Monte Carlo study of the pseudogap and superconductivity emerging from quantum magnetic fluctuations

Abstract

The origin of the pseudogap behavior, found in many high-Tc superconductors, remains one of the greatest puzzles in condensed matter physics. One possible mechanism is fermionic incoherence, which near a quantum critical point allows pair formation but suppresses superconductivity. Employing quantum Monte Carlo simulations of a model of itinerant fermions coupled to ferromagnetic spin fluctuations, represented by a quantum rotor, we report numerical evidence of pseudogap behavior, emerging from pairing fluctuations in a quantum-critical non-Fermi liquid. Specifically, we observe enhanced pairing fluctuations and a partial gap opening in the fermionic spectrum. However, the system remains non-superconducting until reaching a much lower temperature. In the pseudogap regime the system displays a “gap-filling" rather than “gap-closing" behavior, similar to the one observed in cuprate superconductors. Our results present direct evidence of the pseudogap state, driven by superconducting fluctuations.

Measuring Rényi entanglement entropy with high efficiency and precision in quantum Monte Carlo simulations

“…Here we show that previously difficult task can be greatly optimized and improved via the nonequilibrium increment method, and in this way, one can investigate the scaling behavior of EE in many (2 + 1)d quantum many-body systems with very large system sizes, controlled errorbars, and minimal computational costs. Starting from the three representative cases shown here, one can foresee the implementation and measurement of EE via our algorithm for other topological ordered phases and phase transitions, interacting fermionic systems such as the Gross-Neveu QCPs with critical Dirac fermions 70 , the deconfined QED 3 problems of gauge fields coupled to fermion matter fields [71][72][73] and the more complicated situations of non-Fermi-liquid and quantum critical metals [74][75][76][77][78][79][80][81][82] and hopefully make further suggestions to the on-going experimental search for these strongly entangled quantum matter.…”

Analysis of the Influence of Sports on College Students’ Music Vocalization Training Based on Monte Carlo and Dynamic Adjustment Factor Algorithm

“…Vocal training methods are mainly based on college students' age, gender, BMI, grade, vocal types, and comprehensive analysis of college students' vocal training [ 7 ]. During initialization T =( d i ∩ b i |i =nature), the exercise training content is the same, and the breathing, coordination, and muscle control ability are comprehensively analyzed [ 8 ]. Firstly, the sports content is randomly selecte and optimized in the sports exercise content with better evaluation results, and the optimal combination of sports schemes is obtained by comparison, which is determined by the least square method.…”

“…From formula (8), it can be seen that when the initial adjustment is made, ] andw are relatively large [12], its purpose is to expand the scope of exercise content and keep the diversity of exercise content as much as possible. In the later adjustment stage, ] andw are relatively small, and the judgment range is continuously reduced to improve the accuracy of the calculation results.…”

“…e relationship between sports training content vocal training standard sports training content and vocal training standard and comprehensive adjustment factors is dynamic and should be adjusted constantly to improve the accuracy of the analysis. From formula (8), it can be seen that, in the initial judgment of exercise content, the scope of exercise content should be continuously expanded, and in the later judgment, attention should be paid to the judgment of breathing, coordination, muscle control ability, and other indicators, so different exercise contents should be based on corresponding evaluation standards. e application scope of the Monte Carlo algorithm is di erent, and its strategies are also di erent.…”

Superconductivity near the (2+1)-Dimensional Ferromagnetic Quantum Critical Point

“…As temperature lowers or 𝛽 increases, the density of states starts to show a dip at zero frequency, which becomes deeper as 𝛽 increases. This indicates the appearance of a pseudogap, [34] and the onset temperature of the pseudogap can be estimated as 𝛽 = 3. Compared to the BCS result of 𝛽c = 6.06 given above, the two temperature scales agree qualitatively.…”