# Dresden 2017 – wissenschaftliches Programm

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# TT: Fachverband Tiefe Temperaturen

## TT 35: Low-Dimensional Systems: 2D - Theory

### TT 35.5: Vortrag

### Dienstag, 21. März 2017, 15:00–15:15, HSZ 304

**Spontaneous particle-hole symmetry breaking of correlated fermions on the Lieb lattice** — •Martin Bercx^{1}, Johannes S. Hofmann^{1}, Fakher F. Assaad^{1}, and Thomas C. Lang^{1,2} — ^{1}Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Germany — ^{2}Institute for Theoretical Physics, University of Innsbruck, Austria

We study spinless fermions with nearest-neighbor repulsive interactions (*t*-*V* model) on the two-dimensional three-band Lieb lattice. At half-filling, the free electronic band structure consists of a flat band at zero energy and a single cone with linear dispersion. The flat band is expected to be unstable upon inclusion of electronic correlations, and a natural channel is charge order. However, due to the three-orbital unit cell, commensurate charge order implies an imbalance of electron and hole densities and therefore doping away from half-filling. Our numerical results show that below a finite-temperature Ising transition a charge density wave with one electron and two holes per unit cell and its partner under particle-hole transformation are spontaneously generated. Our calculations are based on recent advances in auxiliary-field and continuous-time quantum Monte Carlo simulations that allow sign-free simulations of spinless fermions at half-filling. It is argued that particle-hole symmetry breaking provides a route to access levels of finite doping, without introducing a sign problem.