Search for: All records

Abstract There is tremendous interest in employing collective excitations of the lattice, spin, charge, and orbitals to tune strongly correlated electronic phenomena. We report such an effect in a ruthenate, Ca₃Ru₂O₇, where two phonons with strong electron-phonon coupling modulate the electronic pseudogap as well as mediate charge and spin density wave fluctuations. Combining temperature-dependent Raman spectroscopy with density functional theory reveals two phonons,B₂^PandB₂^M, that are strongly coupled to electrons and whose scattering intensities respectively dominate in the pseudogap versus the metallic phases. TheB₂^Psqueezes the octahedra along the out of planec-axis, while theB₂^Melongates it, thus modulating the Ru 4d orbital splitting and the bandwidth of the in-plane electron hopping; Thus,B₂^Popens the pseudogap, whileB₂^Mcloses it. Moreover, theB₂phonons mediate incoherent charge and spin density wave fluctuations, as evidenced by changes in the background electronic Raman scattering that exhibit unique symmetry signatures. The polar order breaks inversion symmetry, enabling infrared activity of these phonons, paving the way for coherent light-driven control of electronic transport. 

Abstract Biobased poly(γ-methyl-α-methylene-γ-butyrolactone) (PMMBL), an acrylic polymer bearing a cyclic lactone ring, has attracted increasing interest because it not only is biorenewable but also exhibits superior properties to petroleum-based linear analog poly(methyl methacrylate) (PMMA). However, such property enhancement has been limited to resistance to heat and solvent, and mechanically both types of polymers are equally brittle. Here we report the expeditious synthesis of well-defined PMMBL-based ABA tri-block copolymers (tri-BCPs)—enabled by dual-initiating and living frustrated Lewis pairs (FLPs)—which are thermoplastic elastomers showing much superior mechanical properties, especially at high working temperatures (80–130 °C), to those of PMMA-based tri-BCPs. The FLPs consist of a bulky organoaluminum Lewis acid and a series of newly designed bis(imino)phosphine superbases bridged by an alkyl linker, which promote living polymerization of MMBL. Uniquely, such bisphosphine superbases initiate the chain growth from both P-sites concurrently, enabling the accelerated synthesis of tri-BCPs in a one-pot, two-step procedure. The results from mechanistic studies, including the single crystal structure of the dually initiated active species, detailed polymerizations, and kinetic studies confirm the livingness of the polymerization and support the proposed polymerization mechanism featuring the dual initiation and subsequent chain growth from both P-sites of the superbase di-initiator. 

Abstract The emergence of magnetism in quantum materials creates a platform to realize spin-based applications in spintronics, magnetic memory, and quantum information science. A key to unlocking new functionalities in these materials is the discovery of tunable coupling between spins and other microscopic degrees of freedom. We present evidence for interlayer magnetophononic coupling in the layered magnetic topological insulator MnBi 2 Te 4 . Employing magneto-Raman spectroscopy, we observe anomalies in phonon scattering intensities across magnetic field-driven phase transitions, despite the absence of discernible static structural changes. This behavior is a consequence of a magnetophononic wave-mixing process that allows for the excitation of zone-boundary phonons that are otherwise ‘forbidden’ by momentum conservation. Our microscopic model based on density functional theory calculations reveals that this phenomenon can be attributed to phonons modulating the interlayer exchange coupling. Moreover, signatures of magnetophononic coupling are also observed in the time domain through the ultrafast excitation and detection of coherent phonons across magnetic transitions. In light of the intimate connection between magnetism and topology in MnBi 2 Te 4 , the magnetophononic coupling represents an important step towards coherent on-demand manipulation of magnetic topological phases. 

Correction for ‘Optimizing accuracy and efficacy in data-driven materials discovery for the solar production of hydrogen’ by Yihuang Xionget al.,Energy Environ. Sci., 2021,14, 2335–2348; DOI: 10.1039/D0EE02984J. 

The production of hydrogen fuels, via water splitting, is of practical relevance for meeting global energy needs and mitigating the environmental consequences of fossil-fuel-based transportation. Water photoelectrolysis has been proposed as a viable approach for generating hydrogen, provided that stable and inexpensive photocatalysts with conversion efficiencies over 10% can be discovered, synthesized at scale, and successfully deployed (Pinaud et al. , Energy Environ. Sci. , 2013, 6 , 1983). While a number of first-principles studies have focused on the data-driven discovery of photocatalysts, in the absence of systematic experimental validation, the success rate of these predictions may be limited. We address this problem by developing a screening procedure with co-validation between experiment and theory to expedite the synthesis, characterization, and testing of the computationally predicted, most desirable materials. Starting with 70 150 compounds in the Materials Project database, the proposed protocol yielded 71 candidate photocatalysts, 11 of which were synthesized as single-phase materials. Experiments confirmed hydrogen generation and favorable band alignment for 6 of the 11 compounds, with the most promising ones belonging to the families of alkali and alkaline-earth indates and orthoplumbates. This study shows the accuracy of a nonempirical, Hubbard-corrected density-functional theory method to predict band gaps and band offsets at a fraction of the computational cost of hybrid functionals, and outlines an effective strategy to identify photocatalysts for solar hydrogen generation.