Room-Temperature Pauli Spin Blockade and Current Rectification in 15-13-15 Armchair Graphene Nanoribbon Heterostructures

TL;DR

This work demonstrates that 15-13-15 armchair graphene nanoribbon heterostructures host topologically protected interface states described by the SSH model, forming energy-separated quantum-dot-like subbands suitable for robust transport at elevated temperatures. Finite-length AGNRHs exhibit both end zigzag edge states and topological interface states, with linear Stark shifts under applied bias that modulate tunneling pathways; the interface states function as a serial double quantum dot (SDQD) system whose conductance follows an SDQD form and can reach a maximum when the interdot hopping matches the effective tunneling rate. Employing a Keldysh Green function treatment of the extended Anderson model, the study reveals charge-stability diagrams, Coulomb blockade oscillations, and room-temperature Pauli spin blockade (PSB) current rectification that persists under favorable orbital offsets and coupling, including a thermally activated J_B2 channel at high temperature. The results highlight the potential of bottom-up synthesized, two-gate AGNRH devices for spin-current conversion and quantum information processing, offering advantages over lithographically defined structures due to precise tunability of interface-state parameters and straightforward electrode integration.

Abstract

In this study, we investigate the electronic structures of 13-11-13 and 15-13-15 armchair graphene nanoribbon (AGNR) superlattices (SLs) using a tight-binding model. We demonstrate that the conduction and valence subbands of 15-13-15 AGNR SLs can be accurately described by the Su-Schrieffer-Heeger model, with topologically protected interface states emerging at the junctions between 15-AGNR and 13-AGNR segments. These interface states enable the formation of quantum dot arrays with energy levels well separated from bulk states, making them promising candidates for high-temperature solid-state quantum processors. For 15-13-15 AGNRH segments, we observe both localized zigzag edge states and topologically protected interface states under longitudinal electric fields, with the latter providing efficient tunneling channels in contrast to the less conductive edge states. We further explore nonlinear charge transport through these interface states under Pauli spin blockade, showing that tunneling current spectra reveal charge stability diagrams and Coulomb blockade oscillations, consistent with experimental findings in other serial double quantum dot systems. Additionally, we examine the impact of orbital offsets on tunneling current rectification and demonstrate that significant current rectification is achieved over a wide temperature range when level broadening is optimized. These results highlight the potential of 15-13-15 AGNRHs for robust spin-current conversion and applications in quantum devices, offering advantages over other proposed structures due to precise tunability of key parameters via bottom-up synthesis techniques and the ease of two-gate electrode integration.

Figures (13)

• Figure 1: Schematic diagrams of armchair graphene nanoribbon heterostructures (AGNRHs). (a) $13_{w}-11_{x}-13_{y}$ AGNRH, where the indices $w$, $x$, and $y$ denote the lengths (in unit cells, u.c.) of the respective AGNR segments. The unit cell of the AGNR is labeled by $R_1$, and $R_2$ indicates the super unit cell $13_2-11_3-13_2$ of the AGNR superlattice (AGSL). (b) $15_4-13_3-15_4$ AGNRH with zigzag edge sites coupled to the electrodes. Here, $\Gamma_{L}$ and $\Gamma_R$ represent the electron tunneling rates between the left (right) electrode and the atoms at the corresponding zigzag edge. (c) Schematic diagram of the serial double quantum dot (SDQD) formed by the topologically protected interface states of the AGNRHs. The SDQD, characterized by effective tunneling rates $\Gamma_{e,L}$ and $\Gamma_{e,R}$, is controlled by two gate voltages, $V_{L,g}$ and $V_{R,g}$, as well as an applied voltage $V_{SD}$ between the source and drain electrodes.
• Figure 2: Electronic subband structures of various AGNR superlattice structures: (a) $13_2$-$11_5$-$13_2$, (b) $13_2$-$11_{10}$-$13_2$, (c) $15_2$-$13_5$-$15_2$, and (d) $15_2$-$13_{10}$-$15_2$. Here, $L$ denotes the length of each superlattice.
• Figure 3: Energy levels of AGNR heterostructures as functions of the applied voltage $V_y$ for various structures: (a) $13_4$-$11_5$-$13_4$, (b) $13_4$-$11_{10}$-$13_4$, (c) $15_4$-$13_5$-$15_4$, and (d) $15_4$-$13_{10}$-$15_4$.
• Figure 4: Charge densities of topological states for $13_4$-$11_5$-$13_4$ and $15_4$-$13_5$-$15_4$ AGNRHs. (a) $\Sigma_{c1}$, (b) $\Sigma_{c2}$, and (c) $\Sigma_{c3}$ for the $13_4$-$11_5$-$13_4$ AGNRH; (d) $\Sigma_{c1}$, (e) $\Sigma_{c2}$, and (f) $\Sigma_{c3}$ for the $15_4$-$13_5$-$15_4$ AGNRH. The radius of each circle represents the magnitude of the charge density for the topological states.
• Figure 5: (a) Electrical conductance $G_e$ of the $13_4$-$11_5$-$13_4$ AGNRH with $\Gamma_t = 2.7$ eV and $N_a = 52$ ($L_a = 5.4$ nm) as a function of chemical potential $\mu$ at zero temperature. (b)-(f) Electrical conductance $G_e$ of the $13_4$-$11_5$-$13_4$ AGNRH as functions of $\mu$ at zero temperature for various values of $\Gamma_t$: (b) $\Gamma_t = 72$ meV, (c) $\Gamma_t = 54$ meV, (d) $\Gamma_t = 36$ meV, (e) $\Gamma_t = 18$ meV, and (f) $\Gamma_t = 9$ meV. Symmetrical tunneling rates are considered, with $\Gamma_L = \Gamma_R = \Gamma_t$.