FY 2023 Research & Annual Reports
The Theory of Quantum Matter (TQM) Unit carries out research into a wide range of problems in condensed matter and statistical physics, with an emphasis on the novel phases of matter found in frustrated magnets. Other topics of current interest include the application of machine learning to problems in physics, and algorithmic aspects of quantum computing.
This work is described in the Annual Reports listed in the menu on the left side of this page. These provide details of all of the research carried out by the TQM Unit, publications and presentations by Unit members, outreach activity, and seminars given by visitors to TQM in OIST. Reports are organised by the Japanese financial year, with FY2022 running from April 1st 2022 until March 31st 2023.
Recent research results, and preprints, are described below.
Spin nematics meet spin liquids: Exotic quantum phases in the spin-1 bilinear-biquadratic model with Kitaev interactions
New discoveries are often made on the border between different disciplines. One major discipline in solid state physics is dedicated to quantum spin liquids, an unconventional state of matter accompanied by emergent gauge fields, topological order, and fractionalized excitations. Another concept is that of spin nematics, a magnetically ordered state dominated by quadrupole moments, which breaks spin-rotation symmetry by selecting an axis, while not choosing a particular direction. Usually seen as two separate areas of study, we are interested in combining those two disciplines, by asking the question: “What happens, when a spin nematic and a spin liquid meet?”
To answer this question, we showed that the S=1 Kitaev model under the influence of bilinear-biquadratic interactions hosts many unconventional ordered and disordered phases. We obtain a comprehensive phase diagram including chiral ordered and quadrupolar ordered phases, in addition to already known ferro, antiferro, zigzag and stripy phases. Intriguingly, we find that the competition between Kitaev and positive biquadratic interactions also promotes a noncoplanar finite-temperature spin liquid state, with macroscopic degeneracy and finite scalar chirality
Our results show that the competition between spin liquid and spin nematic phases is a promising way to explore new magnetic states of matter.
Figure: Ground state phase diagram of the S=1 Kitaev model under the influence of bilinear-biquadratic interactions hosts many ordered and disordered phases, such as ferromagnetic (FM), antiferromagnetic (AFM), zigzag, and stripy orders, and spin-nematic ferroquadrupolar (FQ) order. The competition between chiral magnetic order, the Kitaev spin liquid (SL), and quadrupolar semi-order (SO) gives rise to unconventional phases, such as the twisted conical (TC), quasi-one-dimensional (q1D) coplanar, and noncoplanar (NC) ordered phases.
This work was published as "Spin nematics meet spin liquids: Exotic quantum phases in the spin-1 bilinear-biquadratic model with Kitaev interactions", R. Pohle, N. Shannon, Y. Motome, Phys. Rev. B 107, L140403 (2023).