Preparation and properties of the single crystalline AB2-type selenides and tellurides of niobium, tantalum, molybdenum and tungsten

Brixner, L.H.

doi:10.1016/0022-1902(62)80178-x

Cited by 266 publications

(151 citation statements)

References 7 publications

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“…41 The average structure was assessed from raw diffraction data using the General Structure Analysis System operated under EXPGUI utilizing P63/mmc model from the literature. [42][43][44] …”

Section: Methodsmentioning

confidence: 99%

Superconducting order from disorder in 2H-TaSe 2− x S x

Deng

Wang

et al. 2017

npj Quant Mater

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We report on the emergence of robust superconducting order in single crystal alloys of TaSe 2−x S x (0 ≤ × ≤ 2). The critical temperature of the alloy is surprisingly higher than that of the two end compounds TaSe 2 and TaS 2 . The evolution of superconducting critical temperature T c (x) correlates with the full width at half maximum of the Bragg peaks and with the linear term of the high-temperature resistivity. The conductivity of the crystals near the middle of the alloy series is higher or similar than that of either one of the end members 2H-TaSe 2 and/or 2H-TaS 2 . It is known that in these materials superconductivity is in close competition with charge density wave order. We interpret our experimental findings in a picture where disorder tilts this balance in favor of superconductivity by destroying the charge density wave order.npj Quantum Materials (2017) 2:11 ; doi:10.1038/s41535-017-0016-9 INTRODUCTIONThe interplay of disorder and interactions is a fruitful area of investigation. In the absence of electron-electron interactions, disorder can turn a metallic system into an Anderson insulator, 1 but can remain metallic when interactions are important. The additional complexity of competing orders such superconductivity with charge density wave (CDW) or magnetism makes this problem one of the most challenging frontiers in physics. 2-5 A large body of literature is devoted to this interplay in nearly magnetic materials. 6 The interplay of disorder and superconductivity in CDW materials have been less explored than its magnetic analog.Superconductivity and CDW are traditionally viewed as weakcoupling Fermi surface instabilities due to electron-phonon coupling. 7 Arguments have been made both for their cooperation and competition. 8,9 Hexagonal transition metal dichalcogenide 2H-TaSe 2 (P63/mmc space group) undergoes a second-order transition to an incommensurate CDW at 122 K followed by a first-order lock-in transition to a commensurate CDW (CCDW) phase at 90 K, eventually becoming superconducting below 0.14 K upon cooling. 10, 11 2H-TaS 2 has T c = 0.8 K below an in-plane CCDW at 78 K. 10,12 The CDW mechanism in 2H-TaSe 2 involves an electron instability in the bands nested away from the Fermi surface, whereas 2H-TaS 2 features a polar charge and orbital order. 13,14 CDW in 2H-TaSe 2 is dominated by hopping between next-nearest neighbors that creates three weakly coupled triangular sublattices. 15 It is of interest to note that the 2H-TaSe 2 is quasi-twodimensional (2D) metal with pseudogap and with c-axis resistivity 25-50 times higher than the in-plane resistivity, i.e., ρ c (T) >> ρ ab (T). 10,13,[16][17][18] Here, we report that in the 2H-TaSe 2−x S x alloy series the CDW is suppressed and the superconductivity is maximized with

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Section: Methodsmentioning

confidence: 99%

Superconducting order from disorder in 2H-TaSe 2− x S x

Deng

Wang

et al. 2017

npj Quant Mater

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“…The lattice constants of MoSe2 and WSe2 are aMoSe2 = 3.288 A and aWSe2 = 3.280 A [56]. This mismatch gives rise to a Moiré pattern, which can impact the electronic band structure [44] [50].…”

Section: Wse2mentioning

confidence: 99%

“…Although the calculations are done for the individual monolayers, the correct trends should be captured. In particular, hybridization effects in van der Waals HS are known to affect predominantly the electronic bands at the  point and only minor at the -valley, while the Kand K'-points are almost unaffected [25].The lattice constants of MoSe2 and WSe2 are aMoSe2 = 3.288 A and aWSe2 = 3.280 A [56]. This mismatch gives rise to a Moiré pattern, which can impact the electronic band structure [44] [50].…”

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confidence: 99%

Long-Lived Direct and Indirect Interlayer Excitons in van der Waals Heterostructures

et al. 2017

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We investigate the photoluminescence of interlayer excitons in heterostructures consisting of monolayer MoSe2 and WSe2 at low temperatures. Surprisingly, we find a doublet structure for such interlayer excitons. Both peaks exhibit long photoluminescence lifetimes of several ten nanoseconds up to 100 ns at low temperatures, which verifies the interlayer nature of both.The peak energy and linewidth of both show unusual temperature and power dependences.In particular, we observe a blue-shift of their emission energy for increasing excitation powers.At a low excitation power and low temperatures, the energetically higher peak shows several spikes. We explain the findings by two sorts of interlayer excitons; one that is indirect in real space but direct in reciprocal space, and the other one being indirect in both spaces. Our results provide fundamental insights into long-lived interlayer states in van der Waals heterostructures with possible bosonic many-body interactions.Keywords: van der Waals heterostructure, indirect excitons, interlayer exciton, photoluminescence, exciton lifetime, transition metal dichalcogenides; 2 Semiconductor heterostructures (HS) are very often the foundation for the observation of novel phenomena in both fundamental science as well as device applications. The electrical and optical properties of such HS can be engineered in a wide range resulting in precisely tailored functionalities. Of particular interest are optically active HS facilitating many device applications such as photo-detectors, solar cells, light-emitting diodes or lasers and fostering the observation of many-body driven quantum phenomena found in systems with reduced dimensionality such as quantum wells or quantum dots. Excitons are electron-hole pairs coupled by attractive Coulomb interaction which results in a ground state with a reduced energy compared to the corresponding single-particle energies. Exciton ensembles exhibit an intriguing interaction driven phase diagram with different classical and quantum phases including quantum liquids and solids [1][2][3]. The bosonic nature of excitons enables these composite particles even to condensate into macroscopic ground state wave functions forming a Bose-Einstein condensate (BEC) [4].Ensembles of indirect a.k.a. interlayer excitons (IXs) are particularly fascinating systems to explore such classical and quantum phases of interacting bosonic ensembles. IXs are composite bosons that feature enlarged lifetimes due to the reduced overlap of the electronhole wave functions resulting in dense IX ensembles that are thermalized to the lattice temperature. Besides IX ensembles in III-V HS [5][6][7][8][9][10][11][12][13][14][15], hetero-bilayers prepared from semiconducting transition metal dichalcogenides (TMDs) exhibit superior potential for studying interacting IX ensembles [3,[16][17][18][19][20][21][22][23][24][25] with intriguing spin-and valley-properties [26][27][28]. At the same time, TMDs are truly two-dimensional (2D) crystals coupled to each other or to substrat...

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“…In the quest of achieving large MR in crystalline materials, a class of manganese oxides colossal magnetoresistance (CMR) materials was discovered that exhibits a large change in resistance with applied magnetic fields but only at low temperatures [4][5][6] The temperature dependent electrical resistivity, Hall coefficient and thermoelectric power of tungstenditelluride have been known for several decades [13] and a three-carrier semi-metal band model [13,14] was proposed to explain the electrical resistivity. Later on, density-functional based augmented spherical wave (ASW) electronic structure calculations and relatively low resolution ARPES [15] were used to study the electronic properties of WTe 2 and further supported the semimetallic nature of this material.…”

mentioning

confidence: 99%

Temperature-Induced Lifshitz Transition inWTe2

Wu¹,

Jo²,

Ochi³

et al. 2015

Phys. Rev. Lett.

220

200

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We use ultra-high resolution, tunable, VUV laser-based, angle-resolved photoemission spectroscopy (ARPES) and temperature and field dependent resistivity and thermoelectric power (TEP) measurements to study the electronic properties of WTe2, a compound that manifests exceptionally large, temperature dependent magnetoresistance. The temperature dependence of the TEP shows a change of slope at T=175 K and the Kohler rule breaks down above 70-140 K range. The Fermi surface consists of two electron pockets and two pairs of hole pockets along the X-Γ-X direction. Upon increase of temperature from 40K, the hole pockets gradually sink below the chemical potential. Like BaFe2As2, WTe2 has clear and substantial changes in its Fermi surface driven by modest changes in temperature. In WTe2, this leads to a rare example of temperature induced Lifshitz transition, associated with the complete disappearance of the hole pockets. These dramatic changes of the electronic structure naturally explain unusual features of the transport data.The discovery of giant magnetoresistance (GMR) in Fe/Cr superlattice [1,2], opened a new era of applications in magnetic field sensors, read heads in high density hard disks, random access memories, and galvanic isolators [3]. In the quest of achieving large MR in crystalline materials, a class of manganese oxides colossal magnetoresistance (CMR) materials was discovered that exhibits a large change in resistance with applied magnetic fields but only at low temperatures [4][5][6] The temperature dependent electrical resistivity, Hall coefficient and thermoelectric power of tungstenditelluride have been known for several decades [13] and a three-carrier semi-metal band model [13,14] was proposed to explain the electrical resistivity. Later on, density-functional based augmented spherical wave (ASW) electronic structure calculations and relatively low resolution ARPES [15] were used to study the electronic properties of WTe 2 and further supported the semimetallic nature of this material. However due to the low resolution of these early experiments, no details about the Fermi surface or band dispersion were obtained. Recent ARPES [11] and quantum oscillation [16] results revealed presence of small electron and hole pockets of roughly similar size. These findings were consistent with carrier compensation mechanism as the primary source of the MR effect [10,12]. Furthermore, this study also reported a change of the size of the Fermi pockets between 20K and 100K. More recently, Jiang et al.[17] claimed observation of strong spin-orbital coupling effect and proposed that the backscattering protection mechanism also may play a role in the large nonsaturating MR of WTe 2 .In this letter, we present the results from temperature dependent transport and ultra-high resolution, tunable VUV laser based ARPES[18] measurements. Our data show that there are two electron pockets and four hole pockets along the X-Γ-X direction and a fully occupied light "hole" band at the center of the Brillouin Zone (BZ) located j...

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Preparation and properties of the single crystalline AB2-type selenides and tellurides of niobium, tantalum, molybdenum and tungsten

Cited by 266 publications

References 7 publications

Superconducting order from disorder in 2H-TaSe 2− x S x

Superconducting order from disorder in 2H-TaSe 2− x S x

Long-Lived Direct and Indirect Interlayer Excitons in van der Waals Heterostructures

Temperature-Induced Lifshitz Transition inWTe2

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