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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Revealing the Origin of Time-Reversal Symmetry Breaking in Fe-Chalcogenide Superconductor FeTe 1 - x Se x

We report that recently evidence has emerged in the topological superconductor Fe-chalcogenide FeTe 1-x Se x for time-reversal symmetry breaking (TRSB), the nature of which has strong implications on the Majorana zero modes (MZM) discovered in this system. It remains unclear however whether the TRSB resides in the topological surface state (TSS) or in the bulk, and whether it is due to an unconventional TRSB superconducting order parameter or an intertwined order. Here by performing in superconducting FeTe 1-x Se x crystals both surface-magneto-optic-Kerr effect (SMOKE) measurements using a Sagnac interferometer and bulk magnetic susceptibility measurements, we pinpoint the TRSB to the TSS, where we also detect a Dirac gap. Further, we observe surface TRSB in non-superconducting FeTe 1-x Se x of nominally identical composition, indicating that TRSB arises from an intertwined surface ferromagnetic (FM) order. The observed surface FM bears striking similarities to the two-dimensional (2D) FM found in 2D van der Waals crystals, and is highly sensitive to the exact chemical composition, thereby providing a means for optimizing the conditions for Majorana particles that are useful for robust quantum computing.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Nanoscale visualization of the thermally driven evolution of antiferromagnetic domains in FeTe thin films

Antiferromagnetic order, being a ground state of a number of exotic quantum materials, is of immense interest both from the fundamental physics perspective and for driving potential technological applications. For a complete understanding of antiferromagnetism in materials, nanoscale visualization of antiferromagnetic domains, domain walls, and their robustness to external perturbations is highly desirable. Here, we synthesize antiferromagnetic FeTe thin films using molecular-beam epitaxy. We visualize local antiferromagnetic ordering and domain formation using spin-polarized scanning tunneling microscopy. From the atomically resolved scanning tunneling microscopy topographs, we calculate local structural distortions to find a high correlation with the distribution of the antiferromagnetic order. This is consistent with the monoclinic structure in the antiferromagnetic state. Interestingly, we observe a substantial domain-wall change by small temperature variations, unexpected for the low-temperature changes used compared to the much higher antiferromagnetic ordering temperature of FeTe. This is in contrast to electronic nematic domains in the cousin FeSe multilayer films, where we find no electronic or structural change within the same temperature range. Further, our experiments provide the atomic-scale imaging of perturbation-driven magnetic domain evolution simultaneous with the ensuing structural response of the system. The results reveal surprising thermally driven modulations of antiferromagnetic domains in FeTe thin films well below the Néel temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Pressure Evolution of Ultrafast Photocarrier Dynamics and Electron–Phonon Coupling in FeTe 0.5 Se 0.5

Understanding the coupling between electrons and phonons in iron chalcogenides FeTe x Se 1–x has remained a critical but arduous project in recent decades. The direct observation of the electron–phonon coupling effect through electron dynamics and vibrational properties has been lacking. Here, we report the first pressure-dependent ultrafast photocarrier dynamics and Raman scattering studies on an iron chalcogenide FeTe 0.5 Se 0.5 to explore the interaction between electrons and phonons in this unconventional superconductor. The lifetime of the excited electrons evidently decreases as the pressure increases from 0 to 2.2 GPa, and then increases with further compression. The vibrational properties of the A 1g phonon mode exhibit similar behavior, with a pronounced frequency reduction appearing at approximately 2.3 GPa. The dual evidence reveals the enhanced electron–phonon coupling strength with pressure in FeTe 0.5 Se 0.5 . Our results give an insight into the role of the electron–phonon coupling effect in iron-based superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1977

Bulk and thin films of FeTe: A Moessbauer study

Studies of bulk and thin films of FeTe using Moessbauer spectroscopy showed that FeTe has one noncubic Fe (+2) site which is 3d2 4s 4p3 hybridized. The presence of dangling bands was indicated in spectra of FeTe thin films. The films showed a tendency of texture formation. The substrate was observed to influence the film structure and nature of bonds in films.

Escue, W. T.↗
DOE OSTI2020

Materials Data on FeTe by Materials Project

FeTe is Vulcanite structured and crystallizes in the tetragonal P4/nmm space group. The structure is two-dimensional and consists of one FeTe sheet oriented in the (0, 0, 1) direction. Fe2+ is bonded in a 4-coordinate geometry to four equivalent Te2- atoms. All Fe–Te bond lengths are 2.58 Å. Te2- is bonded in a 4-coordinate geometry to four equivalent Fe2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Universal Superconductivity in FeTe and All‐Iron‐Based Ferromagnetic Superconductor Heterostructures

Abstract Ferromagnetism (FM) and superconductivity (SC) are two of the most famous macroscopic quantum phenomena. However, nature normally does not allow SC and FM to coexist without significant degradation. Here, the first fully iron‐based SC/FM heterostructures, composed of Fe(Te,Se) and Fe 3 GeTe 2 , are introduced, and it is shown that this system exhibits both strong FM and high‐temperature SC with an atomically sharp interface. From this study, it is also discovered that minute level of various cationic dopants can drive otherwise non‐superconducting FeTe films into a SC state. This suggests that the ground state of FeTe is so close to the SC state that it can be driven in and out of the SC state with various other perturbations. Altogether, this shows that Fe‐Te‐based heterostructures provide a unique opportunity to manipulate magnetism, superconductivity, and topological physics, paving the way toward new superconducting technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Spatially dispersing Yu-Shiba-Rusinov states in the unconventional superconductor FeTe 0.55 Se 0.45

By using scanning tunneling microscopy (STM) we find and characterize dispersive, energy-symmetric in-gap states in the iron-based superconductor FeTe 0.55 Se 0.45 , a material that exhibits signatures of topological superconductivity, and Majorana bound states at vortex cores or at impurity locations. We use a superconducting STM tip for enhanced energy resolution, which enables us to show that impurity states can be tuned through the Fermi level with varying tip-sample distance. We find that the impurity state is of the Yu-Shiba-Rusinov (YSR) type, and argue that the energy shift is caused by the low superfluid density in FeTe 0.55 Se 0.45 , which allows the electric field of the tip to slightly penetrate the sample. We model the newly introduced tip-gating scenario within the single-impurity Anderson model and find good agreement to the experimental data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Materials Data on FeTe by Materials Project

FeTe crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Fe2+ is bonded in a 6-coordinate geometry to six equivalent Te2- atoms. All Fe–Te bond lengths are 2.69 Å. Te2- is bonded in a 6-coordinate geometry to six equivalent Fe2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Y5(FeTe)2 by Materials Project

Y5(FeTe)2 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. there are three inequivalent Y sites. In the first Y site, Y is bonded in a 7-coordinate geometry to three Fe and four equivalent Te atoms. There are one shorter (2.82 Å) and two longer (2.94 Å) Y–Fe bond lengths. There are two shorter (3.31 Å) and two longer (3.35 Å) Y–Te bond lengths. In the second Y site, Y is bonded in a 6-coordinate geometry to three Fe and three equivalent Te atoms. There are one shorter (2.91 Å) and two longer (2.93 Å) Y–Fe bond lengths. There are one shorter (3.19 Å) and two longer (3.20 Å) Y–Te bond lengths. In the third Y site, Y is bonded in a 4-coordinate geometry to two Fe and two equivalent Te atoms. There are one shorter (2.99 Å) and one longer (3.44 Å) Y–Fe bond lengths. Both Y–Te bond lengths are 3.22 Å. There are two inequivalent Fe sites. In the first Fe site, Fe is bonded in a 9-coordinate geometry to seven Y and two equivalent Fe atoms. Both Fe–Fe bond lengths are 2.29 Å. In the second Fe site, Fe is bonded in a 9-coordinate geometry to seven Y and two equivalent Fe atoms. Te is bonded in a 8-coordinate geometry to eight Y atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Fe 0.6 Pd 0.4 Te 2 : A New Polymorph of FeTe 2 and PdTe 2 Stable at Ambient Pressure

Whereas pyrite space group is a high pressure polymorph of FeTe 2 , here we report pyrite-type single crystal Fe 0.6 Pd 0.4 Te 2 prepared using Pd substitution on Fe atomic site with ambient pressure crystal growth methods. Here, Fe 0.6(1) Pd 0.4(1) Te 2 single crystals show metal behavior above 15 K abided by Bloch-Grüneisen relation, and display resistivity upturn below 15 K due to disorder-related scattering of correlated electronic states.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Kondo interaction in FeTe and its potential role in the magnetic order

Finding d-electron heavy fermion states has been an important topic as the diversity in d-electron materials can lead to many exotic Kondo effect-related phenomena or new states of matter such as correlation-driven topological Kondo insulator. Yet, obtaining direct spectroscopic evidence for a d-electron heavy fermion system has been elusive to date. Here, we report the observation of Kondo lattice behavior in an antiferromagnetic metal, FeTe, via angle-resolved photoemission spectroscopy, scanning tunneling spectroscopy and transport property measurements. The Kondo lattice behavior is represented by the emergence of a sharp quasiparticle and Fano-type tunneling spectra at low temperatures. The transport property measurements confirm the low-temperature Fermi liquid behavior and reveal successive coherent-incoherent crossover upon increasing temperature. We interpret the Kondo lattice behavior as a result of hybridization between localized Fe 3d xy and itinerant Te 5p z orbitals. Our observations strongly suggest unusual cooperation between Kondo lattice behavior and long-range magnetic order.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Correlation-driven electronic reconstruction in FeTe 1−x Se x

Electronic correlation is of fundamental importance to high temperature superconductivity. While the low energy electronic states in cuprates are dominantly affected by correlation effects across the phase diagram, observation of correlation-driven changes in fermiology amongst the iron-based superconductors remains rare. Here we present experimental evidence for a correlation-driven reconstruction of the Fermi surface tuned independently by two orthogonal axes of temperature and Se/Te ratio in the iron chalcogenide family FeTe 1−x Se x . We demonstrate that this reconstruction is driven by the de-hybridization of a strongly renormalized d xy orbital with the remaining itinerant iron 3 d orbitals in the emergence of an orbital-selective Mott phase. Our observations are further supported by our theoretical calculations to be salient spectroscopic signatures of such a non-thermal evolution from a strongly correlated metallic phase into an orbital-selective Mott phase in d xy as Se concentration is reduced.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Orbital Ingredients and Persistent Dirac Surface State for the Topological Band Structure in FeTe 0.55 Se 0.45

FeTe 0.55 Se 0.45 (FTS) occupies a special spot in modern condensed matter physics at the intersections of electron correlation, topology, and unconventional superconductivity. The bulk electronic structure of FTS is predicted to be topologically nontrivial due to the band inversion between the d x z and p z bands along Γ − Z . However, there remain debates in both the authenticity of the Dirac surface states (DSSs) and the experimental deviations of band structure from the theoretical band inversion picture. Here we resolve these debates through a comprehensive angle-resolved photoemission spectroscopy investigation. We first observe a persistent DSS independent of k z . Then, by comparing FTS with FeSe, which has no band inversion along Γ − Z , we identify the spectral weight fingerprint of both the presence of the p z band and the inversion between the d x z and p z bands. Furthermore, we propose a renormalization scheme for the band structure under the framework of a tight-binding model preserving crystal symmetry. Our results highlight the significant influence of correlation on modifying the band structure and make a strong case for the existence of topological band structure in this unconventional superconductor. Published by the American Physical Society 2024

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Materials Data on Tl(FeTe)3 by Materials Project

TlFe3Te3 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. there are three inequivalent Fe sites. In the first Fe site, Fe is bonded in a 10-coordinate geometry to six Fe and four Te atoms. There are two shorter (2.50 Å) and four longer (2.58 Å) Fe–Fe bond lengths. There are a spread of Fe–Te bond distances ranging from 2.66–2.68 Å. In the second Fe site, Fe is bonded in a 10-coordinate geometry to six Fe and four Te atoms. There are one shorter (2.50 Å) and two longer (2.58 Å) Fe–Fe bond lengths. There are a spread of Fe–Te bond distances ranging from 2.66–2.68 Å. In the third Fe site, Fe is bonded in a 10-coordinate geometry to six Fe and four Te atoms. There are a spread of Fe–Te bond distances ranging from 2.66–2.68 Å. Tl is bonded in a distorted trigonal planar geometry to nine Te atoms. There are a spread of Tl–Te bond distances ranging from 3.46–3.61 Å. There are three inequivalent Te sites. In the first Te site, Te is bonded in a 5-coordinate geometry to four Fe and three equivalent Tl atoms. In the second Te site, Te is bonded in a 7-coordinate geometry to four Fe and three equivalent Tl atoms. In the third Te site, Te is bonded in a 7-coordinate geometry to four Fe and three equivalent Tl atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on FeTe(PO4)2 by Materials Project

Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on FeTe(PO4)2 by Materials Project

Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K(FeTe)2 by Materials Project

KFe2Te2 is Parent of FeAs superconductors-derived structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. K is bonded in a body-centered cubic geometry to eight equivalent Te atoms. All K–Te bond lengths are 3.58 Å. Fe is bonded in a 8-coordinate geometry to four equivalent Fe and four equivalent Te atoms. All Fe–Fe bond lengths are 2.74 Å. All Fe–Te bond lengths are 2.64 Å. Te is bonded in a 8-coordinate geometry to four equivalent K and four equivalent Fe atoms.

36 MATERIALS SCIENCE↗