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Latest articles for Reports on Progress in Physics
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Two-dimensional material/group-III nitride hetero-structures and devices
Two-dimensional (2D) material (graphene, MoS2, WSe2, MXene, etc)/group-III nitride (GaN, AlN, and their compounds) hetero-structures have been given special attention, on account of their prospective applications in remarkable performance broadband photodetectors, light-emitting diodes, solar cells, memristors, hydrogen sensors, etc. The utilization of advantages of the above two kind materials provides a solution to the dilemma of the degradation of device performance and reliability caused by carrier mobility, contact resistance, lattice mismatch, interface, and other factors. Therefore, the summary of the recent progress of 2D material/group-III nitride hetero-structures is urgent. In this work, it elaborates on interface interaction and stimulation, growth mechanism and device physic of 2D material/group-III nitride hetero-structures. Initially, it investigates the properties of the hetero-structures, combining the theoretical calculations on interface interaction of the heterojunction with experimental study, particularly emphasizing on interface effects on the performance of hetero-materials. The structure modification (band alignments, band edge position, synergetic work function and so on) at interface contributes to the outstanding properties of these hetero-structures. Subsequently, the growth of 2D material/group-III nitride hetero-structures is introduced in detail. The problems solved by the advancing synthesis strategies and the corresponding formation mechanisms are discussed in particular. Afterwards, based on the 2D material/group-III nitride hetero-structures, extending from optoelectronics, electronics, to photocatalyst and sensors, etc, are reviewed. Finally, the prospect of 2D material/group-III nitride hetero-structures is speculated to pave the way for further promotion.
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Perturbative framework for engineering arbitrary Floquet Hamiltonian
We develop a systematic perturbative framework to engineer an arbitrary target Hamiltonian in the Floquet phase space of a periodically driven oscillator based on Floquet–Magnus expansion. The high-order errors in the engineered Floquet Hamiltonian are mitigated by adding high-order driving potentials perturbatively. We introduce a transformation method that allows us to obtain an analytical expression of the leading-order correction drive for engineering a target Hamiltonian with discrete rotational and chiral symmetries in phase space. We also provide a numerically efficient procedure to calculate high-order correction drives and apply it to engineer the target Hamiltonian with degenerate eigenstates of multi-component cat states that are important for fault-tolerant hardware-efficiency bosonic quantum computation.
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Liquid–liquid crystalline phase separation of filamentous colloids and semiflexible polymers: experiments, theory and simulations
Liquid–liquid crystalline phase separation (LLCPS) is the process by which an initially homogenous single-phase solution composed of a solvent-most frequently water- and a solute-typically rigid or semiflexible macromolecules, polymers, supramolecular aggregates, or filamentous colloids-demixes into two (or more) distinct phases in which one phase is depleted by the solute and features properties of isotropic solutions, whereas the other is enriched by the solute and exhibits liquid crystalline anisotropic properties. Differently from the more common liquid–liquid phase separation (LLPS) of flexible macromolecules, which is a trade-off between entropy and enthalpy, LLCPS is mostly an entropy-controlled process in which the morphology, composition and properties of the new phases depend primarily on kinetics and thermodynamic factors and, unexpectedly, on the history followed to reach a specific point in the phase diagram. This review aims to comprehensively discuss the process of LLCPS from experimental, theoretical, and simulation standpoints. We discuss the main systems and experimental approaches followed over the past decades to induce and control LLCPS, then we delve into the main theoretical and modeling approaches available to rationalize this process, and finally, we expand on how numerical simulations can significantly enrich the understanding of LLCPS. A final section touches on possible applications and the significance of LLCPS beyond pure physics, that is, in the broader context of biology, nanotechnology, and everyday life.
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Transport resistance strikes back: unveiling its impact on fill factor losses in organic solar cells
The fill factor ( ) is a critical parameter for solar cell efficiency, but its analytical description is challenging due to the interplay between recombination and charge extraction processes. A significant factor contributing to losses, beyond recombination, that has not received much attention is the influence of charge transport. In most state-of-the-art organic solar cells, the primary limitations of the do not just arise from non-radiative recombination, but also from low conductivity of the organic semiconductors. A closer look reveals that even in the highest efficiency cells, performance losses due to transport resistance are significant. This finding highlights the need for refined models to predict the accurately. Here, we extend the analytical model for transport resistance to a more general case by incorporating energetic disorder. We introduce a straightforward set of equations to predict the of a solar cell, enabling the differentiation of losses attributed to recombination and transport resistance. Our analytical model is validated with a large set of experimental current–voltage and light intensity-dependent open-circuit voltage data for a wide range of temperatures. Based on our findings, we provide valuable insights into strategies for mitigating losses, guiding the development of more efficient solar cell designs and optimisation strategies.
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A cordial introduction to double scaled SYK
We review recent progress regarding the double scaled Sachdev–Ye–Kitaev model and other p-local quantum mechanical random Hamiltonians. These models exhibit an expansion using chord diagrams, which can be solved by combinatorial methods. We describe exact results in these models, including their spectrum, correlation functions, and Lyapunov exponent. In a certain limit, these techniques manifest the relation to the Schwarzian quantum mechanics, a theory of quantum gravity in AdS2. More generally, the theory is controlled by a rigid algebraic structure of a quantum group, suggesting a theory of quantum gravity on non-commutative q-deformed AdS2. We conclude with discussion of related universality classes, and survey some of the current research directions.