arXiv subjects

Susumu Yamada

Publications and source records attributed to Susumu Yamada.

5 recordsLinked to original sources

arXiv2016

Emergence of $η$-pairing ground-state in population-imbalanced attractive Fermi-gases filling $p$ orbitals on 1-D optical lattice

We explore the ground states in population-imbalanced attractive 1-D fermionic optical lattice filling $p$ orbitals over the lowest $s$ one by using the density-matrix-renormalization-group (DMRG) method. The DMRG calculations find the occurrence of spatially non-uniform off-diagonal long-range order. In contrast to Fulde-Ferrel Larkin-Ovchinikov pair as observed in the single-band Hubbard model. The spatial oscillation period of the pair correlation function is widely fixed to be $π$ irrespective of the mismatch between spin-split Fermi surfaces. The ground-state $π$ order corresponds to $η$-pair condensate predicted by Yang [Phys. Rev. Lett. \textbf{63}, 2144 (1989)]. Taking account of the effects of harmonic traps, we confirm that the $η$-pair state distinctly emerges at the center of the trap potential surrounded by perfectly-polarized states even in the trapped cases.

cond-mat.supr-con↗

arXiv2016

Superconductivity in repulsively interacting fermions on a diamond chain: flat-band induced pairing

To explore whether a flat-band system can accommodate superconductivity, we consider repulsively interacting fermions on the diamond chain, a simplest quasi-one-dimensional system that contains a flat band. Exact diagonalization and the density-matrix renormalization group (DMRG) are used to show that we have a significant binding energy of a Cooper pair with a long-tailed pair-pair correlation in real space when the total band filling is slightly below $1/3$, where the dispersive band interacts with the flat band that is empty but close to $E_F$. Pairs selectively formed across the outer sites of the diamond chain are responsible for the pairing correlation. At exactly $1/3$-filling an insulating phase emerges, where the entanglement spectrum indicates the particles on the outer sites are highly entangled and topological. These come from a peculiarity of the flat band in which "Wannier orbits" are not orthogonalizable.

cond-mat.supr-con↗

arXiv2014

Quantum phases in $p$-orbital degenerated attractive 1D fermionic optical lattices

We examine quantum phases emerged by double degeneracy of $p$-orbital bands in attractive atomic Fermi gases loaded on a 1D optical lattice. Our numerical simulations by the density-matrix renormalization group predict the emergence of a state with a charge excitation gap, the Haldane insulator phase. A mapping onto an effective spin-$1$ model reveals its physical origin. Moreover, we show that population imbalance leads to richer diversity of the quantum phases, including a phase-separated polarized state. Finally, we study the effects of harmonic trap potential in this 1D chain.

cond-mat.quant-gas↗

arXiv2012

Nontrivial Haldane phase of an atomic two-component Fermi gas trapped in a 1d optical lattice

We propose how to create a non-trivial Haldane phase in atomic two-component Fermi-gas loaded on one-dimensional (1-D) optical lattice with trap potential. The Haldane phase is naturally formed on $p$-band Mott core in a wide range of the strong on-site repulsive interaction. The present proposal is composed of two steps, one of which is theoretical derivation of an effective 1-D S=1 interacting-chain model from the original tight-binding Hamiltonian handling the two $p$-orbitals, and the other of which is numerical demonstration employing the density-matrix renormalization-group for the formation of the Haldane phase on $p$-band Mott core and its associated features in the original tight-binding model with the harmonic trap potential.

cond-mat.quant-gas↗

arXiv2011

Ground-state properties of the one-dimensional attractive Hubbard model with confinement: a comparative study

We revisit the one-dimensional attractive Hubbard model by using the Bethe-ansatz based density-functional theory and density-matrix renormalization method. The ground-state properties of this model are discussed in details for different fillings and different confining conditions in weak-to-intermediate coupling regime. We investigate the ground-state energy, energy gap, and pair-binding energy and compare them with those calculated from the canonical Bardeen-Cooper-Schrieffer approximation. We find that the Bethe-ansatz based density-functional theory is computationally easy and yields an accurate description of the ground-state properties for weak-to-intermediate interaction strength, different fillings, and confinements. In order to characterize the quantum phase transition in the presence of a harmonic confinement, we calculate the thermodynamic stiffness, the density-functional fidelity, and fidelity susceptibility, respectively. It is shown that with the increase of the number of particles or attractive interaction strength, the system can be driven from the Luther-Emery-type phase to the composite phase of Luther-Emery-like in the wings and insulating-like in the center.

cond-mat.quant-gas↗