correlated Electrons
3D- (H-theta-phi) magnetic phase diagram of antiferromagnetic metal GdB6 with electron and lattice instability
A. N. Azarevich, A. V. Bogach, T. F. Garipova et al. (+10 more)
The origin of charge transport and magnetization anisotropy was studied in GdB6, an antiferromagnetic (AF) metal (Néel temperature TN ~ 15.5 K) with cubic
lattice and Gd S-type
magnetic ions. Both small static Jahn-Teller distortions and nanoscale electronic instabilities (dynamic charge stripes) were found in precise low temperature X-ray diffraction measurements. The detailed
magnetic field (H) vs temperature (T) phase diagrams were constructed with two main
magnetic phases AF(I) and AF(II). Using the angular phi-dependences of magnetoresistance and magnetization, impeller-type patterns of the H-phi
magnetic phase diagrams in the (110) and (111) planes were found at helium temperatures, which included the AF phases I and II separated from each other by radial and circular boundaries. The results argue in favor of the important role of the
spin density wave 5d- component in the
magnetic structure of AF(II) state. Charge fluctuations in stripes are proposed to be responsible for the suppression of the Ruderman-Kittel-Kasuya-Yoshida (RKKY) indirect exchange between the first and second neighboring Gd3+ ions located along the <100> and <110> directions. These dynamic charge stripes and vibrationally coupled Gd-Gd pairs produce unusual anisotropy of charge scattering and the impeller-type diagrams in GdB6 with S-type
magnetic ion.
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All authors A. N. Azarevich, A. V. Bogach, T. F. Garipova, V. V. Voronov, M. Rajnak, S. Gabani, K. Flachbart, N. B. Bolotina, O. N. Khrykina, V. M. Gridchina, A. Yu. Tsvetkov, S. Yu. Gavrilkin, N. E. Sluchanko
Quantum Gases · Cross-listed from quant-ph
Programmable Cavity Squeezing for Distributed Sensing in a Tweezer Array
Youssef Trifa, Marco Fattori and Luca Pezzè
Field sensing with state-of-the-art atom interferometers is restricted to the use of uncorrelated devices op- erating in parallel. We can overcome this limitation by using distributed sensing protocols where
quantum correlations among spatially-separated devices are engineered in the spatial mode carrying the signal. We show that a tweezer array in a cavity offers an ideal testbed to engineer
quantum states for distributed sensing, with the possibility to generate
entanglement both within and between the clouds. The competition between local and intercloud cavity-mediated exchange allows the sign and spatial pattern of the intercloud couplings to select the squeezed mode. For two ensembles, positive coupling produces uniform collective squeezing, whereas negative coupling generates strong staggered, nonlocal squeezing. A semiclassical analysis reveals a counter-twisting- like phase-space flow, qualitatively distinct from standard one-axis twisting. The analysis and results can be further generalized to a larger number of ensembles. We apply the scheme to differential Ramsey interferometry with common phase noise spanning the full 2 \pi range, the resulting staggered states reduce the phase uncertainty below the standard
quantum limit, with an ellipse
estimator approaching the Cramèr-Rao bound. These results establish programmable cavity interactions as a scalable route to
entanglement tailored to distributed signals.
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Materials Science
Emergent Skyrmion Hall Effect in $d$-wave Altermagnets at Finite Temperature
Tingting Liu, Bingyu Sun, Fengyue Zhu et al. (+4 more)
Altermagnets combine compensated
magnetic order with unconventional
symmetry-dependent responses, offering a promising platform for spintronic applications. Here, we show that a voltage-controlled
magnetic-anisotropy gradient drives altermagnetic (ATM) skyrmions in a nearly rectilinear, Hall-free manner in the absence of thermal fluctuations, owing to their strongly compensated gyrotropic response. Thermal
magnons qualitatively modify this behavior by increasing the longitudinal drag through
magnon–skyrmion scattering and generating a transverse reaction force through handedness-dependent skew scattering. Owing to the anisotropic altermagnetic
magnon band structure, the relative transport weights of the two
magnon handednesses are interchanged between propagation along the $x$ and $y$ directions, resulting in transverse skyrmion drifts of opposite sign. By contrast, along the high-
symmetry direction, the two
magnon handednesses remain degenerate and their transverse contributions cancel, preserving Hall-free motion even at finite temperature. We thus uncover a thermally emergent anisotropic skyrmion Hall effect whose direction-dependent magnitude and sign originate from the intrinsic
symmetry-dependent
magnon spectrum, making it a generic finite-temperature dynamical feature of ATM skyrmions. Our results establish a low-power route toward electrically controlled and thermally tunable ATM skyrmion transport.
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All authors Tingting Liu, Bingyu Sun, Fengyue Zhu, Zhihui Zhang, Peiyu Zhang, Yang Liu, Minghui Qin
Statistical Mechanics
Localization Delocalization Transition in Diffusion with Adaptive Resetting
Tommer D. Keidar and Shlomi Reuveni
Stochastic resetting can localize
diffusion and generate nonequilibrium steady states, but the conditions under which spatially dependent resetting produces localization remain unclear. Here, we establish a general classification for
diffusion under adaptive resetting, where the resetting rate $r(x)$ depends on position. For rates with the asymptotic scaling $r(x)\sim |x|^\lambda$, we identify a sharp threshold at $\lambda=-2$. For $\lambda>-2$, the steady state is localized and exhibits stretched-exponential tails, whereas for $\lambda<-2$, resetting is asymptotically too weak to localize the particle. Precisely at the marginal scaling $r(x)\sim |x|^{-2}$, a qualitatively new regime emerges: the steady state develops power-law tails with a temperature-dependent exponent and exhibits a finite-temperature delocalization transition. Thus, inverse-square resetting plays the role of the logarithmic potential in
equilibrium, establishing a nonequilibrium counterpart of the temperature-driven delocalization seen there.
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Materials Science
Laser induced ultrafast Co 3d and Ho 4f spin dynamics in CoHo ferrimagnetic alloys
Deeksha Gupta, Boonthum Kunyangyuen, Matthias Riepp et al. (+8 more)
The transition metal (TM) / rare-earth (RE)
alloys have received renewed interest lately as model systems to decipher the origin of all-optical helicity-independent switching (AO-HIS) by femtosecond
laser pulses. Recently, a distinct single-pulse magnetization reversal mechanism, based on domain-wall motion and coalescence, has been reported in CoDy and CoHo
alloys, as well as in Co/Gd ultrathin bilayers. It has been claimed that this specific toggle switching is achieved when the Co sublattice is fully demagnetized and the characteristic demagnetization times {\tau}RE of the RE (Gd, Dy or Ho) sublattices is longer than that of the Co and the angular momentum transferred to Co is reduced. Element- and time-resolved X-ray spectroscopy studies of CoDy
alloys have reported characteristic demagnetization times of {\tau}Co = 0.2 ps and {\tau}Dy = 0.6 ps at room temperature. Similarly, Ho is expected to exhibit a slower response, but its ultrafast 4f
spin dynamics remain experimentally unexplored. Here, we report on element- and time-resolved investigations of femtosecond
laser induced ultrafast dynamics of the Co 3d and Ho 4f
spins in ferrimagnetic Co_{80}Ho_{20}
alloys to verify this prediction. We observed characteristic demagnetization times {\tau}Co = 0.22 +/- 0.01 ps and {\tau}Ho = 0.87 +/- 0.15 ps at room temperature. These results show that Ho demagnetizes substantially more slowly than Co in Co_{80}Ho_{20}, supporting the proposed condition for domain-wall-mediated all-optical toggle switching
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All authors Deeksha Gupta, Boonthum Kunyangyuen, Matthias Riepp, Karsten Holldack, Radu-Marius Abrudan, Torsten Kachel, Niko Pontius, Christian Schüßler-Langeheine, Mircea Vomir, Michel Hehn, Nicolas Bergeard
Mesoscale and Nanoscale Physics
Giant bulk photovoltaic effect driven by interfacial symmetry breaking in MoS2/Ta2NiSe5 heterostructures
Jianwen Ma, Pengliang Leng, Lei Peng et al. (+16 more)
Van der Waals (vdW)
heterostructures offer a versatile platform for engineering unconventional bulk photovoltaic (BPV) effect through interfacial
symmetry breaking. However, the coexistence of multiple photophysical mechanisms, driven by structural complexity, spontaneous charge transfer, and strong interlayer coupling, often obscures the microscopic origin of the BPV response and hinders its rational optimization. Here, we demonstrate a pronounced BPV effect localized at the overlap region of a cross-bar MoS2/Ta2NiSe5 vdW
heterostructure, where
symmetry breaking induced by vertical stacking lifts the inversion center of MoS2. The orthogonal device geometry enables the independent probing of intralayer and interfacial photoresponse pathways, facilitating clear separation of competing mechanisms. Spontaneous interfacial charge transfer between MoS2 and Ta2NiSe5 further establishes a strong interlayer electronic coupling. By modulating the interlayer potential landscape through gate voltage and vertical electric fields, we achieve an optimized zero-bias photocurrent density of 247 A/cm2 and a BPV coefficient of 0.99 V-1. Supported by theoretical modelling, our results illustrate how minimalist device geometry can transform complex
heterostructures into experimentally tractable platforms. This strategy paves the way for analyzing and optimizing interface-driven BPV effect, with implications for self-powered optoelectronics, broadband photodetection, and energy-harvesting nanodevices.
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All authors Jianwen Ma, Pengliang Leng, Lei Peng, Congming Hao, Xianghao Meng, Jiaqi Liu, Yang Gan, Min Luo, Zifan Zhang, Jiaming Gu, Qinghang Liu, Lidan Duan, Du Xiang, Wu Shi, Peng Wang, Weibin Chu, Xiang Yuan, Weida Hu, Cheng Zhang
Materials Science
THz-induced phonomagnetism in diamagnetic quantum paraelectric KTaO$_3$
C. Kadlec, F. Kadlec, D. Repček et al. (+13 more)
The current efforts striving to develop new ways of data manipulation are aimed at ultrafast control of magnetization in
magnetic materials, as well as at inducing
magnetic moments in diamagnetics. We demonstrate that in the diamagnetic
quantum paraelectric KTaO$_3$, the electric field of circularly polarized THz pulses with an amplitude of $\sim 300\,$kV/cm induces a transient
magnetic-like response by resonantly exciting its degenerate soft polar
phonon. This
phonon-mediated response was measured using the THz pump—optical probe technique via the time-resolved magneto-optic Faraday effect. Our detection scheme was set up to cancel out the major part of the electro-optic Kerr effect which also usually significantly contributes to the transient response. The Kerr-effect-related signal was further suppressed by subtracting the experimental data related to oppositely circularly polarized THz radiation. Thus, we were able to unambiguously identify a temperature-dependent
magnetic-like behavior of the KTaO$_3$
crystal manifested by the extracted Faraday rotation. We developed a theoretical model describing well quantitatively the measured curves of the transient Faraday effect signal. However, their amplitudes exhibit an unexpected temperature dependence, which might be a key to a deeper understanding of the observed phonomagnetic effect.
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All authors C. Kadlec, F. Kadlec, D. Repček, P. Kužel, M. Basini, J.-C. Deinert, S. Kovalev, T. Tadano, M. Udina, I. Ilyakov, T.V.A.G. de Oliveira, A. Ponomaryov, A. Arshad, A. Maia, S. Bonetti, S. Kamba
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Fast On-Chip Thermometry with TiN Kinetic Inductance Resonators in 22 nm Process Technology
Johann Drayne, George Ridgard, Lorenzo Peri et al. (+9 more)
Understanding the temporal and spatial dependence of temperature is critical in high-performance cryogenic devices. Typical thermometry techniques struggle to simultaneously combine high bandwidth, sensitivity and on-chip integration, limiting their ability to measure fast intra-device thermal fluctuations. Here, we demonstrate a time-resolved thermometry platform based on TiN kinetic inductance resonators integrated in a 22 nm FDSOI chip. By tracking temperature-dependent shifts in the resonant frequency, we achieve sub-millikelvin temperature sensitivity down to temperatures of 100 mK. Time-resolved on-chip pulsed heating experiments as a function of distance reveal an onset delay, consistent with a quasi-ballistic heat propagation velocity of 3.9 ${\pm}$ 0.1 mm ${\mu}$s${}^{-1}$. We also show that elevated temperatures increase net thermal conductance, shortening thermal relaxation times across all spatial separations. This behaviour manifests in two distinct regimes: a substrate-limited regime at 100 mK, where cooling rates vary with heater distance, and a Kapitza boundary-limited regime at 400 mK, where thermal relaxation becomes more spatially uniform. These measurements demonstrate kinetic inductance thermometry's ability to rapidly probe non-
equilibrium temperature dynamics in cryogenic devices such as
quantum processors.
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All authors Johann Drayne, George Ridgard, Lorenzo Peri, Frederic Schlattner, Fabio Olivieri, Mathieu de Kruijf, Isaac Harris, Grayson Noah, James Kirkman, Alberto Gomez-Saiz, M. Fernando Gonzalez-Zalba, Thomas Swift
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
A Superconducting Phase Transition Single-Electron Transistor
Gorka Aizpurua-Iraola, Thomas H. Swift, Felix-Ekkehard von Horstig et al. (+6 more)
Quantum computers require fast and accurate methods for
qubit state detection. Phase-transition sensors exploit the abrupt change between two physical states of a material to achieve enhanced sensitivity and have enabled advanced detectors for
quantum technologies, such as superconducting nanowire single-
photon detectors. However, this sensing principle has not yet been applied to
semiconductor spin qubits. Here, we demonstrate a superconducting phase-transition
radio-frequency single-electron transistor (PTSET), a charge sensor for
semiconductor spin qubits whose response is enhanced by a superconducting-to-normal phase transition. The transition is engineered by linking the sensor current to a low-critical-current, high-kinetic-inductance inductor integrated into the
radio-frequency matching network. We demonstrate improvements in sensitivity of one and two orders of magnitude over conventional rfSETs in the large- and small-signal regimes, respectively. Our results establish phase-transition sensing as a route towards ultrasensitive, integrated charge sensors for
semiconductor quantum computing and point to broader applications, including cryogenic
photon detection for
radio astronomy.
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All authors Gorka Aizpurua-Iraola, Thomas H. Swift, Felix-Ekkehard von Horstig, Domenic Prete, James Kirkman, Grayson M. Noah, Fabio Olivieri, Alberto Gomez-Saiz, M. Fernando Gonzalez-Zalba
Materials Science · Cross-listed from physics.flu-dyn
High-resolution in situ analysis of biomass pyrolysis by combining quantitative synchrotron $\mu$CT and 3D particle-resolved simulations
Emeric Boigné, Mohamed M. Ahmed, Collin Foster et al. (+7 more)
Understanding the coupling between transport, chemical kinetics, and structural response within solid fuel combustion requires in situ measurements at high spatial resolution. To examine the dynamics of biomass pyrolysis, we optimize synchrotron X-ray micro-computed
tomography ($\mu$CT), and conduct 3D particle-resolved simulations. A micro-focused heating
cell with controlled heating and flow rate is employed, achieving temperatures of up to 1240 K and 3D imaging at 3.24 $\mu$m spatial and sub-minute temporal resolutions. The pyrolysis of three biomass materials at sample heating rates of 10-14 K/min are examined. The $\mu$CT measurements capture pore deformation, cracking, anisotropic shrinkage, and provide simultaneous thermogravimetric and thermovolumetric analyses to examine specific secondary pyrolysis pathways. Complementary 3D simulations considering detailed kinetics and structural response reproduce the key trends observed, and identify deficiencies in capturing simultaneous mass and volume losses during pyrolysis.
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All authors Emeric Boigné, Mohamed M. Ahmed, Collin Foster, Edna R. Toro, Dilworth Y. Parkinson, Alastair A. MacDowell, Harold S. Barnard, Francesco Panerai, Chiara Saggese, Matthias Ihme
Quantum Gases
Crossing the Rotational Sound Barrier in a Quantum Solvent
Baptiste Coquinot, Giacomo Bighin, Mikhail Lemeshko et al. (+1 more)
Molecules embedded in superfluids provide an experimentally controllable platform for investigating impurity physics. Here, we investigate a driven molecule rotating in a superfluid environment, including helium and Bose–Einstein condensates, at rotation frequencies similar to the bath dynamics. Within the experimentally relevant platform of an optical centrifuge, we show that the rotor remains localized up to a characteristic harmonic frequency that can realistically exceed the excitation energies of the bath, enabling access to ultrafast rotating impurities. In the co-rotating frame, the bath excitations experience a rotational Doppler shift, generating angular-momentum-resolved resonances absent in
equilibrium angulon theory. We identify a dissipative rotational sound barrier at which the molecule resonantly emits bath excitations and undergoes strong angular momentum exchange with the surrounding medium. Overall, we establish the dynamical phase diagram of the driven rotor in a
quantum solvent and introduce a generic platform for investigating fast driven rotating impurities in
quantum many-body systems.
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All authors Baptiste Coquinot, Giacomo Bighin, Mikhail Lemeshko, Ragheed Alhyder
Materials Science
Intrinsic anomalous Hall response in the bilayer kagome ferromagnet Co$_3$Sn
Yuqi Qin, Soumya Sankar, Xingkai Cheng et al. (+4 more)
Transition-metal kagome magnets provide a rich platform for investigating the interplay between layer stacking,
magnetic order, and band
topology. Here, we report the molecular beam epitaxy and experimental investigation of high-quality thin films of the kagome metal Co$_3$Sn, which has not been synthesized in bulk form yet. Structural and chemical analyses confirm a hexagonal
lattice structure ($P6_3/mmc$) composed of direct A-B stacked Co$_3$Sn kagome bilayers. Magnetometry reveals robust easy-plane ferromagnetism with a Curie temperature exceeding $300\,\text{K}$. Magneto-transport measurements demonstrate metallic behavior (carrier density $n\approx5.01\times10^{22}\,\text{cm}^{-3}$) alongside a temperature-independent anomalous Hall conductivity of $\sigma_{\rm AHE}\approx90\,\Omega^{-1}\cdot{\rm cm}^{-1}$, extending from $2\,\text{K}$ up to room temperature. Results from first-principles density functional theory calculations attribute this anomalous Hall response to intrinsic Berry
curvature hotspots near the Fermi level in the
spin-split band structure. Our results establish Co$_3$Sn as a room-temperature kagome ferromagnet and highlight the impact of the layer stacking sequence on the material properties of kagome metals from the CoSn family.
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All authors Yuqi Qin, Soumya Sankar, Xingkai Cheng, Yifan Jiang, Shiming Lei, Junwei Liu, Berthold Jäck
Materials Science
Atomic-scale composition of the ternary III-V semiconductor (Al,Ga)Sb visualized by cross-sectional scanning tunneling microscopy
Hitesh Kumar, Vladimir Kaganer, Zijin Lei et al. (+3 more)
Cross-sectional scanning tunneling microscopy at 5 K is used to investigate cation mixing in (Al,Ga)Sb layers grown by molecular beam epitaxy, via direct atom counting at the (1-10) and (110) cleavage planes. Electronic contrast between Al and Ga surface cations enables statistical analysis of the metal sublattice along the non-equivalent <110> directions within the zincblende (001) surface and along the [001] growth direction. The cation distribution is found to be random both along the growth direction and within the growth plane, with no evidence of long-range order or anisotropic growth kinetics; notably, the mean numbers of consecutive cations of the same type along the two in-plane directions are equal, possibly due to statistical averaging over randomly distributed subsurface cations. The results are compatible with either strain-mediated interactions during cation incorporation at the growth front or ideal, uncorrelated cation mixing. Overall, the examined (Al,Ga)Sb
alloy shows an exceptionally high degree of atomic-level homogeneity.
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All authors Hitesh Kumar, Vladimir Kaganer, Zijin Lei, Rüdiger Schott, Werner Wegscheider, Stefan Fölsch
Mesoscale and Nanoscale Physics
Rui-Chang Shen, Yihao Yang and Haoran Xue
High-frequency artificial phononic
crystals offer a low-loss platform compatible with on-chip integration, yet realizing Chern phononic phases at GHz frequencies remains challenging. Here, we propose a
magnon-induced phononic Chern
insulator in a honeycomb phononic
crystal hybridized with ferromagnetic islands at the hexagon centers. A circularly polarized Kittel mode couples to the surrounding
phonons with a phase winding, which breaks time-reversal
symmetry and opens a full Chern gap. In the large-detuning regime, this mechanism leads to an effective Haldane-type phononic model with
magnon-induced complex hopping. By tuning the
magnon-
phonon interaction, the full hybrid system accesses Chern phases with tunable Chern numbers |C|=1 and |C|=2. The predicted gaps can exceed realistic
phonon and
magnon linewidths, enabling their observation in GHz acoustic devices. Our work establishes chiral
magnon–
phonon hybridization as a route to magnetically reconfigurable topological phononics.
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Materials Science
Topology-Controlled Phonon Dielectric Response Beyond Density Scaling in Metal-Organic Frameworks
Debayan Mondal, Jiahao Ye, Lorenzo Donà et al. (+1 more)
Effective-medium theory treats material porosity as passive dilution. Using ab initio density functional theory and high-resolution synchrotron terahertz (THz) spectroscopy on isochemical zeolitic-imidazolate frameworks, we show that while the electronic permittivity obeys Clausius-Mossotti density scaling, the
phonon contribution violates the conventional density scaling rules. Identical Born charges rule out the role of local chemistry. Instead, the framework connectivity localizes the THz response, where the coherency of
phonon eigenvectors determines the mode-effective charges. Long-range architecture of framework
topology ubiquitous in metal-organic frameworks is therefore a dielectric degree of freedom beyond the density scaling of conventional solids.
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All authors Debayan Mondal, Jiahao Ye, Lorenzo Donà, Jin-Chong Tan
Mesoscale and Nanoscale Physics
Spin preservation in screw-symmetric molecules
Jonas Bloch, Fedor Baranov and Maxim Breitkreiz
In electronic transport through long molecules,
spin is expected to be preserved only when the dwell time is much shorter than the characteristic
spin-mixing timescale $\hbar/\Delta$, where $\Delta$ is the magnitude of a
spin-dependent potential, such as
spin-orbit coupling. We show that, in molecules featuring discrete screw
symmetry,
spin preservation can be enhanced far beyond this timescale owing to strong
spin separation in quasi-momentum. This
spin fidelity in long molecules is consistent with chirality-induced
spin selectivity (CISS), suggesting
spin-dependent transport in long, chiral molecules with amplified
spin-splitting mechanisms. We provide analytical derivation of the enhanced
spin preservation and test it on tight-binding models, which confirm that the effect gradually weakens when the screw
symmetry is broken or changes from discrete to continuous. Furthermore, we perform transport simulations to show that a strong magnetoresistance trace of
symmetry-protected
spin fidelity emerges in a
spin-valve setup with two
magnetic leads, which we propose as an experimentally accessible signature.
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Mesoscale and Nanoscale Physics
Hall effect in viscous flows of two-dimensional electrons in samples with edges of arbitrary roughness
A.V. Gert and P.S. Alekseev
In ultra-clean conductors, fast inter-particle collisions can lead to the formation of a viscous electron fluid and realization of the hydrodynamic transport regime. Here we develop a theory of hydrodynamic magnetotransport of two-dimensional (2D) electrons in samples with low densities of defects and edges of arbitrary roughness. Within our model the roughness is described by a single parameter with the dimension of speed in the boundary conditions on sample edges. The electron-fluid flow profiles in long samples, as well as the corresponding longitudinal and Hall resistances, are calculated. The contribution to the Hall resistance associated with the relaxation processes exhibits a saturation in the limit of high
magnetic field and a minimum as a function of the
magnetic field for sufficiently rough edges. The minimum disappears as the edge roughness decreases or the sample width and bulk scattering by defects increase. These properties of the Hall resistance can serve as the signs to identify the hydrodynamic regime of electron transport in experiments and can be used to determine its parameters, in particular, the degree of edge roughness.
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Materials Science
Electronic Structure and Band-Edge Character of Ga-Substituted $\alpha$-Al$_2$O$_3$: A First-Principles Study
Z. S. Machavariani, R. Ya. Kezerashvili and T. Tchelidze
We present a first-principles density functional theory study of substitutional Ga incorporation in an $\alpha$-Al$_2$O$_3$-derived host, isolating chemical
embedding effects without explicit
geometric quantum confinement. Using a 30-atom $\alpha$-Al$_2$O$_3$ supercell with two substituted Ga atoms, we examine three nonequivalent Ga-pair configurations and combine configuration-dependent energetics, local structural analysis, Ga-centered distortion metrics, and electronic-structure calculations.% to establish the relationship between local coordination distortion and band-edge modification. The energetically preferred configuration is governed not solely by Ga–O bond expansion but by the ability of the host
lattice to accommodate bond-length and angular distortions around substituted Ga centers. Ga incorporation narrows the band gap relative to pristine $\alpha$-Al$_2$O$_3$ without generating mid-gap states, primarily modifying the conduction-band
manifold while preserving the oxygen-dominated valence edge. Band-edge charge densities and charge-density-difference maps show that the electronic response remains localized around the Ga-centered coordination environment. These results establish a chemically resolved baseline for understanding Ga incorporation in ultrawide-band-gap oxides and for future studies of confinement and interface effects in Ga-containing oxide nanostructures.
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Materials Science
Scalable conformal electronics based on roll-to-roll exfoliated van der Waals semiconductors
Yigit Sozen, Esteban Zamora-Amo, Juan J. Riquelme et al. (+1 more)
Integrating electronic devices onto surfaces with complex topography such as skin, textiles, and biological tissues requires fabrication strategies that combine mechanical conformability with high electronic performance and scalable manufacturing. While two-dimensional (2D)
semiconductors are promising materials for such applications, their integration into conformal electronic systems remains challenging because scalable
liquid-phase processing typically yields films with limited electronic performance, whereas high-quality CVD materials require complex synthesis and transfer processes. Here we establish a scalable route toward conformal electronics based on semiconducting van der Waals materials by combining high-throughput roll-to-roll mechanical exfoliation with commercially available temporary tattoo and waterslide decal transfer substrates. This approach enables the fabrication of ultrathin MoS2-based electronic devices that can be transferred onto rough and curved surfaces such as skin, synthetic leather, and plant leaves. The resulting devices operate reliably after transfer and exhibit strong electronic and optoelectronic performance, including photodetectors with responsivities up to approximately 3.5 A W$^{-1}$, thermistors with temperature coefficients of resistance from -2 to -3.5% per degree Celsius, and ionic-gel-gated field-effect transistors with mobilities reaching approximately 18 cm$^2$ V$^{-1}$ s$^{-1}$.
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All authors Yigit Sozen, Esteban Zamora-Amo, Juan J. Riquelme, Andres Castellanos-Gomez
Quantum Gases
Vortex lattices in coupled one-dimensional Bose-Einstein condensates with a synthetic magnetic field
Holly A. J. Middleton-Spencer, Rose Davies, David G. Reid et al. (+3 more)
We investigate the mean-field ground states of coupled one-dimensional Bose-Einstein condensates subject to a synthetic
magnetic field. The resulting interacting coupled-wire model has one continuous and one discrete spatial direction, providing a controlled way to interpolate between the physics of few-leg ladders and extended
vortex lattices. For two wires, we study the
vortex-like, biased-density, and Meissner-like states, exploring how the finite longitudinal size of the system modifies the transitions between them. Increasing the number of wires, the ground state evolves towards an extended
vortex lattice. We find numerically that periodic boundary conditions in the discrete direction can favour staggered arrays of like-signed
vortices resembling an Abrikosov
lattice, while open boundaries in small finite-size systems confine the
vortices into rows near the centre of the synthetic direction. Our results explore how finite size effects and boundary conditions govern the emergence and spatial organisation of
vortices in continuous-discrete
quantum fluids, with relevance to future experiments in tunnel-coupled atomic wires or with synthetic dimensions.
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All authors Holly A. J. Middleton-Spencer, Rose Davies, David G. Reid, Anna Dalmasso, Theodore Kazanas, Hannah M. Price
Materials Science · Cross-listed from cs.LG
Packora: Systematic Design for Generative Molecular Crystal Structure Prediction
Nayoung Kim, Kiyoung Seong and Sungsoo Ahn
Molecular
crystal structure prediction (CSP) is important in pharmaceuticals, agrochemicals, and organic electronics, where subtle differences in molecular conformation and packing can strongly affect material properties. We present Packora, a flow-based generative model for molecular CSP that jointly predicts atomic coordinates and the
lattice from molecular graphs. Packora supports multi-component and organometallic
crystals and can condition on any subset of molecular conformers, stereochemical labels, and space-group information within a single model. Inspired by the CCDC CSP blind test, we evaluate generation and ranking separately, using generation to isolate generator quality and ranking to measure end-to-end performance under a common relaxation and ranking pipeline. We also systematically study architecture, training, conditioning, inference, and scaling, identifying an effective design based on cacheable pairwise
reasoning, training objective and numerical solver choices, conditioning dropout, and balanced scaling of pairwise and single representations. Packora outperforms the baselines on both structure generation and ranking
benchmarks, achieving the best matched-budget coverage across all six generation
benchmarks, as well as higher experimental-form recovery, lower experimental-form ranks, and faster convergence in ranking.
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Materials Science
Decoupled domain-texture switching from magnetic easy axis in kagome ferromagnet EuTi3Bi4
Yunhao Wang, Shiyu Zhu, Guohao Xi et al. (+13 more)
Magnetic anisotropy defines the easy axis of a
magnetic material and governs the spatial arrangement of its domains. To date, anisotropy engineering has focused on reorienting the easy axis or tuning the anisotropy energy, both of which demand substantial energy input. Here, we demonstrate that
magnetic domain textures can be switched without reorienting the easy axis, as observed in a kagome ferromagnet EuTi3Bi4
crystal. Using low-temperature
magnetic force microscopy, we observe that the preferred orientation of
magnetic domains switches from the a-axis to the b-axis upon temperature variation, and that this switching can also be triggered by an out-of-plane
magnetic-field reset. Magnetization measurements and density functional theory calculations confirm a robust c-axis easy magnetization, ruling out a conventional
spin-reorientation transition. Instead, the texture switching is governed by the temperature dependence of the in-plane variation of the
Magnetic anisotropy energy landscape, which arises from two competing interactions with different decay rates: single-ion anisotropy favors a-oriented
spin components, while nearest-neighbor anisotropic exchange favors b-oriented ones. Furthermore, the critical switching temperature is substantially elevated in a mechanically exfoliated EuTi3Bi4 flake. Our findings establish that macroscopic
magnetic textures can be effectively manipulated by tuning the competition between in-plane anisotropic interactions, without the energy cost of reorienting the easy axis.
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All authors Yunhao Wang, Shiyu Zhu, Guohao Xi, Runnong Zhou, Ruwen Wang, Jianfeng Guo, Jiali Liu, Zichao Chen, Kailin Xu, Cong Wang, Chengmin Shen, Jiang Xiao, Haitao Yang, Xiaoli Dong, Wei Ji, Hong-Jun Gao
Disordered Systems and Neural Networks
Low-temperature magnetism and spin dynamics in the disordered triangular-lattice Yb$^{3+}$ compound LiCaYb$_5$(BO$_3$)$_6$
Monika Jawale, Saikat Nandi, Prashanta K. Mukharjee et al. (+2 more)
The interplay between
geometric frustration,
spin–orbit coupling, and structural disorder can give rise to unconventional
magnetic ground states in rare-earth triangular-
lattice magnets. We report low-temperature
magnetic and $^7$Li NMR investigations of the disordered triangular-
lattice compound LiCaYb$_5$(BO$_3$)$_6$ (LCYBO). Rietveld refinement confirms a hexagonal $P6_522$ structure with partial Ca/Yb antisite disorder and fractional Li occupancy.
Magnetic susceptibility and magnetization measurements indicate a well-isolated effective $J_{\mathrm{eff}}=1/2$ Kramers doublet with weak antiferromagnetic interactions ($\theta_{\mathrm{CW}} \approx -0.54$~K). The specific heat reveals a weak anomaly near 0.43 K, suggesting the development of short-range correlated magnetism rather than conventional long-range order. $^7$Li NMR spectra broaden strongly upon cooling, consistent with increasingly inhomogeneous internal
magnetic fields. The
spin-
lattice relaxation exhibits two relaxation components consistent with disorder-induced distributions of local
magnetic environments arising from antisite disorder and competing exchange pathways. Our results establish LCYBO as a structurally disordered frustrated triangular-
lattice magnet with correlated low-energy
spin dynamics.
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All authors Monika Jawale, Saikat Nandi, Prashanta K. Mukharjee, Philipp Gegenwart, A.V. Mahajan
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Isotropic Nanoscale Quantum Sensor at Room-Temperature
Daniel T. Möller, Baha Sakar, Ekrem T. Güldeste et al. (+9 more)
Color-center based
quantum sensors provide nanoscale resolution under ambient conditions, yet their applicability remains limited. Because the quantization axes are locked to the host
lattice, conventional color centers suffer severe signal loss in off-axis
magnetic fields. To address this, we report an isotropic magnetometer enabled by the neutrally charged nitrogen-vacancy center (NV0) in diamond. Here,
spin-to-charge dynamics yield an NV0-dark
spin pair whose quantization axis dynamically aligns with the external field. Read out through NV charge-state-selective fluorescence, this system exhibits microsecond room-temperature coherence and nanotesla sensitivity for arbitrary field directions. We demonstrate
alignment-free mapping of steep field gradients and single paramagnetic micro-targets, alongside isotropic readout from randomly oriented nanodiamonds. Resolving longstanding orientation constraints, this platform unlocks unrestricted nanoscale magnetometry across life sciences and
quantum materials.
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All authors Daniel T. Möller, Baha Sakar, Ekrem T. Güldeste, Dhruv Wadhwani, Olt Gashi, Daniel A. García Vaca, Mokessh K. Ciwan, Simone P. Crozier, Christian Laube, Sirswa K. Shree Ram, Matteo Slaviero, Nabeel Aslam
Materials Science
Four-phonon scattering and coherent heat transport in ultrawide-bandgap SrSnO3
Xuejie Li, Xiaoying Wang, Shengying Yue et al. (+4 more)
SrSnO3 is a promising ultrawide-bandgap perovskite oxide whose thermal transport is governed by structural distortions and anharmonic
lattice dynamics. Here, we investigate the
lattice thermal conductivity (kL) of orthorhombic and cubic SrSnO3 within a unified first-principles framework combining self-consistent
phonon renormalization, three- and four-
phonon scattering, and coherent heat transport. Bonding analysis reveals a rigid Sn-O octahedral framework embedded in a weakly bonded Sr sublattice, giving rise to low-frequency vibrational modes susceptible to strong anharmonic effects. Four-
phonon scattering is identified as a key mechanism limiting particle-like heat conduction, reducing the Peierls thermal conductivity by 19.4% at 300 K in the orthorhombic phase and by 52.1% at 1300 K in the cubic phase, while the coherent contribution provides a finite channel that partially compensates this reduction. We further show that the apparent agreement between three-
phonon calculations and experimental thermal conductivity at room temperature is not indicative of a complete physical description. Instead, it arises from a near cancellation between four-
phonon suppression of the particle-like channel and the neglected coherent contribution. This cancellation breaks down when the full temperature dependence is considered, where only the combined treatment improves agreement with the experimentally observed scaling behavior. A physically consistent description of kL therefore requires
phonon renormalization, four-
phonon scattering, and coherent transport to be treated on equal footing rather than inferred from three-
phonon agreement at a single temperature. These results provide microscopic insight into thermal transport in ultrawide-bandgap stannate perovskites and establish a
benchmark for anharmonic transport in strongly distorted oxides.
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All authors Xuejie Li, Xiaoying Wang, Shengying Yue, Turab Lookman, Xiangdong Ding, Jun Sun, Zhibin Gao
Statistical Mechanics
Quenched activity induces nonuniversal scaling in nonreciprocal XY Models and surfaces
Sudip Mukherjee and Abhik Basu
Active XY models and active surfaces are two paradigmatic nonequilibrium systems with distinct microscopic origins. We show that the hydrodynamic theories for a quenched-disordered nonreciprocal random bond two-dimensional XY model and an inversion-symmetric active surface tangentially advected by quenched velocities are identical. This theory predicts sub-logarithmic phase order in the XY model and sub- or super-logarithmic positional order in the surface for short-range disorder with nonuniversal exponents, which vary continuously with the degree of transversality of the disorder variance. We argue that the nonreciprocal random bond XY model can disorder through
vortex proliferation.
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Materials Science
Band offsets and electronic structure at ${\alpha}$/${\beta}$-Ga$_2$O$_3$ and ${\kappa}$/${\beta}$-Ga$_2$O$_3$ phase heterojunctions
D. Q. Fang
Ga$_2$O$_3$ phase heterojunction materials are emerging as promising candidates for deep-ultraviolet optoelectronics. Here, the band offsets at the ${\alpha}$/${\beta}$-Ga$_2$O$_3$ and ${\kappa}$/${\beta}$-Ga$_2$O$_3$ phase heterojunctions are investigated through hybrid functional calculations. Explicit, realistic slab models that satisfy electron counting rules are constructed for the heterojunctions. Our calculations demonstrate that a type-II staggered band
alignment forms at the ${\alpha}$/${\beta}$-Ga$_2$O$_3$ and ${\kappa}$/${\beta}$-Ga$_2$O$_3$ phase heterojunctions, where both the valence and conduction band edges of ${\alpha}$-Ga$_2$O$_3$ and ${\kappa}$-Ga$_2$O$_3$ are higher than those of ${\beta}$-Ga$_2$O$_3$. Strain effects on the band
alignment are also discussed. Spatially resolved local density of states maps are presented, clearly revealing the interfacial electronic structures. These results provide valuable insights into the physical properties of Ga$_2$O$_3$ phase heterojunctions, offering guidance for future device design efforts.
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Materials Science
A novel Grand-Potential Phase-Field Lattice-Boltzmann model for multi-phase solidification with convection
Chirantandip Mahanta, Sanjeev Kumar, Gandham Phanikumar et al. (+1 more)
Melt convection plays a critical role in microstructure
evolution during
alloy solidification, yet accurately capturing its interaction with moving solid-
liquid interfaces remains a significant computational challenge, particularly in multi-phase, multi-component systems. In this work, we develop a computational framework that couples a Grand-Potential phase-field model with the
Lattice Boltzmann method (LBM) to simulate convection-driven solidification within a unified and thermodynamically consistent formulation. The proposed approach rigorously enforces no-slip conditions at evolving solid-
liquid interfaces, while fluid transport is solved using the standard single-relaxation-time Bhatnagar-Gross-Krook collision operator. The framework provides an efficient and robust methodology for resolving the coupled
evolution of interfaces, solute transport, and fluid flow. The versatility of the proposed framework is demonstrated through simulations of dendritic and eutectic solidification under natural convection. The results show that convection significantly modifies solute segregation, destabilizes growth fronts, and induces oscillatory growth modes in both systems. These examples illustrate the capability of the proposed method to capture complex flow-induced morphological instabilities and provide new insights into the mechanisms governing convection-driven microstructure
evolution in
alloy solidification.
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All authors Chirantandip Mahanta, Sanjeev Kumar, Gandham Phanikumar, Abhik N. Choudhury
Mesoscale and Nanoscale Physics
Exceptional point induced by hyperbolicity in an electrostatic spherical shell
Álvaro Buendía, Marcelo S. Barreiro and Nuno M.R. Peres
Exceptional points (EPs) are non–Hermitian degeneracies at which both
eigenvalues and eigenvectors coalesce, usually engineered through balanced gain and loss or non–reciprocity. In this work, we show that the radial electrostatic problem of an anisotropic core–shell nanoparticle realizes an EP without any of the alluded conditons. Written in the logarithmic radial coordinate, the problem is a Cauchy–Euler equation that maps onto a damped oscillator and, equivalently, onto a two-site Hatano–Nelson
Hamiltonian, so that the non-Hermiticity is emulated in space rather than in time and the sole control parameter is the degree of dielectric anisotropy, $\varepsilon_t/\varepsilon_r$. The shell is passive, reciprocal, and lossless, yet it hosts an EP and a non–Hermitian phase transition governed by hyperbolicity alone. Beyond a hyperbolicity threshold the electric field inside the shell turns from monotonic decay into spatial oscillation, producing hotspots at intermediate radii which can be exploited to tailor fluorescence, strong coupling, sensing, or cloaking. More broadly, this establishes
hyperbolic media as a platform to simulate non–Hermitian physics without gain, loss, or non–reciprocity.
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