In this paper,we present an overview on recent progress in studies of QCD at finite temperature and densities within the functional renormalization group(fRG)approach.The f RG is a nonperturbative continuum field appr...In this paper,we present an overview on recent progress in studies of QCD at finite temperature and densities within the functional renormalization group(fRG)approach.The f RG is a nonperturbative continuum field approach,in which quantum,thermal and density fluctuations are integrated successively with the evolution of the renormalization group(RG)scale.The f RG results for the QCD phase structure and the location of the critical end point(CEP),the QCD equation of state(EoS),the magnetic EoS,baryon number fluctuations confronted with recent experimental measurements,various critical exponents,spectral functions in the critical region,the dynamical critical exponent,etc,are presented.Recent estimates of the location of the CEP from first-principle QCD calculations within f RG and Dyson-Schwinger equations,which pass through lattice benchmark tests at small baryon chemical potentials,converge in a rather small region at baryon chemical potentials of about 600 MeV.A region of inhomogeneous instability indicated by a negative wave function renormalization is found withμ_(B)■420 MeV.It is found that the non-monotonic dependence of the kurtosis of the net-proton number distributions on the beam collision energy observed in experiments could arise from the increasingly sharp crossover in the regime of low collision energy.展开更多
Recently,the films of the Ruddlesden-Popper(RP) nickelate superconductors,in which the(La,Pr)_(3) Ni_(2)O_(7) system exhibits a remarkable transition temperature T_(c) exceeding 40 K,were synthesized at ambient pressu...Recently,the films of the Ruddlesden-Popper(RP) nickelate superconductors,in which the(La,Pr)_(3) Ni_(2)O_(7) system exhibits a remarkable transition temperature T_(c) exceeding 40 K,were synthesized at ambient pressure.We systematically investigate the band structures and electronic correlation effects to identify the key factors controlling superconductivity and pathways to enhance T_(c).Based on density functional theory(DFT) calculations,we construct a bilayer two-orbital(3d_(3_(z^(2))-r^(2)) and 3d_(x^(2)-y^(2))) tight-binding model for a series of in-plane compression mimicking the substrate effect.We find the band energy at the M point drops with the compression,leading to an increase in the density of states at the Fermi level,in stark contrast to the behavior of the bulk under pressure.We then apply the functional renormalization group(FRG) method to study the electronic correlation effect on the superconductivity.We find the s_(±)-wave pairing symmetry remains robust in the films,the same as the bulk.But somewhat surprisingly,for the films,we find T_(c) can be enhanced by reducing the in-plane lattice constant,increasing the out-of-plane lattice constant,or further electron-doping.These findings are consistent with the itinerant picture of the superconductivity induced by spin-fluctuations and provide theoretical support for further boosting T_(c) in future experiments.展开更多
Correlations of conserved charges,i.e.,the baryon number,electric charge,and strangeness,are calculated at finite temperature and chemical potentials up to the fourth order.The calculations are done ina 2+1 flavor low...Correlations of conserved charges,i.e.,the baryon number,electric charge,and strangeness,are calculated at finite temperature and chemical potentials up to the fourth order.The calculations are done ina 2+1 flavor low energy effective theory,in which the quantum and thermal fluctuations are encoded through the evolution of flow equations within the functional renormalization group approach.Strangeness neutrality and a fixed ratio of the electric charge to the baryon number density are implemented throughout the computation.We find that higher-order correlations incorporate more sensitive critical dynamics than the quadratic ones.In addition,a non-monotonic dependence of the fourth-order correlations between the baryon number and strangeness,i.e.,-χ_(31)^(BS)/χ_(2)^(S)and χ_(22)^(BS)/χ_(2)^(S),on the collision energy is also observed.展开更多
基金supported by the National Natural Science Foundation of China under Grant No.12175030
文摘In this paper,we present an overview on recent progress in studies of QCD at finite temperature and densities within the functional renormalization group(fRG)approach.The f RG is a nonperturbative continuum field approach,in which quantum,thermal and density fluctuations are integrated successively with the evolution of the renormalization group(RG)scale.The f RG results for the QCD phase structure and the location of the critical end point(CEP),the QCD equation of state(EoS),the magnetic EoS,baryon number fluctuations confronted with recent experimental measurements,various critical exponents,spectral functions in the critical region,the dynamical critical exponent,etc,are presented.Recent estimates of the location of the CEP from first-principle QCD calculations within f RG and Dyson-Schwinger equations,which pass through lattice benchmark tests at small baryon chemical potentials,converge in a rather small region at baryon chemical potentials of about 600 MeV.A region of inhomogeneous instability indicated by a negative wave function renormalization is found withμ_(B)■420 MeV.It is found that the non-monotonic dependence of the kurtosis of the net-proton number distributions on the beam collision energy observed in experiments could arise from the increasingly sharp crossover in the regime of low collision energy.
基金supported by the National Key Research and Development Program of China (Grant Nos.2024YFA1408100,and 2022YFA1403201)the National Natural Science Foundation of China (Grant Nos.12074213,12374147,12274205,and 92365203)the Major Basic Program of Natural Science Foundation of Shandong Province (Grant No.ZR2021ZD01)。
文摘Recently,the films of the Ruddlesden-Popper(RP) nickelate superconductors,in which the(La,Pr)_(3) Ni_(2)O_(7) system exhibits a remarkable transition temperature T_(c) exceeding 40 K,were synthesized at ambient pressure.We systematically investigate the band structures and electronic correlation effects to identify the key factors controlling superconductivity and pathways to enhance T_(c).Based on density functional theory(DFT) calculations,we construct a bilayer two-orbital(3d_(3_(z^(2))-r^(2)) and 3d_(x^(2)-y^(2))) tight-binding model for a series of in-plane compression mimicking the substrate effect.We find the band energy at the M point drops with the compression,leading to an increase in the density of states at the Fermi level,in stark contrast to the behavior of the bulk under pressure.We then apply the functional renormalization group(FRG) method to study the electronic correlation effect on the superconductivity.We find the s_(±)-wave pairing symmetry remains robust in the films,the same as the bulk.But somewhat surprisingly,for the films,we find T_(c) can be enhanced by reducing the in-plane lattice constant,increasing the out-of-plane lattice constant,or further electron-doping.These findings are consistent with the itinerant picture of the superconductivity induced by spin-fluctuations and provide theoretical support for further boosting T_(c) in future experiments.
基金National Natural Science Foundation of China(11775041)。
文摘Correlations of conserved charges,i.e.,the baryon number,electric charge,and strangeness,are calculated at finite temperature and chemical potentials up to the fourth order.The calculations are done ina 2+1 flavor low energy effective theory,in which the quantum and thermal fluctuations are encoded through the evolution of flow equations within the functional renormalization group approach.Strangeness neutrality and a fixed ratio of the electric charge to the baryon number density are implemented throughout the computation.We find that higher-order correlations incorporate more sensitive critical dynamics than the quadratic ones.In addition,a non-monotonic dependence of the fourth-order correlations between the baryon number and strangeness,i.e.,-χ_(31)^(BS)/χ_(2)^(S)and χ_(22)^(BS)/χ_(2)^(S),on the collision energy is also observed.
