Spin-Valley-Locked Tunneling Transport

• Spin–valley-locked tunneling transport is defined by quantum tunneling governed by composite spin–valley selection rules arising from strong spin–orbit coupling and broken symmetries.
• The phenomenon enables ultra-high tunneling magnetoresistance and coherent spin–valley conversion, as evidenced in TMDC heterostructures, Dirac semimetals, and engineered superlattices.
• Emerging applications include energy-efficient spintronic devices and quantum systems, with precise control over carrier spin and valley degrees of freedom driving new device functionalities.

Spin-valley-locked tunneling transport refers to quantum tunneling phenomena in materials and heterostructures where the spin and valley degrees of freedom of charge carriers are entwined by symmetry and spin–orbit coupling, such that tunneling—and its suppression—is dictated by composite spin–valley selection rules. This physics underlies a range of effects including ultra-high tunneling magnetoresistance, quantum filtering, coherent spin–valley conversion, and nonlocal current generation. The mechanism is universal, manifesting in quantum-confined systems, van der Waals spin valves, layered transition metal dichalcogenides, Dirac semimetals, engineered silicene superlattices, as well as in tailored photonic systems. The fundamental origin is the locking of spin to momentum-space valley due to broken inversion or time-reversal symmetry combined with strong spin–orbit interaction.

1. Band Structure Foundations of Spin–Valley Locking

Spin–valley locking arises when Bloch states at distinct time-reversal-related points in the Brillouin zone (valleys) are associated with opposite spin projections, a consequence of strong spin–orbit coupling (SOC) and broken symmetries. In ferromagnetic hexagonal transition-metal dichalcogenides such as 1T-VSe₂, 1T-VS₂, or 2H-VS₂, the DFT-calculated band structure reveals spin-up Fermi pockets localized around K/K′ valleys and spin-down pockets around M points, with minimal overlap elsewhere except near the Γ point (Yan et al., 13 Nov 2025). This separation enables the low-energy dispersion to be written as

$$E_{n,\sigma,\tau}(\mathbf{k}), \quad \sigma = \uparrow, \downarrow, \quad \tau \in \{\text{K}, \text{M}\},$$

implying that a given Fermi contour is indexed by a unique (spin, valley) tuple.

In monolayer WSe₂ and related group-VI TMDCs, the large atomic SOC splits valence-band maxima at K/K′ so that at K the topmost state is predominantly spin-up, while at K′ it is spin-down, enforcing rigid spin–valley locking (Kim et al., 2018). In Dirac materials under proximate exchange or magnetic barriers, this locking can be reflected in the mass term or induced gap structure.

2. Tunneling Transport Formalism and Selection Rules

Quantum tunneling in the spin–valley-locked regime is described by the Landauer–Büttiker approach, resolving transmission by both spin and valley:

$$T_{\sigma, \tau}(E, \mathbf{k}_\perp) = \operatorname{Tr}[\Gamma^L_{\sigma,\tau} G^r \Gamma^R_{\sigma,\tau} G^a].$$

The total conductance is

$$G = \sum_{\sigma, \tau} \frac{e^2}{h} \int_\text{BZ} T_{\sigma, \tau}(E_F, \mathbf{k}_\perp) d^2 k_\perp.$$

The analytic blocking mechanism for tunneling depends on matching both spin and valley quantum numbers across the junction:

$$T^{AP}_{\sigma, \tau}(E_F, \mathbf{k}_\perp) \propto \delta_{\sigma, \sigma'} \delta_{\tau, \tau'} \delta(E^L_{n, \sigma, \tau}(\mathbf{k}_\perp) - E^R_{n', \sigma', \tau'}(\mathbf{k}_\perp)) = 0 \quad (\tau \neq \tau').$$

This locking leads to full suppression of tunneling in the absence of intervalley scattering and when Fermi energies align such that only one spin–valley band per electrode participates.

Photon-assisted or Floquet tunneling introduces additional sidebands (in energy), which can be selectively spin–valley-polarized by field and barrier conditions (Jongchotinon et al., 2019). In layered heterostructures, conservation of in-plane momentum and spin restricts tunneling events to those between bands with the same composite quantum numbers (Kim et al., 2018).

3. Prototypical Systems and Experimental Manifestations

A. Van der Waals Spin-Valve Junctions with SVM Electrodes

In FM/insulator/FM vertical junctions where the electrodes exhibit spin–valley mismatch (SVM), the giant tunneling magnetoresistance (TMR) emerges. For parallel alignment (P), spin–valley channels connect across the junction, yielding finite tunneling. In the antiparallel configuration (AP), no such channels are overlap-matched, leading to

$$MR_o = \frac{G^P - G^{AP}}{G^{AP}} \times 100\%, \qquad MR_p = \frac{G^P - G^{AP}}{G^P} \times 100\%,$$

with $G^{AP} \rightarrow 0$ and $MR_o \gg 10^4\%$ universally across tested TMDC and metallic barriers (Yan et al., 13 Nov 2025).

B. Resonant Tunneling in Twist-Aligned TMDC Heterostructures

In WSe₂–hBN–WSe₂ stacks, zero-bias conductance peaks with sub-meV width occur for 0° twist alignment due to perfect spin–valley matching; the resonance vanishes at 180°, verifying that vertical tunneling is possible only when both momentum and spin–valley indices are preserved (Kim et al., 2018).

C. Magnetic Superlattices and Aperiodicity in Silicene

Aperiodic magnetic silicene superlattices (particularly Thue–Morse stacking) stabilize spin–valley-polarized transport and suppress conductance oscillations, enabling pronounced TMR and flat 100%-polarization plateaus (Villasana-Mercado et al., 2022).

D. Spin–Valley Filtering via Floquet Engineering

Time-periodic potential barriers in silicene (N-TP-N geometry) produce selective photon–sideband tunneling, which can be tuned to allow only one (spin, valley, sideband) channel, with efficiency exceeding 98% (Jongchotinon et al., 2019).

E. Spin–Valley–Locked Thermal and Nonlocal Transport

Spin Seebeck-driven injection in TMDC/ferromagnet systems generates valley-polarized spin currents that display quantized oscillations versus chemical potential and magnetic field due to the underlying Landau-level structure and spin–valley coupling in the TMDC (Hu et al., 6 Feb 2026). In graphene with induced SOC and broken inversion symmetry, a single tunnel barrier can generate transverse spin and valley Hall currents driven solely by the geometric phase acquired during coherent tunneling (Zeng, 2024).

4. Physical Mechanisms and Filtering Conditions

The essential mechanism can be classified as momentum-, spin-, and valley-conservation at the tunneling interface:

• In SVM van der Waals junctions, one spin species occupies a valley in one electrode and a different valley in the other; so even if spin is conserved, tunneling is forbidden if electrons cannot scatter their valley index (i.e., when intervalley processes are absent) (Yan et al., 13 Nov 2025).
• In TMDC vertical heterostructures, strong SOC and specific stacking order enforce the requirement that only identical spin–valley states on both sides are matched, and misalignment (by twist) disrupts this matching, turning off the resonance (Kim et al., 2018).
• In dynamic (Floquet) barriers, the effective Dirac mass for each (spin, valley, sideband) channel can be modulated, allowing only those channels whose Floquet energy matches the appropriate spin–valley resonance to transmit (Jongchotinon et al., 2019).
• In photonic and electronic topological systems, synthetic gauge fields engineered in the spin, valley, and sublattice (chirality) bases can be used to construct one-way (unidirectional) Klein tunneling and edge channels coexisting within a continuum, where only a single spin–valley channel remains gapless and permits perfect transmission (Ni et al., 2017).

Conditions for perfect filtering require (i) strict spin–valley locking, (ii) suppression of intervalley scattering in the barrier or at the interface, and (iii) energetic alignment such that only a single spin–valley channel is active at the Fermi level (Yan et al., 13 Nov 2025).

5. Materials Platforms and Computational Methodologies

Comprehensive computational analyses involve atomistic DFT band-structure calculations, NEGF-based Landauer–Büttiker transport, Floquet theory for time-dependent barriers, and transfer-matrix or tight-binding approaches for nanoscale systems. Representative platforms include:

• Metallic 1T-VSe₂, 1T-VS₂, 2H-VS₂ for SVM electrodes in vdW junctions (Yan et al., 13 Nov 2025).
• Monolayer/bilayer WSe₂, MoSe₂, MoS₂, WS₂ as barrier materials, optimized for lattice matching and strain below 5%.
• Thue–Morse and Fibonacci-modulated silicene superlattice geometries for robust spin–valley polarization (Villasana-Mercado et al., 2022).
• Ferromagnet/TMDC stacks for spin-Seebeck–driven valley-polarized currents (Hu et al., 6 Feb 2026).
• Graphene with proximity-induced SOC for coherent tunneling Hall effects (Zeng, 2024).
• Quantum-dot and double-dot systems in silicon and carbon nanotubes, for which atomistic tight-binding and configuration interaction methods resolve spin–valley–blockaded transport (Lansbergen et al., 2010, Osika et al., 2017).

Experimentally, key signatures include TMR ratios $>$99%, transport gaps approaching 0.7 eV, ultra-narrow resonance peaks, current steps signifying long spin–valley-blockaded lifetimes (τ > 48 ns in Si), and valley-polarization oscillations tied to Landau quantization.

6. Applications and Implications for Device Engineering

Spin–valley-locked tunneling enables:

• Ultra-high TMR spin valves using SVM metals, without the need for rare half-metals (Yan et al., 13 Nov 2025).
• Room-temperature spin–valley filters, transistors, and MRAM elements exploiting the valley degree of freedom and gate-tunability (Kim et al., 2018, Sousa et al., 2022).
• Energy-efficient, all-in-plane-current spin injection schemes (with torque efficiencies $\xi_{DL}\sim0.07$–0.2) competitive with or surpassing conventional MTJs (Sousa et al., 2022).
• Sideband-based spin–valleytronic circuitry for logic and quantum information, combining THz gating and optical control in 2D materials (Jongchotinon et al., 2019).
• Quantum devices harnessing long-lived valley states in silicon and carbon nanostructures, with design strategies informed by the suppression of intervalley scattering (Lansbergen et al., 2010, Osika et al., 2017).
• Photonic isolation, valley/spin demultiplexing, and edge-channel transport in synthetic photonic crystals leveraging engineered spin–valley locking (Ni et al., 2017).

7. Outlook: Robustness, Scalability, and Future Directions

The generality of spin–valley-locked tunneling transport is reinforced by its emergence across multiple material classes and dimensions—from van der Waals metals to quantum-confined silicon and Dirac photonic systems. Robustness depends critically on the absence of intervalley scattering, precise control of energetic alignment, and the preservation of spin–valley quantum numbers throughout the device.

Material choice and stacking configuration (e.g., twist angle in TMDC heterostructures; aperiodicity in silicene superlattices; choice of photonic lattice masses) allow on-demand tuning of selection rules and device functionality. The integration of spin–valley-locked tunneling phenomena in practical devices—memory, logic, or quantum information—will require continued advances in monolayer growth, interface engineering, and dynamic control of both electric/magnetic and optical fields.

The concept of spin–valley locking thus furnishes a powerful framework to engineer quantum transport properties, selectivity, and conversion processes across a wide class of electronic, optoelectronic, and photonic architectures, with implications for both classical and quantum technologies (Yan et al., 13 Nov 2025, Kim et al., 2018, Sousa et al., 2022, Villasana-Mercado et al., 2022, Lansbergen et al., 2010, Zeng, 2024, Ni et al., 2017, Jongchotinon et al., 2019, Jellal et al., 14 Jul 2025, Shandilya et al., 2024, Hu et al., 6 Feb 2026).