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1. Absence of $E_{2g}$ Nematic Instability and Dominant $A_{1g}$ Response in the Kagome Metal ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$

   https://doi.org/10.1103/PhysRevX.14.031015  

   Liu, Zhaoyu; Shi, Yue; Jiang, Qianni; Rosenberg, Elliott W; DeStefano, Jonathan M; Liu, Jinjin; Hu, Chaowei; Zhao, Yuzhou; Wang, Zhiwei; Yao, Yugui; et al (July 2024, Physical Review X)

   Ever since the discovery of the charge density wave (CDW) transition in the kagome metal ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$, the nature of its symmetry breaking has been under intense debate. While evidence suggests that the rotational symmetry is already broken at the CDW transition temperature ( $T_{\mathrm{CDW}}$), an additional electronic nematic instability well below $T_{\mathrm{CDW}}$has been reported based on the diverging elastoresistivity coefficient in the anisotropic channel ( $m_{E_{2g}}$). Verifying the existence of a nematic transition below $T_{\mathrm{CDW}}$is not only critical for establishing the correct description of the CDW order parameter, but also important for understanding low-temperature superconductivity. Here, we report elastoresistivity measurements of ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$using three different techniques probing both isotropic and anisotropic symmetry channels. Contrary to previous reports, we find the anisotropic elastoresistivity coefficient $m_{E_{2g}}$is temperature independent, except for a step jump at $T_{\mathrm{CDW}}$. The absence of nematic fluctuations is further substantiated by measurements of the elastocaloric effect, which show no enhancement associated with nematic susceptibility. On the other hand, the symmetric elastoresistivity coefficient $m_{A_{1g}}$increases below $T_{\mathrm{CDW}}$, reaching a peak value of 90 at $T^{*}=20\mathrm{K}$. Our results strongly indicate that the phase transition at $T^{*}$is not nematic in nature and the previously reported diverging elastoresistivity is due to the contamination from the $A_{1g}$channel. Published by the American Physical Society2024 

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2. QCD critical point, Lee-Yang edge singularities, and Padé resummations

   https://doi.org/10.1103/PhysRevC.110.015203  

   Başar, Gökçe (July 2024, Physical Review C)

   I analyze the trajectory of the Lee-Yang edge singularities of the QCD equation of state in the complex baryon chemical potential ( ${\mu }_B$) plane for different values of the temperature by using the recent lattice results for the Taylor expansion coefficients up to eighth order in ${\mu }_B$and various resummation techniques that blend in Padé expansions and conformal maps. By extrapolating from this information, I estimate for the location of the QCD critical point: $T_c\approx 100$MeV, ${\mu }_c\approx 580$MeV. I also estimate the crossover slope at the critical point to be ${\alpha }_1\approx 9^{\circ }$and further constrain the nonuniversal mapping parameters between the three-dimensional Ising model and QCD equations of state. Published by the American Physical Society2024 

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3. Anomalous Landau Level Gaps Near Magnetic Transitions in Monolayer ${\mathrm{WSe}}_2$

   https://doi.org/10.1103/PhysRevX.14.031018  

   Foutty, Benjamin A; Calvera, Vladimir; Han, Zhaoyu; Kometter, Carlos R; Liu, Song; Watanabe, Kenji; Taniguchi, Takashi; Hone, James C; Kivelson, Steven A; Feldman, Benjamin E (August 2024, Physical Review X)

   First-order phase transitions produce abrupt changes to the character of both ground and excited electronic states. Here we conduct electronic compressibility measurements to map the spin phase diagram and Landau level (LL) energies of monolayer ${\mathrm{WSe}}_2$in a magnetic field. We resolve a sequence of first-order phase transitions between completely spin-polarized LLs and states with LLs of both spins. Unexpectedly, the LL gaps are roughly constant over a wide range of magnetic fields below the transitions, which we show reflects spin-polarized ground states with opposite spin excitations. These transitions also extend into compressible regimes, with a sawtooth boundary between full and partial spin polarization. We link these observations to the important influence of LL filling on the exchange energy beyond a smooth density-dependent contribution. Our results show that ${\mathrm{WSe}}_2$realizes a unique hierarchy of energy scales where such effects induce reentrant magnetic phase transitions tuned by density and magnetic field. Published by the American Physical Society2024 

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4. State selectivity in core ionization of methane

   https://doi.org/10.1103/PhysRevResearch.7.L022021  

   Rajput, J; Stindl, J; Cassimi, A; Gervais, B; Kircher, M; Kastirke, G; McGinnis, O D; Enoki, R; Williams, J B; Davis, V; et al (April 2025, Physical Review Research)

   A clear experimental signature of the population of the lowest triplet state ${}^{3}T_1$of the methane dication is identified in a photoionization experiment. This state is populated only in valence ionization and is absent when the dication is formed by core ionization followed by Auger-Meitner decay. For valence ionization, the total internal energy of the ${\mathrm{CH}}_3^{+}$fragment, formed during the deprotonation of ${\mathrm{CH}}_4{}^{2+}$, is evaluated. Notably, the distribution of this internal energy peaks at the same value regardless of the initially populated electronic state of ${\mathrm{CH}}_4{}^{2+}$. We find that excited electronic states of ${\mathrm{CH}}_3^{+}$are predominantly populated with significant rovibrational excitation. Published by the American Physical Society2025 

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5. Superconductivity from On-Chip Metallization on 2D Topological Chalcogenides

   https://doi.org/10.1103/PhysRevX.14.021051  

   Jia, Yanyu; Yu, Guo; Song, Tiancheng; Yuan, Fang; Uzan, Ayelet J; Tang, Yue; Wang, Pengjie; Singha, Ratnadwip; Onyszczak, Michael; Zheng, Zhaoyi Joy; et al (June 2024, Physical Review X)

   Two-dimensional (2D) transition metal dichalcogenides (TMDs) is a versatile class of quantum materials of interest to various fields including, e.g., nanoelectronics, optical devices, and topological and correlated quantum matter. Tailoring the electronic properties of TMDs is essential to their applications in many directions. Here, we report that a highly controllable and uniform on-chip 2D metallization process converts a class of atomically thin TMDs into robust superconductors, a property belonging to none of the starting materials. As examples, we demonstrate the introduction of superconductivity into a class of 2D air-sensitive topological TMDs, including monolayers of ${\mathrm{T}}_{\mathrm{d}}\text{−}{\mathrm{WTe}}_2$, $1{\mathrm{T}}^{\prime }\text{−}{\mathrm{MoTe}}_2$, and $2\mathrm{H}\text{−}{\mathrm{MoTe}}_2$, as well as their natural and twisted bilayers, metallized with an ultrathin layer of palladium. This class of TMDs is known to exhibit intriguing topological phases ranging from topological insulator, Weyl semimetal to fractional Chern insulator. The unique, high-quality two-dimensional metallization process is based on our recent findings of the long-distance, non-Fickian in-plane mass transport and chemistry in 2D that occur at relatively low temperatures and in devices fully encapsulated with inert insulating layers. Highly compatible with existing nanofabrication techniques for van der Waals stacks, our results offer a route to designing and engineering superconductivity and topological phases in a class of correlated 2D materials. Published by the American Physical Society2024 

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