Experimental Studies of Dzyaloshinskii-Moriya Interaction in Quantum Spin Systems: High-frequency High-field Electron Spin Resonance (ESR) Measurements

In this review, the importance of the Dzyaloshinskii-Moriya Interaction (DMI) to the magnetic properties of quantum spin systems is discussed mainly focusing on the determination of or understanding the role of DMI extracted from highfrequency high-field electron spin resonance (ESR) measurements. This review includes the ESR theories of the S = 1=2 one-dimensional (1D) antiferromagnet with the staggered field (Oshikawa-Affleck theory) and with the uniform DMI, and several related experimental results are shown. Then, the proposed mechanisms of the singlet-triplet transition in quantum spin systems together with the ESR selection rules are introduced in connection with various experimental results. Finally, the role of DMI in the ground state of kagome lattice antiferromagnets and the honeycomb lattice antiferromagnet is discussed with some experimental results.