Superconducting phase in the layered dichalcogenide1T-TaS2upon inhibition of the metal-insulator transition

Abstract

When a Mott metal-insulator transition is inhibited by a small amount of disorder in the layered dichalcogenide 1T-TaS 2 , an inhomogeneous superconducting state arises below T = 2.1 K and coexists with a nearly commensurate charge-density wave. By angle-resolved photoelectron spectroscopy, we show that it emerges from a bad metal state with strongly damped quasiparticles. Superconductivity is almost entirely suppressed by an external magnetic field of 0.1 T. DOI: 10.1103/PhysRevB.81.172503 PACS number͑s͒: 74.62.Dh, 71.30.ϩh, 71.45.Lr, 74.25.Jb One of the most intriguing phenomena in the solid state is the occurrence of electronic instabilities toward broken symmetry states such as superconductivity ͑SC͒, density waves, charge and orbital order, or the Mott insulating state. When two or more instabilities are simultaneously at work, complex phase diagrams and unusual physical properties are found. Understanding such a coexistence or competition is therefore important. A related open issue is the emergence of SC from a normal state where the nature of the quasiparticles ͑QPs͒ is strongly modified by the interactions. Spectroscopic probes of the electronic states with momentum selectivity, namely, angle-resolved photoelectron spectroscopy ͑ARPES͒, can address these issues.Broken-symmetry phases are especially prominent in lowdimensional-quasi-one-dimensional ͑1D͒ and quasi-twodimensional ͑2D͒-materials.1 The 2D transition metal dichalcogenides ͑TMDs͒, in particular, exhibit a variety of charge-density wave ͑CDW͒ transitions.2 In their trigonal prismatic ͑2H͒ polytypes some of them also support SC, with critical temperatures as high as 7.2 K for NbSe 2 . ARPES has been used to identify in the band structure the favorable conditions for electronic instabilities. [3][4][5][6] According to the simplest Peierls scenario, the CDW is the result of a moderately strong electron-phonon ͑e-ph͒ interaction connecting electron and hole states across the well-nested Fermi surface ͑FS͒. SC is also a consequence of e-ph coupling, leading to the formation of Cooper pairs at the FS. Even if alternative scenarios been proposed which do not rely on nesting, 7,8 both CDW and SC tend to gap parts of the same FS and are generally considered to be competing.SC is usually not found in TMDs of the 1 T polytype, with TM ions in octahedral coordination, but it can be induced by doping or by external pressure. Recently, much interest has been raised by the observation that the balance between CDW and SC can be continuously tuned in the TMD TiSe 2 by a controlled intercalation of Cu atoms. 9 Here we consider the occurrence of SC in the isostructural TMD 1T-TaS 2 , which exhibits a unique sequence of CDW and Mott phases, as a result of the interplay of e-ph and Coulomb interactions.2 At room temperature ͑RT͒, the CDW is nearly commensurate ͑NC͒. It consists of a hexagonal array of domains separated by domain walls ͑discommensurations͒ where the CDW phase changes rapidly. The domain size and the CDW amplitude grow as temperature is reduced, ...

Monolayer 1T-NbSe2 as a Mott insulator

“…Although polymorph field effect transistors have recently been reported by using other TMDs such as MoS 2 and MoTe 2 , 8,9 the unique Mott-insulating state of 1T-NbSe 2 , distinct from the states of the band-insulating 2H-MoS 2 and 2H-MoTe 2 , would provide a new means of controlling a device, because the characteristics of the Mott-insulating state in the 1T phase are known to be altered by various physical parameters, such as pressure and disorder. 34,35 Furthermore, as monolayer 2H-NbSe 2 exhibits superconductivity robust against magnetic fields owing to space inversion symmetry breaking and the resultant spin imbalance in the electronic states, 12 the present result also opens a path toward atomic-layer electronics based on superconductor/semiconductor heterojunctions. (a) Surface area ratio between the 2H and 1T domains, plotted as a function of T S , obtained by numerical fits to energy distribution curves (EDCs).…”

Conduction-band electronic structure of 1T-TaS2revealed by angle-resolved inverse-photoemission spectroscopy

“…In order to reveal the electronic structure of 1T -TaS 2 depending on its rich CDW phases, a tremendous number of studies have been carried out based on high-resolution angle-resolved photoemission spectroscopy (ARPES) [6][7][8][9][10][11]. Arita et al compared the Ta 5d z 2 -derived energy dispersions along the -M direction between ICCDW and CCDW phases [7].…”

Topological Dirac surface states and superconducting pairing correlations inPbTaSe2

“…This is a common physical mechanism in TMDs where the CDW and superconductivity compete with each other [19,[23][24][25][26]. Mostly, the CDW predominates in the competition for the gapping of Fermi surfaces.…”

“…Mostly, the CDW predominates in the competition for the gapping of Fermi surfaces. Superconductivity takes place when the CDW is suppressed by either pressurization or doping [19,[24][25][26]. In PbTaSe 2 , the phonon stiffening due to the Pb intercalation makes it energetically unfavorable to form the CDW order, opening the way for the transition into a superconducting phase.…”