Speaker
Description
The integration of 3D topological insulator (TI) materials, such as $\text{Bi}_2 \text{Te}_3$, $\text{Bi}_2 \text{Se}_3$, and $\text{Sb}_2 \text{Te}_3$, into emerging technological platforms has attracted significant research interest across various fields, particularly in spintronics [1]. While their fundamental properties have been extensively studied in crystalline systems, particularly epitaxial films, disorder, finite-size effects, and interfaces can introduce complex parallel conduction pathways that complicate the identification of transport phenomena associated uniquely with the topological surface states (TSS) [2]. This is particularly relevant in disordered systems where direct band-structure probes, such as angle-resolved photoemission spectroscopy (ARPES), become experimentally unfeasible, motivating correlative approaches that combine electronic transport with complementary probes.
In this work, we first investigate the structural and electronic properties of disordered $\text{Bi}_2 \text{Te}_3$ thin films ($13 - 191$ nm) produced through sputtering deposition on flexible, polyimide substrates [3]. Raman spectroscopy, X-ray diffraction, and electron microscopy reveal polycrystalline, granular films whose structural organization is substantially improved following ex-situ annealing at $T_a > 250$ °C. Temperature-dependent resistivity measurements of annealed films ($T_a = 300$ ºC) reveal a meta-metallic transport regime (20 - 100 K), consistent with previous reports on granular films and with competition between bulk (semiconducting) and surface (metallic) conduction contributions. Isothermal magnetoconductance measurements ($3 - 20$ K) show characteristic weak antilocalization (WAL). Analysis via the Hikami–Larkin–Nagaoka model reveals a monotonic increase of the pre-factor $\alpha$ with thickness ($0.5 \to 1$), consistent with the expected thickness-dependent coupling of TSS channels [4]. Concurrently, the decoherence exponent of the phase coherence length ($L_{\mathrm{\phi }}\propto T^{-p}$) shifts from $0.7 \to 0.5$ post-annealing, indicating a shift towards 2D-dominated quantum coherence effects.
Motivated by the growing interest in printed and solution-processable functional 2D and quantum materials, we extend this study to hybrid TI/polymer composites prepared from solvothermally synthesized nano-pellets of $\text{Bi}_2 \text{Te}_3$ embedded in a polymeric matrix, aiming to investigate whether similar transport signatures can persist in such systems. The disordered composite network exhibits temperature-dependent transport consistent with Efros–Shklovskii variable range hopping, while magnetoconductance measurements reveal strongly suppressed 2D WAL contributions within the HLN description ($\alpha \sim 0.001$, $L_\phi \propto T^{-0.5}$).
As a complementary approach for probing surface-state dynamics, we have developed an optical pump–probe setup which uses a femtosecond laser operating at 800 nm. Preliminary measurements of epitaxial $\text{Bi}_2 \text{Se}_3$ reference samples reveal system relaxation consistent with expected contributions from both electron–electron and electron–phonon relaxation processes.
These results highlight the crucial role of structural engineering in enabling robust surface transport and the importance of establishing consistent metrology for surface state signatures in disordered samples, demonstrating the potential of scalable, flexible TI-based platforms for beyond-CMOS applications.
References
[1] Q. L. He, T. L. Hughes, et. al, Nature Materials 21, 15 (2022).
[2] A. Banerjee, O. Deb, K. Majhi, et. al, Nanoscale 9, 6755 (2017).
[3] M. Moreira, A. L. Pires, S. Ferreira‐Teixeira, et. al, Adv. Funct. Mater. 34(45) (2024).
[4] W. J. Wang, K. Gao, Z.-Q. Li, Scientific Reports 6, 25291 (2016).
| Which topic best fits your talk? | Condensed Matter Physics and Nanomaterials |
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| Affiliations | 1. IFIMUP – Institute of Physics for Advanced Materials, Nanotechnology and Photonics, Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal. 2. CF-UM-UP – Centre of Physics of the Universities of Minho and Porto, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal. *Corresponding author: ampereira@up.pt |