Ground-state and spectral properties of an asymmetric Hubbard ladder

TL;DR

This study explores the complex phase diagram of an asymmetric Hubbard ladder, revealing four distinct phases with unique spectral properties, using advanced computational methods to analyze ground-state and spectral characteristics.

Contribution

It provides a comprehensive analysis of the phase diagram of an asymmetric Hubbard ladder, identifying four phases and their spectral signatures using multiple computational techniques.

Findings

Identification of four distinct phases as a function of interaction and hopping.

Different spectral functions for each insulating phase.

Variation in wavenumbers of lowest single-particle excitations across phases.

Abstract

We investigate a ladder system with two inequivalent legs, namely a Hubbard chain and a one-dimensional electron gas. Analytical approximations, the density matrix renormalization group method, and continuous-time quantum Monte Carlo simulations are used to determine ground-state properties, gaps, and spectral functions of this system at half-filling. Evidence for the existence of four different phases as a function of the Hubbard interaction and the rung hopping is presented. First, a Luttinger liquid exists at very weak interchain hopping. Second, a Kondo-Mott insulator with spin and charge gaps induced by an effective rung exchange coupling is found at moderate interchain hopping or strong Hubbard interaction. Third, a spin-gapped paramagnetic Mott insulator with incommensurate excitations and pairing of doped charges is observed at intermediate values of the rung hopping and the interaction. Fourth, the usual correlated band insulator is recovered for large rung hopping. We show that the wavenumbers of the lowest single-particle excitations are different in each insulating phase. In particular, the three gapped phases exhibit markedly different spectral functions. We discuss the relevance of asymmetric two-leg ladder systems as models for atomic wires deposited on a substrate.