# Field-induced double dome and Bose-Einstein condensation in the crossing quantum spin chain system AgVOAsO4

## TL;DR

This study investigates AgVOAsO4, revealing its quantum spin chain nature, a spin gap, and a complex magnetic phase diagram with two field-induced ordered phases suggestive of multi-Q Bose-Einstein condensation, indicating exotic vortex phases.

## Contribution

It provides the first direct measurements of the spin gap and demonstrates a complex, multi-Q BEC phase diagram in AgVOAsO4, a promising candidate for exotic vortex phases.

## Key findings

- AgVOAsO4 is a S=1/2 alternating spin chain with a measurable spin gap.
- The phase diagram shows two distinct field-induced magnetic orders.
- Evidence suggests the presence of multi-Q Bose-Einstein condensation.

## Abstract

We present inelastic neutron scattering data on the quantum paramagnet AgVOAsO4 that establish the system is a S=1/2 alternating spin chain compound and provide a direct measurement of the spin gap. We also present experimental evidence for two different types of field-induced magnetic order between mu_0H_c1 = 8.4T and mu_0H_c2 = 48.9T, which may be related to Bose-Einstein condensation (BEC) of triplons. Thermodynamic measurements in magnetic fields up to 60T and temperatures down to 0.1K reveal a H-T phase diagram consisting of a dome encapsulating two ordered phases with maximum ordering temperatures of 3.8K and 5.3K respectively. This complex phase diagram is not expected for a single-Q BEC system and therefore establishes AgVOAsO4 as a promising multi-Q BEC candidate capable of hosting exotic vortex phases.