Superconductivity in the layered compound 2H-TaS2

Nagata, Satoshi; Aochi, Tsuyoshi; Abe, Tsuyoshi; Ebisu, Shuji; Hagino, Takatsugu; Seki, Y.; Tsutsumi, K.

doi:10.1016/0022-3697(92)90242-6

Cited by 93 publications

(79 citation statements)

References 11 publications

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“…It is also superconducting, with a T c near 0.8 K. (18,19). While there are no previous reports of the effects of Cu doping on the superconductivity of TaS 2 , there are reports that doping with other elements yields a higher temperature superconductor.…”

Section: Introductionmentioning

confidence: 99%

Tuning the charge density wave and superconductivity inCuxTaS2

et al. 2008

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We report the characterization of layered, 2H-type Cu x TaS 2 , for 0 ≤ x ≤ 0.12. The charge density wave (CDW), at 70 K for TaS 2 , is destabilized with Cu doping. The sub-1K superconducting transition in undoped 2H-TaS 2 jumps quickly to 2.5 K at low x, increases to 4.5 K at the optimal composition Cu 0.04 TaS 2 , and then decreases at higher x. The electronic contribution to the specific heat, first increasing and then decreasing as a function of Cu content, is 12 mJ mol -1 K -2 at Cu 0.04 TaS 2 . Electron diffraction studies show that the CDW remains present at the optimal superconducting composition, but with both a changed q vector and decreased coherence length. We present an electronic phase diagram for the system.

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Section: Introductionmentioning

confidence: 99%

Tuning the charge density wave and superconductivity inCuxTaS2

et al. 2008

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“…Superconductivity and the CDW state are two very different cooperative electronic phenomena, and yet both occur due to Fermi surface instabilities and electron-phonon coupling. A number of CDW-bearing materials are also superconducting [8][9][10][11][12][13], and the idea that superconductivity and CDW states are competing electronic states at low temperatures is one of the fundamental concepts of condensed matter physics. Surprisingly, no system has yet been reported in which the emergence of a superconducting state after a charge density wave state has been suppressed via doping has been studied in detail: a transition that implies a deep connection between the two states, i.e., that the same electrons are participating in both transitions.…”

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confidence: 99%

Superconductivity in CuxTiSe2

Morosan

Zandbergen

Dennis³

et al. 2006

Nature Phys

949

963

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2Charge density wave (CDW) transitions are a frequent occurrence in transition metal chalcogenides due to their low structural dimensionality. Layered MX 2 compounds and chain-based MX 3 compounds, where M is a group 4 or 5 metal and X = S, Se, or Te, are the best known examples [1][2][3][4][5][6][7]. These transitions arise to allow electronic systems to minimize their energy by removing electronic states at the Fermi level. This is achieved by introducing a new structural periodicity at the Fermi wave vector, inducing a band gap. Superconductivity and the CDW state are two very different cooperative electronic phenomena, and yet both occur due to Fermi surface instabilities and electron-phonon coupling. A number of CDW-bearing materials are also superconducting [8][9][10][11][12][13], and the idea that superconductivity and CDW states are competing electronic states at low temperatures is one of the fundamental concepts of condensed matter physics. Surprisingly, no system has yet been reported in which the emergence of a superconducting state after a charge density wave state has been suppressed via doping has been studied in detail: a transition that implies a deep connection between the two states, i.e., that the same electrons are participating in both transitions. TiSe 2 was one of the first CDW-bearing compounds known, and is also one of the most frequently studied as the nature of its CDW transition has been controversial for decades. The CDW transition, at approximately 200 K, is to a state with a commensurate (2a,2a,2c) wavevector without an intermediate incommensurate phase [3,16,17]. The commensurate CDW wavevector and electronic structure calculations indicate that, unlike the case in most materials, the CDW in TiSe 2 is not driven by Fermi surface nesting. The normal state is presently believed to be either a semimetal or a semiconductor with a small indirect gap [3, 16, 18 -22] (Fig. 1a, inset). This results in a systematic expansion of the unit cell with Cu content in Cu x TiSe 2 , as evidenced by the lattice parameters shown in Fig. 1a. The expansion of the cell parameters is maintained up to x = 0.11. For higher Cu contents, both a and c remain unchanged from their value at x = 0.11. It can therefore be concluded that the solubility limit for Cu in TiSe 2 is x = 0.11 ± 0.01.Of particular interest is the evolution of the charge density wave with Cu doping.Electron and X-ray diffraction studies of pure TiSe 2 at low temperatures show the presence of reflections corresponding to the basic trigonal structure and also the 2a, 2c superstructure reflections associated with the CDW state [3,19]. increases with Cu content. This suggests that the Cu doping introduces carriers into the conduction band in TiSe 2 , increasing the electronic density of states and therefore the Pauli paramagnetism. This is further confirmed by specific heat measurements, described below. A drop in the susceptibility of pure TiSe 2 is seen as the temperature is lowered below the CDW transition at 200 K, consistent with th...

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“…Lr, 68.47.Gh Most known CDW materials are mediated by strong electron-phonon (el-ph) interaction [1], as confirmed by observation of large kinks in the dispersion by ARPES [2][3][4][5][6]. Some of the best known examples are the layered transition-metal dichacogenides and tellurides [7][8][9], where charge order often coexists and competes with superconductivity, due to their common el-ph origin [4,5,8,[10][11][12][13][14]. A CDW has been discovered within the pseudogap state of the cuprates [15][16][17][18][19][20][21][22][23][24], although its origin remains unclear.…”

mentioning

confidence: 99%

Discovery of an Unconventional Charge Density Wave at the Surface ofK0.9Mo6O17
Mou
¹
,
Sapkota
²
,
Kung
³

et al. 2016
Phys. Rev. Lett.
29
3
22
0
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We use Angle Resolved Photoemission Spectroscopy (ARPES), Raman spectroscopy, Low Energy Electron Diffraction (LEED) and x-ray scattering to reveal an unusual electronically mediated charge density wave (CDW) in K0.9Mo6O17. Not only does K0.9Mo6O17 lack signatures of electron-phonon coupling, but it also hosts an extraordinary surface CDW, with TS CDW =220 K nearly twice that of the bulk CDW, TB CDW =115 K. While the bulk CDW has a BCS-like gap of 12 meV, the surface gap is ten times larger and well in the strong coupling regime. Strong coupling behavior combined with the absence of signatures of strong electron-phonon coupling indicates that the CDW is likely mediated by electronic interactions enhanced by low dimensionality.PACS numbers: 71.45. Lr, 68.47.Gh Most known CDW materials are mediated by strong electron-phonon (el-ph) interaction [1], as confirmed by observation of large kinks in the dispersion by ARPES [2][3][4][5][6]. Some of the best known examples are the layered transition-metal dichacogenides and tellurides [7][8][9], where charge order often coexists and competes with superconductivity, due to their common el-ph origin [4,5,8,[10][11][12][13][14]. A CDW has been discovered within the pseudogap state of the cuprates [15][16][17][18][19][20][21][22][23][24], although its origin remains unclear. The observation of phonon anomalies suggests el-ph coupling may play a role [25][26][27], however, a number of theoretical models suggest that this CDW could be electronically mediated [28][29][30][31]. Electronelectron (el-el) interactions are also thought to be responsible for the CDW found in related cuprate ladder compounds [32].The properties of materials can be dramatically altered at the surface. In CDWs often the transition temperature is enhanced at the surface [33], an effect known as an extraordinary transition [34,35]. Recently such effect was also reported in a monolayer [36][37][38]. The increased T C has been attributed to enhanced interactions due to the decreased dimensionality [39,40]. In this letter, we show that K 0.9 Mo 6 O 17 has an enhanced surface transition temperature, and a surface energy gap an order of magnitude larger than the bulk. Despite the strong coupling nature of the surface order, K 0.9 Mo 6 O 17 shows no signatures of strong el-ph coupling, either in the phonon or electronic structure, making it a new candidate for an el-el mediated CDW. K 0.9 Mo 6 O 17 belongs to a family of materials including both one dimensional (1D) and two dimensional (2D) systems [41] and has been regarded as a model quasi-2D CDW material with T B CDW ∼ 115 K [42]. Its crystal structure [43] consists of a stacking of molybdenumoxygen slabs (Mo 6 O 17 ) along the hexagonal c axis with potassium atoms intercalated between these slabs. The Mo-O layers consist of Mo 2 O 10 zigzag chains along three directions, and the 2D Fermi surface (FS) can be constructed by superimposing three sets of quasi-1D FS lines, with a weak hybridization. The quasi-1D character of the FS is likely critical to the un...

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Superconductivity in the layered compound 2H-TaS2

Cited by 93 publications

References 11 publications

Tuning the charge density wave and superconductivity inCuxTaS2

Tuning the charge density wave and superconductivity inCuxTaS2

Superconductivity in CuxTiSe2

Discovery of an Unconventional Charge Density Wave at the Surface ofK0.9Mo6O17
Mou
¹
,
Sapkota
²
,
Kung
³

et al. 2016
Phys. Rev. Lett.
29
3
22
0
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Superconductivity in the layered compound 2H-TaS2

Cited by 93 publications

References 11 publications

Tuning the charge density wave and superconductivity inCuxTaS2

Tuning the charge density wave and superconductivity inCuxTaS2

Superconductivity in CuxTiSe2

Discovery of an Unconventional Charge Density Wave at the Surface ofK0.9Mo6O17Mou1, Sapkota2, Kung3 et al. 2016Phys. Rev. Lett.293220View full textAdd to dashboardCite

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Discovery of an Unconventional Charge Density Wave at the Surface ofK0.9Mo6O17
Mou
¹
,
Sapkota
²
,
Kung
³

et al. 2016
Phys. Rev. Lett.
29
3
22
0
View full text Add to dashboard Cite