Zi-Xiang Li

Fermion-induced quantum critical points

A unified theory of quantum critical points beyond the conventional Landau–Ginzburg–Wilson paradigm remains unknown. According to Landau cubic criterion, phase transitions should be first-order when cubic terms of order parameters are allowed by symmetry in the Landau–Ginzburg free energy. Here, from renormalization group analysis, we show that second-order quantum phase transitions can occur at such putatively first-order transitions in interacting two-dimensional Dirac semimetals. As such type of Landau-forbidden quantum critical points are induced by gapless fermions, we call them fermion-induced quantum critical points. We further introduce a microscopic model of SU(N) fermions on the honeycomb lattice featuring a transition between Dirac semimetals and Kekule valence bond solids. Remarkably, our large-scale sign-problem-free Majorana quantum Monte Carlo simulations show convincing evidences of a fermion-induced quantum critical points for N = 2, 3, 4, 5 and 6, consistent with the renormalization group analysis. We finally discuss possible experimental realizations of the fermion-induced quantum critical points in graphene and graphene-like materials.Quantum phase transitions are governed by Landau-Ginzburg theory and the exceptions are rare. Here, Li et al. propose a type of Landau-forbidden quantum critical points induced by gapless fermions in two-dimensional Dirac semimetals.

Fermion-sign-free Majarana-quantum-Monte-Carlo studies of quantum critical phenomena of Dirac fermions in two dimensions

Quantum critical phenomena may be qualitatively different when massless Dirac fermions are present at criticality. Using our recently-discovered fermion-sign-free Majorana quantum Monte Carlo (MQMC) method introduced by us in Ref. [1], we investigate the quantum critical phenomena of {\it spinless} Dirac fermions at their charge-density-wave (CDW) phase transitions on the honeycomb lattice having

Nature of the effective interaction in electron-doped cuprate superconductors: A sign-problem-free quantum Monte Carlo study

N_s=2L^2

Irradiation and interface induced formation of a nonequilibrium Ag 3 Co phase predicted by ab initio calculation

sites with largest

Majorana-Time-Reversal Symmetries: A Fundamental Principle for Sign-Problem-Free Quantum Monte Carlo Simulations.

L=24

Charge-4e superconductors: a Majorana quantum Monte Carlo study

. By finite-size scaling, we accurately obtain critical exponents of this so-called Gross-Neveu chiral-Ising universality class of {\it two} (two-component) Dirac fermions in 2+1D:

Edge quantum criticality and emergent supersymmetry in topological phases.

\eta=0.45(2)

Quantum Monte Carlo study of the Tc enhancement mechanism in FeSe on SrTiO3

,

Publisher's Note: Charge- 4e superconductors: A Majorana quantum Monte Carlo study [Phys. Rev. B 95 , 241103(R) (2017)]

\nu=0.77(3)

Majorana-time-reversal symmetries: a fundamental principle for sign-problem-free quantum Monte Carlo

, and