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Intertwined Hyperferroelectricity, Tunable Multiple Topological Phases and Giant Rashba Effect in Wurtzite LiZnAs

Saurav Patel, Paras Patel, Shaohui Qiu, Prafulla K. Jha

TL;DR

This work demonstrates that LiZnAs can host intertwined HyFE, Rashba spin-splitting, and multiple topological phases within a single material. It leverages a multi-code, first-principles framework to compute HyFE properties (including $P_ ext{HyFE} = 0.282~\mathrm{C/m^2}$ and a free-energy depth of $-66$ meV) and to map Rashba effects and topological transitions under biaxial strain, achieving a Weyl semimetal phase at $3.4\%$ BAS and a topological insulator phase at $4\%$ BAS with Rashba coefficients up to $\alpha_R \approx 5.91~\mathrm{eV\,\AA}$. A Wannier-based topological analysis confirms a strong TI with $(\nu_0; \nu_1\nu_2\nu_3)=(1;000)$ and reveals Weyl nodes with characteristic Berry curvature. Crucially, polarization switching reverses the Rashba spin texture, offering an electric route to manipulate spin in hyperferroelectric Rashba topological materials. The findings provide design principles for composite quantum compounds with robust, switchable spin and topological functionalities for nonvolatile spintronic applications.

Abstract

Composite quantum compounds offer a fertile ground for uncovering the complex interrelations between seemingly distinct phenomena in condensed matter physics for advanced nonvolatile and spintronics applications. Beyond topological superconductors and axion insulators, the idea of intertwined Hyperferroelectricity (HyFE), multiple topological phases and Rashba spin-splitting with reversible spin textures represents the local, global and symmetry-driven characteristics of quantum materials, respectively, offering unique pathways for enhanced functionalities. We unveiled a unified framework to achieve this synergy through the presence of crystalline symmetries and spin-orbit coupling in LiZnAs compound using first-principles calculations. HyFE exhibits ability to maintain spontaneous polarization under open-circuit boundary conditions, even with existence of depolarization field while Rashba effect exhibits paradigmatic spin texture in momentum space with tangential vector field. The presence of unstable $A_{2u}(LO)$ mode leads to free energy minimum with significant well depth and polarization of -66 meV and $P_{HyFE} = 0.282~C/m^2$, respectively indicating stable HyFE. The robust HyFE stem from mode-specific effective charges and larger high-frequency dielectric constants. This study also addresses the subtle question of whether critical point of topological phase transition shifts in response to drastically different Rashba spin-splitting values obtained from VASP and WIEN2k. Moreover, biaxial strain (BAS) induced Weyl semimetal (at 3.4% BAS) and topological insulating phase (after 3.4% BAS) is observed with giant Rashba coefficient of 5.91 eV Å and 2.42 eV Å, respectively. Furthermore, switching of bulk polarization leads to spin texture reversal, providing a robust mechanism to leverage spin degrees of freedom in these Hyperferroelectric Rashba topological materials.

Intertwined Hyperferroelectricity, Tunable Multiple Topological Phases and Giant Rashba Effect in Wurtzite LiZnAs

TL;DR

This work demonstrates that LiZnAs can host intertwined HyFE, Rashba spin-splitting, and multiple topological phases within a single material. It leverages a multi-code, first-principles framework to compute HyFE properties (including and a free-energy depth of meV) and to map Rashba effects and topological transitions under biaxial strain, achieving a Weyl semimetal phase at BAS and a topological insulator phase at BAS with Rashba coefficients up to . A Wannier-based topological analysis confirms a strong TI with and reveals Weyl nodes with characteristic Berry curvature. Crucially, polarization switching reverses the Rashba spin texture, offering an electric route to manipulate spin in hyperferroelectric Rashba topological materials. The findings provide design principles for composite quantum compounds with robust, switchable spin and topological functionalities for nonvolatile spintronic applications.

Abstract

Composite quantum compounds offer a fertile ground for uncovering the complex interrelations between seemingly distinct phenomena in condensed matter physics for advanced nonvolatile and spintronics applications. Beyond topological superconductors and axion insulators, the idea of intertwined Hyperferroelectricity (HyFE), multiple topological phases and Rashba spin-splitting with reversible spin textures represents the local, global and symmetry-driven characteristics of quantum materials, respectively, offering unique pathways for enhanced functionalities. We unveiled a unified framework to achieve this synergy through the presence of crystalline symmetries and spin-orbit coupling in LiZnAs compound using first-principles calculations. HyFE exhibits ability to maintain spontaneous polarization under open-circuit boundary conditions, even with existence of depolarization field while Rashba effect exhibits paradigmatic spin texture in momentum space with tangential vector field. The presence of unstable mode leads to free energy minimum with significant well depth and polarization of -66 meV and , respectively indicating stable HyFE. The robust HyFE stem from mode-specific effective charges and larger high-frequency dielectric constants. This study also addresses the subtle question of whether critical point of topological phase transition shifts in response to drastically different Rashba spin-splitting values obtained from VASP and WIEN2k. Moreover, biaxial strain (BAS) induced Weyl semimetal (at 3.4% BAS) and topological insulating phase (after 3.4% BAS) is observed with giant Rashba coefficient of 5.91 eV Å and 2.42 eV Å, respectively. Furthermore, switching of bulk polarization leads to spin texture reversal, providing a robust mechanism to leverage spin degrees of freedom in these Hyperferroelectric Rashba topological materials.

Paper Structure

This paper contains 8 sections, 8 equations, 7 figures, 1 table.

Table of Contents

  1. Introduction
  2. COMPUTATIONAL DETAILS
  3. RESULTS AND DISCUSSION
  4. Structural and Hyperferroelectric Properties of LiZnAs Compound
  5. Electronic Properties of LiZnAs Compound
  6. Topological Properties of LiZnAs Compound
  7. Rashba Spin texture and Switching Barrier of LiZnAs Compound
  8. CONCLUSIONS

Figures (7)

  • Figure 1: Schematic illustrating the intercorelation among ferroelectric distortion, Rashba spin-splitting, intertwined Rashba effect and topological states and switching mechanism of topological insulators, respectively.
  • Figure 2: Structural geometry of LiZnAs compound in the centrosymmetric (paraelectric) P6$_3$/mmc phase (a) and in the noncentrosymmetric (ferroelectric) P6$_3$mc phase (b), respectively. The solid black line elucidates the unit cell of respective phases. The corresponding bulk and (001) surface Brillouin zones (c) and the pressure-enthalpy profile of competing P6$_3$/mmc, P6$_3$mc and cubic $F\overline{4}3m$ phases.
  • Figure 3: The phonon dispersion curves of LiZnAs compound with (a) non analytic correction (NAC) term in P6$_3$/mmc phase and with NAC in P6$_3$mc phase (b), respectively. The calculated phonon eigenvectors for soft longitudinal-optic $A_{2u}(\mathrm{LO})$ (c) and $B_{1g}(\mathrm{LO})$ (d) modes, respectively. The arrows indicate corresponding atomic vibrations and amplitude.
  • Figure 4: The calculated total internal energy $U(\lambda)$ (a), depolarization energy $U_\mathrm{dp}(\lambda)$ (b), and total free energy $F(\lambda)$ (c) as a function of distortion $\lambda$ corresponding to all the intermediate structures along the distortion pathway from the high-symmetry P6$_3$/mmc phase to the low-symmetry P6$_3$mc phase.
  • Figure 5: The calculated relativistic band structure of polar P6$_3$mc phase using VASP (top panel) and WIEN2k (bottom panel). The evolution of electronic bands around the Fermi level under biaxial strain along M--$\Gamma$--K high symmetry path from VASP (a-d) and from WIEN2k (e-h), respectively. The similar nature of bands dispersion with significantly distinct Rashba coefficient was evidenced directly before and after the topological phase transition. The symbols in (a and d) mimics the corresponding orbital contribution
  • ...and 2 more figures