arXiv subjects

Gökhan Öztarhan

Publications and source records attributed to Gökhan Öztarhan.

3 recordsLinked to original sources

arXiv2025

Nagaoka ferromagnetism in semiconductor artificial graphene

We present the emergence of Nagaoka ferromagnetism in semiconductor-based artificial graphene with realistic Coulomb interaction using high-precision variational and diffusion Monte Carlo methods, complemented by exact diagonalization calculations of the generalized Hubbard model. We analyze models of armchair hexagonal geometries nanopatterned on GaAs quantum wells. Our results reveal a distinct magnetic phase transition driven by the absence/addition of a single electron at half-filling. This form of itinerant magnetism predicted rigorously for Hubbard model remained unascertained in large scale realistic systems. We demonstrate that Coulomb scattering terms play a crucial role in stabilizing Nagaoka ferromagnetism, enabling the observation of the phase transition for system parameters near $U/t \approx 60$.

cond-mat.mes-hall↗

arXiv2025

Quantum Monte Carlo study of artificial triangular graphene quantum dots

We investigate the magnetic phases of triangular graphene quantum dots (TGQDs) with zigzag edges using variational and quantum Monte Carlo methods. These systems serve as quantum simulators for bipartite lattices with broken sublattice symmetry, providing a platform to study the extended Hubbard model's emergent magnetic phenomena, including Lieb's magnetism at half-filling, edge depolarization upon single-electron addition, and Nagaoka ferromagnetism. Our non-perturbative quantum Monte Carlo simulations, performed for lattices of up to 61 sites, reveal that TGQDs transition from metallic to insulating regimes as a function of site radius size, while retaining edge-polarized ground states at half-filling. Notably, edge depolarization occurs upon single-electron doping in both metallic and insulating phases, contrasting with the Nagaoka ferromagnetism observed in hexagonal armchair geometries.

cond-mat.mes-hall↗

arXiv2023

Quantum Monte Carlo Study of Semiconductor Artificial Graphene Nanostructures

Semiconductor artificial graphene nanostructures where Hubbard model parameter $U/t$ can be of the order of 100, provide a highly controllable platform to study strongly correlated quantum many-particle phases. We use accurate variational and diffusion Monte Carlo methods to demonstrate a transition from antiferromagnetic to metallic phases for experimentally accessible lattice constant $a=50$ nm in terms of lattice site radius $ρ$, for finite sized artificial honeycomb structures nanopatterned on GaAs quantum wells containing up to 114 electrons. By analysing spin-spin correlation functions for hexagonal flakes with armchair edges and triangular flakes with zigzag edges, we show that edge type, geometry and charge nonuniformity affect the steepness and the crossover $ρ$ value of the phase transition. For triangular structures, the metal-insulator transition is accompanied with a smoother edge polarization transition.

cond-mat.mes-hall↗