Neutron diffraction in a model itinerant metal near a quantum critical point

TL;DR

This study uses neutron diffraction to investigate how spin density wave order in Cr-V alloys evolves near a proposed quantum critical point, revealing persistent and complex magnetic structures rather than simple suppression.

Contribution

It provides detailed experimental evidence of incommensurate spin density waves and multiple Neel temperatures near the QCP in Cr-V alloys, highlighting complex magnetic behavior.

Findings

Neutron diffraction shows continuous suppression of magnetic order with V doping.

Incommensurate SDWs emerge at the QCP, indicating complex nesting.

Electronic structure remains robust, enabling new spin orderings.

Abstract

Neutron diffraction measurements on single crystals of Cr1-xVx (x=0, 0.02, 0.037) show that the ordering moment and the Neel temperature are continuously suppressed as x approaches 0.037, a proposed Quantum Critical Point (QCP). The wave vector Q of the spin density wave (SDW) becomes more incommensurate as x increases in accordance with the two band model. At xc=0.037 we have found temperature dependent, resolution limited elastic scattering at 4 incommensurate wave vectors Q=(1+/-delta_1,2, 0, 0)*2pi/a, which correspond to 2 SDWs with Neel temperatures of 19 K and 300 K. Our neutron diffraction measurements indicate that the electronic structure of Cr is robust, and that tuning Cr to its QCP results not in the suppression of antiferromagnetism, but instead enables new spin ordering due to novel nesting of the Fermi surface of Cr.