Degenerate States Research Articles

Human-derived Biomaterials for Biomedical and Tissue Engineering Applications.

Biomaterials have been utilised since the dawn of time to aid wound healing and to try to restore damaged tissues and organs. Many different materials are now commercially accessible for maintaining and restoring biological functioning, and many more are being researched. New biomaterials have to be developed to meet growing clinical demands. The aim of this study is to propose innovative biomaterials of human origin and their recent applications in tissue engineering and the biomedical field. Recent trends in tissue engineering are summarized in this review highlighting the use of stem cells, 3D printing techniques, and the most recent application of biomaterials to produce a dynamic scaffold resembling natural tissue. Various literature survey was carried out using PubMed, Scopus, Elsevier, google scholar, and others and it was summarized from the study that the extracellular matrix (ECM) offers the opportunity to create a biomaterial consisting of a microenvironment with interesting biological and biophysical properties for improving and regulating cell functions. Based on the literature study, biomaterials have become increasingly important to the development of tissue engineering, which aims to unlock the regeneration capacity of human tissues/organs in a state of degeneration and restore or reestablish normal biological function. Biomaterials have also become increasingly important to the success of biomedical devices. Hence, it can be concluded from the finding of the study that the advances in the understanding of biomaterials and their role in new tissue formation can open new prospects in the field of tissue engineering and regenerative medicine.

Coherent control of symmetry breaking in transverse-field Ising chains using few-cycle pulses

Abstract Coherent control of quantum systems with phase-stable pulses offers enticing new opportunities for lightwave electronics. Here we extend this approach to many-body systems with spin degrees of freedom, demonstrating that a single few-cycle control pulse can create a sizable population asymmetry between the two degenerate polar ground states of the Ising model. This opens a route for femtosecond-scale data processing and storage, allowing one to control the final ground state of a correlated system in an all-optical way.

Destruction of Anderson localization by subquadratic nonlinearity

It is shown based on a mapping procedure onto a Cayley tree that a subquadratic nonlinearity destroys Anderson localization of waves in nonlinear Schrödinger lattices with randomness, if the exponent of the nonlinearity satisfies , giving rise to unlimited subdiffusive spreading of an initially localized wave packet along the lattice. The focus on subquadratic nonlinearity is intended to amend and generalize the special case s = 1, considered previously, by offering a more comprehensive picture of dynamics. A transport model characterizing the spreading process is obtained in terms of a bifractional diffusion equation involving both long-time trappings of unstable modes on finite clusters and their long-haul jumps in wave number space consistent with Lévy flights. The origin of the flights is associated with self-intersections of the higher-order Cayley trees with odd coordination numbers z > 3 leading to degenerate states.

Confined states in the tight-binding model on the hexagonal golden-mean tiling

We study the tight-binding model with two distinct hoppings (tL, tS ) on the two-dimensional hexagonal golden-mean tiling and examine the confined states with E = 0, where E is the eigenenergy. Some confined states found in the case tL = tS are exact eigenstates even for the system with tL ≠ t S, where their amplitudes are smoothly changed. By contrast, the other states are no longer eigenstates of the system with tL ≠ t S. This may imply the existence of macroscopically degenerate states which are characteristic of the system with tL = t S, and that a discontinuity appears in the number of the confined states in the thermodynamic limit.

Frustrated Magnetism: A Case Study of Geometric Frustration

In this research work, frustrations arising from the geometries of triangular lattices have been studied with the aid of Ising and Heisenberg models. The study reveals that geometrical frustrations can generate multiple degeneracies in the ground state. The quantum spin flip terms in the Heisenberg model are observed to play a vital role in the partial lifting up of these degeneracies. Hence, multiple degeneracies as consequence of frustrations are more pronounced for the Ising systems, which are devoid of quantum fluctuations. The observed six- and four-fold ground state degeneracies at zero field for three spins Ising and Heisenberg systems respectively are broken down to half at finite longitudinal fields. For this three-spin system, quantum phase transitions (QPT) are observed at critical longitudinal fields of J and 1.5J respectively for the Ising and Heisenberg models. At these critical fields, the ground states are observed to shift from quasi-antiferromagnet to ferromagnet. However, for the Heisenberg three-spin system in the presence of a transverse field, no transition is observed.

Classifying phases protected by matrix product operator symmetries using matrix product states

We classify the different ways in which matrix product states (MPSs) can stay invariant under the action of matrix product operator (MPO) symmetries. This is achieved through a local characterization of how the MPSs, that generate a ground space, remain invariant under a global MPO symmetry. This characterization yields a set of quantities satisfying the coupled pentagon equations, associated with a module category over the fusion category that describes the MPO symmetry. Equivalence classes of these quantities provide complete invariants for an MPO symmetry protected phase: they are robust under continuous deformations of the MPS tensor, and two phases with the same equivalence class can be connected by a symmetric gapped path. Our techniques match and extend the known renormalization fixed point classifications and facilitate the numerical study of these systems. For MPO symmetries described by a group, we recover the symmetry protected topological order classification for unique and degenerate ground states. Moreover, we study the interplay between time reversal symmetry and an MPO symmetry and we also provide examples of our classification, together with explicit constructions based on groups. Finally, we elaborate on the connection between our setup and gapped boundaries of two-dimensional topological systems, where MPO symmetries also play a key role.

6,6'-Biindeno[1,2-b]anthracene: An Open-Shell Biaryl with High Diradical Character.

We report in situ generation of a 6,6'-biindeno[1,2-b]anthracene (BIA) derivative as an open-shell biaryl with high diradical character, which could be identified by mass spectrometry, NMR spectroscopy, single-crystal X-ray analysis, UV-vis-NIR absorption spectroscopy, and electron paramagnetic resonance (EPR) spectroscopy. Theoretical calculations by various methods and variable-temperature EPR analyses were performed to tackle the elusive ground state of BIA diradical, suggesting a singlet ground state with a nearly degenerate triplet state. These results provide insight into the design of unique open-shell biaryls.

Ground state degeneracy of the Ising cage-net model

The Ising cage-net model, first proposed in Phys. Rev. X 9, 021010 (2019), is a representative type I fracton model with nontrivial non-abelian features. In this paper, we calculate the ground state degeneracy of this model and find that, even though it follows a similar coupled layer structure as the X-cube model, the Ising cage-net model cannot be "foliated" in the same sense as X-cube as defined in Phys. Rev. X 8, 031051 (2018). A more generalized notion of "foliation'' is hence needed to understand the renormalization group transformation of the Ising cage-net model. The calculation is done using an operator algebra approach that we develop in this paper, and we demonstrate its validity through a series of examples.

Multichannel Topological Kondo Effect

A Coulomb blockaded M-Majorana island coupled to normal metal leads realizes a novel type of Kondo effect where the effective impurity "spin" transforms under the orthogonal group SO(M). The impurity spin stems from the nonlocal topological ground state degeneracy of the island and thus the effect is known as the topological Kondo effect. We introduce a physically motivated N-channel generalization of the topological Kondo model. Starting from the simplest case N=2, we conjecture a stable intermediate coupling fixed point and evaluate the resulting low-temperature impurity entropy. The impurity entropy indicates that an emergent Fibonacci anyon can be realized in the N=2 model. We also map the case N=2, M=4 to the conventional four-channel Kondo model and find the conductance at the intermediate fixed point. By using the perturbative renormalization group, we also analyze the large-N limit, where the fixed point moves to weak coupling. In the isotropic limit, we find an intermediate stable fixed point, which is stable to "exchange" coupling anisotropies, but unstable to channel anisotropy. We evaluate the fixed point impurity entropy and conductance to obtain experimentally observable signatures of our results. In the large-N limit, we evaluate the full crossover function describing the temperature-dependent conductance.

Geometry of Degeneracy in Potential and Density Space

In a previous work [J. Chem. Phys. 155, 244111 (2021)], we found counterexamples to the fundamental Hohenberg-Kohn theorem from density-functional theory in finite-lattice systems represented by graphs. Here, we demonstrate that this only occurs at very peculiar and rare densities, those where density sets arising from degenerate ground states, called degeneracy regions, touch each other or the boundary of the whole density domain. Degeneracy regions are shown to generally be in the shape of the convex hull of an algebraic variety, even in the continuum setting. The geometry arising between density regions and the potentials that create them is analyzed and explained with examples that, among other shapes, feature the Roman surface.

Chloroplast and outside-chloroplast interference of light inside leaves

Our research explored leaf optical patterns when light falls on the leaf’s inner surface and interacts to chloroplasts pigments or with the outside-chloroplast components (structural apparatus) of leaves. Six species of variegated leaves were used to detect effects of chlorophylls (green leaves), carotenoids (yellow leaves – without chlorophylls) and outside-chloroplasts components (albino leaves – without functional chloroplasts) to deep our understand of behavior of light inside leaf beyond spectral interference of pigments. High absorbance at wavelengths shorter than 530 nm in albino leaves (absence of chloroplasts) in addition to high scattering at longer wavelengths (considering the 400–700 nm range) were detected. Changes in measurements of chlorophyll fluorescence spectroscopy performed simultaneously on both side of leaves and using a high fluorescence in red absorption (R) to low effects on fluorescence in far-red (FR) as a proxy, the ratio of fluorescence (R/FR) were associated to differences in penetrability of different wavelengths. From the leaf optical system point of view, internal reflectance and degenerate chlorophyll quantum state are important physical mechanisms that maximize the absorption of wavelengths of low absorptivity, as in the case of green light.

Continuous transition from a Landau quasiparticle to a neutral spinon

We examine a wavefunction ansatz in which a doped hole can experience a quantum transition from a charge $+e$ Landau quasiparticle to a neutral spinon as a function of the underlying spin-spin correlation. As shown variationally, such a wavefunction accurately captures all the essential features revealed by exact diagonalization and density matrix renormalization group simulations in a two-leg $t$-$J$ ladder. Hence its analytic form can provide an explicit understanding of the mechanism for the unconventional ground state. The transition in the phase diagram is accompanied by a change of the hole composite from a tight charge-spin binding to a loosely-bound hole-spin pair. In the latter, the hole carries a \emph{finite} spin current but with vanishing charge current in the degenerate ground states. We show that the charge of the hole composite here is dynamically diminished due to an internal relative hole-spin motion, which is fundamentally distinct from a simple charge-spin separation in a one-dimensional case. We further show that the same effect is also responsible for a strong pairing between two doped holes in such a non-Landau quasiparticle regime.

Hidden Zeeman-type spin polarization in bulk crystals

Exploring hidden effects that have been overlooked given the nominal global crystal symmetry but are indeed visible in solid-state materials has been a fascinating subject of research recently. Here, we introduce a novel hidden Zeeman-type spin polarization (HZSP) in nonmagnetic bulk crystals with sublattice structures. In the momentum space of these crystals, the doubly degenerate bands formed in a certain plane can exhibit a uniform spin configuration with opposite spin orientations perpendicular to this plane, whereas such degenerate states are spatially separated in a pair of real-space sectors. Interestingly, we find that HZSP can manifest itself in both centrosymmetric and non-centrosymmetric materials. We further demonstrate the important role of nonsymmorphic twofold screw-rotational symmetry played in the formation of HZSP. Moreover, two representative material examples, i.e., centrosymmetric WSe$_2$ and noncentrosymmetric BaBi$_4$O$_7$, are identified to show HZSP via first-principles calculations. Our finding thus not only opens new perspectives for hidden spin polarization research but also significantly broadens the range of materials towards spintronics applications.

Three-dimensional solid particle self-assembly in thermovibrational flow: The case with unidirectional temperature gradient and concurrent vibrations

As a follow-up to earlier work [Crewdson and Lappa, “Spatial and temporal evolution of three-dimensional thermovibrational convection in a cubic cavity with various thermal boundary conditions,” Phys. Fluids 34, 014108 (2022)], where the main focus was on the modes of convection in a three-dimensional cubic enclosure filled with a Pr = 7 liquid undergoing vibrations in a direction “parallel” to the imposed temperature gradient, the present study considers the modes of particle clustering, which occur when solid spheres, with density ratio ξ = 1.85 or 0.3 and Stokes number (St) between 0.5 and 3.5 × 10−5, are added to the fluid. Starting from a uniform distribution of solid particles and fluid in quiescent conditions, the governing equations for the involved phases are numerically solved in their complete, time-dependent, and non-linear form for a representative vibrational Rayleigh number (8.34 × 104), angular frequency Ω = 50, and non-dimensional acceleration amplitude (γ) spanning the interval 0.4 × 107 ≤ γ ≤ 3.4 × 107. It is shown that, while for relatively high values of St and/or γ, only degenerate states are obtained, where all particles collapse on planar structures, for intermediate values of such parameters, interesting (heretofore unseen) patterns are enabled. The hallmark of these phenomena is an endless squeezing and expansion of the particle formations along the direction of the temperature gradient. As confirmed by the numerical simulations, the underlying formation mechanisms rely on the combined action of the body force acting on particles due to their different densities with respect to the host fluid and the additional drag that is produced when the carrier thermovibrational flow enters a specific stage, known as “convective burst,” where the magnitude of the fluid velocity increases dramatically.

Topological magnon modes of a chain of magnetic spheres in a waveguide

We study topological features of a bipartite chain of magnetic spheres embedded in a rectangular metallic waveguide. The coherently coupled chain via the waveguide mode can host two topologically distinct phases identified by the Zak phase. A finite chain supports a pair of doubly degenerate topological edge states within the gap when the intercoupling dominates over the intracoupling, demonstrating that despite the strong coupling to the waveguide mode, the bulk-edge correspondence still holds. The nontrivial (trivial) topological phase is determined by the intracell and intercell coupling of magnetic spheres which depend on the separation, the external magnetic inductions, and the waveguide dimensions. Magnetically tunable topological magnon modes may enable unprecedented topological photonic devices.

Honeycomb‐Layered Oxides With Silver Atom Bilayers and Emergence of Non‐Abelian SU(2) Interactions (Adv. Sci. 6/2023)

Silver Degenerate States In article number 2204672, using high-resolution transmission electron microscopy (HRTEM), Titus Masese, Godwill Mbiti Kanyolo, and co-workers report novel honeycomb layered oxides exhibiting silveratom bilayers. The bilayers are theoretically understood via emergent SU(2) interactions with three distinct states of silver associated with fractional valency (sub-valent) states, alongside conventional U(1) (electromagnetic) interaction. Breaking the SU(2)×U(1) symmetry, analogous to electroweak theory, generates silver mass terms manifesting as the bilayered structure.

Hands-On Quantum Sensing with NV− Centers in Diamonds

The physical properties of diamond crystals, such as color or electrical conductivity, can be controlled via impurities. In particular, when doped with nitrogen, optically active nitrogen-vacancy centers (NV), can be induced. The center is an outstanding quantum spin system that enables, under ambient conditions, optical initialization, readout, and coherent microwave control with applications in sensing and quantum information. Under optical and radio frequency excitation, the Zeeman splitting of the degenerate states allows the quantitative measurement of external magnetic fields with high sensitivity. This study provides a pedagogical introduction to the properties of the NV centers as well as a step-by-step process to develop and test a simple magnetic quantum sensor based on color centers with significant potential for the development of highly compact multisensor systems.

Enhanced Electronic g-Factors in Magic Number Main Group Bimetallic Nanoclusters

We report the observation of large electronic g-factors in magic number main group bimetallic nanoclusters by performing Stern-Gerlach deflection experiments at 10 K. The clusters AlPb12 and InPb12 exhibit values of g = 3.5-4.0, whereas GaPb12 clusters surprisingly reveal a value of g < 2.0. Multireference ab initio methods are applied to unmask the origin of the g-factors and to gain insight into the electronic structure. The interplay of the pyritohedral molecular symmetry, a particularly strong spin-orbit coupling involved in the ground state, and the presence of low-lying degenerate excited states causes large positive g-factors in AlPb12 and InPb12. Contrarily, the spin-orbit coupling in the GaPb12 ground state is completely quenched. This is due to the d-block contraction lowering the nonbonding Ga 5s orbital and consequently forming an icosahedral ground state. Thus, endohedral p-doped tetrel clusters, composed of purely main group elements, state a novel and unique class of magnetic compounds and their study contributes to a more profound understanding of the metal-metal interaction in polynuclear clusters as well as magnetism at the molecular level.

Interdomain dynamics in human Replication Protein A regulates kinetics and thermodynamics of its binding to ssDNA.

Human Replication Protein A (hRPA) is a multidomain protein that interacts with ssDNA intermediates to provide the latter much-needed stability during DNA metabolism and maintain genomic integrity. Although the ssDNA organization with hRPA was studied recently through experimental means, characterizing the underlying mechanism at the atomic level remains challenging because of the dynamic domain architecture of hRPA and poorly understood heterogeneity of ssDNA-protein interactions. Here, we used a computational framework, precisely tailored to capture protein-ssDNA interactions, and investigated the binding of hRPA with a 60 nt ssDNA. Two distinct binding mechanisms are realized based on the hRPA domain flexibility. For a rigid domain architecture of hRPA, ssDNA binds sequentially with hRPA domains, resulting in slow association kinetics. The binding pathway involves the formation of stable and distinct intermediate states. On contrary, for a flexible domain architecture of hRPA, ssDNA binds synergistically to the A and B domains followed by the rest of hRPA. The domain dynamics in hRPA alleviates the free energy cost of domain orientation necessary for specific binding with ssDNA, leading to fast association kinetics along a downhill binding free energy landscape. An ensemble of free energetically degenerate intermediate states is encountered that makes it arduous to characterize them structurally. An excellent match between our results with the available experimental observations provides new insights into the rich dynamics of hRPA binding to ssDNA and in general paves the way to investigate intricate details of ssDNA-protein interactions, crucial for cellular functioning.

Coherent correlation imaging for resolving fluctuating states of matter

Fluctuations and stochastic transitions are ubiquitous in nanometre-scale systems, especially in the presence of disorder. However, their direct observation has so far been impeded by a seemingly fundamental, signal-limited compromise between spatial and temporal resolution. Here we develop coherent correlation imaging (CCI) to overcome this dilemma. Our method begins by classifying recorded camera frames in Fourier space. Contrast and spatial resolution emerge by averaging selectively over same-state frames. Temporal resolution down to the acquisition time of a single frame arises independently from an exceptionally low misclassification rate, which we achieve by combining a correlation-based similarity metric1,2 with a modified, iterative hierarchical clustering algorithm3,4. We apply CCI to study previously inaccessible magnetic fluctuations in a highly degenerate magnetic stripe domain state with nanometre-scale resolution. We uncover an intricate network of transitions between more than 30 discrete states. Our spatiotemporal data enable us to reconstruct the pinning energy landscape and to thereby explain the dynamics observed on a microscopic level. CCI massively expands the potential of emerging high-coherence X-ray sources and paves the way for addressing large fundamental questions such as the contribution of pinning5–8 and topology9–12 in phase transitions and the role of spin and charge order fluctuations in high-temperature superconductivity13,14.