arXiv subjects

A. E. Feiguin

Publications and source records attributed to A. E. Feiguin.

43 records · Page 3Linked to original sources

arXiv2006

Cooper-pair transport through a Hubbard chain sandwiched between two superconductors: Density matrix renormalization group calculations

We present a numerical approach to study the coherent transport of Cooper pairs through a Hubbard chain, and study the role of the contacts in achieving perfect Andreev reflection. We calculate the pair transport using the Density Matrix Renormalization Group by measuring the response of the system to quantum pair fields with complex phases on the two ends of an open system. This approach gives an effective superfluid weight which is in close agreement with the Bethe Ansatz results for the superfluid weight for closed Hubbard rings.

cond-mat.str-el↗

arXiv2006

Universal emergence of the one-third plateau in the magnetization process of frustrated quantum spin chains

We present a numerical study of the magnetization process of frustrated quantum spin-S chains with S=1, 3/2, 2 as well as the classical limit. Using the exact diagonalization and density-matrix renormalization techniques, we provide evidence that a plateau at one third of the saturation magnetization exists in the magnetization curve of frustrated spin-S chains with S>1/2. Similar to the case of S=1/2, this plateau state breaks the translational symmetry of the Hamiltonian and realizes an up-up-down pattern in the spin component parallel to the external field. Our study further shows that this plateau exists both in the cases of an isotropic exchange and in the easy-axis regime for spin-S=1, 3/2, and 2, but is absent in classical frustrated spin chains with isotropic interactions. We discuss the magnetic phase diagram of frustrated spin-1 and spin-3/2 chains as well as other emergent features of the magnetization process such as kink singularities, jumps, and even-odd effects. A quantitative comparison of the one-third plateau in the easy-axis regime between spin-1 and spin-3/2 chains on the one hand and the classical frustrated chain on the other hand indicates that the critical frustration and the phase boundaries of this state rapidly approach the classical result as the spin S increases.

cond-mat.str-el↗

arXiv2006

Applying Adaptive Time-Dependent DMRG to Calculate the Conductance of Strongly Correlated Nanostructures

A procedure based on the recently developed ``adaptive'' time-dependent density-matrix-renormalization-group (DMRG) technique is presented to calculate the zero temperature conductance of nanostructures, such as a quantum dots (QD's) or molecular conductors, when represented by a small number of active levels. The leads are modeled using non-interacting tight-binding Hamiltonians. The ground state at time zero is calculated at zero bias. Then, a small bias is applied between the two leads, the wave-function is DMRG evolved in time, and currents are measured as a function of time. Typically, the current is expected to present periodicities over long times, involving intermediate well-defined plateaus that resemble steady states. The conductance can be obtained from those steady-state-like currents. To test this approach, several cases of interacting and non-interacting systems have been studied. Our results show excellent agreement with exact results in the non-interacting case. More importantly, the technique also reproduces quantitatively well-established results for the conductance and local density-of-states in both the cases of one and two coupled interacting QD's. The technique also works at finite bias voltages, and it can be extended to include interactions in the leads.

cond-mat.str-el↗

arXiv2005

Finite Temperature Density Matrix Renormalization using an enlarged Hilbert space

We apply a generalization of the time-dependent DMRG to study finite temperature properties of several quantum spin chains, including the frustrated $J_1-J_2$ model. We discuss several practical issues with the method, including use of quantum numbers and finite size effects. We compare with transfer-matrix DMRG, finding that both methods produce excellent results.

cond-mat.str-el↗

arXiv2003

Spectral Function in Mott Insulating Surfaces

We show theoretically the fingerprints of short-range spiral magnetic correlations in the photoemission spectra of the Mott insulating ground states realized in the triangular silicon surfaces K/Si(111)-B and SiC(0001). The calculated spectra present low energy features of magnetic origin with a reduced dispersion ~10-40 meV compared with the center-of-mass spectra bandwidth ~0.2-0:3 eV. Remarkably, we find that the quasiparticle signal survives only around the magnetic Goldstone modes. Our findings would position these silicon surfaces as new candidates to investigate non-conventional quasiparticle excitations.

cond-mat.str-el↗

arXiv1999

Influence of finite Hund rules and charge transfer on properties of Haldane systems

We consider the Kondo-Hubbard model with ferromagnetic exchange coupling $% J_{H}$, showing that it is an approximate effective model for late transition metal-O linear systems. We study the dependence of the charge and spin gaps $Δ_{C}$, $Δ_{S}$, and several spin-spin correlation functions, including the hidden order parameter $Z(π)$, as functions of $J_{H}/t$ and $U/t$, by numerical diagonalization of finite systems. Except for $Z(π)$, all properties converge slowly to the strong-coupling limit. When $J_{H}/t\sim 2$ and $U/t\sim 7$ (the effective parameters that we obtain for Y_2BaNiO_5), $Δ_{S}$ is roughly half of the value expected from a strong-coupling expansion.

cond-mat↗

arXiv1997

Numerical Study of the Incommensurate Phase in Spin-Peierls Systems

We analyze several properties of the lattice solitons in the incommensurate phase of spin-Peierls systems using exact diagonalization and quantum Monte Carlo. These systems are modelled by an antiferromagnetic Heisenberg chain with nearest and next-nearest neighbor interactions coupled to the lattice in the adiabatic approximation. Several relations among features of the solitons and magnetic properties of the system have been determined and compared with analytical predictions. We have studied in particular the relation between the soliton width and the spin-Peierls gap. Although this relation has the form predicted by bosonized field theories, we have found some important quantitative differences which could be relevant to describe experimental studies of spin-Peierls materials.

cond-mat↗