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Ge as an orbitronic platform: giant in-plane orbital magneto-electric effect in a 2-dimensional hole gas

James H. Cullen, Dimitrie Culcer

Abstract

Increasing demand for computational power has initiated the hunt for energy efficient and stable memory devices. This is the overarching motivation behind the recent rise of \textit{orbitronics}, which looks to harness the orbital angular momentum of charge carriers in computing devices. Orbitronic devices require materials with efficient generation of orbital angular momentum (OAM). In 2D materials, OAM can be electrically generated via the orbital magneto-electric effect (OME). In this paper we report the calculation of the OME in 2 dimensional hole gases (2DHGs). We show that the OME in Ge holes is very large, for an applied electric field of the order $10^4$ V$/$m the OAM density is of the order $10^{12}$ $\hbar/$cm$^{2}$. Furthermore, we find the OME to be an order of magnitude larger than the Rashba-Edelstein effect in 2DHGs. The OME we calculated in 2DHGs generates OAM aligned in the plane and arises due to transitions between heavy and light hole states, which is unique to this system. Our results put Ge, as well as other p-type semiconductors, forward as strong candidates for building future orbitronic devices.

Ge as an orbitronic platform: giant in-plane orbital magneto-electric effect in a 2-dimensional hole gas

Abstract

Increasing demand for computational power has initiated the hunt for energy efficient and stable memory devices. This is the overarching motivation behind the recent rise of \textit{orbitronics}, which looks to harness the orbital angular momentum of charge carriers in computing devices. Orbitronic devices require materials with efficient generation of orbital angular momentum (OAM). In 2D materials, OAM can be electrically generated via the orbital magneto-electric effect (OME). In this paper we report the calculation of the OME in 2 dimensional hole gases (2DHGs). We show that the OME in Ge holes is very large, for an applied electric field of the order Vm the OAM density is of the order cm. Furthermore, we find the OME to be an order of magnitude larger than the Rashba-Edelstein effect in 2DHGs. The OME we calculated in 2DHGs generates OAM aligned in the plane and arises due to transitions between heavy and light hole states, which is unique to this system. Our results put Ge, as well as other p-type semiconductors, forward as strong candidates for building future orbitronic devices.
Paper Structure (7 sections, 6 equations, 5 figures)

This paper contains 7 sections, 6 equations, 5 figures.

Table of Contents

  1. Introduction
  2. Methodology
  3. Results
  4. Discussion
  5. Conclusions and Outlook
  6. Supplementary Material
  7. Acknowledgements

Figures (5)

  • Figure 1: The OAM density per unit field in a Ge 2DHG for a confinement of 20 nm and relaxation time $100$ ps for various Fermi energies and gate fields.
  • Figure 2: The OAM and spin densities per unit field in a Ge 2DHG for a confinement of 20 nm, relaxation time $100$ ps and a gate field of $F=10^5$ V$/$m.
  • Figure 3: The OAM densities per unit field for Ge for various well widths. The OAM densities are plotted for Fermi energies from the bottom of the heavy hole band to the energy of the first excited state. The relaxation time is $100$ ps and the gate field is $F=10^5$ Vm$^{-1}$.
  • Figure 4: The OAM densities per unit field for Ge and GaAs for a confinement of 20 nm. The OAM densities are plotted for Fermi energies from the bottom of the heavy hole band to the energy of the first excited state. Here we use a relaxation time of $100$ ps and a gate field of $F=10^5$ Vm$^{-1}$ for both materials.
  • Figure 5: The (a) OAM density per unit field in a Ge 2DHG and, (b) spin density per unit field in TI surface states. The 2DHG has a confinement of 20 nm and a gate field of $F=10^5$ Vm$^{-1}$. The TI surface state has Fermi velocity $v_F = 6.1\times10^5$ m/s. We choose typical relaxation time values of $100$ ps for the 2DHG and $1$ ps for the TI.