Chromium at High Pressures: Weak Coupling and Strong Fluctuations in an Itinerant Antiferromagnet

TL;DR

This study investigates chromium's quantum critical behavior under high pressure, revealing weak coupling and strong fluctuations, and compares pressure-induced and doping-induced phase transitions in itinerant antiferromagnets.

Contribution

It provides direct measurements of spin and charge order parameters under pressure, demonstrating weakly-coupled BCS-like ground state and differences between pressure and doping effects.

Findings

Exponential decrease of diffraction intensities with pressure

Confirmation of harmonic scaling of spin and charge

Evidence of weakly-coupled, BCS-like ground state

Abstract

The spin- and charge-density-wave order parameters of the itinerant antiferromagnet chromium are measured directly with non-resonant x-ray diffraction as the system is driven towards its quantum critical point with high pressure using a diamond anvil cell. The exponential decrease of the spin and charge diffraction intensities with pressure confirms the harmonic scaling of spin and charge, while the evolution of the incommensurate ordering vector provides important insight into the difference between pressure and chemical doping as means of driving quantum phase transitions. Measurement of the charge density wave over more than two orders of magnitude of diffraction intensity provides the clearest demonstration to date of a weakly-coupled, BCS-like ground state. Evidence for the coexistence of this weakly-coupled ground state with high-energy excitations and pseudogap formation above the ordering temperature in chromium, the charge-ordered perovskite manganites, and the blue bronzes, among other such systems, raises fundamental questions about the distinctions between weak and strong coupling.