2H-TaS2 Nanowires: Superconductivity & CDW

• 2H-TaS2 nanowires are one-dimensional forms of hexagonal tantalum disulfide that exhibit enhanced superconductivity (Tc ≈ 3.6 K) compared to bulk materials.
• Their synthesis via a two-step conversion from TaS3 precursors preserves high-aspect-ratio morphology, with widths ranging from 80 to 700 nm and lengths up to 1 mm.
• Dimensional confinement in these nanowires suppresses charge-density-wave signatures and results in complex vortex dynamics, including flux jumps and a second magnetization peak.

2H-TaS$_2$ nanowires are one-dimensional wire-like realizations of hexagonal 2H-phase tantalum disulfide in which reduced dimensionality, preserved anisotropic morphology, and the competition between superconductivity and charge-density-wave (CDW) order become central materials issues. In the direct nanowire literature represented here, they are obtained by conversion of TaS$_3$ nanowire precursors into 2H-TaS$_2$, yielding high-aspect-ratio nanowires with enhanced superconductivity relative to bulk 2H-TaS$_2$, a reported $T_c \approx 3.6$ K, $\mu_0H_{c2}(2\,\mathrm{K}) \approx 5$ T, and nontrivial vortex behavior including flux jumps and a second magnetization peak (Pollard et al., 21 Jul 2025). Closely related reduced-dimensional TaS$_2$ systems—ultra-narrow nanoribbons, suspended membranes, intercalated thin flakes, atomically thin free-hanging layers, and vertical Josephson heterostructures—do not constitute nanowires in a strict geometric sense, but they define the broader confinement regime in which 2H-TaS$_2$ exhibits strong sensitivity to CDW order, disorder, interlayer coupling, and multiband superconducting phase structure (Cain et al., 2020).

1. Material identity and dimensional realization

The directly studied nanowire material is explicitly 2H-TaS$_2$ in nanowire form, with the hexagonal 2H-TaS$_2$ phase identified by XRD after conversion from monoclinic TaS$_3$0 precursors (Pollard et al., 21 Jul 2025). The reported morphology is retained from the precursor: cross-sectional widths of 80–700 nm, lengths up to a millimeter, and a preserved 1D morphology after conversion. XRD shows dominant reflections of hexagonal 2H-TaS$_3$1 and a strong (002) reflection interpreted as preferred orientation along the c-axis (Pollard et al., 21 Jul 2025).

This nanowire form should be distinguished from other reduced-dimensional TaS$_3$2 geometries. The nearest quasi-1D analogue in the literature provided here is the ultra-narrow TaS$_3$3 nanoribbon grown inside multi-walled carbon nanotubes, with widths as low as 2.5 nm, an average width of 3.8 nm, typical thicknesses of 1–3 layers, and lengths commonly $_3$4 nm; these are ribbon-shaped rather than cylindrical, but they demonstrate the quasi-1D confinement limit of H-phase TaS$_3$5 (Cain et al., 2020). Suspended exfoliated drums, intercalated flakes, and atomically thin free-hanging sheets are likewise not nanowires, yet they are relevant because they isolate thickness, disorder, surface exposure, and interlayer-decoupling effects that are likely to matter strongly in nanowire geometries (Lee et al., 2021).

2. Synthesis and structural characterization

The direct nanowire synthesis is a two-step conversion route in which preformed TaS$_3$6 nanowires serve as a morphological template for the final 2H-TaS$_3$7 nanowires (Pollard et al., 21 Jul 2025). In the first step, Ta and S powders of 99.999% purity are mixed at a nominal Ta:S = 1:3.03, sealed in an evacuated quartz ampoule with inner diameter 10 mm and length ~10 cm, heated to 750 $_3$8C at 1 $_3$9C/min, held for 48 h, and cooled at 2 $_2$0C/min to produce monoclinic TaS$_2$1 nanowires. In the second step, these TaS$_2$2 nanowires are sealed again in a quartz ampoule with Ta powder placed separately at the opposite end, evacuated to $_2$3 torr, heated to 590 $_2$4C, held for 12 h, and cooled at 2 $_2$5C/min (Pollard et al., 21 Jul 2025).

The conversion is described by the equilibrium reaction

$_2$6

Within this scheme, the Ta powder acts as a sulfur absorber, producing a self-limiting reaction mechanism in which sulfur is selectively removed and the reaction stops once the Ta is consumed (Pollard et al., 21 Jul 2025). The stated rationale for this sealed-ampoule vapor-phase conversion is to avoid the uncontrolled sulfur loss, oxidation, TaO$_2$7 formation, and morphology collapse associated with direct annealing in flowing inert gas above 300 $_2$8C.

Structural characterization is based primarily on XRD + SEM + EDS. XRD confirms monoclinic TaS$_2$9 before conversion and hexagonal 2H-TaS$_2$0 after conversion. SEM shows a dense network of long, flexible nanowires in the precursor and retention of the one-dimensional morphology after conversion. EDS is cited as compositional confirmation of the converted nanowires as phase-pure 2H-TaS$_2$1. At the same time, the XRD analysis notes several weak peaks marked by asterisks, which might arise from minor secondary phases or slight residual precursor traces; accordingly, the phase-purity claim is strong but not unqualified (Pollard et al., 21 Jul 2025).

Parameter	Reported value	Context
Nanowire width	80–700 nm	Cross-sectional widths
Nanowire length	Up to 1 mm	Preserved 1D morphology
Precursor synthesis temperature	750 $_2$2C	TaS$_2$3 growth
Precursor dwell time	48 h	TaS$_2$4 growth
Conversion temperature	590 $_2$5C	TaS$_2$6 $_2$7 TaS$_2$8
Conversion time	12 h	TaS$_2$9 $T_c \approx 3.6$0 TaS$T_c \approx 3.6$1
Conversion vacuum	$T_c \approx 3.6$2 torr	Sealed ampoule
Preferred orientation	Strong (002) reflection	XRD interpretation

The absence of TEM, HRTEM, SAED, Raman, XPS, and explicit atomic-ratio tables in the direct nanowire study is a material limitation of the current characterization set (Pollard et al., 21 Jul 2025). By contrast, the quasi-1D nanoribbon literature establishes that H-phase TaS$T_c \approx 3.6$3 under stronger lateral confinement can remain structurally ordered while developing ordered S-vacancy superstructures and edge-localized electronic states, which suggests that atomic-scale defect topology may become increasingly important as 2H-TaS$T_c \approx 3.6$4 wires approach the few-nanometer regime (Cain et al., 2020).

3. Superconductivity, magnetotransport, and vortex dynamics

The defining electronic result for directly synthesized 2H-TaS$T_c \approx 3.6$5 nanowires is enhanced superconductivity relative to bulk 2H-TaS$T_c \approx 3.6$6 (Pollard et al., 21 Jul 2025). The paper reports a superconducting transition at

$T_c \approx 3.6$7

observed in resistivity / magnetotransport, AC susceptibility, and DC magnetization. The transport data show a clear superconducting transition near 3.6 K in TaS$T_c \approx 3.6$8 nanowire bundles, whereas the TaS$T_c \approx 3.6$9 precursor nanowires remain semiconducting and non-superconducting down to 2 K (Pollard et al., 21 Jul 2025). AC susceptibility shows a sharp diamagnetic onset at $\mu_0H_{c2}(2\,\mathrm{K}) \approx 5$0 K, while DC magnetization shows pronounced ZFC diamagnetic shielding below $\mu_0H_{c2}(2\,\mathrm{K}) \approx 5$1, with a less diamagnetic FC curve attributed to trapped flux.

The nanowire superconducting transition is compared explicitly with the bulk value $\mu_0H_{c2}(2\,\mathrm{K}) \approx 5$2 K, so the nanowire $\mu_0H_{c2}(2\,\mathrm{K}) \approx 5$3 is described as roughly 4.5× higher than in bulk 2H-TaS$\mu_0H_{c2}(2\,\mathrm{K}) \approx 5$4 (Pollard et al., 21 Jul 2025). The field scale is likewise strongly enhanced: $\mu_0H_{c2}(2\,\mathrm{K}) \approx 5$5 compared in the paper to a bulk literature value

$\mu_0H_{c2}(2\,\mathrm{K}) \approx 5$6

or approximately ~4.3× larger than the cited bulk value (Pollard et al., 21 Jul 2025). The $\mu_0H_{c2}(2\,\mathrm{K}) \approx 5$7 points are extracted from field-dependent resistance curves and display a linear decrease with increasing temperature over the measured range. The exact resistive criterion used for $\mu_0H_{c2}(2\,\mathrm{K}) \approx 5$8 extraction is not specified.

The magnetic characterization indicates a type-II mixed state with strong pinning and nontrivial vortex dynamics. At 2 K, isothermal $\mu_0H_{c2}(2\,\mathrm{K}) \approx 5$9 shows pronounced flux jumps and a second magnetization peak or fishtail effect, interpreted as signatures of strong vortex pinning, magnetic instability, and a crossover from elastic to plastic vortex regimes (Pollard et al., 21 Jul 2025). The first flux-jump field is stated to occur at higher-than-predicted values, possibly because of significant flux creep. The measurement geometry is, however, only partially specified: the samples are bundles of TaS$_2$0 nanowires measured in a Quantum Design PPMS using two-probe electrical contacts made with room-temperature-cured silver paste, while field orientation and applied current density are not stated (Pollard et al., 21 Jul 2025).

The standard Ginzburg–Landau relation

$_2$1

is relevant to the reported upper critical field. An inferred estimate, explicitly labeled as such in the source details, gives

$_2$2

when $_2$3 T is inserted into this expression (Pollard et al., 21 Jul 2025). This suggests a coherence scale substantially smaller than the reported nanowire widths, although the value itself is not an author-reported experimental extraction.

4. Charge-density-wave competition and confinement effects

The direct nanowire study frames the superconducting enhancement in terms of dimensional confinement, suppression of charge density wave order, enhanced electron-phonon coupling, and an increased density of states at the Fermi level (Pollard et al., 21 Jul 2025). Experimentally, the support for CDW suppression within that paper is limited but concrete: no CDW transition is observed in the resistance data of the TaS$_2$4 nanowires. The argument is therefore transport-based rather than microscopic, and the paper explicitly does not provide Raman, ARPES, STM, or direct CDW diffraction evidence for the nanowires themselves (Pollard et al., 21 Jul 2025).

Bulk and suspended-flake studies define the relevant CDW benchmarks. In bulk single-crystalline 2H-TaS$_2$5, temperature-dependent four-probe transport identifies an incommensurate charge-density-wave transition at

$_2$6

while Raman spectroscopy shows a two-phonon mode near 182 cm$_2$7, an in-plane $_2$8 mode near 290 cm$_2$9, an out-of-plane $_2$0 mode near 404 cm$_2$1, and low-temperature collective features at approximately 48, 77, and 95 cm$_2$2 associated with amplitude and zone-folded CDW modes (Rawat et al., 2023). The same work argues that Raman anomalies in the 2ph and $_2$3 modes persist up to $_2$4 K, above the transport-defined $_2$5, and reports fitted parameters $_2$6 and $_2$7 for the 2ph-mode analysis (Rawat et al., 2023).

Suspended nanoscale 2H-TaS$_2$8 membranes add a separate but highly relevant result: nanomechanical resonance detects the CDW transition near the expected pristine value of 75–77 K, but ambient-air degradation can shift $_2$9 upward to 105 K in one device and as high as 129 K in another, while a locally damaged membrane exhibits multiple transitions at 87 K, 103 K, and 118 K with hysteresis (Lee et al., 2021). The same study also reports that stronger disorder introduced by laser oxidation or FIB milling yields no observable CDW transition (Lee et al., 2021). This does not constitute nanowire evidence, but it establishes that reduced-dimensional 2H-TaS$_2$0 can have CDW scales that are highly sensitive to thickness, disorder, air exposure, local structural nonuniformity, and mechanical boundary conditions.

Taken together, these results support a cautious synthesis. The direct nanowire literature supports the statement that enhanced superconductivity coexists with the absence of a visible CDW signature in $_2$1 (Pollard et al., 21 Jul 2025). A plausible implication is that future nanowire-specific CDW work should combine transport with Raman or diffraction, because the broader TaS$_2$2 literature shows that CDW behavior in reduced dimensions can be shifted, fragmented, or even rendered spatially nonuniform without a simple bulk-like transport signature (Lee et al., 2021).

5. Related reduced-dimensional 2H-TaS$_2$3 platforms

Several adjacent TaS$_2$4 systems are not nanowires, yet they delimit the physical landscape into which 2H-TaS$_2$5 nanowires fit. The most relevant examples concern extreme lateral confinement, interlayer decoupling, nanoplasmonics, and unconventional Josephson response.

System	Geometry	Key relevance to nanowires
Ultra-narrow TaS$_2$6 nanoribbons (Cain et al., 2020)	Encapsulated quasi-1D ribbons inside MWCNTs	Widths 2.5–6 nm, 1–3 layers, ordered S-vacancy supermodulation, flat bands near $_2$7
Suspended 2H-TaS$_2$8 membranes (Lee et al., 2021)	Exfoliated circular drums	$_2$9 near 75 K pristine, shifted to 105 K and 129 K after degradation
Intercalated 2H-TaS$_2$0 flakes (Pereira et al., 28 Oct 2025)	Tens-of-nm-thick contacted flakes	CDW suppression, superconducting onset above 3 K, midpoint $_2$1 K, zero-resistance state
Atomically thin free-hanging TaS$_2$2 (Do et al., 2024)	Suspended monolayers and bilayers	Plasmons up to $_2$3, confinement ratio $_2$4, group velocity $_2$5
TaS$_2$6/NbSe$_2$7 Josephson junctions (Margineda et al., 1 May 2026)	Vertical van der Waals heterojunctions	Zero-field Josephson diode effect, diode efficiency $_2$8, evidence for multiband TRSB

The quasi-1D nanoribbon study is particularly informative because it pushes H-phase TaS$_2$9 far deeper into the confinement regime than the direct nanowire work (Cain et al., 2020). In those nanotube-encapsulated ribbons, DFT predicts CDW-type distortions and partial gap openings of about $_3$00 eV, while atomic-resolution STEM reveals a zig-zag defect supermodulation with a period of approximately 9 unit cells, assigned to ordered arrays of linearly formed S vacancies (Cain et al., 2020). This indicates that once the lateral scale is reduced to a few nanometers, edge thermodynamics and ordered defect arrays can become as important as the ideal 2H lattice itself.

The intercalation study on contacted flakes shows a different route to enhanced superconductivity: amylamine or AM:ACN intercalation expands the interlayer spacing from 6.03 Å to 10.3 Å, suppresses the CDW anomaly near 80 K, raises the superconducting onset to above 3 K, and in the AM:ACN = 1:2 case produces a fully developed zero-resistance state with midpoint $_3$01 K (Pereira et al., 28 Oct 2025). This is not a nanowire experiment, but it demonstrates that weakening interlayer coupling can move 2H-TaS$_3$02 toward a monolayer-like superconducting regime.

The atomically thin plasmonics study and the Josephson nonreciprocity study show that reduced-dimensional 2H-TaS$_3$03 is not only a superconductor/CDW material but also a metallic platform for highly confined optical modes and multiband superconducting phase phenomena. In monolayer and bilayer free-hanging TaS$_3$04, near-IR plasmons remain outside the electron-hole continuum up to $_3$05, with a reported confinement ratio of $_3$06 and group velocity $_3$07 (Do et al., 2024). In TaS$_3$08/NbSe$_3$09 heterojunctions, a zero-field Josephson diode effect with $_3$10 is interpreted as evidence for an intrinsic multiband TRSB phase structure in superconducting 2H-TaS$_3$11 (Margineda et al., 1 May 2026). These results do not directly transfer to nanowire mode structures or wire transport, but they imply that nanowire experiments may need to account for multiband, interfacial, and nonlocal electrodynamic effects rather than treating 2H-TaS$_3$12 as a simple single-band metal.

6. Limitations and open problems

The present direct literature on 2H-TaS$_3$13 nanowires is substantial enough to establish a real nanowire platform, but still incomplete in several technically important respects (Pollard et al., 21 Jul 2025). The nanowire paper does not report heat capacity, $_3$14, penetration depth $_3$15, GL parameter $_3$16, anisotropy, critical current density $_3$17, or irreversibility field $_3$18 numerically. It does not specify the field orientation or the applied current / current density in the magnetotransport data. Nor does it provide nanowire-resolved microscopic evidence for CDW suppression, leaving the absence of a CDW anomaly in $_3$19 as the sole direct CDW-related observation (Pollard et al., 21 Jul 2025).

The structural side is likewise open. Because the direct nanowire characterization is limited to XRD + SEM + EDS, several issues remain unresolved: defect topology, local stoichiometric variation, edge chemistry, polytype uniformity at the nanoscale, and the degree to which weak extra XRD peaks reflect residual precursor or secondary phases (Pollard et al., 21 Jul 2025). This is especially consequential because the nanoribbon literature shows that confined H-phase TaS$_3$20 can host ordered vacancy arrays and edge-localized states not visible in bulk-sensitive probes (Cain et al., 2020).

Thematically, three research directions stand out. First, direct microscopic confirmation of CDW suppression in nanowires remains absent; Raman, diffraction, or local probes would be needed to test whether the nanowire state is truly CDW-free or instead contains broadened, short-range, or spatially inhomogeneous CDW correlations (Rawat et al., 2023). Second, the nanowire paper itself identifies the need for a systematic study of diameter dependence and for a clearer separation of the roles of confinement, disorder, stoichiometry, and strain (Pollard et al., 21 Jul 2025). Third, the observed flux jumps and second magnetization peak indicate rich vortex matter physics, but the present analysis remains qualitative; deeper analysis of vortex avalanche dynamics and the elastic-to-plastic crossover is still open (Pollard et al., 21 Jul 2025).

A cautious overall assessment follows from the available literature. Directly measured 2H-TaS$_3$21 nanowires already constitute a distinct superconducting nanomaterial class with enhanced $_3$22, enhanced $_3$23, and complex vortex behavior (Pollard et al., 21 Jul 2025). At the same time, adjacent reduced-dimensional TaS$_3$24 studies indicate that nanowire behavior is likely to be highly contingent on confinement scale, disorder, air exposure, defect ordering, interlayer coupling, and interface design (Lee et al., 2021). This suggests that “2H-TaS$_3$25 nanowires” should be understood not as a single fixed materials state, but as a family of reduced-dimensional superconducting objects whose observable phase behavior is strongly process- and geometry-dependent.