Université de Fribourg

Photoinduced enhancement of excitonic order

Murakami, Yuta ; Golež, Denis ; Eckstein, Martin ; Werner, Philipp

In: Physical Review Letters, 2017, vol. 119, no. 24, p. 247601

We study the dynamics of excitonic insulators coupled to phonons using the time- dependent mean-field theory. Without phonon couplings, the linear response is given by the damped amplitude oscillations of the order parameter with a frequency equal to the minimum band gap. A phonon coupling to the interband transfer integral induces two types of long-lived collective oscillations of the...

Université de Fribourg

Pressure-driven insulator-metal transition in cubic phase UO 2

Huang, Li ; Wang, Yilin ; Werner, Philipp

In: EPL (Europhysics Letters), 2017, vol. 119, no. 5, p. 57007

Understanding the electronic properties of actinide oxides under pressure poses a great challenge for experimental and theoretical studies. Here, we investigate the electronic structure of cubic phase uranium dioxide at different volumes using a combination of density functional theory and dynamical mean-field theory. The ab initio calculations predict an orbital-selective insulator-metal...

Université de Fribourg

Multitier self-consistent $GW+\text{EDMFT}$

Nilsson, Fredrik ; Boehnke, Lewin ; Werner, Philipp ; Aryasetiawan, Ferdi

In: Physical Review Materials, 2017, vol. 1, no. 4, p. 043803

We discuss a parameter-free and computationally efficient ab initio simulation approach for moderately and strongly correlated materials, the multitier self-consistent GW+EDMFT method. This scheme treats different degrees of freedom, such as high- energy and low-energy bands, or local and nonlocal interactions, within appropriate levels of approximation, and provides a fully self-consistent...

Université de Fribourg

Ultrafast electronic band gap control in an excitonic insulator

Mor, Selene ; Herzog, Marc ; Golež, Denis ; Werner, Philipp ; Eckstein, Martin ; Katayama, Naoyuki ; Nohara, Minoru ; Takagi, Hide ; Mizokawa, Takashi ; Monney, Claude ; Stähler, Julia

In: Physical Review Letters, 2017, vol. 119, no. 8, p. 086401

We report on the nonequilibrium dynamics of the electronic structure of the layered semiconductor Ta2NiSe5 investigated by time- and angle-resolved photoelectron spectroscopy. We show that below the critical excitation density of FC=0.2 mJ cm−2, the band gap narrows transiently, while it is enhanced above FC. Hartree-Fock calculations reveal that this effect can be explained by the presence...

Université de Fribourg

Tracing the nonequilibrium topological state of Chern insulators

Schüler, Michael ; Werner, Philipp

In: Physical Review B, 2017, vol. 96, no. 15, p. 155122

Chern insulators exhibit fascinating properties, which originate from the topologically nontrivial state characterized by the Chern number. How these properties change if the system is quenched between topologically distinct phases is, however, not fully understood. In this paper, we investigate the quench dynamics of the prototypical massive Dirac model for topological insulators in two...

Université de Fribourg

Magnetic moment evolution and spin freezing in doped BaFe 2 As 2

Pelliciari, Jonathan ; Huang, Yaobo ; Ishii, Kenji ; Zhang, Chenglin ; Dai, Pengcheng ; Chen, Gen Fu ; Xing, Lingyi ; Wang, Xiancheng ; Jin, Changqing ; Ding, Hong ; Werner, Philipp ; Schmitt, Thorsten

In: Scientific Reports, 2017, vol. 7, no. 1, p. 8003

Fe-K β X-ray emission spectroscopy measurements reveal an asymmetric doping dependence of the magnetic moments μbare in electron- and hole-doped BaFe2As2. At low temperature, μbare is nearly constant in hole-doped samples, whereas it decreases upon electron doping. Increasing temperature substantially enhances μbare in the hole-doped region, which is naturally explained by the...

Université de Fribourg

Hund’s coupling driven photocarrier relaxation in the two-band Mott insulator

Strand, Hugo U. R. ; Golež, Denis ; Eckstein, Martin ; Werner, Philipp

In: Physical Review B, 2017, vol. 96, no. 16, p. 165104

We study the relaxation dynamics of photocarriers in the paramagnetic Mott insulating phase of the half-filled two-band Hubbard model. Using nonequilibrium dynamical mean-field theory, we excite charge carriers across the Mott gap by a short hopping modulation, and simulate the evolution of the photodoped population within the Hubbard bands. We observe an ultrafast charge-carrier relaxation...

Université de Fribourg

Anisotropic Harper-Hofstadter-Mott model: Competition between condensation and magnetic fields

Hügel, Dario ; Strand, Hugo U. R. ; Werner, Philipp ; Pollet, Lode

In: Physical Review B, 2017, vol. 96, no. 5, p. 054431

We derive the reciprocal cluster mean-field method to study the strongly interacting bosonic Harper-Hofstadter-Mott model. The system exhibits a rich phase diagram featuring band insulating, striped superfluid, and supersolid phases. Furthermore, for finite hopping anisotropy, we observe gapless uncondensed liquid phases at integer fillings, which are analyzed by exact diagonalization. The...

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...