Some new superconducting group Va dichalcogenides

Maaren, M.H. van; Schaeffer, G.

doi:10.1016/0375-9601(67)91005-5

Cited by 63 publications

(21 citation statements)

References 6 publications

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“…It has also been demonstrated that the interaction between an STM tip and the sample can induce a reversible 2H to 1T phase transition in NbSe 2 [30]. On the other hand, bulk NbTe 2 takes on the 1T-structure but with a significant 3 × 1 CDW distortion [33], and also exhibits superconductivity at temperatures below 1 K [48]. The niobium-based TMDCs are d 1 materials, so the simplest ionic picture would predict metallic behavior with a single half-filled band crossing the Fermi surface.…”

Section: T-type Tmdc Materials Propertiesmentioning

confidence: 99%

Effects of structural distortions on the electronic structure of T -type transition metal dichalcogenides

et al. 2020

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Single-layer transition metal dichalcogenides (TMDCs) can adopt two distinct structures corresponding to different coordination of the metal atoms. TMDCs adopting the T-type structure exhibit a rich and diverse set of phenomena, including charge density waves (CDW) in a √ 13 × √ 13 supercell pattern in TaS2 and TaSe2, and a possible excitonic insulating phase in TiSe2. These properties make the T-TMDCs desirable components of layered heterostructure devices. In order to predict the emergent properties of combinations of different layered materials, one needs simple and accurate models for the constituent layers which can take into account potential effects of lattice mismatch, relaxation, strain, and structural distortion. Previous studies have developed ab initio tight-binding Hamiltonians for H-type TMDCs [1]. Here we extend this work to include T-type TMDCs. We demonstrate the capabilities of our model using three example systems: a 1-dimensional sinusoidal ripple, the 2×2 CDW in TiSe2, and the √ 13 × √ 13 CDW in TaS2. Using the technique of band unfolding we compare the electronic structure of the distorted crystals to the pristine band structure and find excellent agreement with direct DFT calculations, provided the magnitude of the distortions remains in the linear regime.

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Section: T-type Tmdc Materials Propertiesmentioning

confidence: 99%

Effects of structural distortions on the electronic structure of T -type transition metal dichalcogenides

et al. 2020

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“…In numerous studies, these compounds attract attention because of the existence of the charge density wave (CDW) phenomenon [1][2][3][4][5][6][7][8] (like in NbSe 2 , TaS 2 , and TaSe 2 ), while in others (like in NbTe 2 , TaS 2 , and TaSe 2 ) the interest lies in superconducting properties. [9][10][11][12] Very recently, an interesting observation on the electron dynamics in some of these compounds has been reported. 13,14 By means of electron energy-loss spectroscopy (EELS) the anomalous dispersion of a collective electron excitation-plasmon-at low energies has been demonstrated.…”

Section: Introductionmentioning

confidence: 99%

Role of band structure and local-field effects in the low-energy collective electronic excitation spectra of 2H-NbSe2

2012

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We present a study of the electron dynamics in the layered compound 2H -NbSe 2 . First-principles calculations are used to obtain the band structure employed in the evaluation of the loss function with inclusion of local-field (LF) effects. Two different symmetry directions [(100) and (010)] were explored in the hexagonal basal plane. In both cases, a low-energy charge-carrier plasmon (CCP) at ∼1 eV presenting a negative dispersion over a wide momentum transfer range is found, in agreement with recent experimental results [Wezel et al., Phys. Rev. Lett. 107, 176404 (2011)]. On the contrary, in the (001) perpendicular direction, the CCP has negative dispersion at small momenta only, presenting strong positive dispersion at larger momenta. Our calculations reveal that this behavior can be explained without invoking many-body effects, as long as band structure effects are properly included in the evaluation of the excitation spectra. In addition to this CCP mode, we find another one with an arclike oscillating dispersion along the perpendicular direction, as well as the appearance of a CCP replica at high momenta due to LF effects.

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“…This is not the case, but it must be kept in mind that T c for the dichalcogenide 2H-TaSe 2 is very small (T c = 0.15 K) 28 and its pressure dependence dT c /dP< 1.3xlO* 5 K/kbar. 29 The electron-phonon interaction is probably too weak to make TaSe 3 superconducting (the molar weight of Ta is much higher than that of Nb), or, because of a different unit cell, the Fermi surface may be much less pressure dependent.…”

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confidence: 99%

Superconductivity of the Linear Trichalcogenide NbSe3under Pressure

Monçeau¹,

Peyrard²,

Richard³

et al. 1977

Phys. Rev. Lett.

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We show that the linear compound NbSe 3 becomes superconducting under pressure. We have measured the initial slope of the magnetization of NbSe 3 as a function of pressure down to temperatures as low as 50 mK. A very small pressure is necessary in order for the superconductivity to occur. T c is strongly pressure dependent. We find that the initial slope dT c /dP = 0S K/bar. We attribute this huge variation of T C to changes in tne band structure induced by pressure.Until recently very few measurements of the electronic properties of transition-metal trichal-cogenidesTXj (T: Ti, Zr, Hf, Nb, Ta; X: Se, S, Te) have been reported. All these compounds have structures made up of infinite chains of trigonal prisms TX 6 extending parallel to the b axis of their monoclinic cell. 1 " 3 The trichalcogenides of the group-IV transition elements as well as the sulfide compounds of group VB are semiconductors. Only TaSe 3 4 ' 5 and NbSe 3 6 show a metallic behavior from room temperature down to the helium range. In particular, NbSe 3 has very spectacular properties 6 * 7 : NbSe 3 exhibits two phase transitions at T cl = 145 K and T c2 = 59 K where a sharp increase in resistivity occurs. These anomalies in resistivity were ascribed to the formation of charge-density waves (CDW). Applying pressure causes the critical temperature of CDW formation to decrease. 7 It was also shown that the resistivity anomalies are strongly nonlinear 8 -a small electric field ( -0.5 V/cm" 1 ) is enough to cause the breakdown of these anomalies. Here we have extended the pressure measurements at lower temperatures and we report on the discovery that NbSe 3 becomes a superconductor under pressure.

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Some new superconducting group Va dichalcogenides

Cited by 63 publications

References 6 publications

Effects of structural distortions on the electronic structure of T -type transition metal dichalcogenides

Effects of structural distortions on the electronic structure of T -type transition metal dichalcogenides

Role of band structure and local-field effects in the low-energy collective electronic excitation spectra of 2H-NbSe2

Superconductivity of the Linear Trichalcogenide NbSe3under Pressure

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