Condensed Matter Phenomena Research Articles

Interfacial Charge Transfer in One-Dimensional AgBr Encapsulated inside Single-Walled Carbon Nanotube Heterostructures.

The advent of one-dimensional van der Waals heterostructure (1D vdWH) nanomaterials has provided valuable opportunities for the advancement of electronic or optical devices, as well as for exploring various condensed matter phenomena. Electron transfer is a fundamental process in host-guest interactions, significantly influencing nanoscale physicochemical processes. Elucidating the mechanism by which the host influences the electronic structure of the guest is essential for elucidating these interactions. This study reports the successful synthesis of a material system consisting of precisely resolved AgBr nanowires encapsulated within single-walled carbon nanotubes (SWCNTs) that has been successfully synthesized and utilized to investigate the intrinsic electron transfer across 1D vdWHs. Cyclic voltammetry (CV) was employed to investigate the 1D vdWH interaction between AgBr and SWCNTs, which provided a more intuitive and accurate characterization of the charge transfer from SWCNTs to AgBr. Furthermore, Kelvin probe force microscopy showed a 149 mV reduction in the average surface potential of carbon nanotubes after AgBr filling, supporting the efficacy of CV in probing electron dynamics in 1D vdWHs. Finally, theoretical calculations indicated a charge transfer of 0.11 e- per simulation cell, reinforcing the effectiveness of CV in assessing the interactions within 1D vdWHs.

Advances and Applications of Oxidized van der Waals Transition Metal Dichalcogenides

AbstractThe surface oxidation of 2D transition metal dichalcogenides (TMDs) has recently gained tremendous technological and fundamental interest owing to the multi‐functional properties that the surface oxidized layer opens up. In particular, when integrated into other 2D materials in the form of van der Waals heterostructures, oxidized TMDs enable designer properties, including novel electronic states, engineered light‐matter interactions, and exceptional‐point singularities, among many others. Here, the evolving landscapes of the state‐of‐the‐art surface engineering technologies that enable controlled oxidation of TMDs down to the monolayer‐by‐monolayer limit are reviewed. Next, the use of oxidized TMDs in van der Waals heterostructures for different electronic and photonic device platforms, materials growth processes, engineering concepts, and synthesizing new condensed matter phenomena is discussed. Finally, challenges and outlook for future impact of oxidized TMDs in driving rapid advancements across various application fronts is discussed.

A rotational/roto-translational constraint method for condensed matter.

Molecular rotations influence numerous condensed matter phenomena but are often difficult to isolate in molecular dynamics (MD) simulations. This work presents a rotational/roto-translational constraint algorithm designed for condensed matter simulations. The method is based on the velocity Verlet scheme, ensuring a direct constraint on velocity and simplifying implementation within material simulation software packages. We implemented the algorithm in a customized version of a CP2K package and validated its effectiveness through MD simulations of molecule and crystal. The results demonstrate successful selective constraint of rotational and roto-translational motions, enabling stable long-term simulations. This capability opens avenues for studying rotation-related phenomena (e.g., paddle-wheel mechanism in solid-state electrolytes) and constrained sampling.

Probing Site-Resolved Current in Strongly Interacting Superconducting Circuit Lattices.

Transport measurements are fundamental for understanding condensed matter phenomena, from superconductivity to the fractional quantum Hall effect. Analogously, they can be powerful tools for probing synthetic quantum matter in quantum simulators. Here we demonstrate the measurement of insitu particle current in a superconducting circuit lattice and apply it to study transport in both coherent and bath-coupled lattices. Our method utilizes controlled tunneling in a double-well potential to map current to on-site density, revealing site-resolved current and current statistics. We prepare a strongly interacting Bose-Hubbard lattice at different lattice fillings, and observe the change in current statistics as the many-body states transition from superfluid to Mott insulator. Furthermore, we explore nonequilibrium current dynamics by coupling the lattice to engineered driven-dissipative baths that serve as tunable particle source and drain. We observe steady-state current in discrete conduction channels and interaction-assisted transport. These results establish a versatile platform to investigate microscopic quantum transport in superconducting circuits.

Machine Learning Classification of Local Environments in Molecular Crystals.

Identifying local structural motifs and packing patterns of molecular solids is a challenging task for both simulation and experiment. We demonstrate two novel approaches to characterize local environments in different polymorphs of molecular crystals using learning models that employ either flexibly learned or handcrafted molecular representations. In the first case, we follow our earlier work on graph learning in molecular crystals, deploying an atomistic graph convolutional network combined with molecule-wise aggregation to enable per-molecule environmental classification. For the second model, we develop a new set of descriptors based on symmetry functions combined with a point-vector representation of the molecules, encoding information about the positions and relative orientations of the molecule. We demonstrate very high classification accuracy for both approaches on urea and nicotinamide crystal polymorphs and practical applications to the analysis of dynamical trajectory data for nanocrystals and solid-solid interfaces. Both architectures are applicable to a wide range of molecules and diverse topologies, providing an essential step in the exploration of complex condensed matter phenomena.

Free-energy calculations in condensed matter: from early challenges to the advent of umbrella sampling

The investigation of condensed matter transformations hinges on the precision of free-energy calculations. This article charts the evolution of molecular simulations, tracing their development from the techniques of the early 1960s, through the emergence of free-energy calculations toward the end of the decade, and leading to the advent of umbrella sampling in 1977. The discussion explores the inherent challenges and limitations of early simulational endeavors, such as the struggle with accurate phase-space sampling and the need for innovative solutions like importance sampling and multistage sampling methods. Taken together, the initial hurdles and subsequent adoption of advanced techniques exemplify the leap from analytical methods to effective computational strategies that enabled more reliable simulations. Further analysis of this narrative reveals the methodological breakthroughs as well as the setbacks that transformed the theoretical and practical understanding of condensed matter phenomena. A follow-up study will examine the shifts in free-energy calculations from the late 1970s into the 1980s.

Ferroelectric polymorphic phenomena in the layered antiferromagnet Cu(OH)2

Ferroic orders and their associated structural phase transitions are paramount in the understanding of a multitude of unconventional condensed matter phenomena. On this note, our investigation focuses on the polymorphic ferroelectric (FE) phase transitions of Copper(II) hydroxide, Cu(OH)2, considering an antiferromagnetic ground state. By employing the first-principles studies and group theory analysis, we have provided a systematic theoretical investigation of vibrational properties in the hypothetical Cmcm high-symmetry phase to unveil the symmetry-allowed ferroic phases. We identified a non-polar to polar ( Cmc21 ) phase transition, in which the displacive transformation is primarily responsible for the phase change induced by two B1u ( i.e. Γ2− ) phonon modes within the centrosymmetric phase. We also observed the existence of two polar structures with the same space group and different degrees of polarization ( i.e. Ps = 3.06 µC·cm−2 and Ps = 42.41 µC·cm−2), emerging from the high symmetry non-polar structure. According to the structural analysis the FE order, of a geometric nature, is driven by the Γ2− mode in which the O- and H-sites displacements lead the polar distortion with a minor contribution from the Cu-sites. Interestingly, the 3d 9:Cu2+ Jahn–Teller distortion coupled with the orientational shifts of O–H atoms enhances the polarization.

Polariton creation in coupled cavity arrays with spectrally disordered emitters

Integrated photonics has been a promising platform for analog quantum simulation of condensed matter phenomena in strongly correlated systems. To that end, we explore the implementation of all-photonic quantum simulators in coupled cavity arrays with integrated ensembles of spectrally disordered emitters. Our model is reflective of color center ensembles integrated into photonic crystal cavity arrays. Using the Quantum Master equation and the Effective Hamiltonian approaches, we study energy band formation and wavefunction properties in the open quantum Tavis–Cummings–Hubbard framework. We find conditions for polariton creation and (de)localization under experimentally relevant values of disorder in emitter frequencies, cavity resonance frequencies, and emitter-cavity coupling rates. To quantify these properties, we introduce two metrics, the polaritonic and nodal participation ratios, that characterize the light-matter hybridization and the node delocalization of the wavefunction, respectively. These new metrics combined with the Effective Hamiltonian approach prove to be a powerful toolbox for cavity quantum electrodynamical engineering of solid-state systems.

Phase behaviour of coarse-grained fluids.

Soft condensed matter structures often challenge us with complex many-body phenomena governed by collective modes spanning wide spatial and temporal domains. In order to successfully tackle such problems, mesoscopic coarse-grained (CG) statistical models are being developed, providing a dramatic reduction in computational complexity. CG models provide an intermediate step in the complex statistical framework of linking the thermodynamics of condensed phases with the properties of their constituent atoms and molecules. These allow us to offload part of the problem to the CG model itself and reformulate the remainder in terms of reduced CG phase space. However, such exchange of pawns to chess pieces, or 'Hamiltonian renormalization', is a radical step and the thermodynamics of the primary atomic and CG models could be quite distinct. Here, we present a comprehensive study of the phase diagram including binodal and interfacial properties of a dissipative particle dynamics (DPD) model, extended to include finite-range attraction to support the liquid-gas equilibrium. Despite the similarities with the atomic model potentials, its phase envelope is markedly different featuring several anomalies such as an unusually broad liquid range, change in concavity of the liquid coexistence branch with variation of the model parameters, volume contraction on fusion, temperature of maximum density in the liquid phase and negative thermal expansion in the solid phase. These results provide new insight into the connection between simple potential models and complex emergent condensed matter phenomena.

Coherent electron Compton scattering and the non-diagonal electron momentum density of solids

Experimental techniques that probe the electronic structure of crystalline solids are vital for exploring novel condensed matter phenomena. In coherent Compton scattering the Compton signal due to interference of an incident and Bragg diffracted beam is measured. This gives the projected, non-diagonal electron momentum density of the solid, a quantity that is sensitive to both the amplitude and phase of the electron wavefunction. Here coherent electron Compton scattering is demonstrated using electron energy loss spectroscopy in the transmission electron microscope. The technique has several advantages over coherent X-ray Compton scattering, such as a superior spatial resolution and the use of smaller specimens to generate Bragg beams of sufficient intensity. The conditions for a directly interpretable coherent electron Compton signal are established. Results are presented for the projected, non-diagonal electron momentum density for silicon under 004 and 2¯20 Bragg beam set ups.

Designing light-element materials with large effective spin-orbit coupling

Spin-orbit coupling (SOC), which is the core of many condensed-matter phenomena such as nontrivial band gap and magnetocrystalline anisotropy, is generally considered appreciable only in heavy elements. This is detrimental to the synthesis and application of functional materials. Therefore, amplifying the SOC effect in light elements is crucial. Herein, focusing on 3d and 4d systems, we demonstrate that the interplay between crystal symmetry and electron correlation can significantly enhance the SOC effect in certain partially occupied orbital multiplets through the self-consistently reinforced orbital polarization as a pivot. Thereafter, we provide design principles and comprehensive databases, where we list all the Wyckoff positions and site symmetries in all two-dimensional (2D) and three-dimensional crystals that could have enhanced SOC effect. Additionally, we predict nine material candidates from our selected 2D material pool as high-temperature quantum anomalous Hall insulators with large nontrivial band gaps of hundreds of meV. Our study provides an efficient and straightforward way for predicting promising SOC-active materials, relieving the use of heavy elements for next-generation spin-orbitronic materials and devices.

Inseparable Time-Crystal Geometries on the Möbius Strip.

Description of periodically and resonantly driven quantum systems can lead to solid state models where condensed matter phenomena can be investigated in time lattices formed by periodically evolving Wannier-like states. Here, we show that inseparable two-dimensional time lattices with the Möbius strip geometry can be realized for ultracold atoms bouncing between two periodically oscillating mirrors. Effective interactions between atoms loaded to a lattice can be long-ranged and can be controlled experimentally. As a specific example, we show how to realize a Lieb lattice model with a flat band and how to control long-range hopping of pairs of atoms in the model.

Quantum repetition codes as building blocks of large-period discrete time crystals

Discrete time crystals (DTCs) are nonequilibrium phases of matter with exotic observable dynamics. Among their remarkable features is their response to a periodic drive at a fraction of its frequency. Current successful experiments are however only limited to realizing DTCs with period-doubling and period-tripling observable dynamics, forming only a very small subset of DTC phases. Creating larger periodic DTCs in the lab remains a longstanding challenge, yet it is necessary for developing the technological applications of DTCs, e.g., as a quantum memory for highly-entangled qubits, or exploring interesting features beyond subharmonic dynamics, e.g., condensed matter phenomena in the time domain. By highlighting the connection between DTCs and quantum error correction, we devise a general and realistic scheme for building DTCs exhibiting any large period observable dynamics, which is observable even at sufficiently small system sizes. Our proposal uses an array of spin-1/2 chains to simulate a repetition code at the hardware level, which has essential properties to realize robust observable dynamics. It is readily implemented with existing superconducting or trapped-ion quantum processors, making new families of DTCs experimentally accessible in the immediate future.

Nanoscale magnetic field imaging for 2D materials

Nanometer-scale imaging of magnetization and current density is the key to deciphering the mechanisms behind a variety of new and poorly understood condensed matter phenomena. The recently discovered correlated states hosted in atomically layered materials such as twisted bilayer graphene or van der Waals heterostructures are noteworthy examples. Manifestations of these states range from superconductivity, to highly insulating states, to magnetism. Their fragility and susceptibility to spatial inhomogeneities limits their macroscopic manifestation and complicates conventional transport or magnetization measurements, which integrate over an entire sample. In contrast, techniques for imaging weak magnetic field patterns with high spatial resolution overcome inhomogeneity by measuring the local fields produced by magnetization and current density. Already, such imaging techniques have shown the vulnerability of correlated states in twisted bilayer graphene to twist-angle disorder and revealed the complex current flows in quantum Hall edge states. Here, we review the state-of-the-art techniques most amenable to the investigation of such systems, because they combine the highest magnetic field sensitivity with the highest spatial resolution and are minimally invasive: magnetic force microscopy, scanning superconducting quantum interference device microscopy, and scanning nitrogen-vacancy center microscopy. We compare the capabilities of these techniques, their required operating conditions, and assess their suitability to different types of source contrast, in particular magnetization and current density. Finally, we focus on the prospects for improving each technique and speculate on its potential impact, especially in the rapidly growing field of two-dimensional (2D) materials.

General-relativistic spin system

The models of spin systems defined on Euclidean space provide powerful machinery for studying a broad range of condensed matter phenomena. While the non-relativistic effective description is sufficient for most of the applications, it is interesting to consider special and general relativistic extensions of such models. Here, we introduce a framework that allows us to construct theories of continuous spin variables on a curved spacetime. Our approach takes advantage of the results of the non-linear field space theory, which shows how to construct compact phase space models, in particular for the spherical phase space of spin. Following the methodology corresponding to a bosonization of spin systems into the spin wave representations, we postulate a representation having the form of the Klein-Gordon field. This representation is equivalent to the semi-classical version of the well-known Holstein-Primakoff transformation. The general-relativistic extension of the spin wave representation is then performed, leading to the general-relativistically motivated modifications of the Ising model coupled to a transversal magnetic field. The advantage of our approach is its off-shell construction, while the popular methods of coupling fermions to general relativity usually depend on the form of Einstein field equations with matter. Furthermore, we show equivalence between the considered spin system and the Dirac-Born-Infeld type scalar field theory with a specific potential, which is also an example of k-essence theory. Based on this, the cosmological consequences of the introduced spin field matter content are preliminarily investigated.

Creation of one dimensional array of magnetic field by tightly focused phase modulated azimuthal and radial variant vector beam

A new approach for generating sub wavelength scale one dimensional chain of magnetic spot, hole, flattop and bubble profiled segments using tightly focused phase modulated azimuthal and radial variant vector (ARVV) beam is proposed and investigated numerically using vector diffraction theory. Numerical result shows that by using a well optimized single Complex Phase Filter (CPF), one can generated and tune the geometry of the 1D chain of magnetic field distribution from sub wavelength scale hole to spot and then to a chain of flattop profiled and bubble structure segments by properly tuning the radial index of the incident azimuthal- and radial-variant vector beam. Such an approach is simple and usable for simulate condensed matter phenomena.

Nano-second exciton-polariton lasing in organic microcavities

Organic semiconductors are a promising platform for ambient polaritonics. Several applications, such as polariton routers, and many-body condensed matter phenomena are currently hindered due to the ultra-short polariton lifetimes in organics. Here, we employ a single-shot dispersion imaging technique, using 4 ns long non-resonant excitation pulses, to study polariton lasing in a λ/2 planar organic microcavity filled with BODIPY-Br dye molecules. At a power threshold density of 1.5 MW/cm2, we observe the transition to a quasi-steady state, 1.2 ns long-lived, single-mode polariton lasing and the concomitant superlinear increase in photoluminescence, spectral line-narrowing, and energy blueshift.

Creating big time crystals with ultracold atoms

We investigate the size of discrete time crystals s (ratio of response period to driving period) that can be created for a Bose–Einstein condensate (BEC) bouncing resonantly on an oscillating mirror. We find that time crystals can be created with sizes in the range s ≈ 20–100 and that such big time crystals are easier to realize experimentally than a period-doubling (s=2) time crystal because they require either a larger drop height or a smaller number of bounces on the mirror. We also investigate the effects of having a realistic soft Gaussian potential mirror for the bouncing BEC, such as that produced by a repulsive light-sheet, which is found to make the experiment easier to implement than a hard-wall potential mirror. Finally, we discuss the choice of atomic system for creating time crystals based on a bouncing BEC and present an experimental protocol for realizing big time crystals. Such big time crystals provide a flexible platform for investigating a broad range of non-trivial condensed matter phenomena in the time domain.

Control of electron-electron interaction in graphene by proximity screening

Electron-electron interactions play a critical role in many condensed matter phenomena, and it is tempting to find a way to control them by changing the interactions’ strength. One possible approach is to place a studied system in proximity of a metal, which induces additional screening and hence suppresses electron interactions. Here, using devices with atomically-thin gate dielectrics and atomically-flat metallic gates, we measure the electron-electron scattering length in graphene and report qualitative deviations from the standard behavior. The changes induced by screening become important only at gate dielectric thicknesses of a few nm, much smaller than a typical separation between electrons. Our theoretical analysis agrees well with the scattering rates extracted from measurements of electron viscosity in monolayer graphene and of umklapp electron-electron scattering in graphene superlattices. The results provide a guidance for future attempts to achieve proximity screening of many-body phenomena in two-dimensional systems.

Basin Mapping Method for Extracting Comparative Assessments of Protein Phase Behavior from In Vivo Measurements

To uncover sequence-encoded driving forces for and the mechanisms of protein-specific phase transitions, we require knowledge of the underlying phase diagram, the degree of supersaturation, and the distance from critical point. Recent technological developments [1] based on Distributed Amphifluoric FRET (DAmFRET) allow the quantitative tracking of phase transitions as a function of protein expression in yeast. These in vivo experiments afford unprecedented throughput while enabling quantitative comparisons of protein-specific phase behavior. For a given protein, the DAmFRET dataset provides 2-dimensional histograms of AmFRET values and expression levels. Here, we adapt advances from energy landscape theory, specifically the inherent structure formalism of Stillinger and coworkers [2], to uncover protein-specific free energy functionals that underlie the phase behavior observed in DAmFRET measurements. We have developed and deployed a hybrid steepest-descent basin mapping method that identifies and quantifies major expression level dependent basins using the 2-dimensional histograms extracted from DAmFRET measurements. This approach identifies; (i) basins, which are envelopes in the 2-dimensional histograms; (ii) the relative weights of basins, and (iii) the centers of basins as defined by the steepest descent mapping. Results from the basin mapping procedure are used to infer protein-specific free energy functionals and these free energy functionals are used to reconstruct phase diagrams. Our analysis enables quantitative comparisons of phase transitions encoded by different protein sequences in a model cellular system. 1. T. Khan et al., (2018), Molecular Cell, 71: 155-168. 2. F. H. Stillinger, Energy Landscapes, Inherent Structures, and Condensed Matter Phenomena, Princeton University Press, 2016.