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Hildebrand, B.; Didiot, Clément; Novello, Anna Maria; Monney, Gaël; Scarfato, Alessandro; Ubaldini, Alberto; Berger, H.; Bowler, David R.; Renner, Christoph; Aebi, Philipp

doi:10.1103/physrevlett.112.197001

Phys. Rev. Lett.

2014

DOI: 10.1103/physrevlett.112.197001

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Doping Nature of Native Defects in1T−TiSe2

B. Hildebrand

Clément Didiot

Anna Maria Novello

et al.

Abstract: The transition-metal dichalcogenide 1T-TiSe2 is a quasi-two-dimensional layered material with a charge density wave (CDW) transition temperature of T(CDW) ≈ 200 K. Self-doping effects for crystals grown at different temperatures introduce structural defects, modify the temperature-dependent resistivity, and strongly perturbate the CDW phase. Here, we study the structural and doping nature of such native defects combining scanning tunneling microscopy or spectroscopy and ab initio calculations. The dominant nat… Show more

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Cited by 81 publications

(94 citation statements)

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“…The relative orientation of these mostly triangular features further confirm the local 1T-polytype of the single crystals investigated. Intercalated Ti was shown to show two different topographic patterns depending on its relative position with respect to the CDW superlattice [28]. In the case of Cu, no topographic difference is seen instead.…”

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confidence: 98%

“…The two distinct STM images in Fig. 2 have been aligned with atomic scale precision based on single atom defects identified in previous studies [28,31]. Such precise identification of single atom defects resolved by STM permits exquisite insight into the microscopic nature of the material and the CDW.…”

mentioning

confidence: 99%

“…While STM imaging readily revealed specific patterns of intercalated Ti and three other dominant single atom defects in 1T-TiSe 2 [28], the footprint of intercalated Cu proved far more elusive. Guided by DFT modeling, we find that intercalated Cu atoms are only resolved with atomic resolution in a reduced energy window around −1.2 V, with a perfect correspondence between model and data [Figs.…”

mentioning

confidence: 99%

“…Modeling the STM fingerprints of Cu ( Fig. 1) and Ti [28] shows they intercalate on the same lattice site in the vdW gap of 1T-TiSe 2 . Both contribute electrons to the system.…”

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confidence: 99%

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Stripe and Short Range Order in the Charge Density Wave of 1T−CuxTiSe2

et al. 2017

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We study the impact of Cu intercalation on the charge density wave (CDW) in 1T-Cu x TiSe 2 by scanning tunneling microscopy and spectroscopy. Cu atoms, identified through density functional theory modeling, are found to intercalate randomly on the octahedral site in the van der Waals gap and to dope delocalized electrons near the Fermi level. While the CDW modulation period does not depend on Cu content, we observe the formation of charge stripe domains at low Cu content (x < 0.02) and a breaking up of the commensurate order into 2 × 2 domains at higher Cu content. The latter shrink with increasing Cu concentration and tend to be phase shifted. These findings invalidate a proposed excitonic pairing as the primary CDW formation mechanism in this material. DOI: 10.1103/PhysRevLett.118.017002 Correlated electron systems are prone to develop distinct electronic ground states, such as superconductivity, charge density waves (CDWs), and spin ordered phases. The nature of the interplay between these ground states is the focus of intense research efforts. A CDW is a spatial modulation of the electron density associated with local lattice distortions. CDWs are found in a number of quasitwo-dimensional superconductors, including transition metal dichalcogenides [1], intercalated graphite [2], cuprates [3-5] and pnictides [6]. Of particular interest, largely driven by the puzzle of high temperature superconductivity, is whether charge order is competing, cooperating, or simply coexisting with superconductivity [7]. The layered transition metal dichalcogenide 1T-TiSe 2 offers an attractive playground to explore the interplay between these two electronic ground states, thus potentially contributing to resolving similar outstanding questions in cuprate superconductors and other strongly correlated materials.1T-TiSe 2 consists of a stack of van der Waals (vdW) coupled layers allowing in situ preparation of surfaces ideally suited for scanning probe investigations by cleaving. When cooled below T CDW ≃ 200 K, it undergoes a second-order phase transition into a commensurate 2 × 2 × 2 CDW superlattice [8,9]. There is currently no consensus on the origin of the CDW in this material. Two possible scenarios are being considered, one based on a purely electronic process characterized by an excitonic instability [8], while the other one involves a Jahn-Teller (JT) distortion [10]. More refined theories also propose a mixture of these two possible contributions, in the so called indirect JT transition [11][12][13].1T-TiSe 2 becomes superconducting when intercalating more than x ¼ 0.04 copper into the vdW gap, with a maximum critical temperature T c ¼ 4.1 K near x ¼ 0.08 [14]. Transport measurements [14,15] indicate the CDW is suppressed upon increasing the Cu content which would suggest a competition with superconductivity. A more recent report of an incommensurate CDW above the superconducting dome in pristine crystals under pressure [16] suggests a more complex scenario, where CDW fluctuations promote superconductivity. Traces of ...

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confidence: 98%

mentioning

confidence: 99%

mentioning

confidence: 99%

“…Modeling the STM fingerprints of Cu ( Fig. 1) and Ti [28] shows they intercalate on the same lattice site in the vdW gap of 1T-TiSe 2 . Both contribute electrons to the system.…”

mentioning

confidence: 99%

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Stripe and Short Range Order in the Charge Density Wave of 1T−CuxTiSe2

et al. 2017

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“…The bias voltages of ±150mV have been chosen to enable the simultaneous resolution of the 2a 0 ×2b 0 CDW reconstruction on the selenium layer and atomic lattice features at opposite polarities. Defects (A-D) correspond to the dominant native atomic defects in 1T -TiSe 2 identified in a recent STM/DFT study based on images recorded at a larger bias voltage where the CDW is not resolved [29]. These defects are Se surface vacancies (A), iodine (B) and oxygen (C) substitution for bulk Se and titanium intercalated into the VdW gap (D).…”

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Scanning tunneling microscopy of the charge density wave in1T−TiSe2in the presence of single atom defects

et al. 2015

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We present a detailed low temperature scanning tunneling microscopy study of the commensurate charge density wave (CDW) in 1T -TiSe2 in the presence of single atom defects. We find no significant modification of the CDW lattice in single crystals with native defects concentrations where some bulk probes already measure substantial reductions in the CDW phase transition signature. Systematic analysis of STM micrographs combined with density functional theory modelling of atomic defect patterns indicate that the observed CDW modulation lies in the Se surface layer. The defect patterns clearly show there are no 2H-polytype inclusions in the CDW phase, as previously found at room temperature [Titov A.N. et al, Phys. Sol. State 53, 1073. They further provide an alternative explanation for the chiral Friedel oscillations recently reported in this compound [J. Ishioka et al., Phys. Rev. B 84, 245125, (2011)].PACS numbers: 68.37. Ef, 71.15.Mb, 74.70.Xa, 73.20.Hb The transition metal dichalcogenide (TMD) 1T -TiSe 2 has kept the scientific community wondering about a number of its striking physical properties for more than four decades [1][2][3][4][5][6][7]. 1T -TiSe 2 is a layered compound consisting of a hexagonal layer of Ti sandwiched between two hexagonal layers of Se to form Se-Ti-Se sandwiches that stack via weak Van-der-Waals (VdW) forces to form a single crystal. The band structure of 1T -TiSe 2 , as determined by angle-resolved photoemission spectroscopy, consists primarily of a Se 4p-valence band at the Γ point and a Ti 3d-conduction band at the L point of the Brillouin zone. But it is still debated whether it is a semiconductor or a semimetal with evidences claimed for both alternatives [6,[8][9][10].Below T CDW ≈ 202K, 1T -TiSe 2 undergoes a second order phase transition into a commensurate charge density wave (CDW). A comprehensive theory of this CDW formation is yet to be developed. Two main mechanisms are currently considered, driven either by a JahnTeller distortion [4,11] or an excitonic ground state [2,9,12,13]. The CDW phase has been found to melt upon copper intercalation [5] or when applying pressure [7]. In both instances, superconductivity develops in a dome shaped region around some optimal doping or optimal pressure, with a maximum critical temperature of 4.1K and 1.8K, respectively. More recently, chiral properties have been reported for the CDW in pristine and copper intercalated 1T -TiSe 2 based on polarized optical reflectometry and scanning tunneling microscopy (STM) [14][15][16].Here we focus on the CDW instability in 1T -TiSe 2 in the presence of native atomic scale defects. Past studies performed using macroscopic probes including resistivity, magnetic susceptibility and optical reflectivity have found atomic intercalation and substitution to be detrimental to the CDW [1,17]. This compound is usually non-stoichiometric with a strong correlation between increasing crystal growth temperature and Ti self-doping leading to the collapse of the CDW phase transition signature in temperature ...

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Cu Intercalation and Br Doping to Thermoelectric SnSe₂ Lead to Ultrahigh Electron Mobility and Temperature‐Independent Power Factor

Zhou

Zhang

et al. 2019

Adv Funct Materials

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Due to its single conduction band nature, it is highly challenging to enhance the power factor of SnSe 2 by band convergence. Here, it is reported that simultaneous Cu intercalation and Br doping induce strong Cu-Br interaction to connect SnSe 2 layers, otherwise isolated, via "electrical bridges." Atom probe tomography analysis confirms a strong attraction between Cu intercalants and Br dopants in the SnSe 2 lattice. Density functional theory calculations reveal that this interaction delocalizes electrons confined around SnSe covalent bonds and enhances charge transfer across the SnSe 2 slabs. These effects dramatically increase electron mobility and concentration. Polycrystalline SnCu 0.005 Se 1.98 Br 0.02 shows even higher electron mobility than pristine SnSe 2 single crystal and the theoretical expectation. This results in significantly improved electrical conductivity without reducing effective mass and Seebeck coefficient, thereby leading to the highest power factor of ≈12 µW cm −1 K −2 to date for polycrystalline SnSe 2 and SnSe. It even surpasses the value for the state-of-the-art n-type SnSe 0.985 Br 0.015 single crystal at elevated temperatures. Surprisingly, the achieved power factor is nearly independent of temperature ranging from 300 to 773 K. The engineering thermoelectric figure of merit ZT eng for SnCu 0.005 Se 1.98 Br 0.02 is ≈0.25 between 773 and 300 K, the highest ZT eng ever reported for any form of SnSe 2 -based thermoelectric materials.

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Doping Nature of Native Defects in1T−TiSe2

Cited by 81 publications

References 26 publications

Stripe and Short Range Order in the Charge Density Wave of 1T−CuxTiSe2

Stripe and Short Range Order in the Charge Density Wave of 1T−CuxTiSe2

Scanning tunneling microscopy of the charge density wave in1T−TiSe2in the presence of single atom defects

Cu Intercalation and Br Doping to Thermoelectric SnSe₂ Lead to Ultrahigh Electron Mobility and Temperature‐Independent Power Factor

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Product

Resources

About

Doping Nature of Native Defects in1T−TiSe2

Cited by 81 publications

References 26 publications

Stripe and Short Range Order in the Charge Density Wave of 1T−CuxTiSe2

Stripe and Short Range Order in the Charge Density Wave of 1T−CuxTiSe2

Scanning tunneling microscopy of the charge density wave in1T−TiSe2in the presence of single atom defects

Cu Intercalation and Br Doping to Thermoelectric SnSe2 Lead to Ultrahigh Electron Mobility and Temperature‐Independent Power Factor

Contact Info

Product

Resources

About

Cu Intercalation and Br Doping to Thermoelectric SnSe₂ Lead to Ultrahigh Electron Mobility and Temperature‐Independent Power Factor