Quantum criticality and spin liquid phase in the Shastry-Sutherland model

Deconfined quantum criticality and emergent symmetry in SrCu2(BO3)2

“…Below 1.8 K, the FWHM in Fig. 3b rises sharply and The DQCP separates a line of first-order QPTs and a QSL [16]. The first-order DS-PS transition at H = 0 extends further up in T and terminates at an Ising critical point (green circle) [30].…”

“…At the highest pressure, 2.4 GPa, 1/T 1 exhibits critical scaling for T between 0.2 and 2 K, indicating sufficient proximity to the DQCP for realizing the characteristic quantum-critical fan [44]. The lack of scaling at 2.1 GPa, and the stronger first-order signals, makes the scenario of first-order transitions with emergent symmetry induced by a nearby multi-critical DQCP [7,8,13,14,16] more likely than a line of generic DQCPs on the enitire PS-AFM boundary [1,36].…”

“…The DQCP has long been associated with unconventional phenomena including fractional spinon excitations and deconfined gauge fluctuations [3][4][5], and further intensive investigation of the DQCP scenario has introduced emergent symmetries [6][7][8][9][10] and exotic firstorder transitions [11,12]. In a very recent scenario, the DQCP is multi-critical [13,14] and generically connected to a gapless quantum spin liquid (QSL) [15][16][17][18][19].…”

“…The 2D S = 1/2 Heisenberg model with uniform frustrated interactions on square-lattice offers a more frequently studied close analogy to the SSM, though hosting a four-fold degenerate dimerized phase in place of the two-fold degenerate PS phase of the SSM. A QSL phase exists in an extended parameter space between the dimerized and AFM phases [15,19,[38][39][40] and terminates at a DQCP with emergent SO(5) symmetry [14,16,17]. Beyond the DQCP, the direct PS-AFM transition is expected to be first-order, with the coexistence state inheriting (and breaking) the emergent symmetry of the DQCP [7][8][9]14].…”

“…Early calculations indicated a first-order PS-AFM transition in the SSM [26], but in more recent work a DQCP with emergent O(4) symmetry [from the O(3) AFM and scalar PS order parameters] was proposed [36]. Other works argued that interactions beyond the SSM are required for reaching the DQCP [10] and that the SSM as well hosts a gapless QSL between the PS and AFM phases [14,16,18].…”