Exact diagonalization study for nanographene: Modulation of charge and spin, magnetic phase diagram, and thermodynamics
Abstract
We investigate the many-body-instability-driven electronic, magnetic, and thermodynamic properties of graphene nanoflakes described by an extended Hubbard model using exact diagonalization. Our exact results lead to a complete magnetic phase diagram in n-V space, where n is the filling and V is the nonlocal Coulomb interaction. The phase diagram is found to consist of reentrant phases with net magnetic moment, separated by those with zero magnetic moment. The interplay of local and nonlocal Coulomb interaction, geometry, and filling gives rise to complex magnetic phases with coexisting antiferromagnetic and ferromagnetic correlations, of both short-range and long-range nature. A small change in temperature or in the strength of the nonlocal Coulomb interaction is found to drive the change in the magnetic state. The low-temperature thermodynamic behavior, driven by the crossover of eigenstates of contrasting magnetic characters, is signaled by a sharp peak in the specific heat.
- Publication:
-
Physical Review B
- Pub Date:
- October 2014
- DOI:
- 10.1103/PhysRevB.90.155433
- Bibcode:
- 2014PhRvB..90o5433C
- Keywords:
-
- 75.75.-c;
- 73.22.-f;
- 71.10.Fd;
- 75.10.Jm;
- Electronic structure of nanoscale materials: clusters nanoparticles nanotubes and nanocrystals;
- Lattice fermion models;
- Quantized spin models