Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe

TT: Fachverband Tiefe Temperaturen

TT 4: Graphene, 2D and Twisted Materials

TT 4.5: Vortrag

Montag, 9. März 2026, 10:30–10:45, HSZ/0105

Charge neutrality phase diagram of twisted bilayer graphene from sign-free Monte Carlo simulations — •Johannes S. Hofmann¹, Jong Yeon Lee², Patrick Ledwith³, Eslam Khalaf⁴, Ashvin Vishwanath⁴, and Erez Berg⁵ — ¹Max Planck Institute for the physics of complex systems, Dresden, Germany — ²University of Illinois at Urbana-Champaign, Urbana, USA — ³Massachusetts Institute of Technology, Cambridge, USA — ⁴Harvard University, Cambridge, USA — ⁵Weizmann Institute of Science, Rehovot, Israel

We study the phase diagram of twisted bilayer graphene at charge neutrality as a function of twist angle θ, uniaxial heterostrain ε, and temperature T using sign-problem-free quantum Monte Carlo simulations. At T=0 and zero strain, we find a continuous transition from a Dirac semimetal to a gapped Kramers inter-valley coherent (KIVC) phase as θ decreases toward the magic angle. With finite strain, the KIVC phase undergoes a further continuous transition at smaller θ into an anisotropic semimetal with gapless excitations near the center of the moiré Brillouin zone. In the KIVC regime, the entropy rises sharply with temperature and plateaus at 15 K T 40 K near the value expected from a Mott-like regime of localized electrons with nearly uncorrelated spin, valley, and orbital degrees of freedom. The spectral function evolves continuously with θ: at low T, a gap opens at the K points and the minimal gap shifts to Γ as θ decreases; at intermediate T, the spectral function smoothly interpolates between a Dirac semimetal spectrum with coherent K-point quasiparticles and a spectrum with gapless Γ-centered quasiparticles near the magic angle.

Keywords: Twisted bilayer graphene; charge neutrality; Quantum Monte Carlo; Phase diagram