Spin-orbit coupling in the band structure of reconstructed<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>1</mml:mn><mml:mi>T</mml:mi><mml:mtext>−</mml:mtext><mml:msub><mml:mi>TaS</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>

Roßnagel, Kai; Smith, N. V.

doi:10.1103/physrevb.73.073106

Cited by 116 publications

(108 citation statements)

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“…2a), which occurs at temperatures below 180-200 K (depending on cooling or heating), is rather well understood as a combined Peierls-Mott insulating phase 8,10,24 : the strong periodic lattice distortion, which is coupled to the CDW, splits the occupied part of the lowest-lying Ta 5d band into three subband manifolds so that the uppermost, half-filled manifold becomes susceptible to a Mott-Hubbard-type transition creating a deep pseudogap at E F . The spectroscopic signatures of this scenario are remarkably strong and momentum selective.…”

Section: Systemsmentioning

confidence: 99%

“…Two prominent examples are 1T-TaS 2 and 1T-TiSe 2 . In these two compounds, the electronic structures [8][9][10][11][12][13][14][15] and ultrafast spectral responses [16][17][18][19] indicate the presence of significant electron correlation effects. In both compounds, electron-electron interactions may in fact have an important role in CDW formation [12][13][14][18][19][20] and in the emergence of superconductivity from CDW states upon intercalation 21 or under pressure 22,23 .…”

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Time-domain classification of charge-density-wave insulators

et al. 2012

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Distinguishing insulators by the dominant type of interaction is a central problem in condensed matter physics. Basic models include the Bloch-Wilson and the Peierls insulator due to electron-lattice interactions, the mott and the excitonic insulator caused by electron-electron interactions, and the Anderson insulator arising from electron-impurity interactions. In real materials, however, all the interactions are simultaneously present so that classification is often not straightforward. Here, we show that time-and angle-resolved photoemission spectroscopy can directly measure the melting times of electronic order parameters and thus identify-via systematic temporal discrimination of elementary electronic and structural processes-the dominant interaction. specifically, we resolve the debates about the nature of two peculiar charge-density-wave states in the family of transition-metal dichalcogenides, and show that Rb intercalated 1T-Tas 2 is a Peierls insulator and that the ultrafast response of 1T-Tise 2 is highly suggestive of an excitonic insulator.

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Section: Systemsmentioning

confidence: 99%

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Time-domain classification of charge-density-wave insulators

et al. 2012

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“…Band calculations show that band folding creates a cluster of bands near the Fermi surface. Rossnagel and Smith (9) found that, due to spin-orbit interaction, a very narrow band is split off, which crosses the Fermi level with a 0.1-to 0.2-eV gap to the other subbands. The narrow bandwidth means that a weak residual repulsion is sufficient to form a Mott insulator, thus supporting the proposal of Fazekas and Tosatti, and distinguishes 1T-TaS2 from other TMD.…”

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confidence: 99%

“…However, their argument depends sensitively on the assumption of a cubic environment for the Ta atoms, which is now known not to be true. In fact, Rossnagel and Smith (9) Freely available online through the PNAS open access option. 1 To whom correspondence should be addressed.…”

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1T-TaS ₂ as a quantum spin liquid

Law

Lee

2017

Proc. Natl. Acad. Sci. U.S.A.

267

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1T-TaS 2 is unique among transition metal dichalcogenides in that it is understood to be a correlation-driven insulator, where the unpaired electron in a 13-site cluster experiences enough correlation to form a Mott insulator. We argue, based on existing data, that this well-known material should be considered as a quantum spin liquid, either a fully gapped Z2 spin liquid or a Dirac spin liquid. We discuss the exotic states that emerge upon doping and propose further experimental probes.spin liquid | Mott insulator | transition metal dichalcogenide T he transition metal dichalcogenide (TMD) is an old subject that has enjoyed a revival recently due to the interests in its topological properties and unusual superconductivity. The layer structure is easy to cleave or intercalate and can exist in singlelayer form (1, 2). This material was studied intensively in the 1970s and 1980s and was considered the prototypical example of a charge density wave (CDW) system (3). Due to imperfect nesting in two dimensions, in most of these materials, the onset of CDW gaps out only part of the Fermi surface, leaving behind a metallic state that often becomes superconducting. Conventional band theory and electron-phonon coupling appear to account for the qualitative behavior (3). There is, however, one notable exception, namely 1T-TaS2. The Ta forms a triangular lattice, sandwiched between two triangular layers of S, forming an ABCtype stacking. As a result, the Ta is surrounded by S, forming an approximate octahedron. In contrast, the 2H-TaS2 forms an ABA-type stacking, and the Ta is surrounded by S, forming a trigonal prism. In a single layer, inversion symmetry is broken in 2H structure. The system is a good metal below the CDW onset around 90 K, and, eventually, the spin-orbit coupling gives rise to a special kind of superconductivity called Ising superconductivity (4-6). In 1T-TaS2, inversion symmetry is preserved. The system undergoes a CDW transition at about 350 K with a jump in the resistivity. It is known that this transition is driven by an incommensurate triple-Q CDW (ICDW). A similar transition is seen in 1T-TaSe2 at 470 K. However, whereas TaSe2 stays metallic below this transition, 1T-TaS2 exhibits a further resistivity jump around 200 K that is hysteretic, indicative of the firstorder nature of this transition. These transitions are also visible in the spin susceptibility data shown in Fig. 2. In early samples, the resistivity rises only by about a factor of 10 as the temperature is lowered from 200 K to 2 K and, below that, obeys Mott hopping law (log resistivity goes as T −1/3 ) (7). More recent samples show better insulating behavior, and it is generally agreed that the ground state is insulating. The 200 K transition is accompanied by a lock-in to a commensurate CDW (CCDW), forming a √ 13 × √ 13 structure. As shown in Fig. 1, this structure is described as clusters of stars of David where the sites of the stars move inward toward the site in the middle. The stars of David are packed in such a way that they form ...

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“…However, the 12 electrons occupy the states below the distortion-induced gap and the thirteenth one dominates the states above the gap, resulting in a Mott insulating state that accounts for the high resistivity of the CCDW phase [14][15][16] , (2) the neighbouring NCCDW phase contains the star-of-David clusters as well albeit that they are less homogeneously arranged 7 , (3) with the rise of temperature, the Mott phase melts into the NCCDW phase with an extremely fast charge response and a sudden drop in resistivity, where several tens of stars organize into roughly hexagonal domains 10,17 . These reproduce locally the CCDW Mott phase, signifying that the CCDW mechanism is beyond the framework of the Peierls picture [18][19][20][21][22] .…”

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Atomistic origin of an ordered superstructure induced superconductivity in layered chalcogenides

et al. 2015

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Interplay among various collective electronic states such as charge density wave and superconductivity is of tremendous significance in low-dimensional electron systems. However, the atomistic and physical nature of the electronic structures underlying the interplay of exotic states, which is critical to clarifying its effect on remarkable properties of the electron systems, remains elusive, limiting our understanding of the superconducting mechanism. Here, we show evidence that an ordering of selenium and sulphur atoms surrounding tantalum within star-of-David clusters can boost superconductivity in a layered chalcogenide 1T-TaS 2 À x Se x , which undergoes a superconducting transition in the nearly commensurate charge density wave phase. Advanced electron microscopy investigations reveal that such an ordered superstructure forms only in the x area, where the superconductivity manifests, and is destructible to the occurrence of the Mott metal-insulator transition. The present findings provide a novel dimension in understanding the relationship between lattice and electronic degrees of freedom.

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Spin-orbit coupling in the band structure of reconstructed1T−TaS2

Cited by 116 publications

References 15 publications

Time-domain classification of charge-density-wave insulators

Time-domain classification of charge-density-wave insulators

1T-TaS ₂ as a quantum spin liquid

Atomistic origin of an ordered superstructure induced superconductivity in layered chalcogenides

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Spin-orbit coupling in the band structure of reconstructed1T−TaS2

Cited by 116 publications

References 15 publications

Time-domain classification of charge-density-wave insulators

Time-domain classification of charge-density-wave insulators

1T-TaS 2 as a quantum spin liquid

Atomistic origin of an ordered superstructure induced superconductivity in layered chalcogenides

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Product

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1T-TaS ₂ as a quantum spin liquid