Our group and collaborators are dedicated to the understanding of QSL behaviors and the identification of QSLs in experiments. Quantum spin liquids (QSLs) are an exotic phase of matter in some magnetic systems which, unlike conventional magnets, lack long-range magnetic order down to extremely low temperatures due to strong quantum fluctuations that arise from frustrated interactions. QSLs exist beyond the Landau paradigm which is considered to cover all forms of magnetic order, as there is no local order parameter or broken symmetry. While this negative definition captures the essential phenomenology of the novel emergence in quantum magnetism, it turned out to be inadequate to fully characterize the notion of QSLs, so we instead are looking for sharp, affirmative signatures of QSL behavior.
Publications:
Two-magnon bound states in the Kitaev model in a [111] field, S. Pradhan, N. D. Patel, N. Trivedi, Phys. Rev. B 101, 180401(R) (2020).
Magnetic field-induced intermediate quantum spin liquid with a spinon Fermi surface, N. D. Patel, N. Trivedi, Proc. Natl. Acad. Sci (PNAS) 116, 12199 (2019).
Signatures of magnetic-field-driven quantum phase transitions in the entanglement entropy and spin dynamics of the Kitaev honeycomb model, D. C. Ronquillo, A. Vengal, N. Trivedi, Phys. Rev. B 99, 140413(R) (2019).
Fractionalization and Braiding
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Besides the absence of order, QSLs exhibit many unusual properties, such as fractionalized spin excitations (that carry spin 1/2 quantum numbers compared to integer spin excitations of conventional magnets) and a high degree of quantum entanglement. In the search of a QSL, it is important to bear in mind that some subset of the degrees of freedom should look essentially topological, therefore we are looking for fractionalized excitations and emergent gauge fields in quantum frustrated systems. Our main focus is to find sharp observable signatures of fractionalization and braiding statistics of anyons. No experiment has yet observed sharp definite signatures of such fractionalization. We propose using pump-probe non-linear response, in which a sequence of applied magnetic pulses excite anyons that wind around each other and leave distinct fingerprints in the measured signal, providing a smoking gun signature for anyons in quantum spin liquids.
Publications:
Detection of anyon braiding through pump-probe spectroscopy. Yang, X., Buechele, R., & Trivedi, N. arXiv:2503.22792 (2025).
One-Dimensional Magnetism
In contrast to its higher dimensional counterparts, particles in 1D systems are highly affected by quantum fluctuations which prevent the breaking of continuous symmetries due to the tight constraint in space; they are much more likely to exhibit collective behavior because they cannot escape interactions with each other. This makes 1D systems an excellent playground for studying quantum phase transitions (QPT), fractionalized excitations and disordered quantum spin liquid (QSL) state. Our group has discovered new phases in one-dimensional quantum magnets in a magnetic field using density matrix renormalization group methods. Our results allows us to connect with exact results in certain limits and to make predictions with quasi-1D magnetic materials. We discovered that the quantum phase transitions in certain 1D spin models can undergo a novel phase transition without the closing or opening of an energy gap, i.e. a gapless-to-gapless transition, which can be understood as a novel Lifshitz transition without Fermi surface, involving the topological change of spinon bands in lieu of electron bands.
Dynamical structure factor of the quantum spin chain with Uimin-Lai-Sutherland (ULS) interaction under different magnetic field. It is a quantum phase transition characterized by the evolution of soft modes as a function of magnetic field, and a gapless-to-gapless transition made explicit by the fact that all modes retain zero energy during these evolution.
Publications:
Gapless to gapless phase transitions in quantum spin chains, S. Feng, G. Alvarez, N. Trivedi, Phys. Rev. B 105, 014435 (2022).
Magnetic phase transitions in quantum spin-orbital liquids, S. Feng, N. D. Patel, P. Kim, J. H. Han, N. Trivedi, Phys. Rev. B 101, 155112 (2020).