7 research outputs found
Fermiologie, réduction de dimensionalité et couplage électron-phonon dans les métaux de transition dichalcogénides
Le dosage des matĂ©riaux en couches avec les mĂ©taux alcalins est devenue une stratĂ©gie commune dans la technique de photoĂ©mission rĂ©solue en angle ARPES (angle-resolved photoemission spectroscopy), mais exactement ce qui se passe structurellement et Ă©lectroniquement est restĂ© dĂ©bĂątĂ©. Ici, on rĂ©alise une Ă©tude de 1T-HfTe2, un semimetal prototypique de la famille des mĂ©taux de transition dichalcogĂ©nides TMDs (transition metal dichalcogenides). En utilisant ARPES en dĂ©pendance de lâĂ©nergie de photons, nous avons examinĂ© la structure Ă©lectronique de ce matĂ©riau en fonction de dosage avec le potassium K. DâaprĂšs nos spectres de kz, on a observĂ© lâapparence de 2D Ă©tats Ă©lectronique aprĂšs le dosage, avec une amĂ©lioration remarquable de la qualitĂ© des data mesurĂ©es, en accord avec le confinement de la fonction dâonde Ă la plus haute monocouche. A notre niveau de dosage le plus Ă©levĂ©, la structure Ă©lectronique mesurĂ©e est similaire Ă celle dâune monocouche, attestant lâintercalation des atomes alcaline dans le gap de van der Waals. En ramenant le top de la bande de valence en dessous du niveau de Fermi, nous avons directement mesurĂ© le gap nĂ©gatif dâune valeur de 0.2 eV. Toutefois, des Ă©tats Ă©lectroniques de volumes contribuent toujours au spectre mĂȘme aprĂšs une quantitĂ© considĂ©rable du dosage. Enfin, la bande de valence de HfTe2 contient un point de Dirac et un gap inversĂ©, en analogie avec tous les TMDs du mĂȘme groupe de symĂ©trie. Dans notre deuxiĂšme projet, nous avons Ă©tudiĂ© les deux polytypes de NbS2, notamment 2H-NbS2 et 3R-Nb(1+x)S2 en utilisant ARPES et les calculs DFT (density functional theory). Les deux surfaces de Fermi mesurĂ©es montrent une grande diffĂ©rence en taille, indiquant un remplissage de bande plus import dans le 3R phase en raison dâatomes interstitielles de Nb. Donc nous avons trouvĂ© que câest plutĂŽt la stoichiomĂ©trie est le facteur le plus important dans la diffĂ©rence des propriĂ©tĂ©s Ă©lectronique et physiques des deux phases, et pas lâempilement de couche. Nos data avec la meilleure rĂ©solution de 2H-NbS2 montrent de forts âkinksâ dans la fonction spectrale, tĂ©moignant lâĂ©lectron-phonon couplage dans ce systĂšme. Nous avons trouvĂ© que ce couplage est plus fort dans les sections de bandes dĂ©rivĂ©es de Nb 4dx2ây2 ,xy orbitales que celles de Nb 4d3z2âr2 orbitales. Nos rĂ©sultats prĂ©sentent un cadre expĂ©rimental pour lâinterprĂ©tation des deux gaps supraconducteurs et lâabsence de lâonde de densitĂ© de charge dans 2H-NbS2.The dosing of layered materials with alkali metals has become a commonly usedstrategy in ARPES experiments. However, precisely what occurs under such conditions, both structurally and electronically, has remained a matter of debate. Here we performed a systematic study of 1T-HfTe2, a prototypical semimetal of the transition metal dichalcogenide family. By utilizing photon energy-dependent angle-resolved photoemission spectroscopy (ARPES), we have investigated the electronic structure of this material as a function of Potassium (K) deposition. From the kz maps, we observed the appearance of 2D dispersive bands after electron dosing, with an increasing sharpness of the bands, consistent with the wavefunction confinement at the topmost layer. In our highest-dosing cases, a monolayer-like electronic structure emerges, presumably as a result of intercalation of the alkali metal. Here, by bringing the topmost valence band below EF, we could directly measure a band overlap of ⌠0.2 eV. However, 3D bulk-like states still contribute to the spectra even after considerable dosing. Our work on HfTe2 provides a reference point for the increasingly popular studies of the alkali metal dosing of semimetals using ARPES. In our second work, we investigated the electronic band structure of the two polytypes of NbS2, namely 2H-NbS2 and 3R-Nb1+xS2 combining ARPES and DFT calculations again. The measured Fermi surfaces show a remarkable difference in size, reflecting a significantly increased band filling in 3R-Nb1+xS2 due to the presence of additional Nb interstitials. Thus we found that the stoichiometry, rather than the stacking arrangement, is the most important factor in the difference in electronic and physical properties of the two phases. Our high resolution data on the 2H phase shows strong kinks in the spectral function that are fingerprints of the electron-phonon coupling. However, the strength of the coupling is found to be much larger for the the sections of bands withNb 4dx2-y2,xy character than for the Nb 4d3z2-r2. Our results provide an experimental framework for interpreting the two-gap superconductivity and latent CDW in 2H-NbS
Fermiology, 3D to 2D dimensionality crossover and electron-phonon coupling in the electronic structure of transition metal dichalcogenides
The dosing of layered materials with alkali metals has become a commonly usedstrategy in ARPES experiments. However, precisely what occurs under such conditions, both structurally and electronically, has remained a matter of debate. Here we performed a systematic study of 1T-HfTe2, a prototypical semimetal of the transition metal dichalcogenide family. By utilizing photon energy-dependent angle-resolved photoemission spectroscopy (ARPES), we have investigated the electronic structure of this material as a function of Potassium (K) deposition. From the kz maps, we observed the appearance of 2D dispersive bands after electron dosing, with an increasing sharpness of the bands, consistent with the wavefunction confinement at the topmost layer. In our highest-dosing cases, a monolayer-like electronic structure emerges, presumably as a result of intercalation of the alkali metal. Here, by bringing the topmost valence band below EF, we could directly measure a band overlap of ⌠0.2 eV. However, 3D bulk-like states still contribute to the spectra even after considerable dosing. Our work on HfTe2 provides a reference point for the increasingly popular studies of the alkali metal dosing of semimetals using ARPES. In our second work, we investigated the electronic band structure of the two polytypes of NbS2, namely 2H-NbS2 and 3R-Nb1+xS2 combining ARPES and DFT calculations again. The measured Fermi surfaces show a remarkable difference in size, reflecting a significantly increased band filling in 3R-Nb1+xS2 due to the presence of additional Nb interstitials. Thus we found that the stoichiometry, rather than the stacking arrangement, is the most important factor in the difference in electronic and physical properties of the two phases. Our high resolution data on the 2H phase shows strong kinks in the spectral function that are fingerprints of the electron-phonon coupling. However, the strength of the coupling is found to be much larger for the the sections of bands withNb 4dx2-y2,xy character than for the Nb 4d3z2-r2. Our results provide an experimental framework for interpreting the two-gap superconductivity and latent CDW in 2H-NbS2Le dosage des matĂ©riaux en couches avec les mĂ©taux alcalins est devenue une stratĂ©gie commune dans la technique de photoĂ©mission rĂ©solue en angle ARPES (angle-resolved photoemission spectroscopy), mais exactement ce qui se passe structurellement et Ă©lectroniquement est restĂ© dĂ©bĂątĂ©. Ici, on rĂ©alise une Ă©tude de 1T-HfTe2, un semimetal prototypique de la famille des mĂ©taux de transition dichalcogĂ©nides TMDs (transition metal dichalcogenides). En utilisant ARPES en dĂ©pendance de lâĂ©nergie de photons, nous avons examinĂ© la structure Ă©lectronique de ce matĂ©riau en fonction de dosage avec le potassium K. DâaprĂšs nos spectres de kz, on a observĂ© lâapparence de 2D Ă©tats Ă©lectronique aprĂšs le dosage, avec une amĂ©lioration remarquable de la qualitĂ© des data mesurĂ©es, en accord avec le confinement de la fonction dâonde Ă la plus haute monocouche. A notre niveau de dosage le plus Ă©levĂ©, la structure Ă©lectronique mesurĂ©e est similaire Ă celle dâune monocouche, attestant lâintercalation des atomes alcaline dans le gap de van der Waals. En ramenant le top de la bande de valence en dessous du niveau de Fermi, nous avons directement mesurĂ© le gap nĂ©gatif dâune valeur de 0.2 eV. Toutefois, des Ă©tats Ă©lectroniques de volumes contribuent toujours au spectre mĂȘme aprĂšs une quantitĂ© considĂ©rable du dosage. Enfin, la bande de valence de HfTe2 contient un point de Dirac et un gap inversĂ©, en analogie avec tous les TMDs du mĂȘme groupe de symĂ©trie. Dans notre deuxiĂšme projet, nous avons Ă©tudiĂ© les deux polytypes de NbS2, notamment 2H-NbS2 et 3R-Nb(1+x)S2 en utilisant ARPES et les calculs DFT (density functional theory). Les deux surfaces de Fermi mesurĂ©es montrent une grande diffĂ©rence en taille, indiquant un remplissage de bande plus import dans le 3R phase en raison dâatomes interstitielles de Nb. Donc nous avons trouvĂ© que câest plutĂŽt la stoichiomĂ©trie est le facteur le plus important dans la diffĂ©rence des propriĂ©tĂ©s Ă©lectronique et physiques des deux phases, et pas lâempilement de couche. Nos data avec la meilleure rĂ©solution de 2H-NbS2 montrent de forts âkinksâ dans la fonction spectrale, tĂ©moignant lâĂ©lectron-phonon couplage dans ce systĂšme. Nous avons trouvĂ© que ce couplage est plus fort dans les sections de bandes dĂ©rivĂ©es de Nb 4dx2ây2 ,xy orbitales que celles de Nb 4d3z2âr2 orbitales. Nos rĂ©sultats prĂ©sentent un cadre expĂ©rimental pour lâinterprĂ©tation des deux gaps supraconducteurs et lâabsence de lâonde de densitĂ© de charge dans 2H-NbS2
Fermiologie, réduction de dimensionalité et couplage électron-phonon dans les métaux de transition dichalcogénides
Le dosage des matĂ©riaux en couches avec les mĂ©taux alcalins est devenue une stratĂ©gie commune dans la technique de photoĂ©mission rĂ©solue en angle ARPES (angle-resolved photoemission spectroscopy), mais exactement ce qui se passe structurellement et Ă©lectroniquement est restĂ© dĂ©bĂątĂ©. Ici, on rĂ©alise une Ă©tude de 1T-HfTe2, un semimetal prototypique de la famille des mĂ©taux de transition dichalcogĂ©nides TMDs (transition metal dichalcogenides). En utilisant ARPES en dĂ©pendance de lâĂ©nergie de photons, nous avons examinĂ© la structure Ă©lectronique de ce matĂ©riau en fonction de dosage avec le potassium K. DâaprĂšs nos spectres de kz, on a observĂ© lâapparence de 2D Ă©tats Ă©lectronique aprĂšs le dosage, avec une amĂ©lioration remarquable de la qualitĂ© des data mesurĂ©es, en accord avec le confinement de la fonction dâonde Ă la plus haute monocouche. A notre niveau de dosage le plus Ă©levĂ©, la structure Ă©lectronique mesurĂ©e est similaire Ă celle dâune monocouche, attestant lâintercalation des atomes alcaline dans le gap de van der Waals. En ramenant le top de la bande de valence en dessous du niveau de Fermi, nous avons directement mesurĂ© le gap nĂ©gatif dâune valeur de 0.2 eV. Toutefois, des Ă©tats Ă©lectroniques de volumes contribuent toujours au spectre mĂȘme aprĂšs une quantitĂ© considĂ©rable du dosage. Enfin, la bande de valence de HfTe2 contient un point de Dirac et un gap inversĂ©, en analogie avec tous les TMDs du mĂȘme groupe de symĂ©trie. Dans notre deuxiĂšme projet, nous avons Ă©tudiĂ© les deux polytypes de NbS2, notamment 2H-NbS2 et 3R-Nb(1+x)S2 en utilisant ARPES et les calculs DFT (density functional theory). Les deux surfaces de Fermi mesurĂ©es montrent une grande diffĂ©rence en taille, indiquant un remplissage de bande plus import dans le 3R phase en raison dâatomes interstitielles de Nb. Donc nous avons trouvĂ© que câest plutĂŽt la stoichiomĂ©trie est le facteur le plus important dans la diffĂ©rence des propriĂ©tĂ©s Ă©lectronique et physiques des deux phases, et pas lâempilement de couche. Nos data avec la meilleure rĂ©solution de 2H-NbS2 montrent de forts âkinksâ dans la fonction spectrale, tĂ©moignant lâĂ©lectron-phonon couplage dans ce systĂšme. Nous avons trouvĂ© que ce couplage est plus fort dans les sections de bandes dĂ©rivĂ©es de Nb 4dx2ây2 ,xy orbitales que celles de Nb 4d3z2âr2 orbitales. Nos rĂ©sultats prĂ©sentent un cadre expĂ©rimental pour lâinterprĂ©tation des deux gaps supraconducteurs et lâabsence de lâonde de densitĂ© de charge dans 2H-NbS2.The dosing of layered materials with alkali metals has become a commonly usedstrategy in ARPES experiments. However, precisely what occurs under such conditions, both structurally and electronically, has remained a matter of debate. Here we performed a systematic study of 1T-HfTe2, a prototypical semimetal of the transition metal dichalcogenide family. By utilizing photon energy-dependent angle-resolved photoemission spectroscopy (ARPES), we have investigated the electronic structure of this material as a function of Potassium (K) deposition. From the kz maps, we observed the appearance of 2D dispersive bands after electron dosing, with an increasing sharpness of the bands, consistent with the wavefunction confinement at the topmost layer. In our highest-dosing cases, a monolayer-like electronic structure emerges, presumably as a result of intercalation of the alkali metal. Here, by bringing the topmost valence band below EF, we could directly measure a band overlap of ⌠0.2 eV. However, 3D bulk-like states still contribute to the spectra even after considerable dosing. Our work on HfTe2 provides a reference point for the increasingly popular studies of the alkali metal dosing of semimetals using ARPES. In our second work, we investigated the electronic band structure of the two polytypes of NbS2, namely 2H-NbS2 and 3R-Nb1+xS2 combining ARPES and DFT calculations again. The measured Fermi surfaces show a remarkable difference in size, reflecting a significantly increased band filling in 3R-Nb1+xS2 due to the presence of additional Nb interstitials. Thus we found that the stoichiometry, rather than the stacking arrangement, is the most important factor in the difference in electronic and physical properties of the two phases. Our high resolution data on the 2H phase shows strong kinks in the spectral function that are fingerprints of the electron-phonon coupling. However, the strength of the coupling is found to be much larger for the the sections of bands withNb 4dx2-y2,xy character than for the Nb 4d3z2-r2. Our results provide an experimental framework for interpreting the two-gap superconductivity and latent CDW in 2H-NbS
Fermiology and electron-phonon coupling in the 2 H and 3 R polytypes of Nb S 2
International audienceWe investigate the electronic structure of the 2H and 3R polytypes of NbS2. The Fermi surfaces measured by angle-resolved photoemission spectroscopy show a remarkable difference in size, reflecting a significantly increased band filling in 3RâNb1+xS2 compared to 2HâNbS2, which we attribute to the presence of additional interstitial Nb, which act as electron donors. Thus, we find that the stoichiometry, rather than the stacking arrangement, is the most important factor in the difference in electronic and physical properties of the two phases. Our high resolution data on the 2H phase shows kinks in the spectral function that are fingerprints of the electron-phonon coupling. However, the strength of the coupling is found to be much larger for the the sections of bands with Nb 4dx2ây2,xy character than for the Nb 4d3z2âr2. Our results provide an experimental framework for interpreting the two-gap superconductivity and latent charge density wave in 2HâNbS2
Angle-resolved photoemission calculations of WTe2 compared to experiment
Molybdenum dichalcogenides are probably the most studied single layer TMDCs by virtue of being appealing for sundry possible applications suchlike transistors, diodes, solar cells or more fundamental studies of spin or valley pseudospin and their interactions. Tungsten-based counterparts are on the other hand evincing much stronger spin-orbit coupling due to which all the spin-related effects are more stable at room temperature and thus more feasible for application. WTe2, a type-II Weyl semimetal is in particular interesting due to having two pairs of spin-differentiated Weyl points above Fermi energy. We have conducted several experiments following the evolution of the band dispersion in the vicinity of X and Y points of the Brillouin zone of WTe2 which is substantial for understanding the fundamental properties of the structure-property relation of the system. Ab-initio set of photoemission calculations was performed using SPR-KKR package and compared to experimental results
Objemové a povrchové elektronické stavy v dopovaném polokovu HfTe2
ÄlĂĄnek se zabĂœvĂĄ popisem elektronovĂ© struktury dopovanĂ©ho polokovu HfTe2 doplnÄnou o teoretickĂ© vĂœpoÄty.The dosing of layered materials with alkali metals has become a commonly used strategy in ARPES experiments. However, precisely what occurs under such conditions, both structurally and electronically, has remained a matter of debate. Here we perform a systematic study of 1T-HfTe2, a prototypical semimetal of the transition metal dichalcogenide family. By utilizing photon energy-dependent angle-resolved photoemission spectroscopy (ARPES), we have investigated the electronic structure of this material as a function of potassium (K) deposition. From the kz maps, we observe the appearance of 2D dispersive bands after electron dosing, with an increasing sharpness of the bands, consistent with the wave-function confinement at the topmost layer. In our highest-dosing cases, a monolayerlike electronic structure emerges, presumably as a result of intercalation of the alkali metal. Here, by bringing the topmost valence band below EF, we can directly measure a band overlap of âŒ0.2 eV. However, 3D bulklike states still contribute to the spectra even after considerable dosing. Our work provides a reference point for the increasingly popular studies of the alkali metal dosing of semimetals using ARPES
Spin, time, and angle resolved photoemission spectroscopy on WTe2
We combined a spin resolved photoemission spectrometer with a high-harmonic generation (HHG) laser source in order to perform spin, time, and angle resolved photoemission spectroscopy (STARPES) experiments on the transition metal dichalcogenide bulk WTe2, a possible Weyl type-II semimetal. Measurements at different femtosecond pump-probe delays and comparison with spin resolved one-step photoemission calculations provide insight into the spin polarization of electrons above the Fermi level in the region where Weyl points of WTe2 are expected. We observe a spin accumulation above the Weyl points region, which is consistent with a spin-selective bottleneck effect due to the presence of spin-polarized conelike electronic structure. Our results support the feasibility of STARPES with HHG, which despite being experimentally challenging provides a unique way to study spin dynamics in photoemission