Université de Fribourg

Quantum Monte Carlo impurity solvers for multi-orbital problems and frequency-dependent interactions

Shinaoka, Hiroshi ; Assaad, F. ; Blümer, N. ; Werner, Philipp

In: The European Physical Journal Special Topics, 2017, vol. 226, no. 11, p. 2499–2523

The solution of an auxiliary quantum impurity system is the computationally expensive step in dynamical mean field theory simulations of lattice models and materials. In this review, we discuss Monte Carlo based impurity solvers, which are suitable for a wide range of applications. In particular, we present an efficient implementation of the hybridization expansion approach, which enables the...

Université de Fribourg

Continuous-time hybridization expansion quantum impurity solver for multi-orbital systems with complex hybridizations

Shinaoka, Hiroshi ; Gull, Emanuel ; Werner, Philipp

In: Computer Physics Communications, 2017, vol. 215, p. 128–136

We describe an open-source implementation of the continuous-time hybridization- expansion quantum Monte Carlo method for impurity models with general instantaneous two-body interactions and complex hybridization functions. The code is built on an updated version of the core libraries of ALPS (Applications and Libraries for Physics Simulations) [ALPSCore libraries].

Université de Fribourg

Fidelity susceptibility perspective on the Kondo effect and impurity quantum phase transitions

Wang, Lei ; Shinaoka, Hiroshi ; Troyer, Matthias

In: Physical Review Letters, 2015, vol. 115, no. 23, p. 236601

The Kondo effect is a ubiquitous phenomenon appearing at low temperature in quantum confined systems coupled to a continuous bath. Efforts in understanding and controlling it have triggered important developments across several disciplines of condensed matter physics. A recurring pattern in these studies is that the suppression of the Kondo effect often results in intriguing physical phenomena...

Université de Fribourg

Charge-spin-orbital fluctuations in mixed valence spinels: Comparative study of ${\mathrm{AlV}}_{2}{\mathrm{O}}_{4}$ and ${\mathrm{LiV}}_{2}{\mathrm{O}}_{4}$

Uehara, Amane ; Shinaoka, Hiroshi ; Motome, Yukitoshi

In: Physical Review B, 2015, vol. 92, no. 19, p. 195150

Mixed valence spinels provide a fertile playground for the interplay between charge, spin, and orbital degrees of freedom in strongly correlated electrons on a geometrically frustrated lattice. Among them, AlV2O4 and LiV2O4 exhibit contrasting and puzzling behavior: self-organization of seven-site clusters and heavy fermion behavior. We theoretically perform a comparative study of...

Université de Fribourg

Phase diagram of pyrochlore iridates: all-in\char21{}All-out magnetic ordering and non-Fermi-liquid properties

Shinaoka, Hiroshi ; Hoshino, Shintaro ; Troyer, Matthias ; Werner, Philipp

In: Physical Review Letters, 2015, vol. 115, no. 15, p. 156401

We study the prototype 5d pyrochlore iridate Y2Ir2O7 from first principles using the local density approximation and dynamical mean-field theory (LDA+DMFT). We map out the phase diagram in the space of temperature, on-site Coulomb repulsion U, and filling. Consistent with experiments, we find that an all-in–all-out ordered insulating phase is stable for realistic values of U. The trigonal...

Université de Fribourg

Accuracy of downfolding based on the constrained random-phase approximation

Shinaoka, Hiroshi ; Troyer, Matthias ; Werner, Philipp

In: Physical Review B, 2015, vol. 91, no. 24, p. 245156

We study the reliability of the constrained random-phase approximation (cRPA) method for the calculation of low-energy effective Hamiltonians by considering multiorbital lattice models with one strongly correlated “target” band and two weakly correlated “screening” bands. The full multiorbital system and the effective model are solved within dynamical mean-field theory (DMFT) in a...

Université de Fribourg

Hybridization expansion Monte Carlo simulation of multi-orbital quantum impurity problems: matrix product formalism and improved sampling

Shinaoka, Hiroshi ; Dolfi, Michele ; Troyer, Matthias ; Werner, Philipp

In: Journal of Statistical Mechanics: Theory and Experiment, 2014, vol. 2014, no. 6, p. P06012

We explore two complementary modifications of the hybridization-expansion continuous-time Monte Carlo method, aiming at large multi-orbital quantum impurity problems. One idea is to compute the imaginary-time propagation using a matrix product state representation. We show that bond dimensions considerably smaller than the dimension of the Hilbert space are sufficient to obtain accurate results...