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Altermagnetism emerges as the third fundamental collinear magnetism recently. Associating nontrivial topology and quantum orders to this newly established magnetism is an important physical topic and may lead to interesting physics such as unusual quantum spin Hall effect with time-reversal-symmetry breaking, topological superconductivity and spin-valley locking. Here, we first generalize the spinless Haldane model from the usual honeycomb lattice to the otherwise simpler square lattice. We then restore the doublet spin degree of freedom, the resulted spinful model resembles the Kane-Mele model and is able to describe the unprecedented physics which intertwine C -paired spin-valley locking, Dirac physics, nontrivial band topology and altermagnetism. Our works shed lights on future studies and applications in spintronics and valleytronics for altermagnetic materials, the lattice theories developed in this article may also find their broad applications to optical lattice with ultra cold atoms, photonic lattice, etc. other than the usual electronic systems. [ABSTRACT FROM AUTHOR]

Semiconductor heterojunctions have garnered extensive interest in photocatalytic hydrogen generation, yet the limited light absorption and charge transfer efficiencies still restrict the photocatalytic performance. The topological insulator has unique surface states and high‐mobility electrons, demonstrating the significant potential for enhancing photocatalysis. Herein, a ternary photocatalyst based on a topological insulator, in which CdS and ZnS nanoparticles are grown on Bi2Se3 nanotube, is prepared for efficient photocatalysis driven by topological surface state for the first time. Under simulated solar light irradiation, the CdS/ZnS/Bi2Se3 nanotubes display a robust photocatalytic hydrogen production rate of 7.13 mmol h−1 g−1, which is 69.2 times of CdS and comparable to many CdS‐based photocatalysts. The unique hollow structure, topological surface state of Bi2Se3, and cooperative bandgap excitations of the three components endow the hybrids with wide light response to harvest solar energy. Meanwhile, the multichannel charge transfer facilitated by topological surface state and internal electric fields within the hybrids effectively suppresses the recombination of the photogenerated charge carriers. This mechanism maintains a high concentration of stable electrons on Bi2Se3, resulting in highly efficient hydrogen production. This work provides a new inspiration for designing heterojunction photocatalysts based on topological insulators for high‐efficiency solar‐driven energy conversion. [ABSTRACT FROM AUTHOR]

The report carried out detailed first‐principle calculations of Mercury chalcogenides (HgX; X = Te, Se and S) using density functional theory, verifying the bulk band inversion property with different exchange‐correlation functionals. The Wannier function method is used to study the non‐trivial topology of HgX systems, spin Berry curvature, and intrinsic spin Hall conductivity. Quantized intrinsic spin Hall conductivity is observed in the HgX systems. Large intrinsic spin Hall conductivity is found in the systems due to a strong spin Berry curvature accumulation near the triply degenerate points in the Brillouin zone. Calculation shows that the intrinsic spin Hall conductivity for all three HgX systems has stable plateaus, with Mercury Telluride having a maximum width of up to 1.05 eV. The maximum intrinsic spin Hall conductivity of –931ℏ$\hbar$/e (Scm−1${\rm Scm}^{-1}$) is obtained in mercury sulfide, higher than the reported values for spin Hall conductivity and the plateau width in typical topological insulators such as Bi2Se3$\text{Bi}_{2}\text{Se}_{3}$, Bi2Te3$\text{Bi}_{2}\text{Te}_{3}$, and Sb2Se3$\text{Sb}_{2}\text{Se}_{3}$ as well as in transition metal pnictides (TaX, X = As, P and N) and transition metal iridates. [ABSTRACT FROM AUTHOR]

An interest in the study of the structural and optical properties of topological insulators, led to the selection of Bismuth telluride thin films. Among the topological insulators, Bismuth telluride is one of the promising materials that exhibit applications in the field of thermoelectric power generation. The films were prepared using the thermal evaporation method under vacuum conditions of 10−5 mbar on glass substrates maintained at a temperature of 120∘C. The thickness of the film samples ranges from 400 Å to 1400 Å. Pure phases of Bi2Te3 with a rhombohedral structure are confirmed using X-ray Diffraction. The crystallite size was calculated using Debye–Scherrer’s formula. Structural morphology and compositions are examined using SEM and EDAX. The UV–Vis study reflects the optical behavior of the thin film samples. The absorption spectra gives the direct and allowed transition band gap of the Bi2Te3 thin film samples for various thicknesses. The band gap decreases with the increase in the thickness of the Bi2Te3 thin films, suggesting that the material has significant absorption towards the visible spectrum. The Photoluminescence (PL) emissions for Bi2Te3 thin film samples of various thicknesses are examined and analysed. Raman study reveals the presence of two active modes. [ABSTRACT FROM AUTHOR]

In this study, first‐principles calculations are used to systematically study the structural, mechanical, and optical properties of the honeycomb AuTe monolayer, as well as the influence of layered structures on their stability and electronic properties. Additionally, the effect of alkali metal atoms decorating AuTe‐X (X = Li, Na, K) and related structural, electronic, optical, and topological insulator properties, along with the biaxial strain on the lithium‐decorated AuTe‐Li monolayer are investigated. The AuTe monolayer shows metallic characteristics, and when alkali metal atoms are decorated onto it, the resulting structures remain dynamically stable. Notably, the introduction of Li, Na, and K atoms induces bandgap opening in the decorated Li and Na monolayers near the Fermi level, causing metal‐to‐narrow bandgap semiconductor and Dirac semi‐metal transitions. Conversely, the metallic nature of the decorated AuTe‐K monolayer is retained. The emergence of a bandgap near the Fermi level, caused by alkali metal decoration, triggers a topological phase transition in AuTe‐Li, AuTe‐Na, and AuTe‐K monolayers. Optical analyses reveal that AuTe‐K decorated structure enhances light absorption in the visible spectrum. Consequently, the findings provide insights into the decoration of these two‐dimensional material monolayers, potentially advancing research and motivating the production of such monolayers for current nanodevice applications. [ABSTRACT FROM AUTHOR]

Searching for controllable topological state by means of external stimuli in 2D material‐based van der Waals (vdW) heterostructures is currently an active field for both the underlying physics and practical applications. Herein, a vdW heterostructure formed by vertically stacking AlSb and InSe monolayers is designed and its stacking configuration, stability, electronic structure, and effect of external electric field are investigated using first‐principles calculations. The AlSb/InSe heterobilayer studied, possessing both dynamical and thermal stabilities, is direct bandgap semiconductor and forms a Z‐scheme heterojunction. With inclusion of spin–orbit coupling (SOC) and applying external electric field, the bandgap of AlSb/InSe heterobilayer decreases at first and then increases, and a trivial insulator to topological insulator phase transition is achieved. For the topological insulator phase, band inversion is ascribed to the strong SOC of p orbitals of Sb. In this work, the way is paved for the design and application of multifunctional nanoscale devices such as topological field‐effect transistor. [ABSTRACT FROM AUTHOR]

Quantum spin Hall (QSH) insulators represent a quintessential example of a topological phase of matter, characterized by a conducting edge mode existing within a bulk energy gap. The pursuit of a tunable QSH state stands as a pivotal objective in the development of QSH-based topological devices. In this study, we employ first-principles calculations to identify three strain-tunable quantum spin Hall (QSH) insulators based on monolayer MAlGaTe4 (where M represents Mg, Ca, or Sr). These monolayers exhibit dynamic stability, with no imaginary modes detected in their phonon dispersion. While MgAlGaTe4 is a normal insulator under zero strain, it transitions into the QSH phase when subjected to external strains. Conversely, CaAlGaTe4 and SrAlGaTe4 already exhibit the QSH phase at zero strain. Intriguingly, upon the application of biaxial strain, these two compounds undergo phase transitions, encompassing metallic (M), normal/trivial insulator (NI), and topological insulator (TI) phases, thereby illustrating their strain-tunable electronic and topological properties. (Ca, Sr)-AlGaTe4, in particular, undergo M-TI/TI-M transitions under applied strain, while MgAlGaTe4 additionally experiences an M-NI/NI-M transition, signifying it as a material featuring a metal–insulator transition (MIT). Remarkably, the observation of metal-trivial insulator-topological insulator transitions in MgAlGaTe4 introduces it as a unique material platform in which both MIT and topological phase transitions can be controlled through the same physical parameter. Moreover, the piezoelectric properties of these materials enable strain-induced tuning, allowing them to be strain-biased for application in novel devices such as reconfigurable circuit components for compact electronic devices and topological field-effect transistors. Our study thus introduces a novel material platform distinguished by highly strain-tunable electronic and topological properties, offering promising prospects for the development of next-generation, low-power topological devices. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Magnetizing the surface states of topological insulators without damaging their topological features is a crucial step for realizing the quantum anomalous Hall (QAH) effect and remains a challenging task. The TI–ferromagnetic material interface system was constructed and studied by the density functional theory (DFT). A two-dimensional magnetic semiconductor CrWI6 has been proven to effectively magnetize topological surface states (TSSs) via the magnetic proximity effect. The non-trivial phase was identified in the Bi2Se3 (BS) films with six quantum layers (QL) within the CrWI6/BS/CrWI6 heterostructure. BS thin films exhibit the generation of spin splitting near the TSSs, and a band gap of approximately 2.9 meV is observed at the Γ in the Brillouin zone; by adjusting the interface distance of the heterostructure, we increased the non-trivial band gap to 7.9 meV, indicating that applying external pressure is conducive to realizing the QAH effect. Furthermore, the topological non-triviality of CrWI6/6QL-BS/CrWI6 is confirmed by the nonzero Chern number. This study furnishes a valuable guideline for the implementation of the QAH effect at elevated temperatures within heterostructures comprising two-dimensional (2D) magnetic monolayers (MLs) and topological insulators. [ABSTRACT FROM AUTHOR]

This article introduces a novel petal-like SAW topology insulator, which can transmit sound waves with low loss and high flexibility in an ultra-wide frequency band by simultaneously adjusting multiple structural parameters of phononic crystals. Using finite element analysis, it was found that adjusting these parameters can generate a broadband gap of 55.8–65.7 MHz. This structure can also achieve defect immunity and sharp bending in waveguide transmission. When this topology insulator is applied to resonators, compared to traditional designs, the insertion loss is reduced by 22 dB, the on-load quality factor is increased by 227%, the off-load quality factor is increased by 1024.5%, and the quality sensitivity is improved by 3.7 times compared to bare devices. [ABSTRACT FROM AUTHOR]

Quantum Hall insulators in artificial systems have become a rapidly developing research field in recent years, and have made significant breakthroughs in observing many novel topological phenomena. However, there are few reports about quantum magnon‐photon Hall insulators. Here, a scheme is proposed for implementing a 1D cavity magnonics lattice that exhibits quantum magnon‐photon Hall insulator behaviors, where each unit cell comprises cavity photons and magnons. By adjusting the system parameters, it is found that not only different energy spectrum structures can be triggered, but also the distribution of the edge states can show the flipping process, which allows the achievement of the multi‐channel topological quantum state transmission. In addition, considering the presence of defects, dissipation, and disorder, it is found that appropriate defects can trigger new topological phases, while dissipation only causes shifts in energy levels without changing the position and period of edge states, and disorder leads to shifts in band structures and edge states, thus demonstrating the robustness of edge states. This work offers an effective way to study topological magnon‐photon Hall insulators, which will have promising applications in magnon‐based quantum information processing. [ABSTRACT FROM AUTHOR]

Abstract Altermagnetism emerges as the third fundamental collinear magnetism recently. Associating nontrivial topology and quantum orders to this newly established magnetism is an important physical topic and may lead to interesting physics such as unusual quantum spin Hall effect with time-reversal-symmetry breaking, topological superconductivity and spin-valley locking. Here, we first generalize the spinless Haldane model from the usual honeycomb lattice to the otherwise simpler square lattice. We then restore the doublet spin degree of freedom, the resulted spinful model resembles the Kane-Mele model and is able to describe the unprecedented physics which intertwine C $\mathcal{C}$ -paired spin-valley locking, Dirac physics, nontrivial band topology and altermagnetism. Our works shed lights on future studies and applications in spintronics and valleytronics for altermagnetic materials, the lattice theories developed in this article may also find their broad applications to optical lattice with ultra cold atoms, photonic lattice, etc. other than the usual electronic systems.

Abstract The formation of the topological surface state originates from bulk band inversion at the top of the valence band and the bottom of the conduction band. The transition between normal and topological insulators is known as a topological phase transition. Here we show spin-polarized electronic states of Pb-based ternary topological insulators Pb(Bi1-x Sb x )2Te4 (x = 0.55, 0.70, 0.79) investigated by spin- and angle-resolved photoemission spectroscopy and first-principles calculations. We visualize a pair of spin-polarized surface resonances dispersing along the upper edge of projected bulk bands in occupied states. Interestingly, a branch of the spin-polarized surface resonances continuously connects to the topological surface state. The coexistence of the topological surface state and the spin-polarized surface resonances can be explained by considering the topological phase transition.

[Display omitted] Two-dimensional layered bismuth telluride (Bi 2 Te 3), a prominent topological insulator, has garnered global scientific attention for its unique properties and potential applications in optoelectronics and electrochemical devices. Notably, there is a growing emphasis on improving photon-to-electron conversion efficiency in dye-sensitized solar cells (DSSCs), prompting the exploration of alternatives to noble metal catalysts like platinum (Pt). This study presents the synthesis of Bi 2 Te 3 and its hybrid nanostructure with single-wall carbon nanotubes (SWCNT) via a straightforward hydrothermal process. The research unveils a novel application for the Bi 2 Te 3 -SWCNT hybrid structure, serving as a counter electrode in platinum-free DSSCs, facilitating the conversion of triiodide (I 3 −) to iodide (I−) and functioning as an active electrode material in a photodetector (n-Bi 2 Te 3 -SWCNT/p-Si). The resulting DSSC employing the Bi 2 Te 3 -SWCNT hybrid counter electrode achieves a power conversion efficiency (PCE) of 4.2 %, a photocurrent density of 10.5 mA/cm2, a fill factor (FF) of 62 %, and superior charge transfer kinetics compared to pristine Bi 2 Te 3 based counter electrode (PCE 2.1 %, FF 34 %). Additionally, a spin coating technique enhances the performance of the n-Bi 2 Te 3 -SWCNT/p-Si photodetector, yielding a responsivity of 2.2 AW−1, detectivity of 1.2 × 10−3 and enhanced external quantum efficiency. These findings demonstrate that the newly developed Bi 2 Te 3 -SWCNT heterostructure enhances interfacial charge transport, electrocatalytic performance in DSSCs, and overall photodetector performance. [ABSTRACT FROM AUTHOR]

In spinless systems, growing attention has recently been attracted to synthetic gauge fields, which redefine the fundamental crystal symmetries by utilizing the projective algebraic relation. Hitherto, synthetic gauge fields have been commonly investigated in single orbital systems, and explorations on hybrid orbitals remain elusive in acoustics. Here, we report the experimental observation of hybrid topological phases induced by hybrid synthetic gauge flux, which is formed by the interaction between p and d orbitals embedded in acoustic cavities. By breaking the translation symmetries of Lx and/or Ly, we unambiguously demonstrate the first-order Möbius edge states and higher-order corner states. This work establishes a platform for seeking exotic topological phases induced by hybrid-orbitals interactions and initializing the framework of hybrid-orbitals-related topological physics. Potential applications can be anticipated in scenarios such as high-quality sensing and robust wave trapping due to the stepwise energy distribution of the hybrid topological phase. [ABSTRACT FROM AUTHOR]

Abstract Bi4Br4 is a material rich in intriguing topological properties. Monolayer Bi4Br4 film exhibits helical edge states characteristic of a quantum spin Hall insulator, while bulk Bi4Br4 represents a higher-order topological insulator with hinge states. However, direct exfoliation from single crystal can only obtain thin nanowires due to the weak van der Waals forces between Bi4Br4 chains, which limits its optical analysis and application, while the growth of Bi4Br4 thin films is also full of challenges due to the extremely narrow growth temperature range and the accurate control of the BiBr3 flux. Here, we reported the controlled growth of α-Bi4Br4 thin films on intrinsic silicon substrates using molecular beam epitaxy. The growth temperature, BiBr3 flux, and the flux ratio of Bi and BiBr3 were accurately controlled. Then, the morphology, composition, and bonding of the prepared films were investigated using atomic force microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. The growth of large, uniform thin films provides an ideal material platform for studying the physical properties of Bi4Br4. Additionally, we utilized Fourier-transform infrared spectroscopy to explore the film’s infrared characteristics, revealing strong absorption in the low frequency range due to the high proportion of one-dimensional topological edge states and laying the groundwork for further exploration of its potential applications in the optoelectronic field.

Here, we explore the sensitivity of the Casimir force between two topological insulator plates on thermal fluctuation using weak and strong magnetizations on the surface of plates via Lifshitz theory. Thermal fluctuations between two plates made of topological insulators in vacuum lead to attractive interactions. By considering a weak magnetization, the influence of thermal fluctuations becomes stronger compared to the magnetoelectric effect in the regime of large separations which leads to generating the strong attractive Casimir force. Moreover, by considering strong magnetizations it is observed that thermal effects cannot make a change in the attractive and repulsive Casimir forces, and magnetoelectric effect determines both the magnitude and direction of Casimir forces. In the range of small magnetization, thermal effects have a significant effect on the repulsive Casimir force. It has been shown that at high temperatures, repulsive interaction due to antiparallel magnetization becomes weak, so that they disappear by increasing the separation.

Bi4Br4 is a material rich in intriguing topological properties. Monolayer Bi4Br4 film exhibits helical edge states characteristic of a quantum spin Hall insulator, while bulk Bi4Br4 represents a higher-order topological insulator with hinge states. However, direct exfoliation from single crystal can only obtain thin nanowires due to the weak van der Waals forces between Bi4Br4 chains, which limits its optical analysis and application, while the growth of Bi4Br4 thin films is also full of challenges due to the extremely narrow growth temperature range and the accurate control of the BiBr3 flux. Here, we reported the controlled growth of α-Bi4Br4 thin films on intrinsic silicon substrates using molecular beam epitaxy. The growth temperature, BiBr3 flux, and the flux ratio of Bi and BiBr3 were accurately controlled. Then, the morphology, composition, and bonding of the prepared films were investigated using atomic force microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. The growth of large, uniform thin films provides an ideal material platform for studying the physical properties of Bi4Br4. Additionally, we utilized Fourier-transform infrared spectroscopy to explore the film's infrared characteristics, revealing strong absorption in the low frequency range due to the high proportion of one-dimensional topological edge states and laying the groundwork for further exploration of its potential applications in the optoelectronic field. [ABSTRACT FROM AUTHOR]

We show that non-trivial two-dimensional topological insulators protected by an odd time-reversal symmetry have absolutely continuous edge spectrum. To accomplish this, we establish a time-reversal symmetric version of the Wold decomposition that singles out extended edge modes of the topological insulator. [ABSTRACT FROM AUTHOR]

The interfaces between superconductors and other materials have long been established as being an important part in the exploration of new physics to aid in our understanding of superconductivity and open us up to new technological advancements. Herein this article we analyse the recent progress made in the understanding of superconductivity at the interfaces involving a wide range of functional materials, mostly looking at two-dimensional (2D) systems. We start off in the first half of this review by focusing on magnetic and superconductive hybrid heterostructures, as well as the resulting physical phenomena from these systems. The first is a section on vortex and anti-vortex phenomena; the second key area is ferromagnet–superconductor hybrid phenomena with particular interest of magnetic skyrmions, the third is the novel frontier based on 2D magnetic and superconductive interfaces particularly examining Ising superconductivity at these interfaces; the fourth is superconductivity at anti-ferromagnetic interfaces and finally half-metals at superconducting interfaces. The second half of this review focuses on superconductivity at insulating and other functional interfaces. Examining firstly, Mott insulator interfaces with wide ranging discussions about how such interfaces can enhance our understanding in high-temperature superconductive cuprates and other unconventional superconductor systems such as the nickelates; in the second section the interface of 2D and 3D ferroelectric materials with superconductors with a key emphasis on devices that have been developed to control the superconducting phase; Topological insulators at interfaces with superconductors is the third section; and lastly 2D twisted material interfaces are explored, including the newly discovered magic angle interfaces discovered with graphene and other van Der Waals materials. It is anticipated that this review will lead to further interest in such interfaces to improve our understanding and expose the exotic science behind these interfaces. [Display omitted] [ABSTRACT FROM AUTHOR]

AbstractIn this paper, we study the propagation of surface waves on an A-shape metasurface, whose structure of the unit-cell is composed regularly of an A-shape surface column (made of steel), a thin magnetorheological plate and a soft thick rubber base. On the basis of the commercial program COMSOL Multiphysics, finite element method (FEM) analyses are carried out. The localization of elastic waves surrounding the surface allows surface waves to be distinguished among various complex wave modes. By adjusting the geometry, the A-shape surface column can be transformed from snowflake to A-shape. Owing to the C3v symmetry system, a Dirac cone of surface wave is observed in a snowflake metasurface. When the surface column changes to A-shape, the C3v symmetry is broken, making the Dirac cone vanish and a new band gap of surface waves arise. The band gap can be opened or closed by changing a geometric parameter, which determines the shape of the surface column changing from gadarene A-shape to snowflake or even upturned A-shape. Furthermore, we discover that although the topological phases of the gadarene A-shape and upturned A-shape metasurfaces are opposite, they share overlapped band gaps. Based on this phenomenon, we design a topological insulator for surface waves, whose super-cell is composed of gadarene A-shape units and upturned A-shape units. Through the calculation of the super-cell band structure, we observe the topologically protected interface states (TPISs). Subsequently, we design several waveguides whose paths are controllable. Up to now, most of the existing metasurfaces are made of passive materials, whose properties cannot be adjusted in real time, making them inconvenient for engineering applications when external conditions are changed. Therefore, we use tunable magnetorheological elastomer (MRE) to control the properties of the topological insulators. The stiffness of the surface layer can be converted by applying a magnetic field, which makes the topological metasurface controllable. These intelligent topological insulators may find important applications in the design of surface acoustic wave (SAW) devices. [ABSTRACT FROM AUTHOR]

This paper concerns the asymmetric transport observed along interfaces separating two-dimensional bulk topological insulators modeled by (continuous) differential Hamiltonians and how such asymmetry persists after numerical discretization. We first demonstrate that a relevant edge current observable is quantized and robust to perturbations for a large class of elliptic Hamiltonians. We then establish a bulk edge correspondence stating that the observable equals an integer-valued bulk difference invariant depending solely on the bulk phases. We next show how to extend such results to periodized Hamiltonians amenable to standard numerical discretizations. A form of no-go theorem implies that the asymmetric transport of periodized Hamiltonians necessarily vanishes. We introduce a filtered version of the edge current observable and show that it is approximately stable against perturbations and converges to its quantized limit as the size of the computational domain increases. To illustrate the theoretical results, we finally present numerical simulations that approximate the infinite domain edge current with high accuracy and show that it is approximately quantized even in the presence of perturbations. [ABSTRACT FROM AUTHOR]

This work reports the formation of a heterojunction composed of Tl2Ba2CaCu2O8 (Tl‐2212) and Bi2Se3 as the high critical temperature superconductor and topological insulator, respectively. The Bi2Se3 film is deposited on the Tl‐2212 by a chemical mechanical polishing process. Due to the rough surface of Tl‐2212, the treated Tl‐2212 is then subjected to post‐annealing at various temperatures. This temperature does not affect the formation of the interfacial layer at the heterojunction; however, an improved layered crystal structure of the Bi2Se3 film is observed at 500 °C. The in‐depth profile of the relative atomic concentration indicates the diffusion of Cu and Tl into the Bi2Se3 film with the Ba diffusion being closer to the interfacial layer. At 500 °C, Cu atoms are more actively diffused into the Bi2Se3 film, thus blocking Tl diffusion, and improving the layered crystal structure of the film. The density functional theory calculations reveal that the lowest formation energy of the Cu vacancy is when Bi2Se3 is in contact with Tl‐2212, which results in the diffusion of Cu atoms from Tl‐2212, thus transforming the interstitial Cu atoms into the film. These atoms have an n‐type doping effect and prefer intercalating at a vdW gap deep inside the layered Bi2Se3. [ABSTRACT FROM AUTHOR]

All‐Van der Waals (vdW)‐material‐based heterostructures with atomically sharp interfaces offer a versatile platform for high‐performing spintronic functionalities at room temperature. One of the key components is vdW topological insulators (TIs), which can produce a strong spin‐orbit‐torque (SOT) through the spin‐momentum locking of their topological surface state (TSS). However, the relatively low conductance of the TSS introduces a current leakage problem through the bulk states of the TI or the adjacent ferromagnetic metal layers, reducing the interfacial charge‐to‐spin conversion efficiency (qICS). Here, a vdW heterostructure is used consisting of atomically‐thin layers of a bulk‐insulating TI Sn‐doped Bi1.1Sb0.9Te2S1 and a room‐temperature ferromagnet Fe3GaTe2, to enhance the relative current ratio on the TSS up to ≈20%. The resulting qICS reaches ≈1.65 nm−1 and the critical current density Jc ≈0.9 × 106 Acm−2 at 300 K, surpassing the performance of TI‐based and heavy‐metal‐based SOT devices. These findings demonstrate that an all‐vdW heterostructure with thickness optimization offers a promising platform for efficient current‐controlled magnetization switching at room temperature. [ABSTRACT FROM AUTHOR]

Topological insulators (TIs) exhibit unconventional quantum phases that can be tuned by external quantum confinements. The geometry of the surface of 3D TIs plays a crucial role. For example, the geometrical crossover from 2D surfaces to a 1D cylinder results in a novel state with a Spin‐Berry Phase (SBP). Surface‐Enhanced Raman Scattering (SERS) with a sub‐micron spatial resolution is utilized to study the quantum‐confinement effects of quasi‐relativistic electrons along the perimeter of the circular bismuth selenide (Bi2Se3) nanowires. The presence of diameter‐dependent SERS in nanowires can be attributed to the self‐interference effect of the electronic wave‐function along the circumferential direction of the TI nanowires. Nanoribbons with rectangular cross‐section do not show this effect. Further gold nanoparticles are applied as plasmonic SERS sensors attached to the distinct topological surface states to manipulate quasi‐relativistic surface states of nanoribbons and nanowires. This technique enables to discriminate between different geometries of TI surface states and also opens a novel pathway to probe the quantum properties of topological surface states. [ABSTRACT FROM AUTHOR]

Non-centrosymmetric topological material has attracted intense attention due to its superior characteristics as compared with the centrosymmetric one, although probing the local quantum geometry in non-centrosymmetric topological material remains challenging. The non-linear Hall (NLH) effect provides an ideal tool to investigate the local quantum geometry. Here, we report a non-centrosymmetric topological phase in ZrTe5, probed by using the NLH effect. The angle-resolved and temperature-dependent NLH measurement reveals the inversion and ab-plane mirror symmetries breaking at <30 K, consistently with our theoretical calculation. Our findings identify a new non-centrosymmetric phase of ZrTe5 and provide a platform to probe and control local quantum geometry via crystal symmetries. [ABSTRACT FROM AUTHOR]

The morphology of the (0001) surface is studied using a scanning probe microscope, and the effect of electrolytic deposition of potassium ions on the surface properties of layered Bi2Se3 and Bi2Te3 crystals is investigated by modulation electroreflectance spectroscopy. The process of prolonged deposition of potassium atoms onto the (0001) surface of Bi2Se3 and Bi2Te3 crystals after adsorption causes their intercalation into van der Waals spaces of the quintets closest to the surface. Surface metallization with potassium and broadening of van der Waals gaps in the near-surface region during intercalation due to an increase in the barrier height lead to a weakening of interlayer interaction, a decrease in the overlap of wave functions of different layers, and a weakening of dispersion. As a result of electrodeposition, potassium intercalates into the interlayer spaces. This entails modification of the surface accompanied by an increase in the concentration of charge carriers and their mobility, which implies a transition of the near-surface region to a metallic state with lower dissipation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We study how to use the surface states in a Bi2Se3 topological insulator ultra-thin film that are affected by finite size effects for the purpose of quantum computing. We demonstrate that: (i) surface states under the finite size effect can effectively form a two-level system where their energy levels lie in between the bulk energy gap and a logic qubit can be constructed, (ii) the qubit can be initialized and manipulated using electric pulses of simple forms, (iii) two-qubit entanglement is achieved through a SWAP operation when the two qubits are in a parallel setup, and (iv) alternatively, a Floquet state can be exploited to construct a qubit and two Floquet qubits can be entangled through a Controlled-NOT operation. The Floquet qubit offers robustness to background noise since there is always an oscillating electric field applied, and the single qubit operations are controlled by amplitude modulation of the oscillating field, which is convenient experimentally. [ABSTRACT FROM AUTHOR]

Abstract 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.

Abstract Topological insulators (TI) hold significant potential for various electronic and optoelectronic devices that rely on the Dirac surface state (DSS), including spintronic and thermoelectric devices, as well as terahertz detectors. The behavior of electrons within the DSS plays a pivotal role in the performance of such devices. It is expected that DSS appear on a surface of three dimensional(3D) TI by mechanical exfoliation. However, it is not always the case that the surface terminating atomic configuration and corresponding band structures are homogeneous. In order to investigate the impact of surface terminating atomic configurations on electron dynamics, we meticulously examined the electron dynamics at the exfoliated surface of a crystalline 3D TI (Bi $$_2$$ 2 Se $$_3$$ 3 ) with time, space, and energy resolutions. Based on our comprehensive band structure calculations, we found that on one of the Se-terminated surfaces, DSS is located within the bulk band gap, with no other surface states manifesting within this region. On this particular surface, photoexcited electrons within the conduction band effectively relax towards DSS and tend to linger at the Dirac point for extended periods of time. It is worth emphasizing that these distinct characteristics of DSS are exclusively observed on this particular surface.

Recently, evidence for a conducting surface state (CSS) below 19 K was reported for the correlated d-electron small gap semiconductor FeSi. In the work reported herein, the CSS and the bulk phase of FeSi were probed via electrical resistivity ρ measurements as a function of temperature T, magnetic field B to 60 T, and pressure P to 7.6 GPa, and by means of a magnetic field-modulated microwave spectroscopy (MFMMS) technique. The properties of FeSi were also compared with those of the Kondo insulator SmB6 to address the question of whether FeSi is a d-electron analogue of an f-electron Kondo insulator and, in addition, a topological Kondo insulator (TKI). The overall behavior of the magnetoresistance of FeSi at temperatures above and below the onset temperature TS = 19 K of the CSS is similar to that of SmB6. The two energy gaps, inferred from the ρ(T) data in the semiconducting regime, increase with pressure up to about 7 GPa, followed by a drop which coincides with a sharp suppression of TS. Several studies of ρ(T) under pressure on SmB6 reveal behavior similar to that of FeSi in which the two energy gaps vanish at a critical pressure near the pressure at which TS vanishes, although the energy gaps in SmB6 initially decrease with pressure, whereas in FeSi they increase with pressure. The MFMMS measurements showed a sharp feature at TS ≈ 19 K for FeSi, which could be due to ferromagnetic ordering of the CSS. However, no such feature was observed at TS ≈ 4.5 K for SmB6.

The defects have a remarkable influence on the electronic structures and the electric transport behaviors of the matter, providing the additional means to engineering their physical properties. In this work, a comprehensive study on the effect of Br‐vacancies on the electronic structures and transport behaviors in the high‐order topological insulator Bi4Br4 is performed by the combined techniques of the scanning tunneling microscopy (STM), angle‐resolved photoemission spectroscopy (ARPES), and physical properties measurement system along with the first‐principle calculations. The STM results show the defects on the cleaved surface of a single crystal and reveal that the defects are correlated to the Br‐vacancies with the support of the simulated STM images. The role of the Br‐vacancies in the modulation of the band structures has been identified by ARPES spectra and the calculated energy‐momentum dispersion. The relationship between the Br‐vacancies and the semiconducting‐like transport behaviors at low temperature has been established, implying a Mott variable ranging hopping conduction in Bi4Br4. The work not only resolves the unclear transport behaviors in this matter, but also paves a way to modulate the electric conduction path by the defects engineering. [ABSTRACT FROM AUTHOR]

We report the growth, structural characterization, and transport studies of Bi2Se3 thin film on single crystalline silicon (Si), Si/SiO2, quartz, and glass substrates by thermal evaporation method. Our results show that 300 °C is the optimum substrate temperature to obtain the c -axis (001) oriented Bi2Se3 films on all the substrates. The film grown on the Si substrate has the minimum crystalline disorder. The energy-dispersive x-ray spectroscopy results show that film on Si substrate is bismuth deficient, the film on Si/SiO2 substrate is selenium deficient, and the film on quartz substrate is near perfect stoichiometric providing a way to tune the electronic properties of Bi2Se3 films through substrate selection. The film grown on quartz shows the highest mobility (2.7 × 104 cm2 V-1s−1) which drops to 150 cm2 V-1s−1 for Si, 60 cm2 V-1s−1 for Si/SiO2, and 0.9 cm2 V-1s−1 for glass substrate. Carrier concentration is n-type for Bi2Se3 films on Si (∼1018 cm−3), quartz (∼1018 cm−3) and Si/SiO2 (∼1019 cm−3) substrate with a clear indication of frozen out effect around 50 K for Si/SiO2 and Si substrate. Longitudinal resistivity of Bi2Se3 film on Si/SiO2 substrate shows different behavior in three different temperature regions: temperature dependent resistivity region due to electron–phonon scattering, a nearly temperature independent resistivity region due to electron–phonon and electron–ion scattering, and a quantum coherent transport region. [ABSTRACT FROM AUTHOR]

We unveil that the holey graphyne (HGY), a two-dimensional carbon allotrope where benzene rings are connected by two −C≡C− bonds fabricated recently in a bottom-up way, exhibits topological electronic states. Using first-principles calculations and Wannier tight-binding modeling, we discover a higher-order topological invariant associated with C 2 symmetry of the material, and show that the resultant corner modes appear in nanoflakes matching to the structure of precursor reported previously, which are ready for direct experimental observations. In addition, we find that a band inversion between emergent g -like and h -like orbitals gives rise to a nontrivial topology characterized by Z 2 invariant protected by an energy gap as large as 0.52 eV, manifesting helical edge states mimicking those in the prominent quantum spin Hall effect, which can be accessed experimentally after hydrogenation in HGY. We hope these findings trigger interests towards exploring the topological electronic states in HGY and related future electronics applications. [ABSTRACT FROM AUTHOR]

The control of the pseudospin of sound wave has attracted increasing attention in recent years. Utilizing the finite-size effect of topological acoustics, we successfully construct an H-shaped acoustic topological pseudospin switcher that sound wave energy can be easily switched through different passages. The interesting phenomenon of pseudospin flipping is numerically and experimentally demonstrated. A quantitative interference theory is proposed that the constructive and destructive interference of pseudospin states leads to pseudospin flipping and preserving in multiple frequencies. We verify the key parameters of the design, including the length of the passage and its interface state dispersion, and the theory can be extended to other topology acoustics and photonics systems. Moreover, the tunable topological sonic crystal we use provides adjustable convenience to pseudospin switcher design. The pseudospin switching behavior offers an efficient method to control the acoustic topological edge state transport, which has great potential in versatile applications, such as integrated acoustics, acoustic security, and information processing. [ABSTRACT FROM AUTHOR]

Optical cavities play crucial roles in enhanced light-matter interaction, light control, and optical communications, but their dimensions are limited by the material property and operating wavelength. Ultrathin planar cavities are urgently in demand for large-area and integrated optical devices. However, extremely reducing the planar cavity dimension is a critical challenge, especially at telecommunication wavelengths. Herein, we demonstrate a type of ultrathin cavities based on large-area grown Bi2Te3 topological insulator (TI) nanofilms, which present distinct optical resonance in the near-infrared region. The result shows that the Bi2Te3 TI material presents ultrahigh refractive indices of >6 at telecommunication wavelengths. The cavity thickness can approach 1/20 of the resonance wavelength, superior to those of planar cavities based on conventional Si and Ge high refractive index materials. Moreover, we observed an analog of the electromagnetically induced transparency (EIT) effect at telecommunication wavelengths by depositing the cavity on a photonic crystal. The EIT-like behavior is derived from the destructive interference coupling between the nanocavity resonance and Tamm plasmons. The spectral response depends on the nanocavity thickness, whose adjustment enables the generation of obvious Fano resonance. The experiments agree well with the simulations. This work will open a new door for ultrathin cavities and applications of TI materials in light control and devices. [ABSTRACT FROM AUTHOR]

The model of the bound states in a double quantum dot formed by three magnetic barriers at the edge of two-dimensional topological insulator based on HgTe/CdTe quantum well is developed. The peculiarities of the energy spectrum, the probability density and the spin density of the quantum states are studied as a function of the orientation of the magnetization vector for the magnetic barriers. The wavefunction localization at the left and at the right of the anticrossing point in the spectrum is studied and the conclusion is made on the possibility of switching between the states with the localization area in different quantum dots by varying the polarization of the middle barrier. [ABSTRACT FROM AUTHOR]

The study of optical topological insulators (PTIs) has revealed intriguing optical properties that diversify the ways in which light can be manipulated, offering significant potential for a wide range of applications. This paper presents a machine learning (ML)-based approach for the reverse design of optical PTIs. Using finite element methods, the paper addresses the challenge of computing the band structure of a dual-band model, enabling the construction of a dataset suitable for ML training. With the goal of maximizing dual-band bandgaps, the study employs the random forest algorithm to predict target parameters and further designs topological edge states. Leveraging these boundary state patterns, two different optical PTI beam splitters are devised, and their transmission coefficients and losses are computed. The results demonstrate that optical devices designed using topological boundary states exhibit enhanced stability and robustness. This approach offers a reliable solution for applications in fields such as optical communication and optical sensing. [ABSTRACT FROM AUTHOR]

Topological insulators have recently received attention in optoelectronic devices because of their high mobility and broadband absorption resulting from their topological surface states. In particular, theoretical and experimental studies have emerged that can improve the spin generation efficiency in a topological insulator‐based p–n junction structure called a TPNJ, drawing attention in optospintronics. Recently, research on implementing the TPNJ structure is conducted; however, studies on the device characteristics of the TPNJ structure are still insufficient. In this study, the TPNJ structure is effectively implemented without intermixing by controlling the annealing temperature, and the photocharacteristics appearing in the TPNJ structure are investigated using a cross‐pattern that can compare the characteristics in a single device. Enhanced photo characteristics are observed for the TPNJ structure. An optical pump Terahertz probe and a physical property measurement system are used to confirm the cause of improved photoresponsivity. Consequently, the photocharacteristics are improved owing to the change in the absorption mechanism and surface transport channel caused by the Fermi level shift in the TPNJ structure. [ABSTRACT FROM AUTHOR]

The modern theory of quantized polarization has recently extended from 1D dipole moment to multipole moment, leading to the development from conventional topological insulators (TIs) to higher‐order TIs, i.e., from the bulk polarization as primary topological index, to the fractional corner charge as secondary topological index. The authors here extend this development by theoretically discovering a higher‐order end TI (HOETI) in a real projective lattice and experimentally verifying the prediction using topolectric circuits. A HOETI realizes a dipole‐symmetry‐protected phase in a higher‐dimensional space (conventionally in one dimension), which manifests as 0D topologically protected end states and a fractional end charge. The discovered bulk‐end correspondence reveals that the fractional end charge, which is proportional to the bulk topological invariant, can serve as a generic bulk probe of higher‐order topology. The authors identify the HOETI experimentally by the presence of localized end states and a fractional end charge. The results demonstrate the existence of fractional charges in non‐Euclidean manifolds and open new avenues for understanding the interplay between topological obstructions in real and momentum space. [ABSTRACT FROM AUTHOR]

Lattice thermal conductivity (κL) of the hexagon‐shaped nanocrystals cluster of Bi2Se3, prepared by the hot‐injection technique using nontoxic solvents, is studied. From the temperature‐dependent Raman spectra of Bi2Se3 nanocrystals, the average Debye temperature (θD) and Gruneisen parameter (γ) are calculated by adopting the bond‐order–length–strength correlation theory. The average room temperature κL of Bi2Se3 nanocrystals evaluated from the Slack model using θD and γ is ≈1.1 Wm−1K−1. The κL of Bi2Se3 nanocrystals is larger than out‐of‐plane κL (≈0.4 Wm−1K−1) but close to the in‐plane κL (≈1.4 Wm−1K−1) simulated using the Boltzmann transport equation for phonon with three‐phonon scatterings. Nanostructuring introduces grain boundaries in the Bi2Se3 that block the long mean free path of phonons physically, reduces the phonon mean free path, and decreases the κL. The anisotropic phonon scattering introduced by the weak van der Waals force between adjacent quintuple layers in the out‐of‐plane direction, in addition to the acoustic–optical phonon scattering and anharmonicity, hinders the efficient transport of thermal energy in the Bi2Se3 and results in a lower κL. By utilizing materials with anisotropic thermal conductivity, thermoelectric devices can be designed to preferentially conduct heat in specific directions while minimizing heat loss in others. [ABSTRACT FROM AUTHOR]

Abstract This work reports the formation of a heterojunction composed of Tl2Ba2CaCu2O8 (Tl‐2212) and Bi2Se3 as the high critical temperature superconductor and topological insulator, respectively. The Bi2Se3 film is deposited on the Tl‐2212 by a chemical mechanical polishing process. Due to the rough surface of Tl‐2212, the treated Tl‐2212 is then subjected to post‐annealing at various temperatures. This temperature does not affect the formation of the interfacial layer at the heterojunction; however, an improved layered crystal structure of the Bi2Se3 film is observed at 500 °C. The in‐depth profile of the relative atomic concentration indicates the diffusion of Cu and Tl into the Bi2Se3 film with the Ba diffusion being closer to the interfacial layer. At 500 °C, Cu atoms are more actively diffused into the Bi2Se3 film, thus blocking Tl diffusion, and improving the layered crystal structure of the film. The density functional theory calculations reveal that the lowest formation energy of the Cu vacancy is when Bi2Se3 is in contact with Tl‐2212, which results in the diffusion of Cu atoms from Tl‐2212, thus transforming the interstitial Cu atoms into the film. These atoms have an n‐type doping effect and prefer intercalating at a vdW gap deep inside the layered Bi2Se3.

Abstract All‐Van der Waals (vdW)‐material‐based heterostructures with atomically sharp interfaces offer a versatile platform for high‐performing spintronic functionalities at room temperature. One of the key components is vdW topological insulators (TIs), which can produce a strong spin‐orbit‐torque (SOT) through the spin‐momentum locking of their topological surface state (TSS). However, the relatively low conductance of the TSS introduces a current leakage problem through the bulk states of the TI or the adjacent ferromagnetic metal layers, reducing the interfacial charge‐to‐spin conversion efficiency (qICS). Here, a vdW heterostructure is used consisting of atomically‐thin layers of a bulk‐insulating TI Sn‐doped Bi1.1Sb0.9Te2S1 and a room‐temperature ferromagnet Fe3GaTe2, to enhance the relative current ratio on the TSS up to ≈20%. The resulting qICS reaches ≈1.65 nm−1 and the critical current density Jc ≈0.9 × 106 Acm−2 at 300 K, surpassing the performance of TI‐based and heavy‐metal‐based SOT devices. These findings demonstrate that an all‐vdW heterostructure with thickness optimization offers a promising platform for efficient current‐controlled magnetization switching at room temperature.

In this work the interface between a Pt film and a Bi2Se3 (0001) surface is investigated using electron microscopy and microanalysis, in order to characterize the structure of the interface and verify if it is chemically stable or an interaction occurs. At room temperature, the Pt film is composed of small clusters (∼10 nm) and the interface is stable. However, already upon mild annealing (200 °C) the interface displays instability and forms an interfacial phase. The interfacial phase, not previously reported in literature, is a long-range ordered ternary Pt:Bi:Se phase aligned with the Bi2Se3 crystal, most probably an intermetallic compound. The presence of a new phase at Pt/Bi2Se3 interface, together with the possible effects on the topological surface states, has to be considered in all the applied studies where this interface is present, as well as in the models for theoretical studies.

Chemical modifications such as intercalation can be used to modify surface properties or to further functionalize the surface states of topological insulators (TIs). Using ambient pressure x-ray photoelectron spectroscopy, we report copper migration in C u x B i 2 S e 3 , which occurs on a timescale of hours to days after initial surface cleaving. The increase in near-surface copper proceeds along with the oxidation of the sample surface and large changes in the selenium content. These complex changes are further modeled with core-level spectroscopy simulations, which suggest a composition gradient near the surface which develops with oxygen exposure. Our results shed light on a new phenomenon that must be considered for intercalated TIs—and intercalated materials in general—that surface chemical composition can change when specimens are exposed to ambient conditions.

The effects of different types of fluoride glass core fibers, from three main groups of fluorozirconate (ZrF4-based), fluoroaluminate (AlF3-based), and fluoroindate (InF3-based) fibers, were investigated in sensing salivary cortisol utilizing surface plasmon resonance (SPR) sensors. These sensors comprised multiple layers, including fluoride glass core, metal (Ag), dielectric, and dielectric grating (SiO2). The comparison was conducted to evaluate the sensor's figure of merit (FOM) and limit of detection (LOD) at 830 nm wavelength while optimizing the thickness of metal layer for different concentration of cortisol and keeping other parameters constant. The largest FOM of 20.83 RIU−1 was observed for the composition of IZBSC (40 InF3-20 ZnF2-15 BaF2-20 SrF2-5 CaF2) from InF3-based group, resulting in an exceptional LOD of 0.986 fg/mL with the intensity interrogation method. This represents a tremendous advancement compared to prior reported results. Furthermore, by implementing a topological insulator Bi1.5 Sb0.5 Te1.8 Se1.2 (BSTS) into this sensor with a ZBLAN fiber for the first time, the LOD was reduced to 0.54 fg/mL, demonstrating remarkable progress in cortisol sensing capability best to our knowledge.