Johannes Reuther

---

The investigation of spin liquids is a fascinating field in condensed
matter physics that is increasingly motivated by experiments. Exhaustive
classifications of spin liquids have been carried out in several systems,
particularly when full SU(2) spin-rotation symmetry is present. Systematic
studies that explore strongly spin-orbit-coupled magnetic compounds (for
which there are many experimental examples) are, however, relatively
scarce. We report on a classification of Z_2 spin liquids on the square
lattice when SU(2) spin symmetry is maximally lifted. Using projective
symmetry group methods, we find that, surprisingly, the lifting of spin
symmetry yields vastly more spin liquid states compared to SU(2)-invariant
systems. A generic feature of the SU(2)-broken case is that the spinons
naturally undergo p+ip pairing; consequently, many of these Z_2 spin
liquids feature a topologically nontrivial spinon band structure
supporting gapless Majorana edge states. These boundary modes are often
protected by a combination of time reversal and lattice symmetries and
hence resemble recently proposed topological crystalline superconductors.

---

FU Berlin
Seminar Room TP 0.03
Contact: Simon Trebst