arXiv subjects

Kai-Yuan Zhang

Publications and source records attributed to Kai-Yuan Zhang.

9 recordsLinked to original sources

arXiv2026

Theory of Chirality-Induced Spin Selectivity in Trefoil-knot Molecules

The origin of chirality-induced spin selectivity (CISS) remains elusive, and ultrahigh spin polarization (SP) in topologically knotted molecules is unexplained. We develop a discrete geometric spin-orbit coupling (SOC) framework for molecular junctions, resolving site-specific curvature and current-partition effects beyond continuous models. For trefoil-knot molecules, it quantifies site-resolved geometric SOC, reaching $\sim$120 meV, nearly two orders of magnitude larger than intrinsic SOC of light atoms. The substrate-coupled benzene unit, carrying the largest current and remarkable geometric SOC, dominates the CISS effect. The framework quantitatively reproduces measured SP, temperature-dependent magnetoresistance (MR) and $Δ$MR trends, establishing discrete geometric SOC as a predictive tool for CISS in topologically knotted molecules.

cond-mat.mtrl-sci↗

arXiv2026

Geometric Spin-Orbit Coupling Resolves the Contradictory CISS Effect in Chiral Single Molecules

Some studies have reported clear chirality-induced spin selectivity (CISS) effect in four classes of chiral single molecules with remarkable spin polarization. In contrast, a recent high-precision measurement involving nearly a thousand individual tests failed to detect significant CISS signals in the same molecular systems (J. Am. Chem. Soc. 2025, \textbf{147}, 25043). These conflicting results cast doubt on whether CISS truly occurs in these chiral systems at the single-molecular level. To resolve this discrepancy, we develop a theoretical framework incorporating geometric spin-orbit coupling and environmental decoherence, enabling systematic study of the CISS in four chiral single molecules with distinct geometries and sizes. Our calculations show that the CISS effect is completely suppressed in both strong-coherence and strong-decoherence regimes, but becomes pronounced in the intermediate-decoherence regime, where observable spin polarization emerges. In the strong-coherence regime, both electron-electron interaction and electron-vibration coupling enhance the CISS effect: the former is more effective in large molecules, whereas the latter plays a more significant role in smaller ones. Increasing temperature further enhances spin polarization. The proposed mechanism unifies contradictory experimental observations and reveals how the CISS effect evolves from regular helical (helical symmetric) to irregular helical (point-symmetric or axially symmetric) chirality. This framework thus provides a basis for unifying CISS phenomena across single-molecule systems, regardless of their specific molecular configurations or symmetry classes.

cond-mat.mes-hall↗

arXiv2026

What Is the Real-Time Atomistic Mechanism Behind Chirality-Induced Spin Selectivity in Donor-Chiral Bridge-Acceptor Molecules?

Chiral-induced spin selectivity (CISS) has been experimentally observed in photo-excited donor-chiral bridge-acceptor (D-Bχ-A) molecules [Science 382, 197-201 (2023)]. However, the microscopic mechanism underlying CISS in such chiral systems remains elusive. Here we develop a quantum dynamical model that precisely maps the atomic structure of binaphthyl-type bridge dimers in isolated D-Bχ-A molecules and introduce a geometric spin-orbit coupling (SOC) mechanism to unveil the intrinsic origin of CISS in axially chiral systems. During photo-excited electron transport along the twisted pathways, the geometric SOC coupling strength exceeds the intrinsic coupling of light atoms by one to two orders of magnitude, readily producing observable high spin polarizations. The resulting spin polarization comprises two components: the CISS-associated polarizations along and perpendicular to the chiral axis are intrinsic to axial chirality, requiring neither external fields nor spin-superexchange transfer, while a non-Abelian curvature correction provides a rigorous mathematical definition of the chiral axis direction. Our calculated polarization components, chirality dependence, and relative magnitudes (30-40\%) quantitatively match time-resolved electron paramagnetic resonance measurements. This geometric SOC framework offers a self-consistent and general physical picture of CISS in axially chiral molecules and provides explicit theoretical guidance for the design of chiral spintronic devices.

cond-mat.mes-hall↗

arXiv2026

Ground-state properties of superheavy $Z=122$ isotopes within the deformed relativistic Hartree-Bogoliubov theory in continuum

The ground-state properties of superheavy $Z = 122$ isotopes are investigated using the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc). Bulk properties, including binding energies, Fermi energies, nucleon separation energies, quadrupole deformations, and root-mean-square radii, are calculated. The results are compared with those obtained from the relativistic continuum Hartree-Bogoliubov (RCHB) theory. By examining the dependence on the angular-momentum cutoff and the effects of triaxial and octupole deformations, a strategy for determining the ground states is suggested. Furthermore, based on an analysis of the Fermi and nucleon separation energies, the proton and neutron drip lines for $Z = 122$ isotopes are determined within both the DRHBc and RCHB frameworks. The possible magic numbers $N=184$, 258, and 350 are also suggested. Finally, the evolution of single-particle levels, deformation, charge and neutron radii as well as average pairing gaps with increasing neutron number, is discussed.

nucl-th↗

arXiv2025

Synergy and Competition of Dual Chirality in the Chirality-Induced Spin Selectivity of Supramolecular Helices

Recent progress in constructing supramolecular assemblies with hierarchical chirality offers new opportunities to investigate the chirality-induced spin selectivity (CISS) effect and its potential applications. In this work, we systematically examine the CISS effect in such multichiral systems by designing a class of multilayer helical architectures constructed of stacked and interfaced individual helical rings, each possessing well-defined local chirality. Through controlled interlayer twisting, a global helical handedness is further imposed, forming a multichiral tubular helix. Theoretical calculations reveal that these two distinct chiral hierarchies lead to several unprecedented CISS phenomena, such as enhanced spin polarization arising from cooperative dual chirality, along with the simultaneous emergence of transverse and longitudinal CISS signals. Moreover, interlayer torsional competition modulates the system's response to external fields. The dual-chiral geometry breaks the conventional symmetry of single helices, inducing an anomalous angular phase shift in magnetoresistance. Furthermore, Floquet analysis reveals that the interplay between local and global chirality enables controlled spin polarization switching under circularly polarized light. These findings provide a basic theoretical framework for studying the CISS in multichiral superstructures and establish design principles for coupled optical, magnetic, and spin manipulations, thereby facilitating the development of multichiral spintronic devices.

cond-mat.mes-hall↗

arXiv2025

Knot-Driven Spin Selectivity: Topological Chirality-Induced Robust Spin Polarization in Molecular Knots

Compared to traditional structural chiral materials (e.g., DNA, helicene), topological chirality in trefoil knot molecules has demonstrated multiple remarkable advantages in chirality-induced spin selectivity (CISS), including ultra-high spin polarization of nearly 90%, conductivity increased by two orders of magnitude, and high-temperature stability (up to 350$^{\circ}$C). However, the underlying physical mechanism remains elusive. This work establishes, for the first time, a fundamental theoretical framework for topological chirality-induced spin selectivity (TCISS) in trefoil knot molecules and identifies the necessary conditions for knot-driven spin selectivity. Our calculation results reveal that a trefoil knot molecule can exhibit spin polarization exceeding 60% along with significant conductivity. Notably, neither reducing the lattice number nor applying strain regulation significantly diminishes this ultra-high spin polarization, highlighting its robustness. Importantly, when the topological knot degenerates into a trivial structure, accompanied by the transition from topological chirality to structural chirality, the spin polarization sharply declines, demonstrating a strong correlation between the ultrahigh spin polarization and the knot topology. Our theory not only successfully elucidates the physical mechanism of TCISS, but also uncovers a new spin-polarized transport phenomenon termed knot-driven spin selectivity, offering new guiding principles for designing nonmagnetic materials for spintronics device applications.

cond-mat.mtrl-sci↗

arXiv2024

Triaxial shape of the one-proton emitter $^{149}$Lu

We revisit the proton emitter $^{149}$Lu utilizing the recently developed triaxial relativistic Hartree-Bogoliubov theory in continuum (TRHBc). By incorporating the microscopic nuclear structure properties from the TRHBc theory into the WKB approximation, we successfully reproduce the measured proton-emission half-life of $^{149}$Lu within experimental uncertainties. A triaxial ground state characterized by ($β=0.17,γ=31^\circ$) has been clarified for $^{149}$Lu. The inclusion of triaxiality significantly changes nuclear density distributions and potentials, which results in enhanced binding of both the nuclear system and the proton-emitting orbital. As a result, a slightly extended half-life for the proton emission of $^{149}$Lu is achieved after considering triaxial deformation degrees of freedom.

nucl-th↗

arXiv2024

The odd-even differences in stability peninsula for $106 \leqslant Z \leqslant 112$ region with the deformed relativistic Hartree-Bogoliubov theory in continuum

The predictive power of the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) with density functional PC-PK1 is demonstrated for superheavy region ($101 \leqslant Z \leqslant 120$) by comparing with available experimental and evaluated data in the AME2020. The DRHBc theory predicts 93 bound nuclei beyond the drip line $N = 258$ in the region of $106 \leqslant Z \leqslant 112$, which form a stability peninsula. The odd-even differences between odd-$N$ and even-$N$ nuclei are remarkable in the stability peninsula; the number of bound odd-$N$ nuclei is less than that of bound even-$N$ nuclei, and the one-neutron separation energy of an odd-$N$ nucleus is smaller than those of its neighboring even-$N$ nuclei due to the blocking effect. The deformation effect is indispensable for the reentrant stability beyond the drip line by significantly affecting the structure of single-particle levels around the Fermi energy. The interplay between deformation and pairing effects affects the position where the odd-$N$ nucleus becomes bound in the stability peninsula. By examining the deformation effect at different orders, it is found that quadrupole deformation makes leading contribution to the appearance of stability peninsula and the effects of hexadecapole and hexacontatetrapole deformations are nonnegligible.

nucl-th↗

arXiv2021

Possible existence of bound nuclei beyond neutron drip lines driven by deformation

Based on the relativistic calculations of the nuclear masses in the transfermium region from No $(Z=102)$ to Ds $(Z=110)$ by the deformed relativistic Hartree-Bogoliubov theory in continuum, the possible existence of the bound nuclei beyond the neutron drip lines is studied. The two-neutron and multi-neutron emission bound nuclei beyond the primary neutron drip line of $N=258$ are predicted in $Z=106,108$ and $110$ isotopes. Detailed microscopic mechanism investigation reveals that nuclear deformation plays a vital role in the existence of the bound nuclei beyond the drip line. Furthermore, not only the quadrupole deformation $β_{2}$, but also the higher orders of deformation are indispensible in the reliable description of the phenomenon of the reentrant binding.

nucl-th↗