Thomas Peter Devereaux

Here, the authors use determinant quantum Monte Carlo simulations to obtain high-resolution single-particle spectra of the doped Hubbard model, uncovering a pronounced electron-hole asymmetry. At low hole doping, proximity to the Mott gap suppresses antinodal coherence and produces Fermi arcs, whereas under electron doping, more coherent quasiparticles and stronger antiferromagnetic correlations generate hot spots. Probe-dependent pseudogap temperatures support a smooth crossover driven by strong correlations rather than a sharp phase transition.

Capturing metastable reaction intermediates through spectroscopy is a fundamental challenge across many fields, as their intrinsic metastability often leads to transformation while being measured. This challenge is acute in oxygen redox in battery intercalation cathodes, where metastable intermediates, despite their long lifetime, remain difficult to capture reliably. Here, we demonstrate that vacuum conditions destabilize oxidized oxygen intermediates and drive their transformation to thermodynamically stable O ₂ in Li _1.13 Ni _0.13 Mn _0.57 O ₂ . To overcome these issues, we employ vacuum-free and cryogenic hard X-ray Raman spectroscopy, circumventing both vacuum and radiation-induced effects. This approach enables direct and reliable detection of metastable oxygen-redox intermediates in this system, while also capturing diverse oxygen-redox features across different cathodes and stoichiometries. Our findings demonstrate a robust method to identify redox intermediates, reconciling experimental observations and theoretical predictions and sharpening our understanding of oxygen-redox mechanisms.

Capturing metastable reaction intermediates through spectroscopy is a fundamental challenge across many fields, as their intrinsic metastability often leads to transformation while being measured. This challenge is acute in oxygen redox in battery intercalation cathodes, where metastable intermediates, despite their long lifetime, remain difficult to capture reliably. Here, we demonstrate that vacuum conditions can destabilize oxidized oxygen intermediates and drive their transformation to thermodynamically stable O2 in Li1.13Ni0.13Mn0.57O2. To overcome these issues, we employ vacuum-free and cryogenic hard X-ray Raman spectroscopy, circumventing both vacuum and radiation-induced effects. This approach enables direct and reliable detection of metastable oxygen-redox intermediates in this system, while also capturing diverse oxygen-redox features across different cathodes and stoichiometries. Our findings demonstrate a robust method to identify intrinsic intermediates, reconciling experimental observations and theoretical predictions and sharpening our understanding of oxygen-redox mechanisms.

Twisted bilayer MoTe 2 ( tMoTe 2 ) is an emergent platform for exploring exotic quantum phases driven by the interplay between nontrivial band topology and strong electron correlations. Direct experimental access to its momentum-resolved electronic structure is essential for uncovering the microscopic origins of the correlated topological phases therein. Here, we report angle-resolved photoemission spectroscopy measurements of tMoTe 2 , revealing pronounced twist-angle-dependent band reconstruction shaped by orbital character, interlayer coupling, and moiré potential modulation. Density functional theory captures the qualitative evolution, yet underestimates key energy scales across twist angles, highlighting the importance of electronic correlations. Notably, the hole effective mass at the K point exhibits a nonmonotonic dependence on twist angle, peaking near 2°, consistent with band flattening at the magic angle predicted by continuum models. Via electrostatic gating and surface dosing, we further visualize the evolution of electronic structure versus doping, enabling direct observation of the conduction band minimum and confirm tMoTe 2 as a direct band gap semiconductor. These results establish a spectroscopic foundation for modeling and engineering emergent quantum phases in this moiré platform.

We performed angle-resolved photoemission spectroscopy studies on the triple-layer Bi₂Sr₂Ca₂Cu₃O_10+δ over a wide doping range. Although the doping level of the inner CuO₂ plane is extremely low in underdoped samples, the d-wave SC gap is enhanced to the unprecedentedly large value of Δ₀ ~ 80–100 meV at the antinode. This gap persists well above T_c without a Fermi arc, indicating a “nodal metal”. We attribute the nodal metallic behavior to the unique local environment of the inner clean CuO₂ plane, sandwiched by nearly optimally-doped two outer planes and hence subject to strong proximity effect from both sides. In the nodal metal, quasiparticle peaks show electron-hole symmetry, suggesting d-wave pairing fluctuations. Thus the proximity effect on the innermost CuO₂ plane is the strongest in the triple-layer cuprates, which explains why the T_c reaches the maximum at the layer number of three in every multi-layer cuprate family.