Topological Insulator Bi2Se3 Research Articles

Assessment of Thermoelectric Properties of Bi2Se3: Insights from Hybrid Functional Studies, Strain Engineering, and Machine Learning Methodology

AbstractThermoelectric properties in topological insulator Bi2Se3 are explored with multifaceted strategies, i.e., hybrid functional with strain and artificial intelligence methodology. The assessment with the experimental band gap values recognizes the limitations of conventional functional and the effectiveness of screened hybrid functionals. A thorough investigation into the impact of biaxial and uniaxial strain on thermoelectric parameters uncovers distinctive behaviors in n‐type and p‐type Bi2Se3, providing insights into optimal strain conditions for improved performance. Furthermore, the studies on the role of topologically non‐trivial surface states (TNSS) in thermoelectric properties reveal that TNSS significantly dominate electronic transport. Dual scattering time approximation elucidates the segregation of thermoelectric transport contributions from bulk and surface states, highlighting the importance of controlling the relaxation time ratio for enhanced thermoelectric performance. Additionally, the prediction of thermoelectric properties using Random Forest and Neural Networks models showcase impressive agreement with density functional theory predictions across varying temperatures, offering a powerful tool for understanding complex temperature‐dependent trends in thermoelectric properties. In summary, this interdisciplinary study presents a unique approach to advancing the understanding and optimization of thermoelectric properties in Bi2Se3. It provides a comprehensive framework for tailoring material behavior for diverse thermoelectric applications.

High-throughput magnetic co-doping and design of exchange interactions in topological insulators

Using high-throughput automation of impurity embedding simulations, we create a database of 3d and 4d transition metal defects embedded into the prototypical topological insulators (TIs) Bi2Te3 and Bi2Se3. We simulate both single impurities as well as impurity dimers at different impurity-impurity distances inside the topological insulator matrix. We extract changes to magnetic moments, analyze the polarizability of nonmagnetic impurity atoms via nearby magnetic impurity atoms and calculate the exchange coupling constants for a Heisenberg Hamiltonian. We uncover chemical trends in the exchange coupling constants and discuss the impurities' abilities with respect to magnetic order in the fields of quantum anomalous Hall insulators and topological quantum computing. In particular, we confirm that co-doping of different magnetic dopants is a viable strategy to engineer the magnetic ground state in magnetic TIs. Published by the American Physical Society 2024

FIB-fabrication of superconducting devices based on Bi2Se3 junctions

Recent advances in quantum technologies are highly influencing the current technological scenario. Hybrid devices combining superconductors and topological insulators represent an excellent opportunity to study the topological superconducting phase, which offers interesting features that might have significant implications in the development of quantum sensing and quantum computing. Furthermore, focused ion beam techniques, whose versatility enables to create sophisticated devices with high degree of customization, can enhance the creation of complex devices. Here, we develop a novel approach for creating single-crystal devices that is applied to the fabrication of superconducting devices based on topological insulator Bi2Se3 in a geometry characteristic of a superconducting quantum interference device. Characterization of these devices reveals that superconductivity is induced in our crystal and the supercurrent is modulated by applying an external magnetic field. These results open the way to tailoring the response of hybrid devices that combine superconductors and topological insulators by focused ion beam techniques.

Investigation of high-detectivity self-powered photodetectors of Rubrene/Bi2Se3 hybrid Van der Waals heterojunction

This paper investigates the Vander Waals heterostructure of organic rubrene and topological insulator Bi2Se3 with an atomically abrupt interface with exciting applications in electronic and optoelectronic devices. This organic/inorganic heterostructure (OIH) was prepared using a simple two-step physical vapor deposition process; based on this hybrid structure, a self-powered photodetector was then constructed. The Dirac surface state at the heterointerface enhances the splitting and transferring of photo-generated carriers, resulting in improved device characteristics. Under 1064 nm, the prepared photodetectors demonstrated a maximum responsivity (6.37 A/W), a high detectivity (3.42 × 1010 Jones), and ultrafast photoresponse speeds with rise time (1.17 µs) and decay time (1.59 µs), respectively. These promising results suggest that these PDs can be used in various photodetection applications and may lead to developing new devices.

Room-Temperature Band-Aligned Infrared Heterostructures for Integrable Sensing and Communication.

The demand for miniaturized and integrated multifunctional devices drives the progression of high-performance infrared photodetectors for diverse applications, including remote sensing, air defense, and communications, among others. Nonetheless, infrared photodetectors that rely solely on single low-dimensional materials often face challenges due to the limited absorption cross-section and suboptimal carrier mobility, which can impair sensitivity and prolong response times. Here, through experimental validation is demonstrated, precise control over energy band alignment in a type-II van der Waals heterojunction, comprising vertically stacked 2D Ta2NiSe5 and the topological insulator Bi2Se3, where the configuration enables polarization-sensitive, wide-spectral-range photodetection. Experimental evaluations at room temperature reveal that the device exhibits a self-powered responsivity of 0.48 A·W-1, a specific directivity of 3.8 × 1011 cm·Hz1/2·W-1, a response time of 151 µs, and a polarization ratio of 2.83. The stable and rapid photoresponse of the device underpins the utility in infrared-coded communication and dual-channel imaging, showing the substantial potential of the detector. These findings articulate a systematic approach to developing miniaturized, multifunctional room-temperature infrared detectors with superior performance metrics and enhanced capabilities for multi-information acquisition.

Research on Quantum State Implementation Based on Topological Insulators

Abstract This paper first introduces the mainstream technology route of quantum computing. The analysis provides the role and advantages of topological insulators in quantum computing, such as providing stable quantum bits, enhancing the coherence and non-locality of quantum bits, and enabling the transmission of quantum information and entanglement allocation. This paper then proposes a quantum state implementation scheme based on Bi2Se3, based on the characteristics and advantages of the quantum Hall effect of topological insulators. It includes calculating the eigenstates of the Hamiltonian of topological insulators, obtaining the spatial distribution of wave functions, and generating a quantum bit platform based on topological insulators. A quantum state implementation system based on topological insulator (Bi2Se3) was constructed, and the system framework and reference configuration were provided. The solution presented in this article is an important research achievement in topological quantum computing, providing more possibilities for the implementation of feasible fault-tolerant quantum computer prototypes.

Role of bulk and surface current carriers in resistivity of thin films of the topological insulator Bi2Se3

Role of bulk and surface current carriers in resistivity of thin films of the topological insulator Bi2Se3

Obtained Berry phase and cyclotron mass of Bi2Se3 topological insulator thin film through weak anti-localization and Shubnikov-de haas oscillation studies

Bi-based binary alloys have drawn enormous attention in modern condensed matter research for their novel topological property. Here, we have explored the quantum-transport properties of a 100 nm Bi2Se3 topological insulator thin film grown by an indigenously developed electron-beam-evaporator through co-deposition technique. A detailed study about the structural, elemental, and morphological analysis has been presented through the GI-XRD, Raman spectroscopy, XPS, EDX, SEM, and AFM characterization. Finally, we have investigated the angle and temperature-dependent magneto-conductance properties of our deposited films, which indicate the surface-electron dominated quantum-transport has occurred. Interestingly, our Bi2Se3 film exhibits 2D weak anti-localization and Subnikov-de Hass oscillation features. From which some novel topological parameters are explored, such as, Berry phase (β), phase-coherence-length (l ϕ ), Fermi velocity (vF), wave vector (kF), Dingle temperature (TD), quantum mobility (μ q), and cyclotron mass (mc). The estimated β = 0.7π and mc = 0.17me, indicate that the topologically protected massless Dirac particles can be achieved in this kind of system.

Surface potential dependence of the topological insulator Bi[formula omitted]Se[formula omitted] studied by scanning photoemission and Kelvin probe microscopy

The atomic composition and electronic structure of topological insulators (TI) Bi2Se3 grown by the two-temperature Physical Vapor Deposition on n-type Si patterned substrates, have been followed in details during slight variations of the growth temperatures and values of thickness close to that of the topological transition (about 6 nm), by means of submicron lateral probe photoemission with enhanced surface sensitivity (less than 1 nm). Raman and atomic force microscopy together with Kelvin probe microscopy provide a coherent picture where the fine tuning of Se doping and of the growth temperatures constrain the on–set of the gapless state at the exact middle point of the gap.

Chiral edge transport along domain walls in magnetic topological insulator nanoribbons

Quantum anomalous Hall insulators are topologically characterized by non-zero integer Chern numbers, the sign of which depends on the direction of the exchange field that breaks time-reversal symmetry. This feature allows the manipulation of the conducting chiral edge states present at the interface of two magnetic domains with opposite magnetization and opposite Chern numbers. Motivated by this broad understanding, the present study investigates the quantum transport properties of a magnetized Bi2Se3 topological insulator nanoribbon with a domain wall (DW) oriented either parallel or perpendicular to the transport direction. Employing an atomistic tight-binding model and a non-equilibrium Green’s function formalism, we calculate the quantum conductance and explore the nature of the edge states. We elucidate the conditions leading to exact conductance quantization and identify the origin of deviations from this behavior. Our analysis shows that although the conductance is quantized in the presence of the horizontal DW, the quantization is absent in the perpendicular DW case. Furthermore, the investigation of the spin character of the edge modes confirms that the conductance in the horizontal DW configuration is spin polarized. This finding underscores the potential of our system as a simple three dimensional spin-filter device.

Interplay between Topological States and Rashba States as Manifested on Surface Steps at Room Temperature.

The unique spin texture of quantum states in topological materials underpins many proposed spintronic applications. However, realizations of such great potential are stymied by perturbations, such as temperature and local fields imposed by impurities and defects, that can render a promising quantum state uncontrollable. Here, we report room-temperature scanning tunneling microscopy/spectroscopy observation of interaction between Rashba states and topological surface states, which manifests local electronic structure along step edges controllable by the layer thickness of thin films. The first-principles theoretical calculation elucidates the robust Rashba states coexisting with topological surface states along the surface steps with characteristic spin textures in momentum space. Furthermore, the Rashba edge states can be switched off by reducing the thickness of a topological insulator Bi2Se3 to bolster their interaction with the hybridized topological surface states. The study unveils a manipulating mechanism of the spin textures at room temperature, reinforcing the necessity of thin film technology in controlling the quantum states.

Study on Saturable Absorption Characteristics of Bi2Se3 Topological Insulators with Film Thickness Dependence and Its Laser Application

In our work, a multi-layer topological insulator (TI) Bi2Se3 thin film was prepared by the chemical vapor deposition method (CVD), and its saturable absorption and damage characteristics were experimentally studied. The results show that when the wavelength is 1064 nm, the saturable absorption parameters of TI: Bi2Se3 film, including modulation depth αs, non-saturable loss αns, and saturation power intensity Isat, increase with the increase in film thickness, and the damage threshold is inversely proportional to the film thickness. The thicker the film layer, the lower the damage threshold. Among them, modulation depth αs is up to 51.2%, minimum non-saturable loss αns is 1.8%, maximum saturation power intensity Isat is 560.8 kW/cm2, and the damage threshold is up to 909 MW/cm2. The influence of the controllable thickness of TI: Bi2Se3 film on passive Q-switching and mode-locking performance of laser is discussed and analyzed when TI: Bi2Se3 film is prepared by the CVD method as a saturable absorber (SA). Finally, the performance of TI: Bi2Se3 thin film applied to nanosecond laser isolation at the 1064 nm band is simulated and analyzed. It has the natural advantage of polarization independence, and the maximum isolation can reach 16.4 dB.

Preservation of Topological Surface States in Millimeter-Scale Transferred Membranes.

Ultrathin topological insulator membranes are building blocks of exotic quantum matter. However, traditional epitaxy of these materials does not facilitate stacking in arbitrary orders, while mechanical exfoliation from bulk crystals is also challenging due to the non-negligible interlayer coupling therein. Here we liberate millimeter-scale films of the topological insulator Bi2Se3, grown by molecular beam epitaxy, down to 3 quintuple layers. We characterize the preservation of the topological surface states and quantum well states in transferred Bi2Se3 films using angle-resolved photoemission spectroscopy. Leveraging the photon-energy-dependent surface sensitivity, the photoemission spectra taken with 6 and 21.2 eV photons reveal a transfer-induced migration of the topological surface states from the top to the inner layers. By establishing clear electronic structures of the transferred films and unveiling the wave function relocation of the topological surface states, our work lays the physics foundation crucial for the future fabrication of artificially stacked topological materials with single-layer precision.

Competitive nature of weak anti-localization and weak localization effect in Cr-doped sputtered topological insulator Bi2Se3 thin film

In the present study, we have investigated the effect of magnetic Cr doping on the transport properties of a sputtered Bi2Se3 thin film on the SrTiO3 (110) substrate. The high-resolution x-ray diffraction and Raman spectroscopy measurements revealed the growth of rhombohedral Bi2Se3 thin films. Further electronic and compositional analysis was done by x-ray photoemission spectroscopy and Rutherford backscattering spectroscopy, and the x-value was estimated to be 0.18 in the Bi2−xCrxSe3 thin film. The variation in the resistivity with temperature (2–300 K) revealed the metallic nature in undoped Bi2Se3 up to 30 K and upturn resistivity below 30 K. The Cr-doped Bi2Se3 resistivity data show a traditional semiconducting nature up to 25 K and take an abrupt upturn resistivity below 25 K. The resistivity behavior of both samples was explained by adopting a model that consists of the total resistance, a combination of bulk and surface resistance in parallel. The bulk bandgap value determined by this method is obtained to be 256 meV in an undoped Bi2Se3 thin film. Magnetoconductance data of the undoped thin film revealed a weak anti-localization (WAL) effect, while the Cr-doped thin film showed a weak localization (WL) effect at low temperatures (<50 K). At low magnetic field and low temperature, a competing nature of WAL and WL effects was prominent in the Cr-doped film. A drastic increase in the electrical resistance suggests that Cr doping can significantly modify the electrical properties of Bi2Se3 thin films, which could have potential applications in futuristic devices.

Transition metals of Pt and Pd on the surface of topological insulator Bi2Se3.

Transition metal catalysts supported on topological insulators are predicted to show improved catalytic properties due to the presence of topological surface states, which may float up to the catalysts and provide robust electron transfer. However, experimental studies of surface structures and corresponding catalytic properties of transition metal/topological insulator heterostructures have not been demonstrated so far. Here, we report the structures, chemical states, and adsorption behaviors of two conventional transition metal catalysts, Pt and Pd, on the surface of Bi2Se3, a common topological insulator material. We reveal that Pt forms nanoparticles on the Bi2Se3 surface. Moreover, the interaction between Pt and surface Se is observed. Furthermore, thermal dosing of O2 onto the Pt/Bi2Se3 heterostructure leads to no oxygen adsorption. Detailed scanning tunneling microscopy study indicates that Pt transforms into PtSe2 after the thermal process, thus preventing O2 from adsorption. For another transition metal Pd, it exhibits approximate layer-island growth on Bi2Se3, and Pd-Se interaction is also observed. Our work provides significant insights into the behaviors of transition metals on top of a common topological insulator material and will assist in the future design of catalysts built with topological materials.

Effect of bending deformation on suspended topological insulator nanowires: Towards a topological insulator based NEM switch

Nanodevices consisting of the suspended and supported parts of topological insulator Bi2Se3 nanowires were fabricated and measured at low and room temperatures. Probing of topological surface states, accompanied by the electrostatic field effect used to dynamically manipulate bending deformation, was carried out to monitor the external strain introduced into the suspended and supported parts within the same Bi2Se3 nanowire. Depending on the device geometry, pure elastic and elastoplastic types of concave deformation, as well as convex buckling deformation, were realized in the suspended parts of the nanowires. For various types of observed deformations, different magnitudes of increase in the Source-Drain resistance of the deformed part compared to the relaxed part of the same devices were determined. All suspended devices exhibit external strain-sensitive Shubnikov-de Haas oscillation frequencies representing the carriers of top and bottom surface states and bulk, whereas, in the case of supported devices, the bottom surface states are masked by a trivial 2DEG. The obtained results may be useful for strain engineering of TI materials, as well as for applications in NEMS and other areas related to suspended nanostructures.

Surface Topological Plexcitons: Strong Coupling in a Bi2Se3 Topological Insulator Nanoparticle-Quantum Dot Molecule

Strong coupling of quantum states with electromagnetic modes of topological matter offer an interesting platform for the exploration of new physics and applications. In this work, we report a novel hybrid mode, a surface topological plexciton, arising from strong coupling between the surface topological plasmon mode of a Bi2Se3 topological insulator nanoparticle and the exciton of a two-level quantum emitter. We study the power absorption spectrum of the system by working within the dipole and rotating-wave approximations, using a density matrix approach for the emitter, and a classical dielectric-function approach for the topological-insulator nanoparticle. We show that a Rabi-type splitting can appear in the spectrum suggesting the presence of strong coupling. Furthermore, we study the dependence of the splitting on the separation of the two nanoparticles as well as the dipole moment of the quantum emitter. These results can be useful for exploring exotic phases of matter, furthering research in topological insulator plasmonics, as well as for applications in the far-infrared and quantum computing.

Intrinsic free carrier absorption limited THz generation from Bi2Te3 and Bi2Se3 topological insulators

We investigate the influence of intrinsic free charge carriers on the ultrashort THz pulse generation efficiency of three-dimensional topological insulators (3dTIs). Wavelength dependence of the optical penetration depth of the femtosecond excitation pulses is exploited to vary the excitation volume within Bi2Te3 and Bi2Se3 crystals and accordingly, the free carrier population, to contribute to THz attenuation. The standard free carrier absorption (FCA) formalism is inadequate to explain wavelength-dependent enhancement in the THz emission as observed in the experiments. Within a modified framework, the THz attenuation by FCA is accounted for accurately, which consistently explains the experimental results for samples having different carrier density and mobility. We conclude that the THz generation efficiency of 3dTIs can be enhanced by engineering samples with high carrier mobility and low intrinsic carrier density and by using excitation wavelengths of minimal penetration depth.

Optical conductivity of a Bi2Se3 topological insulator with a THz transparent top gate

Abstract We have performed an investigation into the optical conductivity and magnetotransport properties of top-gated devices patterned on the topological insulator Bi2Se3 in order to determine the relative effects of the different carrier species that exist within these novel materials. We find that the topologically protected surfaces within our samples are partially screened from the action of the gate by trivial band-bending states formed at the top surface of the topological insulator. Despite this, the mobility of the topological surface carriers is significantly affected by the application of an external gate bias. Additionally, we find that the optical conductivity response is dominated by the topologically protected surface states, and that the optical conductivity is particularly sensitive to the scattering caused by the topological surfaces coupling to trivial states, arising from the bulk or band-bending induced surface states. These results will have interesting applications to the design of future plasmonic devices that incorporate topological materials.

Tailoring Bi2Se3 Topological Insulator for Visible-NIR Photodetectors with Schottky Contacts Using Liquid Phase Exfoliation.

Layered semiconductors of the V-VI group have attracted considerable attention in optoelectronic applications owing to their atomically thin structures. They offer thickness-dependent optical and electronic properties, promising ultrafast response time, and high sensitivity. Compared to the bulk, 2D bismuth selenide (Bi2Se3) is recently considered a highly promising material. In this study, 2D nanosheets are synthesized by prolonged sonication in two different solvents, such as N-methyl-2-pyrrolidone (NMP) and chitosan-acetic acid solution (CS-HAc), using the liquid-phase exfoliation (LPE) method. X-ray diffraction confirms the amorphous nature of exfoliated 2D nanosheets with maximum peak intensity at the same position (015) crystal plane as that obtained in its bulk counterpart. SEM confirms the thin 2D nanosheet-like morphology. Successful exfoliation of Bi2Se3 nanosheets up to five layers is achieved using CS-HAc solvent. The as-synthesized 2D nanosheets in different solvents are employed to fabricate the photodetector. At minimum selected power density, the photodetector fabricated using exfoliated ultrathin 2D nanosheets exhibits the highest range of responsivity, varying from 15 to 2.5 mA/W, and detectivity ranging from 2.83 × 109 to 6.37 × 107. Ultrathin 2D Bi2Se3 nanosheets have fast rise and fall times, ranging from 0.01 to 0.12 and 0.01 to 0.06 s, respectively, at different wavelengths. Ultrathin Bi2Se3 nanosheets have improved photodetection parameters as compared to multilayered nanosheets due to the high surface to volume ratio, reduced recombination and trapping of charge carrier, improved carrier confinement, and faster carrier transport due to the thin layer.