Soft Condensed Matter · Cross-listed from physics.bio-ph
Living Capillary Bridges
Tytti Kärki, Senna Luntama, Yasamin Modabber et al. (+5 more)
Biological tissues exhibit complex behaviors with their dynamics often resembling inert soft matter such as
liquids,
polymers, colloids, and
liquid crystals. These analogies enable physics-based approaches for investigations of emergent behaviors in biological processes. A well-studied case is the spreading of cellular aggregates on solid surfaces, where they display dynamics similar to viscous droplets. In vivo, however,
cells and tissues are in a confined environment with varying geometries and mechanical properties to which they need to adapt. In this work, we compressed cellular aggregates between two solid surfaces and studied their dynamics using microscopy, and computer simulations. The confined cellular aggregates transitioned from compressed spheres into dynamic living capillary bridges exhibiting bridge thinning and a convex-to-concave meniscus
curvature transition. We found that the stability of the bridge is determined by the interplay between
cell growth and
cell spreading on the confining surfaces. This interaction leads to bridge rupture at a critical length scale determined by the distance between the plates. The force distributions, formation and stability regimes of the living capillary bridges were characterized with full 3D computer simulations that included
cell division, migration and growth dynamics, directly showing how mechanical principles govern the behavior of the living bridges; cellular aggregates display jamming and stiffening analogously to granular matter, and
cell division along the long axis enhances thinning. Based on our results, we propose a new class of active soft matter behavior, where cellular aggregates exhibit
liquid-like adaptation to confinement, but with self-organized rupturing driven by biological activity.
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All authors Tytti Kärki, Senna Luntama, Yasamin Modabber, Saila Pönkä, Gonca Erdemci-Tandogan, Mikko Karttunen, Grégory Beaune, Jaakko V. I. Timonen
Strongly Correlated Electrons
$^{23}$Na-NMR study on the one-dimensional superoxide spin-chain compound NaO$_2$
Takayuki Goto, Mizuki Miyajima and Takashi Kambe
We report $^{23}$Na-NMR study of the alkali superoxide NaO$_2$, a candidate one-dimensional
quantum spin system. The Knight shift, linewidth, and
spin-
lattice relaxation rate $1/T_1$ were investigated down to 0.3 K in
magnetic fields up to 16 T. Below $T_{\rm S3} =$ 34 K, $1/T_1$ exhibits thermally activated behavior, indicating the opening of a
spin gap of $\Delta(10.1 {\rm T}) \simeq$ 38.0 K and $\Delta(3.55 {\rm T}) \simeq$ 46 K, The hyperfine coupling constant shows a sudden reduction across the structural transition at $T_{\rm S2} \simeq$ 195 K, reflecting the development the pronounced one-dimensionality in the elctron structure. These results provide microscopic evidence that NaO$_2$ is a rare $\pi$-orbital-based one-dimensional
spin chain that exhibits a
spin-gapped ground state, consistent with a
spin-Peierls-like instability.
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Quantum Gases · Cross-listed from physics.optics
Bloch-Landau-Zener Oscillations in Moiré Lattices
Sergey K. Ivanov, Yaroslav V. Kartashov and Vladimir V. Konotop
We develop a theory of two-dimensional Bloch-Landau-Zener (BLZ) oscillations of wavepackets in incommensurate moiré
lattices under the influence of a weak linear gradient. Unlike periodic systems, aperiodic
lattices lack translational
symmetry and therefore do not exhibit a conventional band-gap structure. Instead, they feature a mobility edge, above which (in the optical context) all modes become localized. When a linear gradient is applied to a moiré
lattice, it enables energy transfer between two or several localized modes, leading to the oscillatory behavior referred to as BLZ oscillations. This phenomenon represents simultaneous tunneling in real space and propagation constant (energy) space, and it arises when quasi-resonance condition for propagation constants and spatial proximity of interacting modes (together constituting a selection rule) are met. The selection rule is controlled by the linear gradient, whose amplitude and direction play a crucial role in determining the coupling pathways and the resulting dynamics. We derive a multimode model describing BLZ oscillations in the linear regime and analyze how both attractive and repulsive nonlinearities affect their dynamics. The proposed framework can be readily extended to other physical systems, including cold atoms and Bose-Einstein condensates in aperiodic potentials.
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Materials Science
Enhanced Secondary Electron Detection of Single Ion Implants in Silicon Through Thin SiO2 Layers
Ella B Schneider, Oscar G Lloyd-Willard, Kristian Stockbridge et al. (+7 more)
Deterministic placement of single dopants is essential for scalable
quantum devices based on group-V donors in silicon. We demonstrate a non-destructive, high-efficiency method for detecting individual ion implantation events using secondary electrons (SEs) in a focused ion beam (FIB) system. Using low-energy Sb ions implanted into undoped silicon, we achieve up to 98% single-ion detection efficiency, verified by calibrated ion-current measurements before and after implantation. The technique attains ~30 nm spatial resolution without requiring electrical contacts or device fabrication, in contrast to ion-beam-induced-current (IBIC) methods. We find that introducing a controlled SiO2 capping layer significantly enhances SE yield, consistent with an increased electron mean free path in the
oxide, while maintaining high probability of successful ion deposition in the underlying substrate. The yield appears to scale with ion velocity, so higher projectile mass (e.g. Yb, Bi etc) requires increased energy to maintain detection efficiency. Our approach provides a robust and scalable route to precise donor placement and extends deterministic implantation strategies to a broad range of material systems and
quantum device architectures.
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All authors Ella B Schneider, Oscar G Lloyd-Willard, Kristian Stockbridge, Mark Ludlow, Sam Eserin, Luke Antwis, David C Cox, Roger P Webb, Ben N Murdin, Steve K Clowes
Strongly Correlated Electrons
Emergent Shastry-Sutherland network from square-kagome Heisenberg antiferromagnet with trimerization
Tomonari Mizoguchi
We study the $S=1/2$ square-kagome
lattice Heisenberg antiferromagnet with the trimarized modulation. In the trimerized limit, each trimer hosts the four-fold degenearte ground states characterized by the
spin and chirality degrees of freedom. We find that, within the first-order perturbation theory with respect to the inter-trimer coupling, the effective
Hamiltonian is the Kugel-Khomskii-type model on a Shastry-Sutherland
lattice. Based on a mean-field decoupling, we propose a dimer-covering ansatz for the effective
Hamiltonian; however, the validity of these states in the low-energy sector remains an open question.
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Materials Science
Ferroelectric amplitude switching and continuous memory
Gye-Hyeon Kim, Tae Hyun Jung, Seungjoon Sun et al. (+11 more)
Although ferroelectric systems inherently exhibit binary switching behavior, recent advances in analog
memory device have spurred growing interest in achieving continuous
memory states. In this work, we demonstrate ferroelectric amplitude switching at the mesoscopic scale in compositionally graded Ba1-xSrxTiO3
heterostructures, enabling continuous modulation of polarization magnitude without altering its direction, which we defined as amplitude switching. Using switching current measurement, piezoresponse force microscopy and Landau-Ginzburg-Devonshire simulations, we reveal that compositionally graded ferroelectric
heterostructure can possess amplitude switching behavior through a double well potential with flattened minima. This behavior supports stable, continuous polarization states and establishes a new platform for analog
memory applications. These findings introduce amplitude switching as a new dynamic of the order parameter, paving the way for energy-efficient and reliable analog
memory systems.
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All authors Gye-Hyeon Kim, Tae Hyun Jung, Seungjoon Sun, Jung Kyu Lee, Jaewoo Han, P. Karuna Kumari, Jin-Hyun Choi, Hansol Lee, Tae Heon Kim, Yoon Seok Oh, Seung Chul Chae, Se Young Park, Sang Mo Yang, Changhee Sohn
Mesoscale and Nanoscale Physics
Cryogenic temperature dependence and hysteresis of surface-trap-induced gate leakage in GaN high-electron-mobility transistors
Ching-Yang Pan, Shi-Kai Lin, Yu-An Chen et al. (+1 more)
This work provides a detailed mapping of various mechanisms of surface-trap-induced gate leakage in GaN HEMTs across a temperature range from room to cryogenic levels. Two-dimensional variable-range hopping is observed at small gate bias. Under higher reverse gate bias, the leakage is dominated by the Poole–Frenkel emission above 220 K, but gradually transitions to the trap-assisted tunneling below 220 K owing to the frozen-trap effect. The trap barrier height extracted from the gate leakage current under the upward gate sweep is 0.65 V, which is 12% higher than that from the downward sweep. The gate leakage current as a function of the gate bias exhibits clockwise hysteresis loops above 220 K but counterclockwise ones below 220 K. This remarkable opposite hysteresis phenomenon is thoroughly explained by the trap mechanisms.
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All authors Ching-Yang Pan, Shi-Kai Lin, Yu-An Chen, Pei-hsun Jiang
Superconductivity
Quasiclassical theory of vortex states in locally non-centrosymmetric superconductors: application to CeRh$_{2}$As$_{2}$
Akihiro Minamide and Youichi Yanase
CeRh$_{2}$As$_{2}$, a heavy
fermion superconductor discovered in 2021, exhibits two distinct superconducting phases under a $c$-axis
magnetic field. This unconventional phase diagram has been attributed to the local inversion
symmetry breaking at the Ce sites. At low
magnetic fields, a conventional even-parity
spin-singlet superconducting state is realized, whereas at higher fields, an odd-parity
spin-singlet superconducting state, in which the order parameter alternates sign between neighboring Ce layers, becomes stabilized. In this study, we employ a quasiclassical approach to investigate the
vortex states of
bilayer superconductors with locally broken inversion
symmetry. We calculate the local density of states (LDOS) in the
vortex lattice state and find that the pairing
symmetry of different superconducting states is clearly manifested in the peak structure of LDOS at the
vortex core. Since LDOS is experimentally observable, our work provides a pathway for experimental verification of the superconducting parity transition in CeRh$_{2}$As$_{2}$.
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Mesoscale and Nanoscale Physics
Linearly polarized light enables chiral edge transport in quasi-2D Dirac materials
Mohammad Shafiei, Farhad Fazileh and Milorad V. Milošević
Floquet engineering with high-frequency light offers dynamic control over topological phases in
quantum materials. While in 3D Dirac systems circularly polarized light is known to induce topological phase transitions via gap opening, linearly polarized light (LPL) has generally been considered ineffective. Here we show that in quasi-2D Dirac materials the second-order momentum term arising from the intersurface coupling can induce a topological phase transition under LPL, leading to
chiral edge channels. Considering an ultrathin Bi$_2$Se$_3$ film as a representative system, we show that this transition occurs at experimentally accessible light intensities. Our results thus promote quasi-2D materials as viable platforms for light-controlled topological phases, expanding the potential of Floquet topological engineering.
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Disordered Systems and Neural Networks
Evidence of de Almeida-Thouless line below six dimensions
M. Aguilar-Janita, V. Martin-Mayor, J. Moreno-Gordo et al. (+1 more)
We study the critical behavior of the Ising
spin glass in five spatial dimensions through large-scale Monte Carlo simulations and finite-size scaling analysis. Numerical evidence for a phase transition is found both with and without an externally applied
magnetic field. The critical exponents are computed in both cases. We compute with a 10% accuracy the lower critical dimension at zero
magnetic field, finding a result consistent with estimates obtained with entirely different methods, by combining our estimates of critical exponents in five dimensions with previous results for other spatial dimensions. When the results in a
magnetic field are compared with previous results in six spatial dimensions, qualitative differences emerge in the scaling behavior of the correlation functions at zero external momentum. This anomalous scaling does not extend to other wavevectors. We do not find indications of a quasi first-order phase transition in a
magnetic field.
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All authors M. Aguilar-Janita, V. Martin-Mayor, J. Moreno-Gordo, J.J. Ruiz-Lorenzo
Statistical Mechanics
The Tracy-Widom distribution at large Dyson index
Alain Comtet, Pierre Le Doussal and Naftali R. Smith
We study the Tracy-Widom (TW) distribution $f_\beta(a)$ in the limit of large Dyson index $\beta \to +\infty$. This distribution describes the fluctuations of the rescaled largest
eigenvalue $a_1$ of the Gaussian (alias Hermite) ensemble (G$\beta$E) of (infinitely) large random
matrices. We show that, at large $\beta$, its probability density function takes the large deviation form $f_\beta(a) \sim e^{-\beta \Phi(a)}$. While the typical deviation of $a_1$ around its mean is Gaussian of variance $O(1/\beta)$, this large deviation form describes the probability of rare events with deviation $O(1)$, and governs the behavior of the higher cumulants. We obtain the rate function $\Phi(a)$ as a solution of a Painlevé II equation. We derive explicit formula for its large argument behavior, and for the lowest cumulants, up to order 4. We compute $\Phi(a)$ numerically for all $a$ and compare with exact numerical computations of the TW distribution at finite $\beta$. These results are obtained by applying saddle-point approximations to an associated problem of energy levels $E=-a$, for a random
quantum Hamiltonian defined by the
stochastic Airy operator (SAO). We employ two complementary approaches: (i) we use the optimal fluctuation method to find the most likely realization of the noise in the SAO, conditioned on its ground-state energy being $E$ (ii) we apply the weak-noise theory to the representation of the TW distribution in terms of a Ricatti
diffusion process associated to the SAO. We extend our results to the full Airy point process $a_1>a_2>\dots$ which describes all edge
eigenvalues of the G$\beta$E, and correspond to (minus) the higher energy levels of the SAO, obtaining large deviation forms for the marginal distribution of $a_i$, the joint distributions, and the gap distributions.
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Materials Science
First-Principles Approach to Spin Excitations in Noncollinear Magnetic Systems
Hsiao-Yi Chen, Ryotaro Arita and Yusuke Nomura
We present a first-principles method based on density functional theory and many-body perturbation theory for computing
spin excitations in
magnetic systems with noncollinear
spin textures. Traditionally, the study of
magnetic excitations has relied on
spin models that assume
magnetic moments to be localized. Beyond this restriction, recent $ab~initio$ methods based on Green's functions within the local
spin-density approximation have emerged as a general framework for calculating
magnetic susceptibilities. However, their application has so far been largely limited to collinear
ferromagnetic and
antiferromagnetic systems. In this work, we extend this framework and enable the treatment of large-scale noncollinear
magnetic systems by leveraging a Wannier-basis representation and implementing an ansatz potential method to reduce computational cost. We apply our method to the
spin-spiral state of LiCu$_2$O$_2$, successfully capturing its steady-state
spin-rotation pitch in agreement with the experimental measurement and resolving the characteristic
magnon dispersion. We further analyze the interplay between the spiral
spin structure and the on-site
spin-exchange splitting, and elucidate the crucial role of
magnetic dipoles on ligand ions in mediating effective
ferromagnetic interaction among the primary
spins on Cu$^{2+}$ ions. Finally, we provide a theoretical prediction of the
magnon dispersion on top of the helical
spin background in high agreement with the experimental measurement. Overall, this work establishes a general and computationally efficient framework for simulating collective
spin dynamics in noncollinear
magnetic systems from first principles, exemplified by – but not limited to –
spin-spiral states.
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Mesoscale and Nanoscale Physics
Electric field-induced spin-valley locking in twisted bilayer buckled honeycomb materials
Harold J.W. Zandvliet, Pantelis Bampoulis, Cristiane Morais Smith et al. (+1 more)
A twisted honeycomb
bilayer exhibits a moiré superstructure that is composed of a hexagonal arrangement of AB and BA stacked domains separated by domain boundaries. In the case of twisted
bilayer graphene, the application of an electric field normal to the
bilayer leads to the opening of inverted band gaps in the AB and BA stacked domains. The inverted band gaps result in the formation of a two-dimensional triangular network of counterpropagating valley protected helical domain boundary states, also referred to as the
quantum valley
Hall effect. Owing to
spin-orbit coupling and buckling, the
quantum valley
Hall effect in twisted
bilayer silicene and germanene is more complex than in twisted
bilayer graphene. We found that there is a range of electric fields for which the
spin degree of freedom is locked to the valley degree of freedom of the electrons in the
quantum valley
Hall states, resulting in a stronger topological protection. For electric fields smaller than the aforementioned range the twisted
bilayer does not exhibit the
quantum valley
Hall effect, whereas for larger electric fields the
spin-valley locking is lifted and the emergent
quantum valley
Hall states are only valley-protected.
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All authors Harold J.W. Zandvliet, Pantelis Bampoulis, Cristiane Morais Smith, Lumen Eek
Materials Science
Multiscale Models For Perovskite Optimisation
Philippe Baranek, James P. Connolly, Antoine Gissler et al. (+3 more)
This paper presents a multiscale approach to evaluate perovskite
solar cell performance which determines material properties at the atomistic scale with first-principles calculations, and applies them in macro-scale device models. This work focuses on the MAPbI3 (MA = CH3NH3) perovskite and how its phase transitions impact on its optical, electronic, and structural properties which are investigated at the first-principles level. The obtained data are coupled to a numerical drift-
diffusion device model enabling evaluation of the performance of corresponding single junction devices. The first-principles simulation applies a hybrid exchange-correlation functional adapted to the studied family of compounds. Validation by available experimental data is presented from materials properties to device performance, justifying the use of the approach for predictive evaluation of existing and novel perovskites. The coupling between atomistic and device models is described in terms of a framework for exchange of optical, vibrational, and electronic parameters between the two scales. The result of this theoretical investigation is a methodology for designing and optimising perovskite materials for both
cell performance and stability, the key obstacle in the societal implementation of these record-breaking new materials.
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All authors Philippe Baranek, James P. Connolly, Antoine Gissler, Philip Schulz, Michel Rérat, Roberto Dovesi
Materials Science
Laser-Induced Heating in Diamonds: Influence of Substrate Thermal Conductivity and Interfacial Polymer Layers
Md Shakhawath Hossain, Jiatong Xu, Thi Ngoc Anh Mai et al. (+9 more)
Diamonds hosting color centers possess intrinsically high thermal conductivity; therefore,
laser-induced heating has often received little
attention. However, when placed on substrates with low thermal conductivity, localized heating of diamonds under
laser excitation can become significant, and the presence of an interfacial
polymer layer between substrate and diamond further amplifies this effect. Yet, the relationship between substrate thermal conductivity,
polymer thickness, and
laser heating remains to be established. Here, a systematic investigation is presented on
laser-induced heating of silicon-vacancy diamond on substrates with varying thermal conductivity and interfacial
polymer thickness. Results reveal that even at a low excitation power of 737~$\mu$W/$\mu$m$^2$, thin amorphous holey carbon – the lowest-conductivity substrate ($\sim$0.2~W~m$^{-1}$~K$^{-1}$) studied – exhibits substantial heating, while glass ($\sim$1.4~W~m$^{-1}$~K$^{-1}$) and polydimethylsiloxane (PDMS, $\sim$0.35~W~m$^{-1}$~K$^{-1}$) show noticeable heating only above 2.95~mW/$\mu$m$^2$. For
polymer interlayers, a thickness of just 2.2~$\mu$m induces significant heating at 2.95~mW/$\mu$m$^2$ and above, highlighting strong influence of both substrate and
polymer thickness on local heating response. Experimental findings are further validated using COMSOL Multiphysics simulations with a steady-state 3D heat transfer model. These results provide practical guidance for substrate selection and sample preparation, enabling optimization of conditions for optical thermometry and
quantum sensing applications.
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All authors Md Shakhawath Hossain, Jiatong Xu, Thi Ngoc Anh Mai, Nhat Minh Nguyen, Trung Vuong Doan, Chaohao Chen, Qian Peter Su, Yongliang Chen, Evgeny Ekimov, Toan Dinh, Xiaoxue Xu, Toan Trong Tran
Strongly Correlated Electrons
Frustration-driven unconventional magnetism in the Mn$^{2+}$ ($S=\frac{5}{2}$) based two-dimensional triangular-lattice antiferromagnet Ba$_{3}$MnTa$_{2}$O$_{9}$
Romario Mondal, Sk. Soyeb Ali, Saikat Nandi et al. (+11 more)
A triple perovskite
oxide Ba$_{3}$MnTa$_{2}$O$_{9}$ has been synthesized and its
magnetic properties have been investigated through dc and ac magnetization, specific heat, electron
spin resonance (ESR) measurements, and density functional theory (DFT) calculations. Mn$^{2+}$ ($S$ = 5/2) ions are the only
magnetic species present in the material. These Mn$^{2+}$ ions constitute a quasi-two-dimensional triangular network in the crystallographic $ab$-plane. Magnetization and specific heat measurements reveal the absence of any long-range
magnetic order down to 0.5\,K despite the presence of
antiferromagnetic correlations between the
magnetic ions, suggesting the presence of
geometric frustration in the material. The
entropy release is lower than the expected theoretical value of $Rln(6)$, further suggesting the presence of frustration. First-principles calculations using density functional theory (DFT) and atomistic
spin dynamics (ASD) simulations further support this lack of static
magnetic order even at low temperatures and identify the competing
magnetic interactions along with the quasi-2D
magnetic dimensionality as the underlying origin of such an unconventional
magnetic behavior.
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All authors Romario Mondal, Sk. Soyeb Ali, Saikat Nandi, S. Chattopadhyay, S. Gaß, L. T. Corredor, A. U. B. Wolter, V. Kataev, B. Büchner, A. Alfonsov, S. Wurmehl, A. V. Mahajan, S. K. Panda, T. Dey
Soft Condensed Matter
Vertical pullout of a non-spherical intruder from a granular medium: From system-wide response to avalanching around the intruder
Dominik Krengel, Jian Chen, Shun Nomura et al. (+2 more)
Intruder mechanics in a granular aggregate is a common subject in engineering and geotechnical applications. However, most studies are limited to spherical intruders or small displacement regimes up to the point of failure. In this work we investigate the vertical pullout of a plate-like intruder buried within a granular aggregate well past the point of failure. While we find the maximum resistance force to depend on the material properties, in the post failure regime the resistance force converges onto the same curve for all friction coefficients. Likewise, the effective geometry of the intruder will always develop the same conical shape on top of the plate, independent of the magnitude of friction, that remains unchanged during the pullout process once established. Further, between the intruder and the aggregate a natural hopper flow develops in which material is transported into the void below the intruder by discrete flow events.
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All authors Dominik Krengel, Jian Chen, Shun Nomura, Shunsuke Ota, Hidenori Takahashi
Superconductivity
Effect of decorating NiO nanoparticles on superconducting properties of YBCO
D.M. Gokhfeld, S.V. Semenov, M.I. Petrov et al. (+4 more)
The influence of adding 23 nm NiO nanoparticles on the
magnetic hysteresis loops and critical current density of the high-temperature
superconductor YBa2Cu3O7-d has been investigated. The samples were prepared using a fast annealing method that prevents chemical interaction between the components and does not reduce the critical temperature of the
superconductor. Compared to the undoped YBCO sample, the critical current density increases in the samples doped with NiO nanoparticles in
magnetic fields greater than 6 kOe. The sample containing 0.5 weight percent of NiO nanoparticles exhibits the greatest enhancement in critical current density at 10 kOe (1.36 times greater than the undoped sample).
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All authors D.M. Gokhfeld, S.V. Semenov, M.I. Petrov, I.V. Nemtsev, M.S. Molokeev, V.L. Kirillov, O.N. Martyanov
Superconductivity
Multi-orbital Dirac superconductors and their realization of higher-order topology
Dao-He Ma and Jin An
Topological nodal
superconductors (SCs) have attracted considerable interest due to their gapless bulk excitations and exotic surface states. In this paper, by establishing a general framework of the effective theory for multi-orbital SCs, we realize a class of three-dimensional (3D) time-reversal (T )-invariant Dirac SCs, with their topologically protected gapless Dirac nodes being located at general positions in the Brillouin zone. By introducing T -breaking pairing perturbations, we demonstrate the existence of Majorana hinge modes in these Dirac SCs as evidence of their realization of higher-order
topology. We also propose a new kind of T -breaking Dirac SCs, whose Dirac nodes possess nonzero even chiralities and so are characterized by surface Majorana arcs.
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Superconductivity
Superconductivity in UTe$_2$ from local noncentrosymmetricity
Ryuji Hakuno and Youichi Yanase
Superconductivity in UTe$_{2}$ has garnered significant
attention, as it is widely recognized as a promising candidate for a
spin-triplet
superconductor. However, the
symmetry of superconductivity and the microscopic origin of
spin-triplet pairing remain subjects of debate. Nevertheless, various experiments imply an intimate coupling between magnetism and superconductivity. In this paper, we analyze a multi-sublattice periodic Anderson model that incorporates a
spin-orbit coupling allowed in locally noncentrosymmetric
crystals to discuss
magnetic fluctuations and superconductivity in UTe$_2$. Due to the sublattice-dependent
spin-orbit coupling,
magnetic fluctuations become anisotropic, and the
spin degeneracy of superconducting states is lifted. Our calculations reveal anisotropic
antiferromagnetic fluctuations along the $b$- and $c$-axes, anisotropic
ferromagnetic fluctuations along the $a$-axis, and their coexistence. These can be tuned by the $f$-electron's level. Superconductivity in the $A_u$ representation is predominant for a wide range of parameters, whereas the $B_{2u}$ representation is almost degenerate and can be stabilized. The direction of the $d$-vector changes as we increase the
spin-orbit coupling. We discuss the consistency between our results and several experiments.
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Materials Science
Magnetization, excitations, and microwave power absorption in transition-metal/rare-earth ferrimagnets with disorder
D. A. Garanin and E. M. Chudnovsky
Efficient numerical routines are developed for numerical studies of the dependence of the
equilibrium magnetic states, excitations, and microwave power absorption on temperature and composition in transition-metal/rare-earth ferrites, including the reversal of the Néel vector occurring on both temperature and the concentration of the rare-earth atoms. It results in a drastic change in the behavior at the magnetization and angular-momentum compensation points. Dominant uniform oscillation modes are obtained by computing the magnetization correlation function. They are compared with the analytical solution, which is analyzed in detail. The fluctuation-dissipation
theorem is used to compute the frequency dependence of the absorbed microwave power. A good agreement with analytical results is demonstrated. Disorder caused by random positions of rare-earth atoms in a diluted RE system leads to multiple localized modes that converge into broad absorption maxima as the size of the system increases. The power absorption integrated over frequency exhibits a minimum at the compensation point.
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Strongly Correlated Electrons
Impurity-induced spin density wave in the thermoelectric layered cobaltite [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$]
Motoya Takenaka, Shogo Yoshida, Yoshiki J. Sato et al. (+1 more)
We investigate the Sn-substitution effect on the thermoelectric transport properties of the layered cobaltite [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$] single
crystals, which exhibit a non-monotonic temperature variation of the electrical resistivity and the Seebeck coefficient owing to the complex electronic and
magnetic states. We find that the onset temperature of the short-range
spin-density-wave (SDW) formation increases with the substituted Sn content, indicating the
impurity-induced stabilization of the SDW order, reminiscent of the disorder/
impurity-induced
spin order in the cuprate
superconductors. The Seebeck coefficient is well related to such
impurity effects, as it is slightly enhanced below the onset temperatures, implying a decrease in the carrier concentration due to a pseudo-gap formation associated with the SDW ordering. We discuss the site-dependent substitution effects including earlier studies, and suggest that substitution to the conducting CoO$_2$ layers is essential to increase the onset temperature, consistent with the
impurity-induced SDW picture realized in the conducting layers with the cylindrical
Fermi surface.
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All authors Motoya Takenaka, Shogo Yoshida, Yoshiki J. Sato, Ryuji Okazaki
Mesoscale and Nanoscale Physics
Magnetic flux induced higher-order topological superconductivity
Jinpeng Xiao, Qianglin Hu, Zuodong Yu et al. (+2 more)
Higher-order topological superconductivity typically depends on
spin-orbit interaction, and often necessitates well designed sample structures, nodal superconducting pairings or complex
magnetic order. In this work, we propose a model that incorporates a Zeeman field,
antiferromagnetic order, and $s$-wave superconducting pairing, all without the need for
spin-orbit interaction. In a two-dimensional system, we realize a second-order topological
superconductor by utilizing a staggered flux, provided that the Zeeman field is oriented perpendicular to the
magnetic order moments. In three-dimensional systems, we achieve second- and third-order topological
superconductors in theory, through stacking the two-dimensional second-order topological
superconductor.
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All authors Jinpeng Xiao, Qianglin Hu, Zuodong Yu, Weipeng Chen, Xiaobing Luo
Materials Science
Comparison of Electroluminescence and Photoluminescence Imaging of Mixed-Cation Mixed-Halide Perovskite Solar Cells at Low Temperatures
Hurriyet Yuce-Cakir, Haoran Chen, Isaac Ogunniranye et al. (+4 more)
Halide perovskites have emerged as promising candidates for high-performance
solar cells. This study investigates the temperature-dependent optoelectronic properties of mixed-cation mixed-halide perovskite
solar cells using electroluminescence (EL) and photoluminescence (PL) hyperspectral imaging, along with current-voltage analysis. Luminescence images, which were converted to EL and PL external radiative efficiency (ERE) maps, revealed significant changes in the optoelectronic behavior of these devices at low temperatures. Specifically, we found that a significant source of heterogeneity in the low-temperature EL ERE maps below 240 K is related to local charge injection and extraction bottlenecks, whereas PL ERE maps show suppressed non-radiative recombination and significant improvements in efficiency throughout the investigated temperature range. The spatial distribution of ERE and its variation with applied current were analyzed, offering insights into charge-carrier dynamics and defect behavior. Our results reveal that while the perovskite layer exhibits enhanced ERE at low temperatures, charge injection barriers at the interfaces of the perovskite
solar cells significantly suppress EL and degrade the fill factor below 240 K. These findings reveal that a deeper understanding of the performance of perovskite
solar cells under low-temperature conditions is an essential step toward their potential application in space power systems and advanced
semiconductor devices.
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All authors Hurriyet Yuce-Cakir, Haoran Chen, Isaac Ogunniranye, Susanna M. Thon, Yanfa Yan, Zhaoning Song, Behrang H. Hamadani
Materials Science
Ferroelasticity tunable altermagnets
Ning Ding, Haoshen Ye, Shan-Shan Wang et al. (+1 more)
Altermagnets have garnered great interest due to their non-relativistic
spin splitting and novel physical properties. However, the control of altermagnetic states remains underexplored. Here, we propose a unique multiferroic state, i.e. ferroelastic altermagnetic state, in which ferroelastic strain couples directly to the
spin-splitting. Through
symmetry analysis and first-principles calculations, we identify the ferroelastic $d$-wave altermagnetism of puckered pentagonal CoSe$_2$ monolayer. Interestingly, uniaxial stress can induce a ferroelastic phase transition, accompanied by a $90\degree$ rotation of the
spin-splitting bands. Cooperative rotation of the
lattice and Néel vectors preserves the sign of Kerr angle, whereas noncooperative rotation reverses it. Our work provides a general strategy for manipulating altermagnetism in multiferroic systems and opens other avenues for exploring emergent magnetoelastic phenomena.
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All authors Ning Ding, Haoshen Ye, Shan-Shan Wang, Shuai Dong
Superconductivity
Experimental Demonstration of a Superconductor SFQ-Based ADC for High-Frequency Signal Acquisition
Beyza Zeynep Ucpinar, Sasan Razmkhah, Mustafa Altay Karamuftuoglu et al. (+1 more)
Superconducting
quantum interference devices (SQUIDs) are among the most sensitive sensors, offering high precision through their well-defined flux-voltage characteristics. Building on this sensitivity, we designed, fabricated, and experimentally demonstrated a superconducting single flux
quantum (SFQ)-based analog-to-digital converter (ADC) capable of detecting small variations in input current signals at high frequencies and converting them into SFQ pulse trains. To improve robustness and reduce errors, the design incorporates a majority
circuit and two types of counters: asynchronous toggle flip-flop-based and synchronous cumulative-based, at the cryogenic stage. The counter collects the SFQ pulse train and converts it into a binary number, simplifying downstream digital readout. The
circuits were implemented using the AIST CRAVITY (QuFab) HSTP process and successfully tested in our cryocooler system, validating both the design methodology and operation. This approach helps build a fully integrated system that combines digital SQUID functionality with cryogenic readout
circuits on a single chip.
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All authors Beyza Zeynep Ucpinar, Sasan Razmkhah, Mustafa Altay Karamuftuoglu, Ali Bozbey
Mesoscale and Nanoscale Physics
Phenomenological Ehrenfest Dynamics with Topological and Geometric Phase Effects and the curious case of Elliptical intersection
Dhruv Sharma
We present a comprehensive computational framework for simulating nonadiabatic molecular dynamics with explicit inclusion of
geometric phase (GP) effects. Our approach is based on a generalized two-level
Hamiltonian model that can represent various electronic state crossings - conical intersections, avoided crossings, and
elliptic intersections - through appropriate parameterization. We introduce a novel prelooping trajectory initialization scheme, allowing us to encode the
memory as an initial phase accumulated due to the adiabatic
evolution over the potential energy surface. This is a unified framework to handle different types of level crossings by incorporating Berry
curvature-based force corrections to Ehrenfest dynamics, ensuring accurate representation of topological effects. For conical intersections, our method incorporates the theoretically expected phase pi, while for
elliptic intersections, it yields a parametrically tunable but loop radius (energy) independent phase different from pi. We also include an eccentricity parameter (e) in the diabatic coupling to model more realistic molecular systems. Numerical simulations demonstrate the consistency of our approach with theoretical predictions for mixing of states and inhibition from mixing due to
geometric phase effects. This framework provides a valuable tool for studying
quantum-classical interactions in molecular systems where
geometric phase effects play a significant role. The elliptical intersection and
geometric phase effect opens avenue for the design and discovery of degenerate materials. It produces a fresh look to help develop a new kind of spectroscopy and potential
qubit applications. This simple
Hamiltonian reveals a pathological phase protection effect E = kr, where k is real, that has great utility in a new spectroscopy design.
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Mesoscale and Nanoscale Physics
Mapping Temperature Using Transmission Kikuchi Diffraction
Yueyun Chen, Xin Yi Ling, Jared Lodico et al. (+3 more)
Electronic devices are engineered at increasingly smaller length scales; new metrologies to understand nanoscale thermodynamics are needed. Temperature and pressure are fundamental thermodynamic quantities whose nanoscale measurement is challenging as physical contact inevitably perturbs the system. Here we demonstrate Kikuchi diffraction thermometry (KDTh), a non-contact scanning electron microscope (SEM) technique capable of mapping nanoscale temperatures and pressures. KDTh detects local volumetric
lattice changes in crystalline samples by precisely fitting Kikuchi patterns. Temperature changes are deduced using the coefficient of thermal expansion (CTE). We map
lattice parameters and temperatures on Joule-heated graphite by rastering a 5.5-nm electron probe across the sample. Our parameter precision is ~0.01% and our temperature sensitivity is 2.2 K/$\sqrt{Hz}$. KDTh offers advanced sensitivity by fitting the entire Kikuchi pattern, even beyond the precision measured in transmission electron microscopy. KDTh can operate in both transmission (transmission Kikuchi diffraction, TKD) and reflection (electron backscatter diffraction, EBSD) modes.
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All authors Yueyun Chen, Xin Yi Ling, Jared Lodico, Tristan P. O`Neill, B. C. Regan, Matthew Mecklenburg
Materials Science
A large spin-splitting altermagnet designed from the hydroxylated MBene monolayer
Xinyu Yang, Shan-Shan Wang and Shuai Dong
The development of altermagnets is fundamentally important for advancing spintronic device technology, but remains unpractical for the weak
spin splitting in most cases, especially in two-dimensional materials. Based on
spin group
symmetry analysis and first-principles calculations, a novel hydroxyl rotation strategy in collinear antiferromagnets has been proposed to design altermagnets. This approach achieves a large chirality-reversible
spin splitting exceeding $1130$ meV in $\alpha_{60}$-Mn$_2$B$_2$(OH)$_2$ monolayer. The system also exhibits intrinsic features of a node-line semimetal in the absence of
spin-orbit coupling. Besides, the angles of hydroxyl groups serve as the primary order parameter, which can switch on/off the altermagnetism coupled with the ferroelastic mechanism. The corresponding magnetocrystalline anisotropy have also been modulated. Moreover, an interesting
spin-related transport property with the
spin-polarized conductivity of 10$^{19}$ $\Omega^{-1}m^{-1}s^{-1}$ also emerges. These findings uncover the hydroxyl rotation strategy as a versatile tool for designing altermagnetic node-line semimetals and opening new avenues for achieving exotic chemical and physical characteristics associated with large
spin splitting.
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