Simulations of strongly-correlated electron systems with coulomb and magnetic interactions in the limit of small movement of carriers

Y. Ohta, Kenji Tsutsui, Wataru Koshibae +1 more

An exact-diagonalization technique on small clusters is used to study the ground states and single-particle excitations of the Hubbard model with on-site (U) and nearest-neighbor (V) Coulombic repulsive interactions. It is shown that the long-range charge-density-wave state realized in a half-filled two-dimensional square lattice for 4V\ensuremath{\gtrsim}U persists up to quarter filling, and that the doped carriers form a small Fermi surface that encloses an area corresponding to the number of doped carriers rather than the total number of electrons involved in the system. The present result offers a well-defined counterexample in the discussion of the Fermi-surface dimensions of strongly correlated electron systems, and may provide a complementary understanding of the large Fermi surface believed to exist in the ordinary Hubbard model.

R. D. Sedgewick

Alexander S. Mayorov, Ping Wang, Xiaokai Yue +16 more

Graphene enables precise carrier-density control via gating, making it an ideal platform for studying electronic interactions. However, sample inhomogeneities often limit access to the low-density regimes where these interactions dominate. Enhancing carrier mobility is therefore crucial for exploring fundamental properties and developing device applications. Here, we demonstrate a significant reduction in external inhomogeneity using a double-layer graphene architecture separated by an ultra-thin hexagonal boron nitride layer. Mutual screening between the layers reduces scattering from random Coulomb potentials, resulting in a quantum mobility exceeding. Shubnikov de-Haas oscillations emerge at magnetic fields below 1 mT, while integer quantum Hall features are observed at 0.002T. Furthermore, we identify a fractional quantum Hall plateau at a filling factor of at 2T. These results demonstrate the platform's suitability for investigating strongly correlated electronic phases in graphene-based heterostructures.

S. Zhang, E. C. Allman

Enrico Arrigoni, Ari Harju, Werner R. Hanke +2 more

We study the competition between long- and short-range interactions among charge carriers in strongly-correlated electronic systems employing a method which combines the density-matrix renormalization-group technique with a self-consistent treatment of the long-range interactions. We apply the method to an extended $t\ensuremath{-}J$ model which exhibits ``stripe'' order. The Coulomb interactions, while not destroying stripes, induce large transverse stripe fluctuations with associated charge delocalization. This leads to a substantial Coulomb-repulsion-induced enhancement of long-range superconducting pair-field correlations.

Qing Feng Zhong