Papers

High-temperature superconductors (high-Tc SCs) host a rich landscape of electronic phases encompassing the pseudogap, strange metal, superconducting, antiferromagnetic insulating, and Fermi-liquid regimes. The superconducting phase is notable for non-dissipative electronic functionality at relatively high temperatures. These phases are commonly probed in thermodynamic phase space by varying temperature or current through the sample. They can also be probed by breaking time-reversal symmetry (TRS) with an external magnetic field, which yields transition signatures distinct from those arising solely from temperature or current tuning. Here we show that electron transport in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ is primarily governed by two-dimensional superconductivity consistent with a Berezinskii-Kosterlitz-Thouless (BKT) topological phase transition, as supported by current-voltage characteristics measured under temperature variation; these measurements preserve TRS. In contrast, when an external magnetic field is applied, the superconducting state is consistently preceded by weak antilocalization (WAL), where bound vortex-antivortex pairs dissociate into a normal metallic state through an intermediate localized phase. We further establish that highly disordered films exhibit transport dominated by three-dimensional weak localization, with superconductivity entirely suppressed.

We demonstrate a gate dielectric engineering approach leveraging an ultrathin, atomic layer deposited (ALD) silicon oxide interfacial layer (SiL) between the amorphous oxide semiconductor (AOS) channel and the high-k gate dielectric. SiL positively shifts the threshold voltage (V$_T$) of AOS transistors, providing at least four distinct $V_T$ levels with a maximum increase of 500 mV. It achieves stable $V_T$ control without significantly degrading critical device parameters such as mobility, on-state current, all while keeping the process temperature below 225 $^{\circ}$C and requiring no additional heat treatment to activate the dipole. Positive-bias temperature instability tests at 85 $^{\circ}$C indicate a significant reduction in negative $V_{T}$ shifts for SiL-integrated devices, highlighting enhanced reliability. Incorporating this SiL gate stack into two-transistor gain-cell (GC) memory maintains a more stable storage node voltage ($V_{SN}$) (reduces $V_{SN}$ drop by 67%), by limiting unwanted charge losses. SiL-engineered GCs also reach retention times up to 10,000 s at room temperature and reduce standby leakage current by three orders of magnitude relative to baseline device, substantially lowering refresh energy consumption.

Detecting Lévy flights of cells has been a challenging problem in experiments. The challenge lies in accessing data in spatiotemporal scales across orders of magnitude, which is necessary for reliably extracting a power-law scaling. Differential dynamic microscopy has been shown to be a powerful method that allows one to acquire statistics of cell motion across scales, which is a potentially versatile method for detecting Lévy walks in biological systems. In this article, we extend the differential dynamic microscopy method to self-propelled Lévy particles, whose run-time distribution has an algebraic tail. We validate our protocol using synthetic imaging data and show that a reliable detection of active Lévy particles requires accessing length scales of an order of magnitude larger than its persistence length, if the variability in particle speed is moderate. Applying the protocol to experimental data of E. coli and E. gracilis, we find that E. coli does not exhibit a signature of Lévy walks, while E. gracilis is better described as active Lévy particles.

Two-dimensional (2D) transition metal dichalcogenides (TMDs), such as MoS2, have the potential to be widely used in electronic devices and sensors due to their high carrier mobility and tunable band structure. In 2D TMD devices, surface and interface cleanness can critically impact the performance and reproducibility. Even sample surfaces prepared under ultra-high vacuum (UHV) can be contaminated, causing disorder. On such samples, trace levels of submonolayer contamination remain largely overlooked, and conventional surface characterisation techniques have limited capability in detecting such adsorbates. Here, we apply scanning helium microscopy (SHeM), a non-destructive and ultra-sensitive technique, to investigate the surface cleanness of 2D MoS2. Our measurements reveal that even minute amounts of adventitious carbon induce atomic-scale disorder across MoS2 surfaces, leading to the disappearance of helium diffraction. By tracking helium reflectivity over time, we quantify the decay of surface order across different microscopic regions and find that flat areas are more susceptible to contamination than regions near edges. These findings highlight the fragility of surface order in 2D materials, even under UHV, and establish SHeM as a powerful tool for non-damaging microscopic 2D material cleanness characterisation. The approach offers a new route to wafer-scale characterisation of 2D material quality.

We present a first-principles study of a carbon-nitrogen (CN) impurity complex in silicon as an isoelectronic alternative to the T center [(CCH)$_\mathrm{Si}$]. The latter has been pursued for applications in quantum information science, yet its sensitivity to the presence of hydrogen is still problematic. Our proposed complex has no hydrogen, thereby eliminating this issue. First, we show that the CN complex is stable against decomposition into substitutional and interstitial defects. Next, we show that due to being isoelectronic to the T center, the CN complex has a similar electronic structure, and therefore could be used in similar applications. We assess several low-energy configurations of the CN complex, finding (CN)$_\mathrm{Si}$ to be stable and have the largest Debye-Waller factor. We predict a zero-phonon line (ZPL) of 828 meV (in the telecom S-band) and a radiative lifetime of 4.2 $\mu$s, comparable to the T center. Due to the presence of a bound exciton, choice of the exchange-correlation functional and also supercell-size scaling of the ZPL and transition dipole moment require special scrutiny; we rigorously justify our extrapolation schemes that allow computing values in the dilute limit.

Computation with the Ising model is central to future computing technologies like quantum annealing, adiabatic quantum computing, and thermodynamic classical computing. Traditionally, computed values have been equated with ground states. This paper generalizes computation with ground states to computation with spin averages, allowing computations to take place at high temperatures. It then introduces a systematic correspondence between Ising devices and neural networks and a simple method to run trained feed-forward neural networks on Ising-type hardware. Finally, a mathematical proof is offered that these implementations are always successful.

Various coils for transcranial magnetic stimulation (TMS) are widely available for clinical and research use. These coils are almost all designed as air coils, which require large levels of energy to achieve a given magnetic flux density and in turn electric field strength, whereas in other sectors, such as power electronics or electrical machines, magnetic materials have been used for a long time to achieve higher efficiencies. We tested the impact on the electric and magnetic properties of different soft magnetic materials, including various ferrite cores, laminated sheet materials of nonisotropic corn-oriented silicon-steel, non-oriented silicon-steel, as well as cobalt-iron, and soft magnetic compound powder cores with insulated particles. Every material led to a reduction in coil current and voltage for the same target electric field strength. For the same field energy, every material yielded lower losses. Most common materials saturated already at very low currents. More material in thicker layers could shift the saturation point but at the cost of high weight. Due to their low saturation flux density, ferrites appear unsuitable for the high amplitude requirements of TMS. Laminated sheet materials and powder cores reduce the pulse energy, but the laminated sheet material adds more weight for the same effect than powder cores. Thus, appropriate magnetic materials can reduce the required pulse energy. Saturation flux density is the most relevant parameter, whereas the permeability beyond a certain base level is practically irrelevant. Most importantly, the weight of a magnetic-core coil may always be increased compared to an air coil for the same target field.

In this study, using nonequilibrium molecular dynamics simulation, the water flow in carbon nanocones is studied using the TIP4P/2005 rigid water model. The results demonstrate a nonuniform dependence of the flow on the cone apex angle and the diameter of the opening where the flow is established, leading to a significant increase in the flow in some cases. The effects of cone diameter and pressure gradient are investigated to explain flow behavior with different system structures. We observed that some cones can optimize the water flow precisely. Nanocones with a larger opening facilitate the sliding of water, significantly increasing the flow, thus being promising membranes for technological use in water impurity separation processes. Nanocones with narrower opening angles limited water mobility due to excessive confinement. This phenomenon is linked to the ability of water to form a larger hydrogen-bond network in typical systems with diameters of this size, obtaining a single-layer water structure. Nanocones act as selective nanofilters capable of allowing water molecules to pass through while blocking salts and impurities. The conical shape of their structures creates a directed flow that improves separation efficiency. Membranes based on carbon nanocones are becoming promising for clean, smart, and efficient technologies. The combination of transport speed, selectivity, and structural control put them ahead of other nanostructures for various purposes.

The coherence of hole spin qubits in germanium planar heterostructures is limited by the hyperfine coupling to the nuclear spin bath due to 29Si and 73Ge isotopes. Thus, removing these nuclear spin-full isotopes is essential to extend the hyperfine-limited coherence times needed to implement robust quantum processors. This work demonstrates the epitaxial growth of device-grade nuclear spin-free 70Ge/28Si70Ge heterostructures on industrial SiGe buffers while minimizing the amounts of highly purified 70GeH4 and 28SiH4 used. The obtained 70Ge/28Si70Ge heterostructures exhibit a dislocation density of 5.3 x 10e6 cm-2 and an isotopic purity exceeding 99.99%, with carbon and oxygen impurities below the detection sensitivity, as revealed by atom probe tomography. Magnetotransport measurements on gated Hall bars demonstrate effective gate control of hole density in nuclear spin-free quantum wells. Negative threshold gate voltages confirm the absence of intentional doping in the wells, while Hall and Shubnikov-de Haas analyses yield consistent carrier densities (1.4 x 10e11 cm-2) and high mobilities (2.4 x 10e5 cm2/Vs). Mobility trends reveal interfacetrap- limited scattering and percolation concentration below 7 x 10e10 cm-2. These analyses, along with atomic-level studies, confirm the high quality of epitaxial 70Ge/28Si70Ge heterostructures and their relevance as a platform for long-coherence spin qubits.

Noncovalent interactions–vdW dispersion, hydrogen/halogen bonding, ion-$\pi$, and $\pi$-stacking–govern structure, dynamics, and emergent phenomena in materials and molecular systems, yet accurately learning them alongside covalent forces remains a core challenge for machine-learned force fields (MLFFs). This challenge is acute for global models that use Coulomb-matrix (CM) descriptors compared under Euclidean/Frobenius metrics in multifragment settings. We show that the mismatch between predominantly covalent force labels and the CM's overrepresentation of intermolecular features biases single-model training and degrades force-field fidelity. To address this, we introduce \textit{$\Delta$-sGDML}, a scale-aware formulation within the sGDML framework that explicitly decouples intra- and intermolecular physics by training fragment-specific models alongside a dedicated binding model, then composing them at inference. Across benzene dimers, host-guest complexes (C$_{60}$@buckycatcher, NO$_3^-$@i-corona[6]arene), benzene-water, and benzene-Na$^+$, \mbox{$\Delta$-sGDML} delivers consistent gains over a single global model, with fragment-resolved force-error reductions up to 75%, without loss of energy accuracy. Furthermore, molecular-dynamics simulations further confirm that the $\Delta$-model yields a reliable force field for C$_{60}$@buckycatcher, producing stable trajectories across a wide range of temperatures (10-400~K), unlike the single global model, which loses stability above $\sim$200~K. The method offers a practical route to homogenize per-fragment errors and recover reliable noncovalent physics in global MLFFs.

Antiperovskite (APV) nitrides exhibit a diverse range of electronic properties, including superconductivity, magnetic effects, and nontrivial topological behaviors. In this study, we propose a new family of APV nitrides by incorporating 4$f$-electron metals, known for strong electron correlations, localized magnetic moments, and spin-orbit coupling, to further explore the unique properties of APVs. A high-throughput density functional theory (DFT) calculation was utilized to identify stable lanthanide APV nitride compounds. To address the challenge of strong electron correlation, we developed a double-screening framework that assumes either a fully itinerant or localized nature of the $f$-electrons during calculations. Using this approach, we systematically identified 37 stable lanthanide APV nitride compounds from both thermodynamic and dynamical perspectives. Furthermore, we report nontrivial topological behaviors observed among these stable lanthanide APV nitride compounds, as computed by DFT. Notably, Dirac and semi-Dirac cones are observed near the Fermi level for Er$_3$TlN. This study opens a pathway to investigate lanthanide APVs, revealing potential novel physical properties by leveraging the rich physics of both APVs and $f$-electrons.

Altermagnets (AMs) are a recently identified class of unconventional collinear compensated antiferromagnets that exhibit momentum-dependent spin splitting despite having zero net magnetization. This unconventional magnetic order gives rise to a range of phenomena, including the anomalous Hall effect, chiral magnons, and nonlinear photocurrents. Here, using spin space group (SSG) symmetry analysis and first-principles calculations, we demonstrate an efficient strategy to control altermagnetism in two-dimensional multiferroics through ferroelectric polarization and interlayer sliding. For material realization, we find that monolayer and bilayer FeCuP2S6 exhibit finite spin splitting when ferroelectric sublattices are connected by nonsymmorphic screw-axis operations rather than pure translation or inversion symmetry. Interlayer sliding further enables reversible switching or suppression of spin splitting through modifications of the SSG. Our calculations further reveal that the anomalous Hall response serves as a direct probe of these spin-split states. These findings establish two-dimensional van der Waals multiferroics as promising platforms for realizing electrically controllable altermagnetism and advancing next-generation spintronic and magnetoelectric technologies.

Soils and sediments are soft, amorphous materials with complex microstructures and mechanical properties, that are also building blocks for industrial materials such as concrete. These Earth-mediated materials evolve under prolonged environmental pressures like mechanical stress, chemical gradients, and biological activity. Here, we introduce geomimicry, a new paradigm for designing sustainable materials by learning from the emergent and adaptive dynamics of Earth-mediated matter. Drawing a parallel to biomimicry, we posit that these geomaterials follow evolutionary design rules, adapting their structure and function in response to persistent natural forces through locally evolved interactions and compositions. Our central argument is that by decoding these rules - primarily through understanding the emergence of novel exotic properties from multiscale interactions between heterogenous components - we can engineer a new class of adaptive, sustainable matter. We propose two complementary approaches here. The top-down approach looks to nature to identify building blocks and map them to functional groups defined by their mechanical behaviors, and then examine how environmental training tunes interactions among these groups. The bottom up approach seeks to leverage and test this framework, building earth materials one component at a time under fluctuating environmental stresses that guide assembly of complex and out-of-equilibrium materials. The goal is to create materials with programmed functionalities, such as erosion resistance or self-healing capabilities. Geomimicry offers a pathway to re-imagine climate-resilient soils and precision agriculture to new insights into planetary terraforming, fundamentally shifting the focus from static compositions to dynamic, evolving systems that are mediated via their environment.

The electronic properties of a material depend on the spatial freedom of the electron wavefunction. A well-known example is graphite, which is a conventional gapless semiconductor, while a single layer of it, graphene, exhibits extremely high electronic conductivity. Nevertheless, graphene ribbons can have different physical properties, such as a tunable band gap, ranging from gapless to a large band gap semiconductor. The purpose of this study is to investigate the electronic structure of few-layer graphene composed of a layer of graphene nanoribbons and graphene sheet(s), where quasi-one-dimensional nanoribbons can interact with a two-dimensional sheet of graphite. Using the tight-binding model for graphite, we show how different configurations of such heterostructures can affect the electronic structure, which is different from that of their components. Our results show that systems composed of semiconducting AGNRs can not be seen as two separate systems. Namely, a local gap of ~0.6 eV at the Dirac point for dispersive bands can be opened in a bilayer configuration composed of a layer of gapless armchair nanoribbon stacked on graphene. We demonstrate that the band steepness in these structures can be tuned, highlighting their potential for electronic applications.

Dynamic conductance and time-of-flight current instability in a quantum wire connected to electron reservoirs under DC bias voltage are studied in the absence of a gate screening the Coulomb interaction of electrons. Due to a strong electron-electron interaction, dramatic rearrangements of the charge density distribution and the potential landscape in the wire occur at a sufficiently high DC bias voltage. The applied voltage is screened mainly near the cathode contact, and an almost flat potential profile is established in the most of the wire. Thus, the size of the region of a population inversion of electronic states greatly increases, and the band of wave vectors that form unstable modes of electronic waves significantly reduces. As a result, the conditions for the occurrence of the time-of-flight instability are greatly facilitated and the negative dynamic conductivity increases.

This monograph presents the results of experimental and theoretical studies of binary and ternary crystalline and glassy silicon tellurides. It provides a detailed description of the methods for synthesizing and growing bulk and nanostructured binary crystals of Si2Te3, SiTe2, and ternary crystals known in the M-Si-Te systems (M = Na, K, Cu, Ag, Al, In), as well as sodium-silicon and tellurium-silicon clathrates. Significant attention is paid to the results of investigations into their electronic structure, optical, electrical, photoelectric, and photoluminescent properties.The publication is intended for researchers and specialists in the fields of semiconductor materials science, physics, and semiconductor technology, as well as lecturers, postgraduate students, and students of relevant specialties.

Scattering by charged impurities is known to mainly determine transport properties of electrons in modern quantum materials, but it remains poorly studied for materials with Mexican hat dispersion. Due to such nontrivial features as a singular density of states and a ring-shaped Fermi surface, electron-electron interaction and electron transitions between different isoenergetic contours are of key importance in this materials. We show that these factors significantly affect both the spatial profile of the screened potential of Coulomb centers and the dependence of mobility on temperature and electron density. The screened potential is calculated within the random phase approximation. The transport properties are determined without using the usual relaxation time approximation, since the distribution function in energy space is a vector defined by a system of two equations.

We show that a planar Josephson junction having $d$-wave superconducting regions, with a skyrmion crystal placed underneath, produces a robust gate-tunable superconducting diode effect. The spatially-varying exchange field of the skyrmion crystal breaks both inversion and time-reversal symmetries, leading to an asymmetric current-phase relation with an anomalous phase shift. Our theoretical calculations, obtained using resistively and capacitively shunted junction model combined with Bogoliubov-de Gennes method, reveal that the diode efficiency is largely tunable by controlling external gate voltage and skyrmion radius. Incorporation of a $d$-wave superconductor such as high-$T_c$ Cuprate enables the diode to function at higher operating temperatures. Our results establish a unique and practically-realizable mechanism for devising tunable field-free superconducting diodes based on magnetic texture-superconductor hybrid platforms.

Recent advances in metamaterials and fabrication techniques have revived interest in mechanical computing. Contrary to techniques relying on static deformations of buckling beams or origami-based lattices, the integration of wave scattering and mechanical memory presents a promising path toward efficient, low-latency elastoacoustic computing. This work introduces a novel class of multifunctional mechanical computing circuits that leverage the rich dynamics of phononic and locally resonant materials. These circuits incorporate memory-integrated components, realized here via metamaterial cells infused with shape memory alloys which recall stored elastic profiles and trigger specific actions upon thermal activation. A critical advantage of this realization is its synergistic interaction with incident vibroacoustic loads and the inherited high speed of waves, as opposed to recent adaptations of mechanically intelligent systems that employ innately slower mechanisms such as elastomeric shape changes and snap-through bistabilities. Through a proof-of-concept physical implementation, the efficacy and reconfigurability of the wave-based gates are demonstrated via output probes and measured wavefields. Furthermore, the modular design of the fundamental gates can be used as building blocks to construct complex combinational logic circuits, paving the way for sequential logic in wave-based analog computing systems.

We investigate the rotation of a vortex around a circular obstacle in dry active matter in the presence of M half-circles distributed around the obstacle. To quantify this effect, we define the parameter {\Pi}M , which is the ratio between the mean angular velocity of the controlled vortex and the root-mean-square angular velocity of the isolated vortex. We identify two rotational regimes determined by the obstacle configuration. In the first regime, where {\Pi}M < 0 corresponding to the flat side of the half-circles facing the vortex, the rotation is clockwise. In the second regime ({\Pi}M > 0), it corresponding to the curved sides facing the vortex, the rotation becomes counterclockwise. We further analyze the impact of this control on vortex stability, showing that the configuration of semi-circles can enhance or suppress stability depending on their geometry and distance from the central obstacle. Our results demonstrate a possible setup to control the spontaneous rotation of dry active matter around circular obstacles.

The phenomenological theory of martensite crystallography (PTMC) developed in the 1950s explains the main crystallographic and microstructural features of martensite in shape memory alloys, such as the habit planes of bi-variant laminate martensite product, and the transformation twins between the variants. It also permits to determine the austenite and martensite lattice parameters that allow supercompatibility, which has driven important research and development of new shape memory alloys with low hysteresis and high cyclability. Supercompatibility takes the form of three mathematical equations called cofactor conditions. The calculations are in great part based mathematical tools from continuum mechanics (polar decompositions and stretch tensors). They were recently replaced by pure crystallographic tools (metric tensors, group of symmetries and correspondence) in an alternative approach called correspondence theory (CT). The CT allows for the direct calculation of the transformation twins and their generic and non-generic characteristics. These twins ensure the compatibility at martensite/martensite (M/M) junction planes. Here, we show that the CT can also be used to determine the conditions of austenite/martensite (A/M) compatibility, and A/M/M supercompatibility.

Scanning tunneling microscopy-induced luminescence (STML) provides access to the optical properties of individual molecules through a cascade of relaxation processes between many-body states. Insufficient charge attachment energies prevent relaxation via optically active states, causing even intrinsically bright molecules to remain dark in STML. Here, we utilize substrate work function control and tip-induced gating of the double-barrier tunnel junction to induce an energy shift of the ionic transition state of a single free-base tetrabenzoporphyrin (H2TBP) to control access to optically active states and bright exciton emission. The experimental observations are validated by a rate equation and a polaron model considering the relaxation energy of the NaCl decoupling layer upon charging of the molecule.

A concrete question is discussed: Can there be conventional s-wave superconductivity in regular 3D (or 2D) metals, i.e., electrons in a jellium background, interacting via the standard Coulomb coupling? We are interested in 'practical' SC that can in principle be observed in experiments, so the $T=0$ ground state being SC is not of interest, or for that matter a $T_c$ which is exponentially small and therefore 'impractical' is also not of interest in the current work. We discuss both 2D and 3D cases, focusing mostly on the 3D case. We find that almost any theory based on the BCS-Migdal-Eliashberg paradigm, with some form of screened Coulomb coupling replacing the electron-phonon coupling in the BCS or Eliashberg theory, would uncritically predict absurdly high $T_c\sim100$ K for s-wave SC in all metals (including the alkali metals, which are well-described by the jellium model) arising from the unavoidable fact that the Fermi, plasmon, and Coulomb potential energy scales are all $>10^4$ K. Therefore, we conclude, based on reduction ad absurdum, that the violation of the venerable Migdal theorem in this problem is sufficiently disruptive that no significance can be attached to numerous existing theoretical publications in the literature claiming plasmon-induced (or other similar Coulomb coupling-induced) practical SC. Using a careful analysis of the Eliashberg gap equations we find that the $T_c$ of the 3D (or 2D) electron gas can be reduced well below $\sim1$ K depending on choices of frequency cut-off parameters that are introduced to satisfy Migdall's theorem but are apriori unknown. The only believable result is the one discovered 60 years ago by Kohn and Luttinger predicting non-s-wave SC arising from Friedel oscillations with exponentially low $T_c$. We provide several theoretical approaches using both BCS and Eliashberg theories and different screening models to make our point.

The electronic properties of two-dimensional (2D) metals are altered by changes in their three-dimensional dielectric environment. In this Letter we propose that superconductivity can be induced in a 2D metal by resonant coupling between its plasmonic collective modes and optical phonons in a nearby polar dielectric. Specifically, we predict that relatively high-temperature superconductivity can be induced in bilayer graphene twisted to an angle somewhat larger than the magic value by surrounding it with a THz polar dielectric. Our conclusions are based on numerical solutions of Eliashberg equations for massless Dirac fermions with tunable Fermi velocities and Fermi energies, and can be understood qualitatively in terms of a generalized McMillan formula.

The emergence of two-dimensional (2D) superconductivity in bulk transition metal dichalcogenides (TMDs) is a fascinating area of research, as their weak interlayer coupling leads to novel superconducting behavior and offers a rich platform to host nontrivial gap structures and interactions with other electronic orders. In this work, we present a comprehensive study of the superconducting properties of bulk single-crystalline $1T$-Ti$_{1-x}$Ta$_x$Se$_2$ for x = 0.2. Our results confirm the weakly coupled anisotropic superconductivity. Angle-dependent upper critical field measurements and observation of a Berezinskii-Kosterlitz-Thouless transition confirm the quasi-2D nature of the superconducting state. These results position $1T$-Ti$_{1-x}$Ta$_x$Se$_2$ as a promising platform for exploring low-dimensional superconducting physics and highlight bulk TMD crystals as a promising platform for realizing intrinsic 2D superconductivity, opening avenues for future quantum applications.

The aim of this work is to study the dynamics of quantum systems subjected to a localized fermionic source in the presence of bulk dephasing. We consider two classes of one-dimensional lattice systems: (i) a non-interacting lattice with nearest-neighbor and beyond, i.e., long-ranged (power-law) hopping, and (ii) a lattice that is interacting via short-range interactions modeled by a fermionic quartic Hamiltonian. We study the evolution of the local density profile $n_i(t)$ within the system and the growth of the total particle number $N(t)$ in it. For case (i), we provide analytical insights into the dynamics of the nearest-neighbor model using an adiabatic approximation, which relies on assuming faster relaxation of coherences of the single particle density matrix. For case (ii), we perform numerical computations using the time-evolving block decimation (TEBD) algorithm and analyze the density profile and the growth exponent in $N(t)$. Our detailed study reveals an interesting interplay between Hamiltonian dynamics and various environmentally induced mechanisms in open quantum systems, such as local source and bulk dephasing. It brings out rich dynamics, including universal dynamical scaling and anomalous behavior across various time scales and is of relevance to various quantum simulation platforms.

We show that the electromagnetic or phononic environment of a topological quantum device can be engineered to actively suppress decoherence. For a Majorana qubit in a superconducting wire, the exponentially small splitting $\epsilon \sim e^{-L/\xi}$ that provides topological protection also makes the qubit vulnerable to low-frequency noise. From a microscopic local interaction, we derive the effective low-energy coupling between the Majorana parity operator and a bosonic field; the coupling strength itself is proportional to $\epsilon$, reflecting the qubit's non-local nature. The resulting pure-dephasing rate scales as $\Gamma_\phi \propto \epsilon^2 S(\epsilon)$, with $S(\epsilon)$ the environmental noise power at frequency $\epsilon$. In the experimentally relevant high-temperature regime ($k_B T \gtrsim \hbar\epsilon$), this gives $\Gamma_\phi \propto \epsilon \rho(\epsilon) T$, where $\rho(\epsilon)$ is the environmental density of states. By engineering an environment with a suppressed low-frequency density of states, $\rho_{\text{eng}}(\omega) = \rho_0 (\omega/\omega_c)^\alpha$ for $\omega < \omega_c$ ($\alpha > 0$), the dephasing rate drops to $\Gamma_\phi^{\text{eng}} \propto \epsilon^{\alpha+1} \propto e^{-(\alpha+1)L/\xi}$. Thus, longer wires yield exponentially better coherence—a direct synergy with topological protection. This "inverse Purcell" effect, which suppresses the density of states at the qubit frequency, provides a quantitative design principle for environmental engineering. Our work establishes spectral density shaping as a practical method for enhancing coherence in topological quantum devices.

A vertex cover on a graph is a set of vertices in which each edge of the graph is adjacent to at least one vertex in the set. The minimal vertex cover (MVC) problem concerns finding vertex covers with the smallest cardinality, which is a typical computationally hard problem among combinatorial optimization on graphs. Here, we follow the idea of the long-range frustration (LRF) in MVC configurations proposed in [Physical Review Letters 94 (2005) 217203]. We correct its analytical framework and further extend it from Erdös-Rényi random graphs to general random graphs. We formulate the framework of LRF into a percolation model, and analytically estimate the energy density of MVCs on uncorrelated random graphs only with their degree distributions. We test our framework on some typical random graph models along with other methods, such as a hybrid algorithm of greedy leaf removal (GLR) procedure combined with survey propagation-guided decimation (SPD) algorithm and an analytical theory based on the GLR procedure which ignores LRF effect. We show that, when there is a percolation of LRF effect, the above three predictions of energy density, say $x_{\rm LRF}$, $x_{\rm GLR + SPD}$, and $x_{\rm GLR}$, follow a scenario as $x_{\rm LRF} > x_{\rm GLR+SPD} > x_{\rm GLR}$ in most cases and $x_{\rm GLR+SPD} > x_{\rm LRF} > x_{\rm GLR}$ in the other cases, and $x_{\rm LRF}$ is much closer to $x_{\rm GLR+SPD}$ than $x_{\rm GLR}$ as $|x_{\rm LRF} - x_{\rm GLR+SPD} | < x_{\rm GLR+SPD} - x_{\rm GLR}$. Our results show that LRF is a proper mechanism for the formation of complex energy landscape in the MVC problem and a theoretical framework of LRF helps to characterize its ground-state properties.

Spin-torque vortex oscillators (STVOs) have been shown to exhibit rich and complex dynamical regimes, which are strongly dependent on the polarizer's configuration. Here, we give an overview of the dynamics in an STVO comprising two vortex free layers, where each layer serves as a dynamic polarizer for the other, increasing the number of degrees of freedom and therefore, the complexity of the system. The dynamics are studied through extensive micromagnetic simulations, performed using our own implementation of the coupled equations of motion, implemented in the open-source micromagnetics code Mumax3. We explore the roles of relative vortex configurations and layer asymmetry on the current-driven dynamics, and find several complex regimes, including self-modulated gyration, the emergence of C-state dynamics, as well as chaotic transitions between regular gyration and this C-state.

The inherent instability of oscillatory flows presents a significant challenge in microfluidics, impairing performance in different applications from particle detachemnt to organs-on-a-chip. Trapped air inside a microfluidic system passively dampens these fluctuations because of the compressible nature of air. However, a foundational theoretical model that describes this effect has remained elusive. Here, a first-principles model that fully characterizes the effects of a trapped air volume in oscillatory microfluidic flow is derived. The model identifies a dimensionless product as the governing parameter, unifying the interplay between air compressibility and fluidic resistance. It precisely predicts the volume displacement dynamics of the liquid front, which compared with the original flow, it presents amplitude reduction, phase shift, and transient drift. The theoretical framework was validated with different experiments across a broad range of conditions. This work transforms trapped air from a source of unpredictability into a powerful, predictable element for tailoring oscillatory flow stability, providing a rigorous design tool for microfluidic systems.