[Paper Review] Layer- and Gate-tunable Spin-Orbit Coupling in a High Mobility Few-Layer Semiconductor

Dmitry Shcherbakov, Petr Stepanov+15 more|arXiv (Cornell University)|Dec 2, 2020

Magnetic and transport properties of perovskites and related materials32 references4 citations

TL;DR

This study demonstrates electric-field and thickness-tunable spin-orbit coupling (SOC) in few-layer InSe, achieving continuous modulation of intrinsic spin splitting from 0 to 20 meV via an out-of-plane gate voltage. The SOC parameter α is thickness-dependent and can be enhanced by up to an order of magnitude, enabling unprecedented control for spintronic and topological device applications in 2D semiconductors.

ABSTRACT

Spin-orbit coupling (SOC) is a relativistic effect, where an electron moving in an electric field experiences an effective magnetic field in its rest frame. In crystals without inversion symmetry, it lifts the spin degeneracy and leads to many magnetic, spintronic and topological phenomena and applications. In bulk materials, SOC strength is a constant that cannot be modified. Here we demonstrate SOC and intrinsic spin-splitting in atomically thin InSe, which can be modified over an unprecedentedly large range. From quantum oscillations, we establish that the SOC parameter αis thickness-dependent; it can be continuously modulated over a wide range by an out-of-plane electric field, achieving intrinsic spin splitting tunable between 0 and 20 meV. Surprisingly, αcould be enhanced by an order of magnitude in some devices, suggesting that SOC can be further manipulated. Our work highlights the extraordinary tunability of SOC in 2D materials, which can be harnessed for in operando spintronic and topological devices and applications.

Motivation & Objective

• To explore tunability of spin-orbit coupling (SOC) in atomically thin InSe, a high-mobility 2D semiconductor.
• To investigate whether SOC strength can be electrically modulated via an external gate field.
• To determine the dependence of SOC on layer thickness and applied electric field.
• To establish the range and mechanism of intrinsic spin splitting tunability in few-layer InSe.
• To assess the potential of InSe for in operando spintronic and topological applications through SOC engineering.

Proposed method

• Extraction of the spin-orbit coupling parameter α from quantum oscillation measurements in high-mobility few-layer InSe devices.
• Application of an out-of-plane electric field via a back-gate to tune the SOC strength continuously.
• Control of layer thickness through mechanical exfoliation to study thickness-dependent SOC behavior.
• Use of magnetotransport measurements to resolve spin-splitting energy levels and extract α.
• Comparison of experimental data with theoretical models to confirm the origin of tunability.
• Identification of devices with enhanced SOC by up to an order of magnitude, suggesting additional tuning mechanisms.

Experimental results

Research questions

• RQ1 Can spin-orbit coupling in few-layer InSe be tuned electrically via a gate voltage?
• RQ2 How does the spin-orbit coupling parameter α vary with the number of layers in InSe?
• RQ3 What is the maximum range of intrinsic spin splitting achievable through gate control in InSe?
• RQ4 Why is an order-of-magnitude enhancement in SOC observed in some devices despite similar thickness and gate conditions?
• RQ5 To what extent can SOC be engineered for practical spintronic and topological applications in 2D materials?

Key findings

• The spin-orbit coupling parameter α in few-layer InSe is thickness-dependent, with measurable variation across different layer counts.
• An out-of-plane gate voltage enables continuous tuning of the intrinsic spin splitting from 0 to 20 meV.
• The SOC strength can be enhanced by up to an order of magnitude in specific devices, indicating strong local tunability beyond average trends.
• Quantum oscillation measurements confirm the presence of spin-splitting and allow precise extraction of α.
• The observed tunability exceeds that of bulk materials and demonstrates a new degree of control in 2D semiconductors.
• The results highlight the potential of InSe as a platform for dynamically reconfigurable spintronic and topological devices.