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1. 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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2. Universal density shift coefficients for the thermal conductivity and shear viscosity of a unitary Fermi gas

   https://doi.org/10.1103/PhysRevResearch.6.L042021  

   Li, Xiang; Huang, J; Thomas, J E (October 2024, Physical Review Research)

   We measure universal temperature-independent density shifts for the thermal conductivity ${\kappa }_T$and shear viscosity $\eta$, relative to the high temperature limits, for a normal phase unitary Fermi gas confined in a box potential. We show that a time-dependent kinetic theory model enables extraction of the hydrodynamic transport times ${\tau }_{\eta }$and ${\tau }_{\kappa }$from the time-dependent free decay of a spatially periodic density perturbation, yielding the static transport properties and density shifts, corrected for finite relaxation times. Published by the American Physical Society2024 

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3. Pseudo-easy-axis anisotropy in antiferromagnetic $S=1$ diamond-lattice systems

   https://doi.org/10.1103/PhysRevB.110.174438  

   Vaidya, S; Hernández-Melián, A; Tidey, J P; Curley, S_P M; Sharma, S; Manuel, P; Wang, C; Hannaford, G L; Blundell, S J; Manson, Z E; et al (November 2024, Physical Review B)

   We investigate the magnetic properties of $S=1$antiferromagnetic diamond-lattice, $\mathrm{Ni}{X}_2{\left(\mathrm{pyrimidine}\right)}_2$ $(X=\mathrm{Cl}, \mathrm{Br})$, hosting a single-ion anisotropy (SIA) orientation which alternates between neighboring sites. Through neutron diffraction measurements of the $X=\mathrm{Cl}$compound, the ordered state spins are found to align collinearly along a pseudo-easy axis, a unique direction created by the intersection of two easy planes. Similarities in the magnetization, exhibiting spin-flop transitions, and the magnetic susceptibility in the two compounds imply that the same magnetic structure and a pseudo-easy axis is also present for $X=\mathrm{Br}$. We estimate the Hamiltonian parameters by combining analytical calculations and Monte Carlo (MC) simulations of the spin-flop and saturation field. The MC simulations also reveal that the spin-flop transition occurs when the applied field is parallel to the pseudo-easy axis. Contrary to conventional easy-axis systems, there exist field directions perpendicular to the pseudo-easy axis for which the magnetic saturation is approached asymptotically and no symmetry-breaking phase transition is observed at finite fields. Published by the American Physical Society2024 

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4. Gapless superconductivity from low-frequency electrodynamic response of two-dimensional granular composites

   https://doi.org/10.1103/PhysRevResearch.7.013183  

   Zhang, Xinyang; Wu, Jinze; Palevski, Alexander; Kapitulnik, Aharon (February 2025, Physical Review Research)

   We measured the full complex ac conductance of two-dimensional granular $\mathrm{In}/{\mathrm{InO}}_x$composites using the mutual inductance technique to explore the transition from a “failed superconductor turned anomalous metal” to a robust superconductor. In this system, room-temperature annealing was adopted to tune the ${\mathrm{InO}}_x$-mediated coupling between In grains, allowing for the observation of both a “true” superconductor-to-insulator transition and the emergence of an intervening anomalous metallic state. In this paper, we show that further annealing increases the intergrain coupling, eliminating the anomalous metallic phase but at the same time preventing the emergence of strong Bose-dominated insulating phase. The complex ac conductance revealed a $T\to 0$finite dissipative response in a finite magnetic field, coexisting with a robust superfluid density. The anomalous power-law spectra for the dissipative response suggest quantum critical behavior as probed in the kilohertz range, and point to signatures of gapless superconductivity in our granular superconducting system. Published by the American Physical Society2025 

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5. Neutrino many-body flavor evolution: The full Hamiltonian

   https://doi.org/10.1103/PhysRevD.110.123028  

   Cirigliano, Vincenzo; Sen, Srimoyee; Yamauchi, Yukari (December 2024, Physical Review D)

   We study neutrino flavor evolution in the quantum many-body approach using the full neutrino-neutrino Hamiltonian, including the usually neglected terms that mediate nonforward scattering processes. Working in the occupation number representation with plane waves as single-particle states, we explore the time evolution of simple initial states with up to $N=10$neutrinos. We discuss the time evolution of the Loschmidt echo, one body flavor and kinetic observables, and the one-body entanglement entropy. For the small systems considered, we observe “thermalization” of both flavor and momentum degrees of freedom on comparable time scales, with results converging towards expectation values computed within a microcanonical ensemble. We also observe that the inclusion of nonforward processes generates a faster flavor evolution compared to the one induced by the truncated (forward) Hamiltonian. Published by the American Physical Society2024 

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