Università della Svizzera italiana

Space-time multilevel Monte Carlo methods and their application to cardiac electrophysiology

Ben Bader, Seif ; Benedusi, Pietro ; Quaglino, Alessio ; Zulian, Patrick ; Krause, Rolf

In: Journal of computational physics, 2021, vol. 433, p. 17 p

We present a novel approach aimed at high-performance uncertainty quantification for time-dependent problems governed by partial differential equations. In particular, we consider input uncertainties described by a Karhunen-Loève expansion and compute statistics of high-dimensional quantities-of-interest, such as the cardiac activation potential. Our methodology relies on a close integration...

Université de Fribourg

NESSi : The Non-Equilibrium Systems Simulation package

Schüler, Michael ; Golež, Denis ; Murakami, Yuta ; Bittner, Nikolaj ; Herrmann, Andreas ; U.R.Strand, Hugo ; Werner, Philipp ; Eckstein, Martin

In: Computer Physics Communications, 2020, vol. 257, no. 2020, p. 107484

The nonequilibrium dynamics of correlated many-particle systems is of interest in connection with pump–probe experiments on molecular systems and solids, as well as theoretical investigations of transport properties and relaxation processes. Nonequilibrium Green’s functions are a powerful tool to study interaction effects in quantum many-particle systems out of equilibrium, and to extract...

Université de Fribourg

Entropy and electronic orders of the three-orbital Hubbard model with antiferromagnetic Hund coupling

Yue, Changming ; Hoshino, Shintaro ; Werner, Philipp

In: Physical Review B, 2020, vol. 102, no. 19, p. 195103

An antiferromagnetic Hund coupling in multiorbital Hubbard systems induces orbital freezing and an associated superconducting instability, as well as unique composite orders in the case of an odd number of orbitals. While the rich phase diagram of the half-filled three-orbital model has recently been explored in detail, the properties of the doped system remain to be clarified. Here, we...

Université de Fribourg

Unconventional free charge in the correlated semimetal Nd2Ir2O7

Wang, K. ; Xu, Bing ; Rischau, C. W. ; Bachar, N. ; Michon, B. ; Teyssier, J. ; Qiu, Y. ; Ohtsuki, T. ; Cheng, Bing ; Armitage, N. P. ; Nakatsuji, S. ; van der Marel, D.

In: Nature Physics, 2020, p. -

Nd2Ir2O7 is a correlated semimetal with the pyrochlore structure, in which competing spin–orbit coupling and electron–electron interactions are believed to induce a time- reversal symmetry-broken Weyl semimetal phase characterized by pairs of topologically protected Dirac points at the Fermi energy1,2,3,4. However, the emergent properties in these materials are far from clear, and exotic...

Université de Fribourg

Alleviating the sign problem in quantum Monte Carlo simulations of spin-orbit-coupled multiorbital Hubbard models

Kim, Aaram J. ; Werner, Philipp ; Valentí, Roser

In: Physical Review B, 2020, vol. 101, no. 4, p. 045108

We present a strategy to alleviate the sign problem in continuous-time quantum Monte Carlo (CTQMC) simulations of the dynamical-mean-field-theory (DMFT) equations for the spin-orbit-coupled multiorbital Hubbard model. We first identify the combinations of rotationally invariant Hund coupling terms present in the relativistic basis which lead to a severe sign problem. Exploiting the fact that...

Université de Fribourg

Unconventional orbital ordering and emergent dimensional reduction in fulleride superconductors

Hoshino, Shintaro ; Werner, Philipp ; Arita, Ryotaro

In: Physical Review B, 2019, vol. 99, no. 23, p. 235133

Nonlocal order parameters in space-time are proposed to characterize the unconventional orbital-selective conducting state in fulleride superconductors, called the Jahn-Teller metal. In previous works, it has been argued that this state can be interpreted as a spontaneous orbital-selective Mott state, in which the electrons in two of the three t1u molecular orbitals are localized, while those...

Université de Fribourg

First-principles studies of spin-orbital physics in pyrochlore oxides

Shinaoka, Hiroshi ; Motome, Yukitoshi ; Miyake, Takashi ; Ishibashi, Shoji ; Werner, Philipp

In: Journal of Physics: Condensed Matter, 2019, vol. 31, no. 32, p. 323001

The pyrochlore oxides A2B2O7 exhibit a complex interplay between geometrical frustration, electronic correlations, and spin–orbit coupling (SOC), due to the lattice structure and active charge, spin, and orbital degrees of freedom. Understanding the properties of these materials is a theoretical challenge, because their intricate nature depends on material-specific details and quantum...

Consortium of Swiss Academic Libraries

A Monte Carlo permutation test for co-occurrence data

Kovács, Balázs

In: Quality & Quantity, 2014, vol. 48, no. 2, p. 955-960