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Landau theory predicts no continuous quantum phase transition between two ordered states with different types of symmetry breaking. However, in recent years, field theories and many-body computations based on some specifically designed models support the existence of a second-order phase transition through a deconfined quantum critical point (DQCP), accompanied by enhanced symmetries and fractional excitations [1]. In this talk, I present our recent NMR evidence of a proximate DQCP [2] revealed in a Shastry-Sutherland compound SrCu 2 (BO 3 ) 2 [3]. A pressure-induced quantum phase transition from a dimerized state (DS) to a plaquette singlet (PS) state [4-7] is confirmed at pressure above 1.8 GPa. With applied field, a weakly first-order quantum phase transition emerges from the PS to the antiferromagnetic (AFM) state through Bose-Einstein condensation. Duality in the power-law scaling of transition temperatures and an anomalous quantum critical scaling in the spin-lattice relaxation rates are revealed near the critical field. These results establish concrete experimental existence of a proximate DQCP, and provide a platform for further investigation of the properties of deconfined quantum criticality.

[1] R. R. P. Singh, Physics, 3, 35 (2010).
[2] Y. Cui et al., Science 380, 1179 (2023).
[3] H. Kageyama, et al., Phys. Rev. Lett. 82, 3168 (1999).
[4] T. Waki et al., JPSJ 76, 073710 (2007)
[5] M. E. Zayed, et al., Nat. Phys. 13, 962 (2017).
[6] J. Guo, et al., Phys. Rev. Lett. 124, 206602 (2020).
[7] J. Larrea Jimenez, et al., Nature 592, 370 (2021).

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