Detecting fractionalization in quantum spin liquids

Quantum spin liquids (QSLs) are a class of highly-entangled quantum states in magnetic systems that do not exhibit any magnetic order. In lack of sharp observable signatures, it has been a longstanding difficulty to experimentally identify QSLs unambiguously, especially gapped QSLs. In this talk, we show that magnetic impurities can provide a smoking gun, which not only sharply distinguish a QSL from other paramagnetic phases, but can also distinguish different QSLs by distinct responses to magnetic impurities.