Spin-gap behaviour in the 2-leg spin-ladder BiCu2PO6

TL;DR

This study investigates the magnetic properties and spin-gap behavior of the BiCu2PO6 compound, revealing strong intra- and inter-ladder couplings and its proximity to quantum criticality through experimental and theoretical analysis.

Contribution

It provides detailed experimental data and theoretical analysis of spin interactions in BiCu2PO6, highlighting its near-critical quantum state and the agreement between experimental and computational results.

Findings

Spin-gap Delta/k_B = 34 K consistent with susceptibility data

Leg coupling J1/k_B ~ 80 K and ratio J2/J1 ~ 0.9

Inter-ladder coupling J2 ~ 0.75J1 indicating proximity to quantum criticality

Abstract

We present magnetic suscceptibility and heat capacity data on a new S=1/2 two-leg spin ladder compound BiCu2PO6. From our susceptibility analysis, we find that the leg coupling J1/k_B is ~ 80 K and the ratio of the rung to leg coupling J2/J1 ~ 0.9. We present the magnetic contribution to the heat capacity of a two-leg ladder. The spin-gap Delta/k_B =3 4 K obtained from the heat capacity agrees very well with that obtained from the magnetic susceptibility. Significant inter-ladder coupling is suggested from the susceptibility analysis. The hopping integrals determined using Nth order muffin tin orbital (NMTO) based downfolding method lead to ratios of various exchange couplings in agreement with our experimental data. Based on our band structure analysis, we find the inter-ladder coupling in the bc-plane J2 to be about 0.75J1 placing the compound presumably close to the quantum critical limit.