https://scholar.dgist.ac.kr/handle/20.500.11750/20604 2026-04-08T15:03:16Z https://scholar.dgist.ac.kr/handle/20.500.11750/60044 Title: Third-order strong-coupling impurity solver for real-frequency dynamical mean field theory: Accurate spectral functions for antiferromagnetic and photodoped states Author(s): Geng, Lei; Kim, Aaram J.; Werner, Philipp Abstract: We present a real-frequency third-order strong-coupling impurity solver which employs quantics tensor cross interpolation (QTCI) for an efficient evaluation of the diagram weights. Applying the method to dynamical mean-field theory (DMFT) calculations of the single-band Hubbard model on the Bethe lattice, we clarify the interaction and temperature range in which the third-order approach yields accurate results. Since the calculations are implemented on the real-time/frequency axis, the detailed structure of spectral functions can be obtained without analytical continuation, as we demonstrate with examples for paramagnetic, antiferromagnetic, and photodoped states. Our work establishes a viable path toward high-order, real-frequency impurity solvers for both equilibrium and nonequilibrium DMFT studies. 2025-11-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/58319 Title: Finite-temperature crossover in resistively shunted Josephson junctions via crossing approximations Author(s): Seok, Ha-Nul; Kim, Aaram J. Abstract: We study the finite temperature behavior of the minimal model of the resistively shunted Josephson junction (RSJJ) using the crossing expansions, particularly the one-crossing approximation (OCA). For a simple benchmark model of the RSJJ, the OCA shows a good agreement with the (numerically) exact method up to deep strong coupling regime. The spin-spin correlation function obtained by the OCA reveals the finite-temperature crossover between the superconductor and the insulator for finite system-bath coupling and local anharmonicity. And the observed insulating regime clearly expands in the parameter space as the temperature is raised. The estimated crossover boundary is qualitatively consistent with the previously reported ground-state phase diagram (K. Masuki et. al, Phys. Rev. Lett. 129, 087001 (2022)), but the quantitative values are sizably different. We discuss the possible origin of the deviations. © The Korean Physical Society 2025. 2025-04-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/58286 Title: Strong coupling impurity solver based on quantics tensor cross interpolation Author(s): Kim, Aaram J.; Werner, Philipp Abstract: Numerical methods capable of handling nonequilibrium impurity models are essential for the study of transport problems and the solution of the nonequilibrium dynamical mean-field theory (DMFT) equations. In the strong correlation regime, the self-consistently resummed hybridization expansion is an appealing strategy, which however has been employed so far mainly in the lowest-order noncrossing approximation. At higher orders, standard implementations become numerically costly, but a significant speed-up can be achieved by evaluating multidimensional integrals in an approximate factorized form. Here we develop a one-crossing approximation solver based on the recently introduced quantics tensor cross interpolation, and demonstrate its accuracy and efficiency with applications to the Anderson impurity model and nonequilibrium steady-state DMFT calculations for the Hubbard model. © 2025 American Physical Society. 2025-02-28T15:00:00Z