Rare-earth high-entropy oxides (RE-HEOs) represent a distinct class of entropy-stabilized ceramics in which multiple lanthanide cations occupy a common crystallographic sublattice, generating strong chemical disorder, lattice distortion, and complex defect landscapes. Unlike transition-metal-based high-entropy oxides, RE-HEOs are governed by localized 4f electronic states, weak crystal-field coupling, and variable redox chemistry, leading to emergent structural, electronic, magnetic, and optical phenomena that challenge conventional solid-state descriptions. This review provides a physics-oriented analysis of RE-HEOs, focusing on the thermodynamic foundations of configurational entropy stabilization, the interplay between enthalpy, entropy, and kinetic trapping, and the consequences of severe chemical disorder for crystal structure and phase stability. We review how lattice distortion, oxygen vacancy disorder, and cation randomness modify phonon spectra, ionic transport pathways, and electronic structures, with particular emphasis on the role of localized 4f states, defect-induced in-gap levels, and disorder-broadened excitation spectra. Spectroscopic manifestations of disorder including crystal-field relaxation, line broadening, lifetime modification, and energy transfer processes are discussed within a unified framework linking local symmetry breaking to macroscopic response. We further discuss the optoelectronic properties of RE-HEOs, including photoluminescence from intra-4f transitions, upconversion mechanisms, and disorder-induced modifications of radiative lifetimes and quantum efficiency. The application landscape spans both energy conversion (electrocatalysis, solid oxide fuel cells, thermal barrier coatings) and optoelectronic technologies (phosphors, scintillators, optical thermometry, and anti-counterfeiting). Likewise, we assess theoretical and computational approaches, including density functional theory with strong correlation corrections, statistical thermodynamics, and emerging machine-learning models, highlighting their ability and current limitations in capturing disorder-driven physics in multi-component oxides. Finally, we identify open questions central to condensed-matter physics, including the nature of entropy-stabilized metastability, the limits of band theoretical descriptions in highly disordered 4f systems, and the role of configurational entropy in tuning electron-phonon and defect interactions. By consolidating experimental and theoretical insights, this review establishes RE-HEOs as a platform for exploring disorder-dominated solid-state physics beyond conventional crystalline oxides.
ZrTe5, a topological material with tunable quantum phenomena, faces conflicting experimental results largely due to sample quality variations. Despite intense interest in stabilizing its quantum states, a clear strategy for controlling intrinsic defects has remained elusive. Through first-principles investigations of intrinsic point defects, we identify a practical route to achieving stable and ideal topological characteristics in ZrTe5. Our study reveals that donor-like Zr interstitials and acceptor-like Te vacancies compete to govern the Fermi level, with defect density determining topological phases. We theoretically propose increasing the Te/Zr ratio during growth to suppress intrinsic defects, stabilizing ZrTe5 in a nearly ideal weak topological insulator state. These predictions are supported by experimental measures, exhibiting a reduction in bulk conduction with increasing Te/Zr ratio. These findings offer clear guidance for defect control and sample optimization, enabling the robust and reproducible realization of topological quantum states in ZrTe5 for future quantum applications.
Quantum sensing with individual spin defects has emerged as a versatile platform to probe microscopic properties of condensed matter systems. Here we demonstrate that quantum relaxometry with nitrogen-vacancy (NV) centers in diamond can reveal the anisotropic spin dynamics of altermagnetic insulators together with their characteristic spin polarised bands. We show that the distance and orientation dependent relaxation rate of a nearby quantum impurity encodes signatures of momentum space anisotropy in the spin diffusion response, a hallmark of altermagnetic order. This directional sensitivity is unprecedented in the landscape of quantum materials sensing, and it enables the distinction of altermagnets from conventional antiferromagnets via local, noninvasive measurements. Our results could spark new NV-sensing experiments on spin transport and symmetry breaking in altermagnets, and highlight the role of NV orientation to probe anisotropic phenomena in condensed matter systems.
The physics in flat bands has emerged as an essential field in condensed matter physics where a plethora of phenomena can be unveiled, such as anomalous transport properties, superconductivity dominated by quantum geometry or exotic topological phases. Our goal here is to show that even in magnetic systems, the presence of flat bands can give rise to unexpected features. More precisely, we address the impact of an Aharonov-Bohm (AB) flux on the exchange couplings in magnetic diamond chains. The most remarkable result is the significant amplification of magnetic couplings at short distances induced by the AB flux, leading to a considerable increase in the thermal conductivity of the magnons. We have also shown that the flux-dependent decaying length of the couplings is connected to the quantum metric of the flat bands. Our results could be of interest for the control of magnetic properties in spintronic devices and relevant for the heat transport by magnons at the nanoscale in quantum technologies.
Detection of the Higgs mode in superconductors using nonlinear terahertz spectroscopy is a key area of interest in condensed matter physics. We investigate the influence of disorder on the nonlinear terahertz response and the Higgs mode in NbN thin films with varying Ioffe-Regel parameters (k_{F}l). In strongly disordered films near the superconductor-insulator transition, we observe an anomalous third-harmonic generation (THG) signal above T_{c}, which is absent in both cleaner superconducting and nonsuperconducting counterparts. The persistence of this normal-state THG signal in a high magnetic field excludes superconducting fluctuations as its origin. Below T_{c}, the THG intensity increases sharply, indicating a dominant contribution from the driven Higgs mode. The THG spectrum of the strongly disordered sample exhibits a broadened, multipeak structure, which we attribute to quantum path interference between distinct channels involving unpaired electrons and Cooper pairs within emergent superconducting islands. Our findings not only demonstrate how disorder tunes the nonlinear terahertz response, but also uncover a strong coupling between electrons responsible for normal-state THG and the superconducting Higgs mode below T_{c} in strongly disordered samples.
Photon condensation in semiconductor microcavities is a transformative technique for engineering quantum states of light at room temperature by tailoring strong but incoherent light-matter inter- actions. While continuous-wave and electrical pumping offer exceptional prospects for miniaturized quantum photonic technologies,harnessing these requires conceptual advances in understanding non- equilibrium light-matter dynamics in semiconductors. We resolve this challenge through an ab initio quantum kinetic theory capturing how Coulomb interactions of optically excited carriers and phonon scattering mediate photon thermalization and condensation in semiconductors. Our microscopic model shows that at high carrier densities, thermalization is dominated by carrier-carrier Coulomb scattering, in clear contrast to the rovibrational relaxation that governs dye-based photon conden- sates. The theory predicts a rich nonequilibrium phase diagram with thermal, Bose-condensed, multimode, and lasing phases, quantitatively in agreement with recent experiments. Crucially, we identify how cavity detuning controls transitions between equilibrium and gain-dominated regimes, enabling tailored design of coherent light sources. This work thus provides the foundation for semiconductor-based quantum photonic devices operating beyond conventional laser paradigms.
The problem of a single Hermitian impurity has long served as a cornerstone in condensed matter physics, offering fundamental insights into the mechanisms of Anderson localization. Yet, despite the increased interest in the spectral and localization properties of non-Hermitian lattices with defects, the non-Hermitian extension of the single impurity problem remains largely unexplored. In this work, we investigate the role of a single complex impurity in one-, two-, and three-dimensional infinite tight-binding lattices. Our study reveals a series of counterintuitive phenomena, including regions where localization vanishes and re-emerges as the impurity strength varies. Next, we study the corresponding finite-sized lattices, which are highly relevant to experimental realizations in readily accessible photonic platforms, revealing a variety of exotic features, such as scale-free localized states and peculiar cross-shaped localized eigenstates, whose profiles deviate from the conventional exponential localization. This work paves the way for future studies on transport phenomena in non-Hermitian disordered lattices.
Quantum transport remains a central yet experimentally challenging problem in condensed matter and quantum physics. Here we report the first complete experimental characterization of the full spectrum of quantum transport behaviors in a one-dimensional Fibonacci chain-the paradigmatic quasicrystalline model-spanning localization, subdiffusion, normal and superdiffusion, and ballistic transport. Using a tunable photonic quantum-walk platform, these regimes are unambiguously resolved through their distinct power-law scalings of the mean square displacement and smooth autocorrelation function, together with pronounced oscillatory dynamical structures. These signatures arise from the intrinsic multifractal spectra and hyperuniform order of the Fibonacci quasicrystal, long predicted but never before experimentally resolved. Beyond mapping a comprehensive transport regime diagram, our highly controllable platform provides a powerful and versatile framework for exploring quasiperiodicity, multifractal criticality, and emergent quantum transport phenomena.
Anomalous Hall effect (AHE), occurring in materials with broken time-reversal symmetry, epitomizes the interplay between magnetic order and electron orbital motions1-4. In two-dimensional (2D) systems, AHE is coupled with out-of-plane orbital magnetization associated with in-plane chiral orbital motions. In three-dimensional (3D) systems, in which sample thickness far exceeds a vertical coherence-transport length lz, the AHE is effectively a thickness-averaged 2D counterpart4-still governed by out-of-plane orbital magnetization arising from in-plane orbital motions. Here we report the experimental observation of a fundamentally new type of AHE that couples both in-plane and out-of-plane orbital magnetizations in multilayer rhombohedral graphene, shown by pronounced Hall resistance hysteresis under both in-plane and out-of-plane magnetic fields. This state emerges from a peculiar metallic phase that spontaneously breaks time-reversal, mirror and rotational symmetries driven by electron-electron interactions. By measuring multiple devices spanning 3-15 layers, we find that this phenomenon emerges only within an intermediate thickness of 2-5 nm. Theoretical calculations show that carriers within this window can sustain coherent orbital motions both within and across the 2D plane. Together, these identify an uncharted 'transdimensional' regime between 2D and 3D, in which the sample thickness is much larger than atomic spacing yet remains comparable to lz, for the emergence of this new state of matter-transdimensional AHE. Our findings point to a distinct class of AHE, opening an unexplored model for correlated and topological physics in transdimensional landscapes.
The kinetic theory of soliton gases (SG) is used to develop a solvable model for wave-mean field interaction in integrable turbulence. The waves are stochastic soliton ensembles that scatter off a critically dense SG or soliton condensate-the mean field. The derived two-fluid kinetic-hydrodynamic equations admit exact solutions predicting an induced mean field and SG filtering. The obtained SG statistical moments agree with ensemble averages of numerical simulations. The developed theory readily generalizes, with applications in fluids, nonlinear optics, and condensed matter.
Spatial confinement strongly affects matter by altering structural stability, relaxation times, and equilibrium properties. Interest in hydrogen storage within carbon nanotube bundles has grown because it addresses practical energy needs while revealing rich confined-fluid physics. Understanding how geometry and defects influence hydrogen structure and dynamics is essential to the development of effective storage materials. Here, we investigate how confinement in single-walled carbon nanotube (SWCNT) bundles with vacancies alters the spatial distribution and phase behavior of physisorbed hydrogen. At low temperature, hydrogen forms solid-like, cylindrical layered structures both inside and outside the tubes. Raising the temperature broadens these layers and produces a liquid-like arrangement within the confined regions. This confined solid-to-liquid crossover controls storage capacity and release behavior and can be tuned by temperature, confinement dimensions, and vacancy defects.
Predicting the rate of crystal nucleation is among the most substantial long-standing challenges in condensed matter. In the system most studied (hard-sphere colloids), the discrepancy between experiments and computer simulations is more than 10 orders of magnitude. The situation with other materials (such as water) is no better. Here, we address this challenge with two developments. First, our work is a marked improvement in the precision of mapping the state point of experiments to simulation. For this, we used a combination of novel machine-learning methods for particle tracking and higher-order correlation functions. Second, we consider the free energy of precritical nuclei using confocal microscopy. These are in agreement with computer simulation. This is the first time that such free energies have been successfully compared between experiment and simulation in any material as far as we are aware.
Ionic conductivity in solids is a topic of great interest in the fields of physics, materials science, and energy applications. Previous studies have primarily focused on the activation energy of ion transport based on classical transition state theory, lacking considerations from the perspective of nuclear quantum effects. Herein, by considering the effects of zero-point energy and quantum tunneling, we examine the quantum behaviors of hydrogen migration in lanthanum trihydrides (LaH3), through the two dominant pathways-concerted migration and single-ion migration. Our first-principles calculations based on instanton rate theory indicate that the quantum rate constants diverge significantly from their classical counterparts at low temperatures. We predict that quantum tunneling becomes dominant over thermal diffusion for concerted hydrogen migration at liquid nitrogen temperature, and emerges even at room temperature when concerted transport is suppressed. We also demonstrate the tuning of migration rates by strain, and the sensitivity of the quantum tunneling rate to the energy barrier geometry. Our findings depict a complete quantum picture of hydrogen transport in lanthanide hydrides and provide a new perspective on ionic conductivity of solid materials.
We investigated the interaction between the monocationic aromatic drug propranolol (PPL) and double-stranded DNA (dsDNA) to elucidate how small molecules can drive higher-order DNA frameworks and nanoparticles (NPs) formation. Single-molecule force spectroscopy with optical tweezers revealed that, at concentrations below 4 mM, PPL interacts with dsDNA through an intercalation-like mode, altering contour length, persistence length, and stretch modulus. At higher concentrations, PPL induced dsDNA compaction, corroborated by atomic force microscopy imaging of condensed structures. Multimolecular assays supported these findings: electrophoretic mobility shift assays revealed progressive mobility loss with increasing PPL concentrations, consistent with aggregate formation, while UV-vis spectroscopy confirmed intercalation-like behavior and strong binding affinity (Kb=1.67 × 10⁶ M⁻¹). At millimolar PPL/DNA ratios (10-14), NPs formulations were obtained with hydrodynamic diameters of 120-244 nm, low polydispersity (0.19-0.30), negative zeta potential (-25 to -35 mV), and particle concentrations up to 5.26 × 10¹¹ NPs/mL. These NPs exhibited very high drug loading (59-72%) and stability under both biological and storage conditions. Collectively, our results demonstrate that PPL engages dsDNA through intercalation-like behavior, compaction, aggregation, and stabilization processes, uncovering a previously unreported mechanism for a monocationic aromatic drug and allowing the efficient formation of NPs. This work expands the current understanding of small molecule-DNA interactions and may be extended to other hydrophilic aromatic drugs, positioning DNA as a versatile building block and ultimately for the development of nucleic acid-based nanomedicines.
Biological systems, including proteins, employ water-mediated supramolecular interactions to adopt specific conformations to support their functions. Here, we present dynamic porous crystals of aliphatic dipeptides with sequence-isomers of variable conformational entropy (leucine (L) and isoleucine (I)) exhibiting shallow-energy landscapes, with various reconfigurable topologies and consequent mechanics accessible through changes in relative humidity and temperature. Specifically, for LI crystals, changes in water chemical potential cause the solid-state porous architecture to reorganize and reversibly transition between perpendicular and parallel honeycomb structures, as well as layered van der Waals structures, leading to significant and distinct variations in macroscopic morphologies, mechanical properties, and photophysical properties. These dynamic crystals are achieved by leveraging non-directional side-chain interactions with confined water, which drive the phase transition while stabilizing the structures. Our findings highlight the potential of minimalistic peptide designs, inspired by protein architecture, to create dynamic solid-state materials that adjust their properties in response to environmental stimuli.
Excitons play a crucial role in optical properties of two-dimensional materials. While significant progress has been made in understanding exciton dynamics on femtosecond timescales, the microscopic details of the earliest stages of exciton formation and evolution remain elusive. Here we explore the ultrafast processes of exciton formation, evolution and dissociation in monolayer hexagonal boron nitride using state-of-the-art time-dependent density functional theory simulations incorporating long-ranged interactions. We find that the exciton forms within ~2.5 fs through a three-step process: free carriers are first generated by photoexcitation; electrons and holes subsequently bind to form a metastable "exciton core"; and finally, the exciton core evolves into a fully-formed exciton. The subsequent dynamics are dominated by exciton-exciton interference, which gives rise to oscillatory electron-occupation signals. These signals serve as a predicted phase-sensitive signature, providing a theoretical basis for experimentally probing the exciton envelope phase. This interference can be further modulated and an anisotropic Mott transition is induced upon increasing laser intensity into the strong field regime.
The dynamics of disordered nuclear spin ensembles are the subject of nuclear magnetic resonance studies. Because of the through-space long-range dipolar interaction, generically, many spins are involved in the time evolution, so that exact brute force calculations are impossible. The recently established spin dynamic mean-field theory (spinDMFT) represents an efficient and unbiased alternative to overcome this challenge. The approach only requires the dipolar couplings as input, and the only prerequisite for its applicability is that each spin interacts with a large number of other spins. Here, we show that spinDMFT can be used to describe spectral spin diffusion in static samples and to simulate zero-quantum line shapes which eluded an efficient quantitative simulation so far to the best of our knowledge. We perform benchmarks for two test substances that establish an excellent match with published experimental data. As spinDMFT combines low computational effort with high accuracy, we suggest to use it for large-scale simulations of spin diffusion, which are important in various areas of magnetic resonance.
Self-assembly at the air/water interface provides a versatile platform for organizing organic ligand-functionalized inorganic nanoparticles (NPs) into two-dimensional monolayers. However, how ligand behavior under interfacial confinement governs collective structural organization of NP assemblies remains poorly understood. Here, we demonstrate that ligand redistribution on Au NPs induces emergent NP shape anisotropy, which in turn drives directional reorganization of interfacial monolayers. A monolayer of Au NPs dual-functionalized with a liquid-crystalline dendron and dodecanethiol reorganizes from island-like arrays to network-like structures upon heating. X-ray reflectometry and grazing-incidence small-angle X-ray scattering further reveal correlated variations in out-of-plane ligand-shell thickness and in-plane lattice constants. Integrating these X-ray results with local structural insights from electron microscopy clarifies that adaptive redistribution of the two coexisting ligands on the NP surface was the key factor that changes the NP shape anisotropy. This ligand-driven anisotropy directly induced directional anisotropy of the macroscopic monolayer structure. Such dynamic ligand redistribution is enabled by a precisely engineered NP surface, dual-functionalized with liquid-crystalline dendrons and simple alkanethiols. Altogether, this work establishes a strategy for designing thermoresponsive NP monolayers with tunable topology at liquid interfaces and highlights how interfacial confinement fundamentally alters ligand-mediated assembly behavior.
Azobenzene derivatives, especially seven-membered cyclic compounds such as dibenzo[b,f][1,4,5]thiadiazepine (DBTD), are considered promising candidates for molecular solar thermal (MOST) energy storage systems due to their significant energy storage capabilities. In contrast, its structural analogue, dibenzo[b,f][1,4,5]oxadiazepine (DBOD), fails to exhibit substantial Z → E photoisomerization, despite possessing a higher isomerization energy. In this study, we investigated the underlying mechanistic causes of this paradox by comparing the photoisomerization dynamics of DBTD and DBOD through electronic structure calculations and nonadiabatic molecular dynamics (NAMD) simulations. Our results revealed that, while photoexcitation leads to the formation of the E-isomer in DBOD, its metastable E-configuration rapidly relaxes back to the Z-form within 400 fs at room temperature. This rapid back-conversion arises from three synergistic factors: (i) a lower thermal isomerization barrier, (ii) substantial kinetic energy retained upon de-excitation, and (iii) preferential allocation of kinetic energy into azo-group torsional modes, which together accelerate the reverse reaction on the ground state. To mitigate this issue, we proposed a synergistic strategy combining fluorine substitution with low-temperature regulation. Fluorination yields perfluorodibenzo[b,f][1,4,5]oxadiazepine (PDOD), which increases the thermal E → Z isomerization barrier while preserving a high isomerization energy of 164.3 kJ/mol. NAMD simulations at 100 K show that the E-isomer of PDOD remained stable for over 400 fs, with a Z → E quantum yield of 26%, significantly higher than the 19% quantum yield of DBOD at 300 K. This study provides mechanistic insights into the "high isomerization energy yet poor stability" paradox observed in DBOD and establishes a practical strategy for developing high-performance MOST photoswitches.
Fe2P compounds have recently attracted significant attention due to their large anisotropy and magnetization, making them promising candidates as hard magnetic materials. However, their relatively low Curie temperature limits practical applications. Previous studies have shown that substituting Si for P or Co for Fe increases the Curie temperature; however, Si substitution induces a hexagonal to orthorhombic structural transformation, while Co substitution reduces saturation magnetization. This work examines the evolution of the crystal structure and magnetic properties upon B substitutions in Fe1.95P0.8-xSi0.2Bx compounds close to the hexagonal/orthorhombic transformation. We show that B can increase the Curie temperature up to 675 K and the saturation magnetization to 139 A·m2·kg-1, while preserving the hexagonal structure beyond the limit allowed by Si substitutions only. X-ray diffraction of magnetically aligned powders confirms a uniaxial easy axis along the c axis and significant room-temperature magnetocrystalline anisotropy. The optimization of the intrinsic magnetic properties based on only metalloid substitutions paves the way for further development of this material family as rare-earth-free permanent magnets.