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Angle-resolved photoemission spectroscopy (ARPES) is a powerful tool for probing the momentum-resolved single-particle spectral function of materials. Historically, in situ magnetic fields have been carefully avoided as they are detrimental to the control of photoelectron trajectory during the photoelectron detection process. However, magnetic field is an important experimental knob for both probing and tuning symmetry-breaking phases and electronic topology in quantum materials. In this paper, we introduce an easily implementable method for realizing an in situ tunable magnetic field at the sample position in an ARPES experiment and analyze magnetic-field-induced artifacts in the ARPES data. Specifically, we identified and quantified three distinct extrinsic effects of a magnetic field: constant energy contour rotation, emission angle contraction, and momentum broadening. We examined these effects in three prototypical quantum materials, i.e., a topological insulator (Bi2Se3), an iron-based superconductor (LiFeAs), and a cuprate superconductor (Pb-Bi2Sr2CuO6+x), and demonstrate the feasibility of ARPES measurements in the presence of a controllable magnetic field. Our studies lay the foundation for the future development of the technique and interpretation of ARPES measurements of field-tunable quantum phases. 

We study the market structure for emerging distribution-level energy markets with high renewable energy penetration. Renewable generation is known to be uncertain and has a close-to-zero marginal cost. In this paper, we use solar energy as an example of such zero-marginal-cost resources for our focused study. We first show that, under high penetration of solar generation, the classical real-time market mechanism can either exhibit significant price-volatility (when each firm is not allowed to vary the supply quantity), or induce price-fixing (when each firm is allowed to vary the supply quantity), the latter of which leads to extreme unfairness of surplus division. To overcome these issues, we propose a new rental-market mechanism that trades the usage-right of solar panels instead of real-time solar energy. We show that the rental market produces a stable and unique price (therefore eliminating price-volatility), maintains positive surplus for both consumers and firms (therefore eliminating price-fixing), and achieves the same social welfare as the traditional real-time market. A key insight is that rental markets turn uncertainty of renewable generation from a detrimental factor (that leads to price-volatility in real-time markets) to a beneficial factor (that increases demand elasticity and contributes to the desirable rental-market outcomes). 

Abstract Topological semimetals with symmetry-protected band crossings have emerged as a rich landscape to explore intriguing electronic phenomena. Nonsymmorphic symmetries in particular have been shown to play an important role in protecting the crossings along a line (rather than a point) in momentum space. Here we report experimental and theoretical evidence for Dirac nodal line crossings along the Brillouin zone boundaries in PtPb 4 , arising from the nonsymmorphic symmetry of its crystal structure. Interestingly, while the nodal lines would remain gapless in the absence of spin–orbit coupling (SOC), the SOC, in this case, plays a detrimental role to topology by lifting the band degeneracy everywhere except at a set of isolated points. Nevertheless, the nodal line is observed to have a bandwidth much smaller than that found in density functional theory (DFT). Our findings reveal PtPb 4 to be a material system with narrow crossings approximately protected by nonsymmorphic crystalline symmetries.