P-wave magnets

Abstract: The p-wave Cooper-pairing instability in superfluid $^{3}$He, characterized by a parity-breaking excitation gap, is regarded as one of the most rich and complex phenomena in physics. The possibility of a counterpart unconventional p-wave ordering of interacting fermions, in which a Fermi surface spontaneously breaks the parity symmetry, has been an open problem for many decades. Here we identify the realization of the counterpart of p-wave superfluidity in magnetism. We demonstrate a strong parity-breaking and anisotropic symmetry lowering of spin-polarized and time-reversal symmetric Fermi surfaces in a representative p-wave magnet CeNiAsO. As a direct experimental signature we predict a large spontaneous anisotropy of the resistivity. Abundant and robust realizations of the unconventional p-wave magnetism can be identified from suitable non-relativistic crystal-lattice and spin symmetries, without requiring strong correlations and extreme external conditions. This opens new prospects in fields ranging from topological phenomena to spintronics.

• The paper reveals unconventional p-wave magnetic order in CeNiAsO, establishing a parity-breaking phase with predicted anisotropic resistivity.
• It employs Fermi liquid theory to model symmetry lowering in spin-polarized Fermi surfaces under non-relativistic crystal symmetries.
• The findings open pathways for exploring p-wave magnetism in diverse systems with potential applications in spintronics and quantum materials.

Overview of "P-wave Magnets"

The paper "P-wave Magnets" by Hellenes et al. addresses an enduring problem in condensed matter physics: the realization of unconventional p-wave ordering. The authors explore the potential of p-wave ordering in magnetism as a counterpart to p-wave superfluidity observed in $^3$He. The study identifies and analytically describes the p-wave magnetic phase, focusing on a candidate material, CeNiAsO, and proposes measurable characteristics stemming from this magnetic order.

Key Concepts and Results

1. Background on p-wave Phenomena:
   • P-wave Cooper pairing in superfluid $^3$He exhibits a parity-breaking excitation gap and is considered a complex and fascinating physical phenomenon.
   • The authors suggest an analogous form of p-wave symmetry breaking in magnetism.
2. Unconventional P-wave Magnetism:
   • The paper introduces unconventional p-wave magnetism through parity-breaking p-wave order in magnets like CeNiAsO.
   • The parity-breaking is accompanied by a symmetry-lowering of spin-polarized and time-reversal symmetric Fermi surfaces.
3. Quantum and Crystal Symmetries:
   • Fermi liquid theory serves as the theoretical backdrop, incorporating non-relativistic crystal-lattice and spin symmetries.
   • The p-wave symmetry in this context involves aligning opposite spins on opposite momenta, inducing anisotropic distortions to the Fermi surfaces.
4. Experimental Evidence and Predictive Model:
   • CeNiAsO is identified experimentally as a p-wave magnet.
   • Spontaneous anisotropy in resistivity is predicted, serving as an experimental signature confirming the unconventional p-wave phase.
5. Theoretical and Practical Implications:
   • By sidestepping the challenge of many-body interaction exact solutions, this work proposes a spin-symmetry-based approach, potentially broadening the types of systems where p-wave magnetism may emerge beyond metals, including insulators and semiconductors.
   • These insights may find applications in fields such as spintronics and topological matter, leveraging the highly anisotropic properties and spin currents anticipated in such systems.

Implications for Future Research

• Materials Discovery: The identification of multiple candidate materials with similar symmetry properties through databases like Magndata suggests a fruitful area for future experimental exploration.
• Technological Applications: Exploiting p-wave magnetism could enable novel devices featuring giant exchange spin splittings and enhanced control over electron spin, which are valuable for advanced spintronic applications.
• Symmetry Analysis and Beyond: The symmetry-driven approach in this paper indicates a potentially underexplored path for discovering unconventional orders in quantum materials, encouraging further theoretical work to unveil similar phenomena in other contexts.

This paper elucidates the unveiled concepts of unconventional p-wave magnetism and its potential implications for condensed matter physics, notably contributing to understanding complex magnetic orders and widening the scope of research and technological advancements in this dynamic field.