From Complexification to Self-Similarity:New Aspects of Quantum Criticality

Quantum phase transitions are a fascinating area of condensed matter physics.The extension through complexification not only broadens the scope of this field but also offers a new framework for understanding criticality and its statistical implications.This mini review provides a concise overview of recent developments in complexification,primarily covering finite temperature and equilibrium quantum phase transitions,as well as their connection with dynamical quantum phase transitions and non-Hermitian physics,with a particular focus on the significance of Fisher zeros.Starting from the newly discovered self-similarity phenomenon associated with complex partition functions,we further discuss research on self-similar systems briefly.Finally,we offer a perspective on these aspects.

Gapless Spin Liquid and Nonlocal Corner Excitation in the Spin-1/2 Heisenberg Antiferromagnet on Fractal

Motivated by the mathematical beauty and the recent experimental realizations of fractal systems,we study the spin-1/2 antiferromagnetic Heisenberg model on a Sierpiński gasket.The fractal porous feature generates new kinds of frustration to exhibit exotic quantum states.Using advanced tensor network techniques,we identify a quantum gapless-spin-liquid ground state in fractional spatial dimension.This fractal spin system also demonstrates nontrivial nonlocal properties.While the extremely short-range correlation causes a highly degenerate spin form factor,the entanglement in this fractal system suggests a long-range scaling behavior.We also study the dynamic structure factor and clearly identify the gapless excitation with a stable corner excitation emerged from the ground-state entanglement.Our results unambiguously point out multiple essential properties of this fractal spin system,and open a new route to explore spin liquid and frustrated magnetism.

Nearly degenerate ground states of a checkerboard antiferromagnet and their bosonic interpretation

The spin-1/2 model system with antiferromagnetic(AF) couplings on a J1-J2checkerboard lattice, known as the planar pyrochlore model, is strongly frustrated and associated with a two-to-one dimensional crossover. Using the Projected Entangled Simplex States tensor network ansatz, we identify a large number of nearly degenerate states in the frustrated region(J_(1)<J_(2)).Specifically, we find the long-sought crossed-dimer valence bond solid(VBS) state to be the ground state at J_(1)≤J_(2), while various 1D AF correlated states take over the rest. We verify the stability of the VBS state against nematic perturbation. The corresponding bosonic picture provides an intuitive understanding of the low-energy physics. Particularly, it predicts weaker VBS states in the easy-plane limit, which we confirm numerically. Our results clarify the most essential ground state properties of this interesting system and demonstrate the usefulness of bosonic picture in dealing with frustrated magnetism.

Few-Atom Copper Catalyst for the Electrochemical Reduction of CO to Acetate:Synergetic Catalysis between Neighboring Cu Atoms

Single-atom catalysts(SACs)are gaining increasing recognition because of their superior catalytic properties for various reactions.However,the performance of SACs is often limited by the lack of neighboring metal centers to cooperate in catalysis.Herein,a synergetic interaction between neighboring Cu atoms of a few-atom catalyst(FAC)on graphdiyne(GDY)is found to greatly enhance the production of acetate in the CO electroreduction reaction relative to Cu SACs.In a 1.0 M KOH electrolyte,this Cu FAC exhibits an acetate Faradaic efficiency of 53.8±1.5%,an ultrahigh relative purity of up to 97 wt%for liquid products,and excellent stability over 23 h continuous electrolysis at–0.8 V versus reversible hydrogen electrode.Theoretical studies suggest that the intersite catalytic communication between two neighboring metal atoms confined in each pore of GDY facilitates the formation of acetic acid through either stepwise hydrogenation of CH_(2)CO^(*)or the direct reaction of H_(2)Owith CH_(2)CO^(*).Our study demonstrates the unprecedented synergetic catalysis of Cu FAC in promoting the selective CO electroreduction toward acetate production.