Te Vacancies Research Articles

Defect dependent electronic properties of WTe2: a first-principles study

Abstract Tungsten ditelluride (WTe2) possesses fascinating electronic structures and exceptional properties that make it highly suitable for use in cutting-edge devices. Defects in WTe2 can have a significant influence on its properties, both in advantageous and disadvantageous ways. Thus, a precise classification is crucial to fully comprehend the potential impacts. Here we report a thorough investigation of the electronic characteristics of intrinsic defects, including point defects, in monolayer WTe2 using first-principles calculations based on density functional theory. Our research suggests that the presence of point defects can cause a notable shift in electronic properties, resulting in a metallic behaviour. This is due to the interesting phenomenon of Fermi-level changing near the band edges. Our research findings indicate that the energy required to form a vacancy in a Te atom is lower compared to that of a vacancy in a W atom. Based on the findings, it appears that Te atom vacancies are more likely to be generated during the synthesis process. Defects like the Te vacancy and Mo substitution in the pristine monolayer of WTe2 result in a subtle reduction in the band gap, while still maintaining its characteristics as a direct band gap semiconductor. Our study reveals that the electronic properties of monolayer WTe2 can be significantly altered by the presence of vacancy defects. This discovery highlights the exciting potential of WTe2 as a promising platform for various electronic applications. Our research is anticipated to have a beneficial impact on the comprehension and control of the characteristics of WTe2, thus expediting the development of nanomaterials in various fields.

Cobalt Ditelluride Meets Tellurium Vacancy: An Efficient Catalyst as a Multifunctional Polysulfide Mediator toward Robust Lithium-Sulfur Batteries.

The commercialization of lithium-sulfur batteries (LSBs) faces significant challenges due to persistent issues, such as the shuttle effect of lithium polysulfides (LiPSs) and the slow kinetics of cathodic reactions. To address these limitations, this study proposes a vacancy-engineered cobalt ditelluride catalyst (v-CoTe2) supported on nitrogen-doped carbon as a sulfur host at the cathode. Density functional theory calculations and experimental results indicate that the electron configuration modulation of v-CoTe2 enhances the chemical affinity and catalytic activity toward LiPS. Specifically, v-CoTe2 can strongly interact with PSs through multisite coordination, effectively facilitating the kinetics of the LiPS redox reaction. Furthermore, the introduction of Te vacancies generates a large number of spin-polarized electrons, further enhancing the reaction kinetics of LiPS. As a result, the v-CoTe2@S cathode demonstrates high initial capacity and excellent cyclic stability, maintaining 80.4% capacity after 500 cycles at a high current rate of 3 C. Even under a high sulfur load of 6.7 mg cm-2, a high areal capacity of 6.1 mA h cm-2 is retained after 50 cycles. These findings highlight the significant potential of Te vacancies in CoTe2 as a sulfur host material for LSBs.

Ultrahigh Power Factor of Sputtered Nanocrystalline N-Type Bi2Te3 Thin Film via Vacancy Defect Modulation and Ti Additives.

Magnetron-sputtered thermoelectric thin films have the potential for reproducibility and scalability. However, lattice mismatch during sputtering can lead to increased defects in the epitaxial layer, which poses a significant challenge to improving their thermoelectric performance. In this work, nanocrystalline n-type Bi2Te3 thin films with an average grain size of ≈110nm are prepared using high-temperature sputtering and post-annealing. Herein, it is demonstrated that high-temperature treatment exacerbates Te evaporation, creating Te vacancies and electron-like effects. Annealing improves crystallinity, increases grain size, and reduces defects, which significantly increases carrier mobility. Furthermore, the pre-deposited Ti additives are ionized at high temperatures and partially diffused into Bi2Te3, resulting in a Ti doping effect that increases the carrier concentration. Overall, the 1µm thick n-type Bi2Te3 thin film exhibits a room temperature resistivity as low as 3.56 × 10-6 Ω∙m. Notably, a 5µm thick Bi2Te3 thin film achieves a record power factor of 6.66mWmK-2 at room temperature, which is the highest value reported to date for n-type Bi2Te3 thin films using magnetron sputtering. This work demonstrates the potential for large-scale of high-quality Bi2Te3-based thin films and devices for room-temperature TE applications.

Zinc Tellurium with Anionic Vacancies Anchored on Ordered Macroporous Carbon Skeleton Enabling Accelerated Polysulfide Conversion for Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LSBs) showcase great promise for large-scale energy storage systems, however, their practical commercialization is seriously hindered by the sluggish redox reaction kinetics and detrimental shuttle effect of soluble polysulfides. Herein, small ZnTe1- x nanoparticles with anionic vacancies firmly anchored on 3D ordered macroporous N-doped carbon skeleton (3DOM-ZnTe1- x@NC) are elaborately constructed as a high-efficiency electrocatalyst for LSBs. The ordered macroporous carbon skeleton not only greatly increases the external surface area to expose sufficient active sites but also facilitates the electrolyte penetration. Additionally, the experimental studies combined with theoretical calculations confirm the presence of Te vacancies optimizes the electronic structure to enhance the intrinsic catalytic activity and chemical absorption. Consequently, LSBs assembled with the 3DOM-ZnTe1- x@NC modified separators exhibit high specific discharge capacity, as well as superior rate performance and good long-term cycling stability. Even under a high sulfur loading of 6.5 mg cm-2 and lean electrolyte, an impressive areal capacity of 5.28 mAh cm-2 is achieved at 0.1C after 100 cycles. More significantly, the 3DOM-ZnTe1- x@NC based pouch cells are also fabricated to demonstrate its potential for practical applications. This work highlights that the rational combination of 3DOM architecture and vacancy engineering is important for designing advanced Li-S electrocatalysts.

Enhancing hydrogen evolution reaction performance through defect engineering in WTeX (X= S, Se) monolayers: A first-principles study

Finding a novel material to substitute the existing noble metal catalysts for the hydrogen evolution reaction (HER) is essential for the further advancement of water electrolysis technology. Herein, we investigated the feasibility of using defect engineering to improve the hydrogen evolution reaction (HER) catalytic performance of WTeX (X = Se, S) materials in the 2H, 1 T, and 1 T′ phases. The results demonstrate that the introduction of defects significantly enhances WTeX monolayers’ HER performance. As exemplary cases, the Gibbs free energy changes for 2H WTeSe with a Te vacancy (2H WTeSe–VTe) and 2H WTeS with a Te vacancy (2H WTeS–VTe) are 0.029 eV and −0.002 eV, respectively. It was found that the active sites in 2H WTeSe–VTe and 2H WTeS–VTe have a substantial number of empty anti-bonding states, which increases the bond strength between H and the catalyst, leading to exceptional catalytic performance. This work demonstrates the feasibility of defect-engineered WTeX structures as electrocatalysts and provides a reliable reference for the study of non-precious metal catalysts.

Heterocontact-Triggered 1H to 1T' Phase Transition in CVD-Grown Monolayer MoTe2: Implications for Low Contact Resistance Electronic Devices.

Single-layer molybdenum ditelluride (MoTe2) has attracted attention due to the smaller energy difference between the semiconducting (1H) and semimetallic (1T') phases with respect to other two-dimensional transition metal dichalcogenides (TMDs). Understanding the phenomenon of polymorphism between these structural phases is of great fundamental and practical importance. In this paper, we report a 1H to 1T' phase transition occurring during the chemical vapor deposition (CVD) synthesis of single-layer MoTe2 at 730 °C. The transformation originates at the heterocontact between monoclinic and hexagonal crystals and progresses to either yield a partial or complete 1H to 1T' phase transition. Microscopic and spectroscopic analyses of the MoTe2 crystals reveal the presence of Te vacancies and mirror twin boundaries (MTB) domains in the hexagonal phase. The experimental observations and theoretical simulations indicate that the combination of heterocontact formation and Te vacancies are relevant triggering mechanisms in the observed transformation. By advancing in the understanding and controlling of the direct synthesis of lateral 1T'/1H heterostructures, this work contributes to the development of MoTe2-based electronic and optoelectronic devices with low contact resistance.

Influence of mono‐ and bi‐vacancy doped alkaline‐earth metals on the optoelectronic properties of monolayer defective state MoTe2: A first‐principles study

AbstractThe effects of single‐vacancy and double‐vacancy doping with alkaline‐earth metals on the stability, electronic structure, charge transfer, and optical properties of molybdenum ditelluride in the monolayer defective state (MoTe2) have been investigated using first‐principles methods. It is found that the structure of the molybdenum ditelluride system is more stable after double Te vacancies, with direct band‐gap to indirect band‐gap transitions occurring in single Te vacancies and Mo vacancies, and semiconductor to quasi‐metal transitions occurring in double Mo vacancies. The binding energy in the defect state system of molybdenum ditelluride after vacancy defects is always negative, and the structure remains stable. In this paper, the most stable double Te vacancy state was selected for substitutional doping with alkaline‐earth metals, and the Be atoms were doped with the largest amount of morphology, and Ca atoms were doped with the most pronounced decrease in band gap value. The direct band‐gap semiconductor is maintained after doping with Be atoms. Doping with Mg, Sr and Ba changes the band‐gap from direct to indirect. The double Te defect state MoTe2 doped with Ca atoms has a tendency to transition to a quasi‐metal. Regarding photoelectric properties, the system is blue‐shifted on both the absorption and reflection peaks.

Defect Engineering of MoTe2 via Thiol Treatment for Type III van der Waals Heterojunction Phototransistor.

Molybdenum ditelluride (MoTe2) nanosheets have displayed intriguing physicochemical properties and opto-electric characteristics as a result of their tunable and small band gap (Eg ∼ 1 eV), facilitating concurrent electron and hole transport. Despite the numerous efforts devoted to the development of p-type MoTe2 field-effect transistors (FETs), the presence of tellurium (Te) point vacancies has caused serious reliability issues. Here, we overcome this major limitation by treating the MoTe2 surface with thiolated molecules to heal Te vacancies. Comprehensive materials and electrical characterizations provided unambiguous evidence for the efficient chemisorption of butanethiol. Our thiol-treated MoTe2 FET exhibited a 10-fold increase in hole current and a positive threshold voltage shift of 25 V, indicative of efficient hole carrier doping. We demonstrated that our powerful molecular engineering strategy can be extended to the controlled formation of van der Waals heterostructures by developing an n-SnS2/thiol-MoTe2 junction FET (thiol-JFET). Notably, the thiol-JFET exhibited a significant negative photoresponse with a responsivity of 50 A W-1 and a fast response time of 80 ms based on band-to-band tunneling. More interestingly, the thiol-JFET displayed a gate tunable trimodal photodetection comprising two photoactive modes (positive and negative photoresponse) and one photoinactive mode. These findings underscore the potential of molecular engineering approaches in enhancing the performance and functionality of MoTe2-based nanodevices as key components in advanced 2D-based optoelectronics.

Designing triple-layer photocatalytic systems based on direct Z-scheme photocatalytic systems: Towards higher solar-to-hydrogen efficiency

Direct Z-scheme photocatalytic systems, with their strong photocatalytic redox capabilities and efficient separation of photogenerated carriers, are beneficial for enhancing photocatalytic efficiency. However, the low solar-to-hydrogen (STH) efficiency of the entire photocatalytic system is caused by the recombination of half of the photogenerated carriers at the interface. Based on this, we first propose monolayer-MoSeTe/SnSe2 and monolayer-WSeTe/SnSe2 heterostructures as direct Z-scheme photocatalytic systems for overall water splitting, with theoretical estimated STH efficiencies of 10.14% and 9.18%, respectively. To enhance the STH efficiency of the proposed direct Z-scheme systems, triple-layer photocatalytic systems are designed based on the proposed direct Z-scheme systems: bilayer-MoSeTe/SnSe2 and bilayer-WSeTe/SnSe2 heterostructures, with STH efficiencies of 11.94% and 10.78%, respectively. Compared to the monolayer-MoSeTe/SnSe2 and monolayer-WSeTe/SnSe2 heterostructures, the triple-layer photocatalytic systems possess higher efficiencies of carrier utilization and the STH efficiencies increased by 17.75% and 17.43%, respectively. Among them, the STH efficiencies of monolayer-MoSeTe/SnSe2, bilayer-MoSeTe/SnSe2 and bilayer-WSeTe/SnSe2 heterostructures exceed the threshold of 10% required for commercial applications. By introducing Te vacancies on the surfaces of Janus TMDCs, all four proposed van der Waals heterostructures can spontaneously perform hydrogen evolution reaction and oxygen evolution reaction processes in a neutral environment under illumination. Thus, our research provides a new strategy for designing highly-efficient photocatalytic systems.

Electrochemical Generation of Te Vacancy Pairs in PtTe for Efficient Hydrogen Evolution.

Two-dimensional (2D) van der Waals materials are increasingly seen as potential catalysts due to their unique structures and unmatched properties. However, achieving precise synthesis of these remarkable materials and regulating their atomic and electronic structures at the most fundamental level to enhance their catalytic performance remain a significant challenge. In this study, we synthesized single-crystal bulk PtTe crystals via chemical vapor transport and subsequently produced atomically thin, large PtTe nanosheets (NSs) through electrochemical cathode intercalation. These NSs are characterized by a significant presence of Te vacancy pairs, leading to undercoordinated Pt atoms on their basal planes. Experimental and theoretical studies together reveal that Te vacancy pairs effectively optimize and enhance the electronic properties (such as charge distribution, density of states near the Fermi level, and d-band center) of the resultant undercoordinated Pt atoms. This optimization results in a significantly higher percentage of dangling O-H water, a decreased energy barrier for water dissociation, and an increased binding affinity of these Pt atoms to active hydrogen intermediates. Consequently, PtTe NSs featuring exposed and undercoordinated Pt atoms demonstrate outstanding electrocatalytic activity in hydrogen evolution reactions, significantly surpassing the performance of standard commercial Pt/C catalysts.

Synergistic enhancement of thermoelectric performance of n-type PbTe by resonant level and single-atom-layer vacancies

Modulating electrical and thermal transport through zero-dimensional point defects and one-dimensional dislocations are extensively investigated. However, the systematic study of exploring single-atom-layer vacancies for improving thermoelectric (TE) performance remains rare. In this study, we modulate the number density of single-atom-layer two-dimensional (2D) Te vacancies in lead telluride (PbTe) for the first time through bismuth and indium doping. DFT calculations reveal (Bi, In) co-doping lowers the formation energy of such defects, confirming the feasibility of this method. 2D Te vacancies simultaneously enhance phonon scattering and evoke bond softening, significantly lowering the lattice thermal conductivity. Meanwhile, indium doping generates resonant level in the energy band, which increases the carrier concentration without deteriorating the Seebeck coefficient drastically. As a result, a peak TE figure of merit (zT) of ∼1.6 and an average zT (zTavg) of 1.17 are achieved in the (Bi, In) co-doped PbTe. Furthermore, a high conversion efficiency of 6.5 % is obtained for the fabricated 2-pair module at a temperature difference of 500 K.

Transport Property Evolution in 2H‐MoTe2−x Mediated by Te‐Deficiency‐Induced Mirror Twin Boundary Networks

The 2H‐MoTe2 is a well‐known layered 2D semiconductor that is considered as a promising material for next‐generation microelectronic and optoelectronic devices. Te‐deficiency‐induced defective structures, like Te vacancy and mirror twin boundary (MTB), would be generated at elevated temperatures. However, the temperature‐dependent evolution of such defects and their influence on the macroscopic electrical transport property of 2H‐MoTe2 is unclear. Herein, the semiconductor–metal transition phenomenon in 2H‐MoTe2−x mediated by the evolving disordered MTB network with increasing Te deficiency is reported on. The samples are grown by molecular beam epitaxy, while the Te deficiency is tuned by post‐growth flash annealing in ultra‐high vacuum. Low‐temperature scanning tunneling microscope investigation discloses the medium‐range disorder evolution of the MTB network incorporated in the 2H‐MoTe2, which eventually transforms to an ordered metallic Mo5Te8 metastable phase. The scanning tunneling spectroscopy shows rich in‐gap states localized at the MTBs, which provide a conducting channel in the semiconductor. The ultra‐high vacuum in situ transport measurement shows a gradual decrease of resistance of the sample upon flash annealing from 50 to 480 °C, confirming the influence of Te deficiency on the transport property, which would play an essential role in the device performance and durability.

Electronic structure and optical properties of alkali metal X (X=Li, Na, K, Rb, Cs) adsorbed in the Te vacancy-deficient molybdenum ditelluride system: A first-principles study

In the framework of density functional theory, based on first principles, the plane wave pseudopotential technique was utilized to investigate the electrical and optical properties of MoTe2 adjusted by alkali metal X adsorption on Te vacancy defects (X[Formula: see text]=[Formula: see text]Li, Na, K, Rb, Cs). The adsorption of alkali metals on Te vacancy-deficient MoTe2 monolayers has been computationally analyzed. Charge transfer, electronic structure, and optical properties of alkali metal adsorption were systematically studied. It is shown that the MoTe2 bandgap is significantly reduced under Te vacancies. Te vacancies are frequently active sites in TMDs materials. With the adsorption of alkali metal atoms X (X = Li, Na, K, Rb, Cs) in the Te vacancy MoTe2 system, Li atoms have the most substantial geometrical deformation and the minor adsorption energy and can improve the adsorption properties more effectively. The MoTe2 system undergoes a change from semiconductor to metal after adsorption. Regarding optical properties, firm absorption and reflection peaks appeared, and a blueshift phenomenon was observed in the mountains. It is expected that these discoveries are likely to guide the use of molybdenum ditelluride in optoelectronics.

How to repair the performance degradation of WSeTe SBFET caused by channel vacancy defects: A first principles study

The QuantumATK software package based on density functional theory and non-equilibrium Green's function is used to predict the performance of a 5.1 nm in-plane contact double-gate WSeTe Schottky barrier SBFET with 1 T-WTe2 as electrodes and Janus WSeTe as channel. It is found that the performance of 5.1 nm WSeTe SBFET meets the prediction parameters of ITRS(2013 version) about high performanc device for the production year 2028, but Te (Se) vacancy defect at the channel near the source will degrade its performance. How to repair the performance of the WSeTe SBFET with Te (Se) vacancy defect at the channel near the source? The effects of O, Cl and N passivation of Te (Se) vacancy defects on the performance of WSeTe SBFET were discussed. The results indicate that O Passivation can repair and even improve the performance of WSeTe SBFET by repairing the DOS changes of monolayer WSeTe induced by Te (Se) vacancy defects.

Strain-induced superstructure evolution and Te vacancy accumulation in AgTe monolayer grown on Ag(111) substrate

Two-dimensional (2D) materials have attracted increasing attention for frontier science and industrial applications in the past few decades. As a 2D materials with honeycomb lattice, AgTe monolayer grown on Ag (111) substrate belongs to the transition metal monochalcogenides (TMMs) family possessing various superstructures and exotic electronic structure. In this report, the AgTe monolayer superstructure is mainly studied using scanning tunneling microscope/spectroscopy (STM/S) measurements. With the increase of Te deposition, the planar structure of the AgTe monolayer becomes the one-dimensional (1D) moiré pattern structure, which transformation is related to the change of strain combing with theoretical analysis. When there is an isotropic strain on the surface, the AgTe monolayer is a flat honeycomb structure. In contrast, the lattice structural strain is released under a uniaxial strain as the AgTe monolayer is transformed into a 1D moiré pattern structure. In addition, Te vacancies in the AgTe monolayer are also affected by the synergistic effect of strain and Ag (111) substrate, and the concentration of Te vacancy changes significantly with the strain transformation. Moreover, both experimental statistics and theoretical calculations verify that Te vacancy tend to appear in the bright ridge (BR) region of the AgTe monolayer with a 1D moiré pattern structure, which is also the result of strain modulation. Our findings open up a new thought for strain transformation control of 2D materials driven by elemental concentration.

2D Ferromagnetic M3GeTe2 (M = Ni/Fe) for Boosting Intermediates Adsorption toward Faster Water Oxidation.

In this work, 2D ferromagnetic M3GeTe2 (MGT, M = Ni/Fe) nanosheets with rich atomic Te vacancies (2D-MGTv) are demonstrated as efficient OER electrocatalyst via a general mechanical exfoliation strategy. X-ray absorption spectra (XAS) and scanning transmission electron microscope (STEM) results validate the dominant presence of metal-O moieties and rich Te vacancies, respectively. The formed Te vacancies are active for the adsorption of OH* and O* species while the metal-O moieties promote the O* and OOH* adsorption, contributing synergistically to the faster oxygen evolution kinetics. Consequently, 2D-Ni3GeTe2v exhibits superior OER activity with only 370mV overpotential to reach the current density of 100mA cm-2 and turnover frequency (TOF) value of 101.6 s-1 at the overpotential of 200mV in alkaline media. Furthermore, a 2D-Ni3GeTe2v-based anion-exchange membrane (AEM) water electrolysis cell (1 cm2) delivers a current density of 1.02 and 1.32 A cm-2 at the voltage of 3V feeding with 0.1 and 1m KOH solution, respectively. The demonstrated metal-O coordination with abundant atomic vacancies for ferromagnetic M3GeTe2 and the easily extended preparation strategy would enlighten the rational design and fabrication of other ferromagnetic materials for wider electrocatalytic applications.

Point defects, doping and the path to n-type SnTe

Point defects in SnTe were studied using first-principles modeling. Sn vacancies were found to be spontaneously formed in SnTe and make it intrinsically a p-type semiconductor, in excellent accord with experiments. The calculated electronic structure for Sn vacancy reveals that the Fermi level is shifted down into the valence band and presents p-type behavior. In contrast, the Fermi level shifts near the conduction band minimum (CBM) for Te vacancy and presents an n-type behavior. All the interstitial sites were considered for a comprehensive intrinsic point defect study. The body-centered (tetrahedral) site was found to be a stable interstitial configuration for Sn, whereas the split<111> interstitial was preferred for Te. We found that the electronic structures due to the interstitial configurations were distinct. Sn interstitials defects, Fermi level was shifted inside the conduction band for body interstitial, near to CBM for split 111 interstitial, whereas inside the bandgap for the base and split 110 interstitial defects. Contrary results were obtained for Te interstitial defects; the Fermi level was found inside the valence band for body interstitial, close to VBM for split 111, while the Fermi level was obtained inside the bandgap for base and split 110 interstitial defects. In addition, extrinsic oxygen impurities and other possible dopants that can transform SnTe to n-type were investigated. Interstitial oxygen was found to be stable at the body-interstitial site and is incorporated easily into the material in both Sn- and Te-rich environments, leading the material to p-type. The Fermi level was obtained inside the bandgap for oxygen substituted in Te vacancy and showed no preferred conductivity behavior. Finally, we find that Sb, Bi, and halogens (in Sn-rich conditions) can significantly improve electron concentrations and be promising dopants to transform the material's intrinsic conductivity from p-type to n-type. Notably, the sample should be prevented from incorporating oxygen impurities while doping sample n-type.

Te-vacancy defect triggering photocatalytic overall water splitting for MoTe2/GeN Z-scheme heterostructure

Developing proper semiconductor photocatalysts is urgently needed to solve energy and environmental crises. Especially, photocatalysts for water splitting with a Z-scheme mechanism are desirable materials. Herein, a two-dimensional VTe-MoTe2/GeN heterostructure (VTe-HS), including single Te vacancy, is theoretically proved to function as a direct Z-scheme photocatalyst with the wide light-harvesting range, the effective spatial separation for carriers, and the high catalytic activity for water splitting. An enhanced optical absorption coefficient of 105 cm−1 is observed and the absorption edge (∼1.0 eV) is red-shifted into the infrared light region. Separating photogenerated electron–hole pairs enhances the photocatalytic efficiency due to the staggered band alignment. Interlayer charge migration of about 0.154 electrons induces an intrinsic built-in electric field in the heterostructure, allowing forming the Z-scheme mechanism with a reduction potential of –4.01 eV and an oxidation potential of –7.13 eV. Gibbs free energies confirm that water redox reactions can proceed spontaneously under sunshine. Moreover, the Heyrovsky reaction is kinetically more favorable than the Tafel reaction because of a little energy barrier (0.071 eV). These features show that the VTe-HS is a desirable water-splitting photocatalyst, providing a valuable clue to constructing high-efficiency photocatalysts.

Te Vacancy‐Driven Anomalous Transport in ZrTe5 and HfTe5

AbstractThe strongly sample‐dependent anomalous transport properties observed in the layered Dirac materials ZrTe5 and HfTe5 are known to strongly correlate with the presence of Te vacancies. One phenomenon, a negative longitudinal magnetoresistance (NLMR), is widely speculated to be a signature of broken chiral symmetry. However, the role of electronic structure in the sample dependence of the transport properties of these materials is poorly understood. This prompts the question as to whether the NLMR is a genuine signature of the chiral anomaly in ZrTe5 and HfTe5. In this work, the effect of Te vacancies on the electronic structure of ZrTe5 and HfTe5 is investigated via first‐principles calculations. Te vacancies serve two purposes: modification of the cell volume via effective compressive strain and production of local changes to the electronic structure. The reorganization of the electronic structure near the Fermi energy indicates that Te vacancies can rationalize conflicting reports in spectroscopic and transport measurements that have remained elusive in prior first‐principles studies. These results show that Te vacancies contribute, in part, to the anomalous transport properties of ZrTe5 and HfTe5 but, critically, do not eliminate the possibility of a genuine manifestation of the chiral anomaly in these materials.

Thickness-Tunable Zoology of Magnetic Spin Textures Observed in Fe5GeTe2.

The family of two-dimensional (2D) van der Waals (vdW) materials provides a playground for tuning structural and magnetic interactions to create a wide variety of spin textures. Of particular interest is the ferromagnetic compound Fe5GeTe2 that we show displays a range of complex spin textures as well as complex crystal structures. Here, using a high-brailliance laboratory X-ray source, we show that the majority (1 × 1) Fe5GeTe2 (FGT5) phase exhibits a structure that was previously considered as being centrosymmetric but rather lacks inversion symmetry. In addition, FGT5 exhibits a minority phase that exhibits a long-range ordered (√3 × √3)-R30° superstructure. This superstructure is highly interesting in that it is innately 2D without any lattice periodicity perpendicular to the vdW layers, and furthermore, the superstructure is a result of ordered Te vacancies in one of the topmost layers of the FGT5 sheets rather than being a result of vertical Fe ordering as earlier suggested. We show, from direct real-space magnetic imaging, evidence for three distinct magnetic ground states in lamellae of FGT5 that are stabilized with increasing lamella thickness, namely, a multidomain state, a stripe phase, and an unusual fractal state. In the stripe phase we also observe unconventional type-I and type-II bubbles where the spin texture in the central region of the bubbles is nonuniform, unlike conventional bubbles. In addition, we find a bobber or a cocoon-like spin texture in thick (∼170 μm) FGT5 that emerges from the fractal state in the presence of a magnetic field. Among all the 2D vdW magnets we have thus demonstrated that FGT5 hosts perhaps the richest variety of magnetic phases that, thereby, make it a highly interesting platform for the subtle tuning of magnetic interactions.