The chequerboard $J-Q$ model was proposed to describe the direct phase transition from the antiferromagnetic (AFM) state to the plaquette-sin glet (PS) solid state observed in SrCu$_2({\rm BO}_3)_2$. In this paper, we present a Monte Carlo study of the ground state of an extended ve rsion of this model. For all parameters investigated, we find only a direct first-order phase transitions from the AFM to the PS phase, with no intermediate phase between them. On the transition line, the system exhibits an emergent $O(4)$ symmetry. Furthermore, we find that the Bi nder ratio of the columnar valence-bond solid state can be used to locate the phase transition. It exhibits a monotonic finite-size scaling b ehavior, allowing for a precise determination of the transition point.

Using density functional theory, we revisit the magnetic properties of a recently proposed family of noncentrosymmetric two-dimensional magnetic materials, chromium chalcohalide monolayers, CrXY (X=S, Se, Te; Y=Cl, Br, I). These systems consist of three atomic planes stacked in the X-Cr-Y sequence, which breaks inversion symmetry, giving rise to their designation as "Janus" monolayers. We consider both 1T and 1H structural polymorphs of CrXY. Among the two polymorphs, the 1T phase is consistently more favorable, with energy gains exceeding 0.55 eV per formula unit. Our total-energy calculations reveal that all dynamically stable CrXY monolayers exhibit ferromagnetic coupling. However, robust out-of-plane magnetic anisotropy is observed only in the CrSI and CrSeI compositions, for both 1T and 1H structures. The perpendicular magnetic anisotropy results from a constructive interplay between single-ion and anisotropic exchange contributions that overcome the dipole-dipole interaction. We further quantify the Dzyaloshinskii-Moriya interaction (DMI) in CrSI and CrSeI for both polymorphs, and reveal a weak-to-moderate DMI strength as compared to the isotropic exchange interaction term. Finally, for systems exhibiting ferromagnetic coupling and perpendicular magnetic anisotropy, the exchange and anisotropy parameters derived from density functional theory calculations are employed as inputs for large-scale atomistic spin dynamics simulations to probe the temperature evolution of real-space magnetic structures. The calculated Curie temperatures are at least 210 K for 1T-CrSI, 235-260 K for 1H-CrSeI, and 370-410 K for 1H-CrSI. In contrast, the sizable DMI in 1T-CrSeI results in a worm-like domain ground state at zero external field and enables the stabilization of skyrmions under a perpendicular magnetic field.

In conventional antiferromagnets a long-range ordered 3D ground state transitions to a disordered paramagnetic state on warming, often via lower dimensional spin correlations within the critical regime. Here we demonstrate a striking departure from this paradigm. Through analysis of neutron powder diffraction data, we show that the magnetic ground state of columnar-ordered quadruple perovskites, Na$R$Mn$_2$Ti$_4$O$_{12}$ ($R$ = Dy, Sm), lacks long-range order, hosting only 2D spin correlations. On warming, this disordered state transitions into a 3D long-range ordered antiferromagnetic structure prior to the phase transition to the paramagnetic state. Our results establish an unconventional order-by-heating mechanism in which intrinsic A-site chemical disorder is coupled to competing exchange interactions between the rare earth and Mn sub-lattices, leading to a novel type of magnetic phase transition.

We investigate the adhesion dynamics of a thin elastic structure in contact with a viscous fluid and retracted at a controlled speed, mimicking natural adhesion mechanisms. During detachment, the viscous fluid confined between the deformable structure and a rigid substrate generates an adhesive force due to a pressure drop within the thin film. We show from dedicated experiments that the structural flexibility introduces a strongly nonlinear mechanical response, which significantly alters both the magnitude and the evolution of the adhesion force with retraction velocity. In contrast to rigid systems, the deformability of the structure enables enhanced and tunable adhesion. To capture this interplay, we develop a theoretical framework that couples elasticity and viscosity, providing new insights into how flexible structures enable adhesion control.

Magnetic skyrmions in synthetic antiferromagnets are promising nanoscale bits, but their usefulness depends on how reliably a written pair survives and can be created. Using a reduced lattice model, we compute minimum energy paths for collapse of an antiferromagnetically bound skyrmion pair and for reverse nucleation from a pinned antiferromagnetic reference state. With antiferromagnetically pinned boundaries, the main saddle energy changes only weakly with pinned-island size, whereas the skyrmion-pair minimum carries a strong size-dependent boundary penalty. For large pinned islands, collapse is layer-sequential and can pass through a single-layer skyrmion intermediate whenever this state satisfies the relaxation criterion. The much larger reverse barrier for nucleation shows a strong asymmetry with collapse in the same pinned-boundary model and is consistent with assisted layer-sequential writing.

The quench action formalism relies on the assumption that the overlap between a generic initial state $\left|Ψ_{0}\right\rangle $ and an eigenstate of an integrable model - defined through the rapidities $\left|k_{1},...k_{N}\right\rangle $ - can be written as: \begin{equation} \left\langle k_{1},...k_{N}\midΨ_{0}\right\rangle =\exp\left(-S_{Ψ_{0}}\left(ρ\left(k\right)\right)\right),\label{eq:Exponential} \end{equation} where $ρ\left(k\right)$ is the quasiparticle density of the state $\left|k_{1},...k_{N}\right\rangle $ and $S_{Ψ_{0}}$ is some smooth function of $ρ\left(k\right)$ that depends on $Ψ_{0}$. In particular the quench action formalism assumes the overlap depends smoothly on the quasiparticle density $ρ\left(k\right)$. In this work, by explicit counter example, we show that this is not the case. We consider the quench between a Mott insulator and a Lieb Liniger gas. We show that the overlap between the ground state of the Mott insulator and arbitrary eigenstates of the Lieb Liniger gas has a highly singular behavior and no expression like Eq. (1) applies. We do so within the Tonks Girardeau limit of the Lieb Liniger gas and to leading order in the $1/c$ expansion for the overlap (with $c$ being the coupling constant of the Lieb Liniger gas). In the Appendix we show similar results for overlaps in the XXZ model with crystal states.

The interplay between chemical disorder and persistence of Berry curvature driven transport phenomena remains an important open question in entropy-stabilized systems. Here, we synthesize an entropy-stabilized Heusler alloy Co$_2$(Ti$_{0.25}$V$_{0.25}$Cr$_{0.25}$Fe$_{0.25}$)Al and systematically investigate its structural, magnetic, and magnetotransport properties using a combination of experimental measurements and density functional theory (DFT) calculations. The system crystallizes in cubic space group $Fm\Bar{3}m$ and exhibits ferromagnetism with saturation magnetization in close agreement with the Slater--Pauling prediction. Transport and magnetotransport measurements reveal metallic behavior and a pronounced anomalous Hall effect with an anomalous Hall conductivity of approximately $134.4~ Ω^{-1}$.cm$^{-1}$. Combined experimental observations and first-principles calculations establish that the anomalous Hall effect is predominantly intrinsic in origin and originates from the Berry curvature of the electronic bands. Remarkably, despite the substantial configurational disorder and the dilution of the constituent parent compounds, the anomalous Hall conductivity remains comparable to the largest values reported in the corresponding parent Heusler systems. This behavior reflects the manifestation of the cocktail effect, one of the core characteristics of entropy-stabilized systems. Our results also demonstrate that Berry curvature mediated transport persists in this chemically disordered system and indicates that entropy engineering can be a promising route for tuning intrinsic anomalous Hall responses.

The second-order Kuramoto model with inertia exhibits different dynamical behaviors than the first-order KM without inertia. A central difference is its lower synchronization due to the emergence of multiple synchronized clusters with different frequencies. We aim to investigate how such lowered synchronization can be improved by applying external perturbations to the system in a steady state, for example, a symmetry-breaking phase lag to a subset of oscillators. We find that this phase lag steers the primary cluster along a specific path and enables it to merge with higher-order clusters, thereby enhancing global synchronization. Our results reveal a mechanism by which controlled phase lag can improve entrainment in inertial oscillator systems, with possible implications for synchronization control in inertial oscillator networks.

We investigate the effect of light on quantum metric-mediated intrinsic nonlinear Hall conductivity in Berry dipole semimetals. We discover that light induces a tunable asymmetry in the off-diagonal part of the quantum metric, which is manifested by an asymmetry in the quantum metric dipole. We show that the nonlinear response can be tuned directly by the light amplitude. In particular, we note that the direction of the nonlinear Hall signal changes when the light amplitude is increased beyond a threshold value. Light thus emerges as a promising stimulus to control the quantum geometric response in topological semimetals.

Graphdiynes constitute an emerging class of two-dimensional sp-sp2 carbon allotropes with tunable electronic properties not accessible by graphene. Although flawless monolayer growth of graphdiyne networks has been attempted by means of on-surface synthesis protocols, the experimental realization of fully covalent and structurally ordered graphdiyne networks remains challenging due to the persistence of metalated intermediates and reaction byproducts, limiting the structural self-organization required for long-range covalent order. Here, we demonstrate that adding minute amounts of Fe atoms on the surface during the growth can exceptionally improve the synthesis of a covalent 2D graphdiyne monolayer framework on Au(111). By means of low-temperature scanning tunneling microscopy and spectroscopy, combined with density functional theory, we unveil the atomic-scale surface dynamics of the reaction. We demonstrate the crucial role of Fe atoms that bond with Br by-products, thereby forming Fe-Br species that promote the removal of Au adatoms and drive the conversion from a metalated network to a purely covalent framework upon mild annealing conditions. Moreover, we show the covalent graphdiyne network to be structurally and electronically decoupled from the underlying metallic substrate, revealing a finite bandgap of about 1.6 eV defined by the position of p_z frontier orbitals. These results establish a viable route for the atomically precise on-surface synthesis of all-carbon graphdiynes, and open the way to semiconducting 2D carbon materials complementing graphene.

We study the critical behavior of a two-dimensional Ising model with nonreciprocal vision-cone interactions, which explicitly violate reciprocity and detailed balance. Extensive Monte Carlo simulations and dynamic renormalization-group analysis show that the asymptotic critical exponents remain fully consistent with the equilibrium Ising universality class over a broad range of nonreciprocal coupling strengths $λ$. In contrast, dimensionless quantities such as the Binder cumulant and the correlation-length ratio display pronounced anisotropic nonequilibrium corrections and systematically deviate from their equilibrium Ising values. The renormalization-group flow further demonstrates that the nonreciprocal perturbation is irrelevant at the Wilson-Fisher fixed point while generating a finite shift of the critical temperature proportional to $λ^2$. Our results demonstrate the remarkable robustness of two-dimensional Ising criticality against this class of directional interactions.

Using density functional theory, we have performed a systematic study of the Heisenberg pairwise exchange interaction and the beyond Heisenberg multi-spin higher-order exchange interactions in unsupported transition-metal trilayers in the presence of external electric fields. The systems consist of a hexagonal atomic Fe layer sandwiched between 4$d$ (Ru, Rh, and Pd) and 5$d$ (Ir) transition-metal layers. Both fcc and hcp stacking of the 4$d$ overlayer has been taken into account. To scan a large part of the magnetic phase space, we have calculated the energy dispersion of spin spirals without and with applied electric fields up to $\pm 1.0$ V/Å. We find that the energy dispersion remains qualitatively the same upon applying the electric fields and the magnetic ground state remains unchanged. The exchange constants obtained by fitting the energy dispersions exhibit a linear dependence on the electric field up to values of about $\pm 0.6$ V/Å. The sign of the calculated pairwise and higher-order exchange constants remain unchanged with electric-field, however, their field induced variation is sensitive to the 4$d$ overlayer. The changes are on the order of a few percent for the nearest-neighbor exchange constant and up to a few ten percent for beyond nearest-neighbor constants. The higher-order exchange constants are calculated based on the total energies of multi-$Q$ states, such as the $uudd$ and the 3$Q$ state. Similar to the pairwise exchange constants, we find a nearly linear field dependence of the higher order constants at small electric fields and variations of up to ten percent. We study the spin-dependent screening of the electric field for the three trilayers and relate the modifications of the pairwise and higher-order exchange interactions to the electric field induced changes of the spin-dependent Fe local density of states and its variation at the Fermi level.

Carrier dynamics in semiconductors is inherently complex owing to the coexistence of different excited species, such as free carriers and excitons, and their interactions among themselves and with traps and phonons. It is usual to use time-resolved responses to identify the processes that contribute to the dynamics. However, the responses often are non-exponential, leading to ambiguity in the interpretation. Here, we propose a frequency domain method to characterize nonlinear dynamics in semiconductors using CdSe as the test system. We show that by analyzing the frequency components in the total photoluminescence induced by a pair of phase-modulated beams, the parameters, such as rates of different types of recombination of free carriers and excitons, can be evaluated. The method can be used as a simple diagnostic tool to characterize ultrafast processes that are relevant to the functionality of semiconductor devices.

Progress in the fabrication of nanoscale transition-metal-oxide heterostructures makes these platforms promising candidates for the realization of spin qubits, mainly due to the $d$-character of their electronic structures, which could potentially result in a reduction of hyperfine interactions and spin decoherence. Here, we present a systematic study of spin control within the SWAP operation in double quantum dots embedded in a two-dimensional electron gas at the LaAlO$_3$/SrTiO$_3$ interface. Our analysis starts with a study of single-electron spin dynamics, focusing on the influence of spin-orbit and interorbital coupling on the spin evolution. In this case, our findings are supported by semiclassical calculations based on the Bloch equations, which show good agreement with full quantum mechanical simulations. We then simulate the SWAP operation by analyzing the crossover between two regimes: (i) large quantum dots, where the electronic structure is dominated by the $d_{xy}$ orbitals and the spin dynamics is affected primarily by Rashba-type spin-orbit interaction; and (ii) small quantum dots, where higher-energy orbitals $d_{xz/yz}$ contribute to the electronic structure, leading to a significant reduction in the SWAP fidelity. In the first regime, particularly relevant from the application point of view, we analyze in detail the anisotropy of the SWAP operation induced by the spin-orbit coupling.

Graphene/hBN moiré superlattices provide a highly tunable platform for exploring emergent quantum phases in low-dimensional systems. Here, we investigate the moiré superlattice formed between hBN and ABA-stacked trilayer graphene (TLG), an inherently multi-band system. We demonstrate that the moiré potential is not merely a perturbation but a tool to hybridize the distinct massless and massive electronic sectors of TLG. By applying a perpendicular displacement field to tune layer polarization, we drive a fundamental reconstruction of the electronic band structure. Specifically, increasing the displacement field evolves the system from a multi-band regime to an effectively single-band regime at low energies, accompanied by a metal--insulator transition at the hole-doped secondary Dirac point. This transition originates from a redistribution of carriers across graphene layers that selectively enhances their coupling to the extrinsic moiré potential. Quantum capacitance measurements provide direct evidence for the suppression of the density of states at the hole-side secondary Dirac point, consistent with gap opening and the emergence of a displacement-field-tuned band gap. Theoretical calculations reproduce these observations and identify layer-selective coupling to the moiré potential as the underlying mechanism. These results demonstrate electrical control of an emergent insulating phase in a low-dimensional moiré system, and highlight that layer polarization and layer-selective coupling in multi-band moiré heterostructures provide a powerful route for engineering topological and correlated phases through band structure reconstruction and electron interactions.

Computational models adequately representing phase transitions and evaluating the critical system parameters are essential for the understanding of the properties of a wide range of materials. Here we propose a machine learning (ML)-based approach to the identification of the critical point in anisotropic spin systems. Our approach implies training of a convolutional neural network (CNN) model from the correlation matrices obtained by Monte Carlo simulations. Next, the pretrained model is employed as a fast estimator of the critical temperature, which can be extracted in several complementary ways from the CNN model inference, this way improving the robustness of the analysis. The ML-based estimates obtained in this study are in very good agreement with the reference Monte Carlo simulation results, while computational costs are about 10x lower compared to the classical thermodynamic approach.

Supply chains are intrinsically vulnerable to stochastic shocks due to their sequential production dependencies. Building on the Feld-Barthelemy framework, we investigate how capacity volatility and input substitutability determine critical demands in stochastic supply chains. By modeling production capacity with a truncated normal distribution, we show that in long supply chains, reducing capacity volatility is often more effective than increasing average capacity, emphasizing the need for firm-level synchronization. Furthermore, introducing a modified Leontief-type production function reveals that input substitutability effectively disperses stochastic shocks. Supplier diversification inherently raises critical demands, even under fixed maximum capacities, by introducing the effect of network topology that independently enhances the resilience of physical stock. Our findings demonstrate that mitigating capacity volatility and structurally diversifying supply routes are just as crucial to supply chain resilience as traditional inventory expansion.

Geometrically frustrated magnets provide an ideal platform for exploring the interplay between lattice geometry and spin degrees of freedom. Here, we investigate the interactions between lattice and spin via thermal-transport measurements on the triangular sawtooth-lattice olivine magnet Fe$_\mathrm{2}$SiSe$_\mathrm{4}$, which exhibits successive magnetic transitions at $T_1 = 110$ K (antiferromagnetic) and $T_2 = 50$ K (ferrimagnetic). Although phonons dominate the thermal conductivity, its temperature dependence displays a pronounced double-peak structure arising from spin-phonon coupling. In the intermediate temperature range between $T_1$ and $T_2$ , resonant scattering of phonons by magnetic excitations around 5 meV produces a broad maximum around 60 K. Below $T_2$, the resonant spin-phonon scattering is strongly suppressed, leading to a rapid increase in thermal conductivity upon cooling and a pronounced low-temperature peak near 11 K, characteristic of heat transport governed by conventional phonon scattering mechanisms. Notably, this low-temperature peak is enhanced by a factor of $\sim 5$ compared to the broad maximum at higher temperatures. These results demonstrate the strong sensitivity of thermal transport to spin-lattice interactions and highlight spin-phonon scattering as an effective mechanism for tailoring thermal conductivity in geometrically frustrated magnets.

Atomic-scale phase-field modeling extends the phase-field framework down to the level of individual atoms by treating the probability density of atomic vibrations as a field variable and constructing a corresponding free-energy functional from this atomic field together with interatomic potentials. In this way, the framework has the potential to visualize local thermodynamic states with atomic-level resolution, just as conventional phase-field modeling has served as a computational microscope for free energy, stress, and related quantities at mesoscopic scales. However, existing formulations mainly assume Gaussian probability distributions for atomic vibrations, which limits their applicability to more complex and heterogeneous systems such as surfaces. In this work, we generalize the atomic-scale phase-field methodology by extending the free-energy functional to include non-Gaussian fluctuations. We apply this approach to monolayer SnTe in the NVT ensemble and show that the predicted equilibrium polarization is in better agreement with molecular dynamics simulations and that the ferroelectric-to-paraelectric phase transition is successfully reproduced. Furthermore, by decomposing the entropy on a per-atom basis, we visualize atomically resolved maps of local entropy and find that Sn atoms contribute more strongly to the entropy than Te atoms at high temperature, which is a driving factor of the ferroelectric-to-paraelectric phase transition. These results broaden the applicability of phase-field approaches to a wider range of atomic systems and suggest a route toward an atom-resolved theory of phase transitions based on high-resolution thermodynamics.

Kagome metals with the formula RM6X6 (R = rare-earth, M = 3d transition metal, and X = Sn/Ge) provide a rich platform for exploring magnetic and electronic phenomena, with tunable properties enabled by the combination of rare-earth elements and transition metals. In this study, we report the structural, electrical and magnetic properties of Kagome metal (NdxGd1-x)V6Sn6. We demonstrate that substituting lighter Nd atoms at the Gd site tunes the complex magnetic ground state of GdV6Sn6 into a ferromagnetic-like one. Moreover, the isotropic magnetization of GdV6Sn6 becomes anisotropic, with the c-axis emerging as the easy axis. Transport measurements reveal a strong coupling between magnetism and electronic properties, with negative magnetoresistance observed at low magnetic fields in all compositions. In addition, a fourfold anisotropy component tends to emerge in end compounds at higher magnetic fields. These findings highlight the role of rare-earth substitution in tuning magnetic anisotropy and magneto-transport behaviour in RM6X6 compounds, featuring a non-magnetic Kagome layer, with potential implications for spintronic and topological applications.

Network theory can be fruitfully used to describe quantum coherence in physical systems. To that purpose we introduce persistent currents in signed directed networks by interpreting the signed magnetic Laplacian as an effective Hamiltonian and the associated edge phases as a discrete gauge field. In a canonical ensemble, persistent currents arise as thermodynamic responses to variations of gauge-invariant fluxes. We show that these fluxes are naturally defined on the cycle space of the network, and that the resulting currents are constrained to the divergence-free subspace and decompose onto independent cycles. This formulation provides a direct generalization of persistent currents from rings and lattices to arbitrary topologies. Detection of persistent currents provides a signature of the quantum phase coherence supported by the network, and a direct signature of the geometry of its cycle space. Such a mapping, not only allows a practical way to deal with quantum coherence for a variety of situations in the field of quantum technologies, but it also allows a physical interpretation of the importance of the Laplacian operator in graph theory, linking its role to the one of Hamiltonian (i.e. a tight-binding one) in physical systems. To test the power of the method, we construct a signed directed network that reproduces the Hofstadter butterfly spectrum.

The cylindrical snap-fit is a ubiquitous fastening method that is both simple to manufacture and assemble, and yet secure. It consists of a partial cylindrical shell that `snaps' onto a cylindrical object. We build on previous work to describe the mechanics of the cylindrical snap-fit as a naturally curved thin elastic shell placed atop a rigid cylinder; we investigate the shell's behaviour when subject to a point force pushing it onto or pulling it off the cylinder. We classify the possible contact regimes according to whether the shell has a nonzero lifting capacity. We term situations with lifting capacity `grip-fits' and show that this includes both the snap-fit and a `stick-fit' regime, which allows lifting despite not having the characteristic `snap'. Regimes without lifting capacity are also characterized for completeness. We show that the different regimes may be characterized entirely by the shell/cylinder geometry and the coefficient of friction. We then consider different metrics for the lifting performance in the grip-fit regime. Our analysis reveals the trade-offs between assembly force, disassembly force, lifting force, and clamping force, providing design principles for secure lifting, easy detachment, and safe handling of fragile objects.

Unconventional lattice geometries provide an effective platform for realizing symmetry-protected topological phonon states that can strongly influence lattice heat transport. In this work, we explore the relationship between topological phonon band features and thermal transport in square--octagonal (so) chalcogenide monolayers, namely MoS2 and SnS, by combining first-principles calculations with phonon Boltzmann transport theory. Symmetry analysis reveals the presence of nontrivial phonon band topology in the form of symmetry-protected nodal lines. Crossings between nodal lines carrying different symmetry eigenvalues produce fourfold Dirac points that enhance the phonon group velocity (vg), whereas nearly flat nodal lines lead to strong suppression of vg. The coexistence of these features, together with substantial phonon softening and enhanced anharmonic scattering around the topological band crossings, markedly suppresses the lattice thermal conductivity ($κ_l$). As a result, room-temperature $κ_l$ values of 4.0 W/mK for so-SnS and 18.7 W/mK for so-MoS2 are obtained, representing reductions by more than a factor of two and eight, respectively, relative to their hexagonal phases. Our results uncover a direct connection between phonon band topology and heat transport in two-dimensional materials, highlighting lattice symmetry and topological band engineering as promising routes for tailoring thermal properties. These findings further suggest opportunities for designing topological phononic and thermoelectric devices with controllable heat flow.

Van der Waals antiferromagnets provide a route to thickness-controlled magnetic order, but few combine high-temperature Ising order with conducting, correlated, and topological electronic structure. Here we show that UOTe realizes this combination. Magnetic susceptibility reveals a strongly anisotropic paramagnetic response, while neutron diffraction establishes c-axis antiferromagnetic order below $T_N \simeq 150$ K with an order-parameter exponent $β= 0.14$, close to the two-dimensional Ising value. Torque magnetometry further shows that the ordered state remains well described by a uniaxial antiferromagnet below the high-field transition. Pulsed-field magnetization up to 73 T shows that the ordered state survives to very large fields applied along the c axis before entering a broad metamagnetic regime that begins near 50 T, and remains unsaturated at the highest measured field. Angle-dependent proximity detector oscillator measurements show that the metamagnetic instability is set by the field component along the ordered moment direction, providing direct evidence for Ising-like field rigidity. UOTe therefore establishes a field-rigid Ising antiferromagnet with giant spin-flip fields in a compensated Van der Waals metal, where high-temperature c-axis order, quasi-two-dimensional magnetic criticality, Kondo-associated uranium 5f hybridization, metallic transport, and symmetry-enabled topology coexist in a single material.

We investigate the expansion of a homogeneous, strongly interacting Fermi gas released into vacuum in a ``shock tube'' geometry. At unitarity, where the gas is scale invariant and nearly inviscid, we find that the resulting rarefaction wave dynamics are self-similar and in excellent agreement with Riemann's solution of the Euler equation for all temperatures probed. Probing interactions away from unitarity within the BEC-BCS crossover, we observe increasing deviations from the Riemann solution as viscosity increases. However, even on the BCS side, where the sound diffusivity is increased twenty-fold, self-similarity is still approximately preserved. This may reflect how 1D Navier-Stokes rarefaction flows approach Euler self-similar solutions at long times. Our work demonstrates the utility of strongly interacting Fermi gases for the study of nonlinear hydrodynamics in a highly controllable setting.

A neutral degenerate plasma of equal numbers of electrons and positively charged fermions (holes) -- the electron-hole gas -- is studied using a simple, physically motivated two-parameter model (density r_s and mass ratio M/m). Two simplifying assumptions are made but not proven: the electron-hole correlation energy is approximately independent of density and does not affect the pressure or bulk modulus, and the electron-hole contribution to the local field factors is zero, allowing use of the known electron-gas local field factors. With these assumptions the phase diagram, instabilities, and effective interactions can be calculated for all mass ratios and densities using simple formulae, reproducible on a laptop. The key new physics is the additional screening provided by the mobile holes. A single function Delta appears in the denominator of all effective interactions and response functions. Near the zeros of Delta at q = 0 (compressibility instability) and at finite q, three phenomena are simultaneously enhanced: charge density waves (for M/m >= 4.97), a large T^2 electrical resistivity from electron-hole scattering, and an attractive electron-electron interaction that is the purely electronic analog of BCS electron-phonon coupling. Crudely estimated superconducting transition temperatures approach room temperature, reaching approximately 275 K at M/m = 9. No claim is made that this model applies to any specific material. The aim is to provoke scrutiny of the assumptions, calculation of the unknown local field factors, and investigation of whether this minimal two-carrier framework maps onto real systems.

Charge-carrier transport in soft-lattice materials, including metal-halide perovskites, is often perceived to be highly heterogeneous across different length scales, and influenced by both the intrinsic (dynamic) thermal electronic disorder and extrinsic (static) disorder due to crystal defects, impurities, grain boundaries, and surface states. As a consequence, the reported carrier mobilities obtained by different electrical and optical measurement techniques frequently disagree, raising a critical question: can a truly intrinsic charge transport regime (that is, a regime not dominated by static disorder) extend across macroscopic single crystals of these materials? Here, we demonstrate such a regime in an exemplary metal-halide perovskite system, epitaxial CsPbBr$_{3}$ single crystals, where the local mobility obtained via optical pump-terahertz probe (OPTP) spectroscopy quantitatively agrees with the macroscopic transport mobility across a broad range of experimental conditions. Using a dedicated device platform that enables concurrent Hall-effect and OPTP measurements on the same single-crystalline sample, we obtain consistent room-temperature mobilities of ~ 30 cm$^{2}$V$^{-1}$s$^{-1}$, among the highest reliably reported for CsPbBr$_{3}$. Both techniques reveal band-like temperature dependence of the hole mobility with similar power exponents, confirming that the same intrinsic transport mechanism governs the ultrafast/local and steady-state/macroscopic responses. These results show that defect-free charge transport is achievable in soft-lattice perovskites on millimetre length scales and establish a robust methodology for benchmarking intrinsic mobility in emerging semiconductors.

The coupling between electronic excitations and lattice degrees of freedom fundamentally dictates the optoelectronic functionality of hybrid perovskites. While the potential energy surfaces (PESs) of the electronic excited states are typically considered static, albeit modulated by thermal disorder, the exact nature of their structural evolution with temperature remains elusive. Here, we demonstrate that the excited-state structural reconfiguration in two-dimensional metal-halide perovskites is explicitly temperature-evolving, governed by lattice compliance. We select a chiral perovskite framework with an exceptionally large, temperature-dependent bond angle variance to maximize the structural compliance. Through phase-resolved resonant impulsive stimulated Raman scattering, we measure the coherent phonon dynamics and resolve the real-time structural pathways of exciton-lattice dressing. We observe a temperature-induced crossover from field-driven Impulsive Stimulated Raman Scattering (ISRS) to population-driven Displacive Excitation of Coherent Phonons (DECP). While momentum-driven ISRS pathways dominate at low temperatures, increasing thermal energy softens the lattice and enhances coordinate-driven displacive pathways, allowing excitons to sample steeper, highly anharmonic regions of the excited-state PES. Our results show that temperature can actively modulate the excited-state structural coordinates of flexible 2D frameworks, offering a practical strategy to tune exciton-lattice interactions in chiral optoelectronics.

Deconfined quantum critical points (DQCPs) describe continuous transitions between ordered phases beyond the Landau paradigm. A simple example is the Néel antiferromagnet (AFM) to valence bond solid (VBS) transition in a 1D antiferromagnetic $J_1-J_2$ model. In analogy to the spin-Peierls instability of critical spin chains, DQCPs are predicted to be unstable towards lattice distortions below a critical phonon frequency. In this work, we use tensor network simulations to investigate this instability in the antiferromagnetic $J_1-J_2$ model coupled to lattice vibrations. We confirm the stability of DQCP for large phonon frequencies and demonstrate that the transition turns strongly first-order below a critical frequency. The instability is caused by a reduction of the Luttinger parameter due to spin-phonon interactions and we identify the effective theory of the behavior as the double sine-Gordon model. The same effective theory is known to describe the classical Ashkin-Teller model, which enables us to show that the critical endpoint is in the four-state Potts universality class. Furthermore, we provide quantitative numerical scaling results for the phonon spectral function, offering an experimental signature to probe DQCP-phonon coupling in low-dimensional materials.

Bootstrap is a numerical many-body method that provides rigorous bounds on ground-state observables by imposing a set of necessary constraints on the expectation values of operators. The quality of the resulting bounds is sensitive to the choice of operators entering the constraints. In particular, bounds on ground-state correlations are often loose in spontaneous symmetry-breaking (SSB) phases, since local operator sets cannot exclude domain-wall excitations. In this work, we introduce non-local, string-like operators into the bootstrap and show that the program can be formulated directly in thermodynamic limit. We then apply our construction to several 1D spin models. First, we obtain a significant tightening of the bounds in the SSB phase of the 1D transverse-field Ising model. Using the 1D axial next-nearest-neighbor Ising model, we further show that this tightening allows for a quantitative estimate of the locations of phase boundaries. Finally, we generalize the string operators to the 1D $\mathbb{Z}_3$ chiral clock model and track the behavior of the bounds across the phase diagram. Our results broaden the class of constraints available to the bootstrap and open a route toward bootstrapping more general symmetry-broken and topological phases, where the relevant constraints may involve non-local or extended operators.