Dirac Kondo effect under magnetic catalysis

Hattori, Koichi*; Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*

Physical Review B, 108(24), p.245110_1 - 245110_11, 2023/12

https://doi.org/10.1103/PhysRevB.108.245110

We develop a mean-field theory of a novel Kondo effect emerging in systems without a Fermi surface, which instead emerges under strong magnetic fields. We determine the magnitude of the Kondo condensate, which is a particle pairing composed of conducting Dirac fermions and localized impurities. We focus on the competition between the Kondo effect and the energy gap formation that stems from the pairing among the Dirac fermions leading to the dynamical chiral symmetry breaking. We find that this competition induces a quantum critical point. We also investigate finite-temperature effects. This system at vanishing fermion density can be studied with Monte Carlo lattice simulations, which do not suffer from the sign problem.

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

Hattori, Koichi*; Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*

EPJ Web of Conferences, 276, p.01015_1 - 01015_5, 2023/03

https://doi.org/10.1051/epjconf/202327601015

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.

Doubly heavy tetraquarks in a chiral-diquark picture

Kim, Y.*; Oka, Makoto; Suzuki, Kei

Physical Review D, 105(7), p.074021_1 - 074021_17, 2022/04

https://doi.org/10.1103/PhysRevD.105.074021

Energy spectrum of doubly heavy tetraquarks, ( with and ), is studied in the potential chiral-diquark model. Using the chiral effective theory of diquarks and the quark-diquark-based potential model, the , , and tetraquarks are described as a three-body system composed of two heavy quarks and an antidiquark. We find several bound states, while no and (deep) bound state is seen. We also study the change of the tetraquark masses under restoration of chiral symmetry.

Kondo effect with Wilson fermions

Ishikawa, Tsutomu*; Nakayama, Katsumasa*; Suzuki, Kei

Physical Review D, 104(9), p.094515_1 - 094515_11, 2021/11

https://doi.org/10.1103/PhysRevD.104.094515

We investigate the Kondo effect with Wilson fermions. This is based on a mean-field approach for the chiral Gross-Neveu model including four-point interactions between a light Wilson fermion and a heavy fermion. For massless Wilson fermions, we demonstrate the appearance of the Kondo effect. We point out that there is a coexistence phase with both the light-fermion scalar condensate and Kondo condensate, and the critical chemical potentials of the scalar condensate are shifted by the Kondo effect. For negative-mass Wilson fermions, we find that the Kondo effect is favored near the parameter region realizing the Aoki phase. Our findings will be useful for understanding the roles of heavy impurities in Dirac semimetals, topological insulators, and lattice simulations.

Survival probabilities of charmonia as a clue to measure transient magnetic fields

Iwasaki, Sachio*; Jido, Daisuke*; Oka, Makoto; Suzuki, Kei

Physics Letters B, 820, p.136498_1 - 136498_6, 2021/09

https://doi.org/10.1016/j.physletb.2021.136498

We investigate time evolution of -wave charmonium populations under a time-dependent homogeneous magnetic field and evaluate survival probabilities of the low-lying charmonia to the goal of estimating the magnetic field strength at heavy-ion collisions. Our approach implements mixing between different spin eigenstates and transitions to radially excited states. We show that the survival probabilities can change even by an extremely short magnetic field. Furthermore, we find that the survival probabilities depend on the initial spin states. We propose the sum of the survival probabilities over spin partners as an observable insensitive to the initial states. We also find that the sum can be approximately given as a function of with a duration time and the maximum strength of the magnetic field .

Spin-orbital magnetic response of relativistic fermions with band hybridization

Araki, Yasufumi; Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*

Physical Review Research (Internet), 3(2), p.023098_1 - 023098_17, 2021/05

https://doi.org/10.1103/PhysRevResearch.3.023098

Spins of relativistic fermions are related to their orbital degrees of freedom. In order to quantify the effect of hybridization between relativistic and nonrelativistic degrees of freedom on spin-orbit coupling, we focus on the spin-orbital (SO) crossed susceptibility arising from spin-orbit coupling. The SO crossed susceptibility is defined as the response function of their spin polarization to the "orbital" magnetic field, namely the effect of magnetic field on the orbital motion of particles as the vector potential. Once relativistic and nonrelativistic fermions are hybridized, their SO crossed susceptibility gets modified at the Fermi energy around the band hybridization point, leading to spin polarization of nonrelativistic fermions as well. These effects are enhanced under a dynamical magnetic field that violates thermal equilibrium, arising from the interband process permitted by the band hybridization. Its experimental realization is discussed for Dirac electrons in solids with slight breaking of crystalline symmetry or doping, and also for quark matter including dilute heavy quarks strongly hybridized with light quarks, arising in a relativistic heavy-ion collision process.

Two relativistic Kondo effects; Classification with particle and antiparticle impurities

Araki, Yasufumi; Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*

Physical Review Research (Internet), 3(1), p.013233_1 - 013233_12, 2021/03

https://doi.org/10.1103/PhysRevResearch.3.013233

We investigate two different types of relativistic Kondo effects, distinguished by heavy-impurity degrees of freedom, by focusing on the energy-momentum dispersion relations of the ground state with condensates composed of a light Dirac fermion and a nonrelativistic impurity fermion. Heavy fermion degrees of freedom are introduced in terms of two types of heavy-fermion effective theories, in other words, two heavy-fermion limits for the heavy Dirac fermion, which is known as the heavy-quark effective theories (HQETs) in high-energy physics. While the first one includes only the heavy-particle component, the second one contains both the heavy-particle and heavy-antiparticle components, which are opposite in their parity. From these theories, we obtain two types of Kondo effects, in which the dispersions near the Fermi surface are very similar, but they differ in the structure at low momentum. We also classify the possible forms of condensates in the two limits. The two Kondo effects will be examined by experiments with Dirac/Weyl semimetals or quark matter, lattice simulations, and cold-atom simulations.

Strange pentaquarks with a hidden heavy quark-antiquark pair

Takeuchi, Sachiko*; Giachino, A.*; Takizawa, Makoto*; Santopinto, E.*; Oka, Makoto

Hadron Spectroscopy and Structure; Proceedings of the 18th International Conference (HADRON 2019), p.333 - 337, 2020/08

https://doi.org/10.1142/9789811219313_0056

Pentaquarks with or heavy quarks are very much interesting. We analyze the strange pentaquark with or in the coupled-channel quark cluster model. We find bound, resonance and cusp like states.

Kondo effect driven by chirality imbalance

Suenaga, Daiki*; Suzuki, Kei; Araki, Yasufumi; Yasui, Shigehiro*

Physical Review Research (Internet), 2(2), p.023312_1 - 023312_13, 2020/06

https://doi.org/10.1103/PhysRevResearch.2.023312

The Kondo effect is induced by the interaction between light fermions near the Fermi surface and heavy impurities, and it affects electric/thermal/transport properties of matter. The chirality (right-handed or left-handed) is one of the unique properties of relativistic (Dirac or Weyl) fermions. In normal matter, the numbers of right- and left-handed particles are equivalent to each other, but environments with a chirality imbalance can also be realized. In this paper, we theoretically propose the Kondo effect driven by a chirality imbalance (or chiral chemical potential) of relativistic light fermions. This effect is caused by the mixing between a right-handed (or left-handed) fermion and a heavy impurity in the chirality imbalanced matter. This is different from the usual Kondo effect induced by finite density (or chemical potential) for light fermions. We construct an effective model with an interaction between a relativistic fermion and a heavy impurity, and we derive the realization of the Kondo effect from both a perturbative calculation and a nonperturbative mean-field approach. We also discuss the temperature dependence, the coupling constant dependence, the susceptibilities, and the order of the phase transition for the Kondo effect. Such a Kondo effect will be tested by future lattice simulations.

Hidden-charm and bottom meson-baryon molecules coupled with five-quark states

Giachino, A.*; Hosaka, Atsushi; Santopinto, E.*; Takeuchi, Sachiko*; Takizawa, Makoto*; Yamaguchi, Yasuhiro*

Recent Progress in Few-Body Physics; Springer Proceedings in Physics, Vol.238, p.621 - 627, 2020/01

https://doi.org/10.1007/978-3-030-32357-8_98