Efficient spin accumulation carried by slow relaxons in chiral crystals

Efficient conversion between charge currents and spin signals is crucial for realizing magnet-free spintronic devices. However, the strong spin-orbit coupling that makes this conversion possible also causes rapid spin relaxation. To detect the spin signals, materials with long spin lifetimes, such as graphene, are needed as channels for spin transport. Recent studies have shown that even in systems with strong spin-orbit coupling, long-range spin transport can occur if the system is chiral material, a system lacking both inversion and mirror symmetry [1,2,3].

Here, we show that spin-momentum entanglement at the Fermi surface of chiral tellurium crystals leads to the appearance of slow collective relaxation modes. These modes, called relaxons, resemble the persistent spin helix, a collective spin-wave excitation with extended lifetime observed in quantum wells. The slow relaxons dominate the electrically generated spin and orbital accumulation in tellurium and make it possible to combine a very high 50% conversion efficiency with a long spin lifetime. These results, obtained from the exact solution of the Boltzmann transport equation, show that chiral crystals can be used for highly efficient generation and transmission of spin signals over long distances in spintronic devices.