arXiv subjects

S. Q. Shen

Publications and source records attributed to S. Q. Shen.

8 recordsLinked to original sources

arXiv2026

Statistical Characteristics of Tunneling States in Strong-Field Atomic Ionization

The state of the tunneling electron under the potential barrier is important in strong laser-atom interaction but is difficult to identify. Recent experiments showed that the tunneling electron may be located in a bound state with high symmetry [Phys. Rev. Lett. 134, 213201 (2025)]. However, the quantitative characteristic of the tunneling state in a tunneling event remains unclear. Here, we study tunneling ionization of atoms in strong circular laser fields. The calculated photoelectron momentum distribution (PMD) through numerical solution of time-dependent Schrödinger equation (TDSE) presents an isotropic ring-shaped distribution and the most probable momentum (MPM) along the ring can be easily identified. The kinetic energy related to MPM is remarkably smaller than that predicted by the strong-field approximation (SFA) that ignores Coulomb potential. Surprisingly, for different target atoms and laser parameters, the kinetic energy difference of MPM between TDSE and SFA is always close to half of the corresponding Coulomb potential at the tunnel exit. This phenomenon can be well described by a proposed model, which indicates that the tunneling electron is in an exit-position-dependent quasibound state agreeing with the virial theorem. These results quantitatively reveal the characteristics of tunneling states from a statistical perspective.

physics.atom-ph↗

arXiv2025

Single-photon ionization of H$_2^+$ in near-circular laser fields with lower photon energy

We study single-photon ionization of aligned H$_2^+$ in low-intensity near-circular laser fields with lower photon energy numerically and analytically. The photoelectron momentum distribution (PMD) within the laser polarization plane, obtained by numerical simulations, shows a remarkable offset angle, which changes with changing the internuclear distance and the laser frequency. This phenomenon is different from that observed in recent experiments [Science 370, 339 (2020)] which is related to the PMD along the propagation direction of the laser. This phenomenon holds even for H$_2^+$ with short-range Coulomb potentials but disappears for atoms, different from that observed in attoclock experiments. We show that the molecular Coulomb potential near the two atomic centers plays an important role here and theory models associated with more accurate continuum wave function of the molecule are needed for reproducing this phenomenon. This phenomenon can be useful for ultrafast probing of molecules with high resolution of several attoseconds or even zeptoseconds.

physics.atom-ph↗

arXiv2003

Spin current in the Kondo lattice model

By using the projection operator technique it is observed that the strong Hund's rule coupling and s-d interaction in transition metal elements may lead to an effective coupling between the spin current and spin spirality. As a result, the spin spirality can be regarded as a driving force to produce a spin current. The spin current may give rise to a novel type of field acting on the spins. A spin battery is designed based on the interactions between the spin current and spin spirality.

cond-mat.str-el↗

arXiv2002

Non-exponential relaxation and quantum tunnel splitting in molecular magnet Fe8

Magnetic relaxation in molecular magnets under a sweeping field is studied by taking into account local stray fields. It is found that the randomness of local stray field leads to a distribution of the relaxation rate which subsequently makes the relaxation deviate from the exponential law as predicted by the Landau-Zener model such that the Landau-Zener method needs to be revised to deduce an exact tunneling splitting. The tunneling splitting and distribution width of local stray fields are derived from the experimental data for molecular magnets Fe8.

cond-mat.mes-hall↗

arXiv2002

Quantum tunneling of two coupled single-molecular magnets

Two single-molecule magnets are coupled antiferromagnetically to form a supramolecule dimer. We study the coupling effect and tunneling process by means of the numerical exact diagonalization method, and apply them to the recently synthesized supramoleculer dimer [Mn4]2 The model parameters are calculated for the dimer based on the tunneling process. The absence of tunneling at zero field and sweeping rate effect on the step height in the hysterisis loops are understood very well in this theory.

cond-mat.mes-hall↗

arXiv2002

Antiferromagnetic Heisenberg model on anisotropic triangular lattice in the presence of magnetic field

We use Schwinger boson mean field theory to study the antiferromagnetic spin-1/2 Heisenberg model on an anisotropic triangular lattice in the presence of a uniform external magnetic field. We calculate the field dependence of the spin incommensurability in the ordered spin spiral phase, and compare the results to the recent experiments in Cs$_{2}$CuCl$_{4}$ by Coldea et al. (Phys. Rev. Lett. 86, 1335 (2001)).

cond-mat.str-el↗

arXiv1995

Pseudospin Symmetry, Peierls Instability, and Charge Density Wave in a One-Dimensional Tight-Binding Model

We show that there is pseudospin SU(2) symmetry in the one-dimensional tight-binding model with the inter-molecular electron-phonon interaction. We discuss the relation between the pseudospin symmetry breaking and the charge-density wave (CDW). For a finite lattice at half-filling, the Peierls instability drives the lattice to {\it dimerization} at low temperature, however, the system remains the SU(2) symmetry invariant and is not CDW state. An attractive on-site electron-electron interaction makes the pseudospin symmetry spontaneously broken in the thermodynamic limit and the CDW state arises as well. Hence, it is clear that spontaneous pseudospin symmetry breaking produces the CDW state.s the pseudospin symmetry spontaneously broken in the thermodynamic limit and the CDW state arises as well. Hence, it is clear that spontaneous pseudospin symmetry breaking produces the CDW state.

cond-mat↗

arXiv1995

Pseudospin SU(2) Symmetry Breaking, Charge Density Wave and Superconductivity in the Hubbard Model

In this paper, we discuss physical consequences of pseudospin SU(2) symmetry breaking in the negative-U Hubbard model at half-filling. If pseudospin symmetry is spontaneously broken while its unique subgroup U(1) remains invariant, it will lead to the charge density wave (CDW) ground state. Furthermore, if the U(1) symmetry is also broken, the ground state will have the off-diagonal long range order (ODLRO), signaling a superconductor. In this case, CDW and superconductivity coexist to form a supersolid. Finally, we show that CDW suppresses, but does not destroy superconductivity.

cond-mat↗