Quantum phases of a frustrated four-leg spin tube

TL;DR

This paper investigates the complex quantum phase diagram of a frustrated four-leg spin tube, revealing multiple gapped phases and phase transitions using diverse computational methods, and highlighting quantum effects on classical behaviors.

Contribution

It provides the first comprehensive analysis of the frustrated four-leg spin tube's ground states, identifying new gapped phases and characterizing phase transitions with multiple techniques.

Findings

Identification of several gapped ground states including plaquette and incommensurate phases

Discovery of weak first-order transitions between phases

Observation of a deconfinement crossover from magnons to spinons at large leg exchange

Abstract

We study the ground state phase diagram of a frustrated spin-1/2 four-leg tube. Using a variety of complementary techniques, namely density matrix renormalization group, exact diagonalization, Schwinger boson mean field theory, quantum Monte-Carlo and series expansion, we explore the parameter space of this model in the regime of all-antiferromagnetic exchange. In contrast to unfrustrated four-leg tubes we uncover a rich phase diagram. Apart from the Luttinger liquid fixed point in the limit of decoupled legs, this comprises several gapped ground states, namely a plaquette, an incommensurate, and an antiferromagnetic quasi spin-2 chain phase. The transitions between these phases are analyzed in terms of total energy and static structure factor calculations and are found to be of (weak) first order. Despite the absence of long range order in the quantum case, remarkable similarities to the classical phase diagram are uncovered, with the exception of the icommensurate regime, which is strongly renormalized by quantum fluctuations. In the limit of large leg exchange the tube exhibits a deconfinement cross-over from gapped magnon like excitations to spinons.