This book features the nature of spin dimer systems, a class of gapped quantum magnets. Spin dimer systems host prototypical quantum phase transitions (QPTs) driven by applied magnetic field and pressure, as well as profound magnetic excitations identical to Nambu–Goldstone and Higgs modes. The book focuses on the physics of QPTs, their criticality, and magnetic excitations in specific materials, and comprehensively reviews up-to-date research in this field.

The book begins with fundamental reviews of spin dimer systems, their excitations, and QPTs, and subsequently delves into individual advanced topics in materials. All contributed chapters feature topical reviews by recognized experts in the field. The book is a valuable resource for graduate students and non-expert readers interested in but not necessarily familiar with the subject. The cutting-edge content enables readers to quickly catch up with the latest research in this exciting area.

Hidekazu Tanaka is a specially appointed professor at the Center for Entrepreneurship Education, Institute of Science Tokyo. His work broadly involves experiments on insulating magnetic materials, ranging from sample preparation to measurements of specific heat, magnetization, electron spin resonance, and neutron scattering. Receiving his Doctor of Science from Tokyo Institute of Technology in 1986, he was an associate professor at Nagoya University and Sophia University and joined the Department of Physics at Tokyo Institute of Technology (currently Institute of Science Tokyo) as an associate professor in 1998. In 2002, he moved to the Research Center for Low Temperature Physics as a professor and returned to the Department of Physics in 2006. He retired in 2022, having reached mandatory retirement age. Professor Tanaka was honored with the Society of Electron Spin Science and Technology (SEST) Award in 2018 and with the Japan Society for Neutron Science Award in 2024.

Masashige Matsumoto is a professor in the Department of Physics at Shizuoka University. His field of research is theoretical condensed matter physics, with particular emphasis on superconductivity and magnetism. His work includes theoretical studies of quantum condensed matter phenomena, including unconventional superconductivity, the Kondo effect, quantum phase transitions in spin dimer systems, and magnetoelectric effects in quantum magnetic materials. He received his Ph.D. in Science from the Tokyo Institute of Technology in 1996. Having joined the Department of Physics at Shizuoka University as a research associate in 1995, Dr. Matsumoto was appointed associate professor in 2005 and became a full professor in 2011. From 2001 to 2003, he was supported by a JSPS Overseas Research Fellowship and worked at the Institute for Theoretical Physics, ETH Zurich. In 2001, he received the 6th Outstanding Paper Award of the Physical Society of Japan.