Spiral magnetic order and pressure-induced superconductivity in transition metal compounds

Yishu Wang,Yejun Feng,J L Luo,T F Rosenbaum,J.-G Cheng,W Wu

doi:10.1038/ncomms13037

Abstract

Magnetic and superconducting ground states can compete, cooperate and coexist. MnP provides a compelling and potentially generalizable example of a material where superconductivity and magnetism may be intertwined. Using a synchrotron-based non-resonant X-ray magnetic diffraction technique, we reveal a spiral spin order in MnP and trace its pressure evolution towards superconducting order via measurements in a diamond anvil cell. Judging from the magnetostriction, ordered moments vanish at the quantum phase transition as pressure increases the electron kinetic energy. Spins remain local in the disordered phase, and the promotion of superconductivity is likely to emerge from an enhanced coupling to residual spiral spin fluctuations and their concomitant suppression of phonon-mediated superconductivity. As the pitch of the spiral order varies across the 3d transition metal compounds in the MnP family, the magnetic ground state switches between antiferromagnet and ferromagnet, providing an additional tuning parameter in probing spin-fluctuation-induced superconductivity.

Highlights

Magnetic and superconducting ground states can compete, cooperate and coexist
Magnetism and superconductivity often compete for preeminence as a material’s ground state, but in the right circumstances the fluctuating remains of magnetic order can induce superconducting pairing
We point out that for a helical arrangement of localized spins, a variable spiral period could provide a unique tuning process from ferromagnetic to antiferromagnetic ground state in the long and short wavelength limits, respectively. Such chemical or pressure adjustable helical order naturally provides the possibility for continuous tuning between ferromagnetically and antiferromagnetically mediated superconductivity

Summary

Introduction

Magnetic and superconducting ground states can compete, cooperate and coexist. MnP provides a compelling and potentially generalizable example of a material where superconductivity and magnetism may be intertwined. As the pitch of the spiral order varies across the 3d transition metal compounds in the MnP family, the magnetic ground state switches between antiferromagnet and ferromagnet, providing an additional tuning parameter in probing spin-fluctuation-induced superconductivity. We point out that for a helical arrangement of localized spins, a variable spiral period could provide a unique tuning process from ferromagnetic to antiferromagnetic ground state in the long and short wavelength limits, respectively Such chemical or pressure adjustable helical order naturally provides the possibility for continuous tuning between ferromagnetically and antiferromagnetically mediated superconductivity. This sensitive probe, suitable for 0.0002 mm[3] single crystal volumes and diamond anvil cell techniques, directly reveals a reduced moment, incommensurate spin state at high pressure proximate to the superconducting state This new magnetic order is most likely a magnetic helix with a tightened pitch in comparison to that at ambient pressure where superconductivity is absent. The extant data correlating magnetic pitch length and superconductivity is sparse but suggestive in the (V/Cr/Mn/Fe/Co/Ni)(P/As/Sb) family[3,4,6,7,8,9,10,11,12,13,14,15,16,17,18,19] and, as discussed in detail below, we suggest this family of spiral magnets as a new venue for tunable, spin-fluctuationmediated superconductivity

Methods

Results

Conclusion