Magnetic Catalysis Research Articles

Phase diagram of the QCD Kondo effect and inactivation of the magnetic catalysis

We investigate the QCD phase diagram in strong magnetic fields with heavy-quark impurities and determine the ground state within the mean-field analysis. The ground state is characterized by magnitudes of the pairing not only between the light quark and antiquark, i.e., chiral condensate, but also between the light quark and heavy-quark impurity, dubbed the Kondo condensate. We propose signatures of the interplay and/or competition between those two pairing phenomena reflected in the magnitude of the chiral condensate that is saturated with respect to the magnetic-field strength and anomalously increases with increasing temperature.

QCD sum rule analysis of heavy quarkonium states in magnetized matter: Effects of magnetic and inverse magnetic catalysis

In-medium masses of the $1S$ and $1P$ states of heavy quarkonia are investigated in the magnetized asymmetric nuclear medium, accounting for the Dirac sea effects, using a combined approach of chiral effective model and QCD sum rule method. Masses are calculated from the in-medium scalar and twist-2 gluon condensates, calculated within the chiral model. The gluon condensate is simulated through the scalar dilaton field, $\ensuremath{\chi}$ introduced in the model through a scale-invariance breaking logarithmic potential. Contribution of the Dirac sea is incorporated through the nucleonic tadpole diagrams. Treating the scalar fields as classical, the dilaton field, $\ensuremath{\chi}$, the isoscalar nonstrange $\ensuremath{\sigma}(\ensuremath{\sim}(⟨\overline{u}u⟩+⟨\overline{d}d⟩))$, strange $\ensuremath{\zeta}(\ensuremath{\sim}⟨\overline{s}s⟩)$ and isovector $\ensuremath{\delta}(\ensuremath{\sim}(⟨\overline{u}u⟩\ensuremath{-}⟨\overline{d}d⟩))$ fields, are obtained by solving their coupled equations of motion as derived from the chiral model Lagrangian. The effects of magnetic field are incorporated through the Dirac sea as well as the Landau energy levels of the protons, and the anomalous magnetic moments of the nucleons. The scalar fields modify appreciably with magnetic field due to the Dirac sea contribution. In-medium masses of the charmonium and bottomonium ground states are observed to have significant modifications with magnetic field due to the effects of (inverse) magnetic catalysis. In presence of an external magnetic field, there is mixing between the longitudinal component of the vector and the pseudoscalar mesons (PV mixing) in both quarkonia sectors, leading to a rise (drop) of the masses of $J/{\ensuremath{\psi}}^{||}({\ensuremath{\eta}}_{c})$ and ${\mathrm{\ensuremath{\Upsilon}}}^{||}(1S)({\ensuremath{\eta}}_{b})$ states. These might show in the experimental observables, e.g., the dilepton spectra in the noncentral, ultrarelativistic heavy ion collision experiments at RHIC and LHC, where the produced magnetic field is huge.

Effect of anomalous magnetic moment on the chiral transition at zero temperature in a strong magnetic field

The effect of the anomalous magnetic moment (AMM) on the chiral restoration is investigated at zero temperature in the strong magnetic fields with the vacuum magnetic regularization scheme. It is shown that the chiral restoration diagram sensitively depends on the AMM in the ultrastrong magnetic fields. In our work, the parameterization of AMM is employed as proportional to the square of the chiral condensate. The critical chemical potential is found to decrease linearly by the increasing coefficient in the AMM scale. At a smaller scale of the AMM, the critical chemical potential could go down and then grow up as the magnetic field increases. But at a larger scale, the magnetic catalysis on the critical chemical potential would not happen anymore.

Open bottom mesons in magnetized matter: Effects of (inverse) magnetic catalysis

In-medium masses of the pseudoscalar and vector open bottom mesons ([Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], [Formula: see text], [Formula: see text]) are studied in the magnetized nuclear matter by considering the effects of Dirac sea, within the chiral effective model. The mass modifications arise due to the interactions of the open bottom mesons with the nucleons and the scalar mesons, calculated in terms of the scalar and number densities of the nucleons and the scalar fields fluctuations, within the chiral model. The effects of the magnetized Dirac sea lead to the considerable changes in the scalar fields with increasing magnetic field, which are related to the condensates of light quark–antiquark pairs. There is observed to be a (reduction) enhancement in the QCD light quark condensates with rising magnetic field, a phenomenon called (inverse) magnetic catalysis. The contribution of the magnetic field on the Fermi sea of nucleons is also taken into account through protons Landau energy levels and anomalous magnetic moments (AMMs) of the nucleons. The additional contribution of the lowest Landau level for the charged mesons is taken into account. In the presence of an external magnetic field, the spin–magnetic field interaction between the longitudinal component of the vector mesons and the pseudoscalar mesons ([Formula: see text], [Formula: see text] and [Formula: see text]) are studied, which lead to level repulsion between their masses with increasing magnetic field. The magnetic fields are observed to have significant contribution on the masses of the open bottom mesons through the Dirac sea effects taking into account the AMMs of nucleons. In vacuum, appreciable medium modifications are obtained due to the magnetized Dirac sea contribution with nonzero nucleonic AMMs.

Pion superfluid phase transition under an external magnetic field including the inverse magnetic catalysis effect

Pion superfluid phase transition under external magnetic field including the inverse magnetic catalysis (IMC) effect is investigated by the Pauli-Villars regularized NJL model. Based on the Goldstone's theorem, we apply the massless Goldstone boson ($\pi^+$ meson) to determine the onset of pion superfluid phase. The inverse magnetic catalysis effect is introduced by the magnetic field dependent coupling $G(eB)$, which is a decreasing function of magnetic field. At fixed temperature and baryon chemical potential, the critical isospin chemical potential for pion superfluid phase transition including IMC effect increases as the magnetic field grows, which is similar as the case without IMC effect. This demonstrates that magnetic field disfavors the pion superfluid phase when considering or ignoring IMC effect. The critical isospin chemical potential at fixed magnetic field, temperature and baryon chemical potential is shifted to higher value by the IMC effect. Since it is more difficult to form pion superfluid with weaker coupling.

Chiral vortical catalysis

Gluon interaction introduces remarkable corrections to the magnetic polarization effects on the chiral fermions, which is known as the inverse magnetic catalysis. It is a natural speculation that the vorticity, which has many similar properties as magnetic field, would bring non-negligible contribution to the chiral rotational suppression. Using an intuitive semi-classical background field method we studied the rotation dependence of the effective strong interaction coupling constant. Contrary to the magnetic field case the rotation increases the effective coupling which would slow down the condensate melting with temperature. This could be named as the chiral vortical catalysis or inverse rotation suppression. Imposing such dependence on the 4-fermion coupling in the NJL model, we numerically checked this analysis qualitatively. The pseudo critical temperature is shown to rise with the rotation and approach saturation eventually which may be induced by the model cutoff.

The role of Debye mass in the chiral crossover in a strong magnetic field

In this paper, the Debye mass of quarks is investigated in the Nambu–Jona-Lasinio model at zero and nonzero chemical potentials. In a uniform plasma, the Debye mass usually behaves as a monotonous increasing function of the temperature, the chemical potential and the magnetic field. At the fixed coupling interaction G, we find that the magnetic catalysis (MC) on the occurrence of the chiral restoration could be revealed by the susceptibility of the Debye mass dm D /dT at low chemical potential and by the quantity Tdm D /dT in the region of moderate densities. However, the inverse MC is realized under a thermomagnetic coupling constant G(B, T) by the behavior of the Debye mass at both zero and nonzero chemical potentials.

Lepton pair production from a hot and dense QCD medium in the presence of an arbitrary magnetic field

In this article, we have explored the very important quantity of lepton pair production from a hot and dense QCD medium in presence of an arbitrary external magnetic field for simultaneous nonzero values of both the parallel (along the direction of the external field) and perpendicular (lying on the transverse plane to the external field) components of the dilepton momentum. As opposed to the zero magnetic field case (the so-called Born rate) or the lowest Landau level approximated rate, where only the annihilation process contributes, here we observe contributions also arising out of the quark and antiquark decay processes. We found the encouraging result of considerable enhancement of lepton pair production in presence of an arbitrary magnetic field. We decompose the total rate into different physical processes and discuss their behaviors for both zero and nonzero baryon density. The whole analysis is then subjected to an effective model treatment, where we have incorporated the magnetic field induced novel effects of magnetic catalysis (MC) and inverse MC (IMC) through a medium dependent scalar coupling, which leads to some further interesting observations.

Anisotropic pressure of magnetized quark matter with anomalous magnetic moment

We investigate magnetic field $(eB)$ dependence of constituent quark mass, the longitudinal and transverse pressure as well as the magnetization and magnetic susceptibility of strongly interacting quark matter. We employ the two-flavor Polyakov Nambu--Jona-Lasinio model with the inclusion of the anomalous magnetic moment (AMM) of the quarks at finite temperature ($T$) and finite quark chemical potential $({\ensuremath{\mu}}_{q})$ capturing different stages of chiral phase transition. We find that the transverse pressure, magnetization, and magnetic susceptibility become highly oscillatory for large values of $eB$ in the chiral symmetry broken phase. However, the oscillations cease to occur at higher values of $T$ and ${\ensuremath{\mu}}_{q}$ when chiral symmetry is (partially) restored and the anisotropic nature of the pressure becomes significant even at smaller values of $eB$. As the inclusion of AMM of the quarks leads to inverse magnetic catalysis of the transition temperature, we observe that the variations of transverse pressure, magnetization, and magnetic susceptibility are significantly modified in the vicinity of the chiral transition temperature. Furthermore, above the chiral transition temperature the magnetic susceptibility is found to remain positive for a wide range of $eB$, indicating a paramagnetic character of the strongly interacting quark matter. Finally, we have also examined the magnetism of strongly interacting matter in the quarkyonic phase. The obtained results could be useful for a magnetohydrodynamic evolution of hot and dense matter created in heavy-ion collisions.

Driving chiral phase transition with ring diagram

We study the dressing of four-quark interaction by the ring diagram, and its feeding back to the quark gap equation, in an effective chiral quark model. Implementing such an in-medium coupling naturally reduces the chiral transition temperature in a class of chiral models, and is capable of generating the inverse magnetic catalysis at finite temperatures. We also demonstrate the important role of confining forces, via the Polyakov loop, in a positive feedback mechanism which reinforces the inverse magnetic catalysis.

Iron decorated defective phosphorene as a viable hydrogen storage medium – A DFT study

2D materials like phosphorene have shown significant potential for hydrogen storage applications because of its large specific surface area and tuneable energetics. In this study, the effect of iron decoration on three defective phosphorene systems - DV-5|8|5-1, SV-5|9 and SV-55|66 - for hydrogen storage were studied theoretically using Density Functional Theory. Hydrogen adsorption energy in Fe-decorated DV-5|8|5-1 was calculated to be −0.562 eV/H2, which is within the DOE stipulated limit. Further analysis of P(3p) and Fe(3d) orbitals in Fe decorated DV-5|8|5-1 showed that both P and Fe contribute to the electronic interaction with H2, which was not seen in the other two single vacancy systems. Moreover, we observed that the magnetic moment of the systems plays an important role in hydrogen adsorption. H2 adsorbed Fe decorated DV-5|8|5-1 system with a magnetic moment of 2.04 μB exhibited the highest H2 adsorption energy. These results indicate that such systems offer potential applications in magnetic heterostructures, catalysis and gas sensing applications.

Inverse catalysis effect of the quark anomalous magnetic moment to chiral restoration and deconfinement phase transitions at finite baryon chemical potential

The effect of quark anomalous magnetic moment (AMM) to chiral restoration and deconfinement phase transitions in baryon chemical potential-temperature $(\mu_B-T)$ plane under magnetic fields is investigated in frame of a Pauli-Villars regularized PNJL model. It's found that the quark AMM plays the role of inverse catalysis to the phase transitions, and large quark AMM will change the magnetic catalysis phenomena of phase transitions to inverse magnetic catalysis in the whole $\mu_B-T$ plane. For a fixed magnetic field, the critical temperature $T_c$ and critical baryon chemical potential $\mu_B^c$ decreases with quark AMM. The stronger the magnetic field is, the inverse catalysis effect of AMM becomes more important. For a small AMM $\kappa=\kappa_1$, it shows the magnetic catalysis effect for critical temperature $T_c$ at vanishing $\mu_B$ with increasing magnetic field, and (inverse) magnetic catalysis effect for critical baryon chemical potential $\mu_B^c$ at vanishing $T$ under (weak) strong magnetic field. At finite $T$ and $\mu_B$, there exist some crossings of the phase transition lines with different magnetic field. For a large AMM $\kappa=\kappa_2$, we obtain the inverse magnetic catalysis effect in the whole $\mu_B-T$ plane, and no crossings of phase transition lines happen.

Effects of the quark anomalous magnetic moment in the chiral symmetry restoration: magnetic catalysis and inverse magnetic catalysis

In this work, we consider the effect of a constant anomalous magnetic moment (AMM) of quarks in the SU(2) Nambu–Jona-Lasinio model in the mean field approximation. To this end, we use the Schwinger ansatz, which represents a linear magnetic field term in the Lagrangian. A regularization method inspired in the vacuum magnetic regularization (VMR) is adopted to avoid ultraviolet divergences. Our results indicate a smooth decrease of the pseudocritical temperature and quark condensates for magnetic fields B le 0.1 GeV^2 when a sizable AMM is considered. We found only a small window for Inverse Magnetic Catalysis (IMC), in contradiction with NJL predictions made in the literature. For a low value of AMM, we observe for all ranges of magnetic fields considered that the pseudocritical temperature increases with the magnetic field, indicating only Magnetic Catalysis (MC). In our approach, for nonvanishing quark AMM, the chiral symmetry restoration happens always as a smooth crossover and never turns into a first order phase transition.

Studying the quark gap equation at finite temperature, magnetic field and different numbers of flavor and color numbers

In recent years, a momentum-independent symmetry preserving vector-vector contact interaction has been used to provide exploratory studies in QCD. It helps calculate different static and dynamic observables of all mesons and baryons. In this work, we revisit how the quark gap equation is affected by changing the number of quark colors and/or flavors, or by placing quarks in a thermal bath in the presence of an external magnetic field. In particular, we describe how the phenomenon of magnetic catalysis and its inverse can be studied.

Magnetism of QCD matter and the pion mass from tensor-type spin polarization and the anomalous magnetic moment of quarks

We investigate the magnetism of QCD matter and pion mass under magnetic field considering the contribution from the tensor-type spin polarization and the anomalous magnetic moment (AMM) of quarks. It is found that the tensor-type spin polarization (TSP) induces the magnetic catalysis of chiral condensate and diamagnetism (negative magnetic susceptibility) of quark matter at low temperature, both neutral and charged pion masses increase quickly with magnetic field in the case of TSP. The anomalous magnetic moment (AMM) of quarks induces magnetic inhibition and a magnetic dependent AMM causes inverse magnetic catalysis at finite temperature, and the neutral pion mass decreases with magnetic field while the charged pion mass shows nonmonotonic behavior with the magnetic field, which is qualitatively in agreement with lattice result. However, the magnetic susceptibility is positive at low temperature with AMM. In the current framework, our results show the irreconcilable contradiction between the diamagnetism and inverse magnetic catalysis.

Magnetically Induced Catalytic Reduction of Biomass-Derived Oxygenated Compounds in Water.

The development of energetically efficient processes for the aqueous reduction of biomass-derived compounds into chemicals is key for the optimal transformation of biomass. Herein we report an early example of the reduction of biomass-derived oxygenated compounds in water by magnetically induced catalysis. Non-coated and carbon-coated core-shell FeCo@Ni magnetic nanoparticles were used as the heating agent and the catalyst simultaneously. In this way it was possible to control the product distribution by adjusting the field amplitude applied during the magnetic catalysis, opening a precedent for this type of catalysis. Finally, the encapsulation of the magnetic nanoparticles in carbon (FeCo@Ni@C) strongly improved the stability of the magnetic catalyst in solution, making its reuse possible up to at least eight times in dioxane and four times in water.

Fundamental Landau levels in a strongly coupled plasma

We use the gauge/gravity correspondence to show that in its context there appear Landau levels when studying the excitations of the fundamental degrees of freedom of a strongly coupled plasma subject to a magnetic field of arbitrary intensity. We work in the phase where mesons are melted by embedding a D7-brane in the 10D uplift that we construct for the 5D background associated with a magnetic brane. By studying the dependence of the lowest quasinormal frequency on both the intensity of the magnetic field and the Landau level, we corroborate that the energy behaves as expected for dissociating Landau levels. The reconstruction of the impact of the magnetic field on the stability of the quasinormal modes allows us to identify inverse magnetic catalysis for intensities of the field below a certain value and magnetic catalysis for those above it.

Tuning Surface‐Electron Spins on Fe3O4 (111) through Chemisorption of Carbon Monoxide

AbstractThe adsorption‐induced flip of electron spin at interfaces is an important but poorly understood phenomenon for magnetic devices, sensors, and heterogeneous catalysis, due to the difficulties in determining the surface spins at atomic resolution. We present an evolutionary magnetic order searching method that allows efficient identification of the ground state spin configuration of magnetic bulk and surfaces. Using this approach, we have discovered for the first time a set of adsorption‐induced near‐degenerate surface magnetic states on the Fe3O4 (111) surface. Molecular adsorption of CO causes a destabilization of the magnetic states of the clean surface leading to a set of near‐degenerate surface magnetic states at medium coverage, which causes an abrupt increase of the magnetic entropy on the surface. The empty 2π* orbital of CO, which could accommodate the back donation of the spin density in the Fe d orbitals, plays a key role for the CO adsorption‐induced spin transition.

Tuning Surface-Electron Spins on Fe3 O4 (111) through Chemisorption of Carbon Monoxide.

The adsorption-induced flip of electron spin at interfaces is an important but poorly understood phenomenon for magnetic devices, sensors, and heterogeneous catalysis, due to the difficulties in determining the surface spins at atomic resolution. We present an evolutionary magnetic order searching method that allows efficient identification of the ground state spin configuration of magnetic bulk and surfaces. Using this approach, we have discovered for the first time a set of adsorption-induced near-degenerate surface magnetic states on the Fe3 O4 (111) surface. Molecular adsorption of CO causes a destabilization of the magnetic states of the clean surface leading to a set of near-degenerate surface magnetic states at medium coverage, which causes an abrupt increase of the magnetic entropy on the surface. The empty 2π* orbital of CO, which could accommodate the back donation of the spin density in the Fe d orbitals, plays a key role for the CO adsorption-induced spin transition.

Magnetic correction to the anomalous magnetic moment of electrons

We investigate the leading order correction of anomalous magnetic moment (AMM) to electrons in a weak magnetic field and find that the magnetic correction is negative and magnetic field dependent, indicating a magnetic catalysis effect for the electron gas. In the laboratory, to measure the g − 2, the magnitude of the magnetic field B is several T, and correspondingly the magnetic correction to the AMM of electron/muon is around 10−34/10−42, therefore the magnetic correction can be safely neglected in the current measurement. However, when the magnitude of the magnetic field strength is comparable with the electron mass, the magnetic correction of the electron’s AMM will become considerable. This general magnetic correction to the charged fermion’s AMM can be extended to study quantum chromodynamic matter under a strong magnetic field.