Differences in Chemical Doping Matter: Superconductivity in Ti1–xTaxSe2 but Not in Ti1–xNbxSe2

Luo, Huixia; Xie, Weiwei; Tao, Jing; Pletikosić, Ivo; Valla, T.; Sahasrabudhe, Girija; Osterhoudt, Gavin B.; Sutton, Erin; Burch, Kenneth S.; Seibel, Elizabeth M.; Krizan, Jason W.; Zhu, Yimei; Cava, R. J.

doi:10.1021/acs.chemmater.6b00288

Cited by 47 publications

(36 citation statements)

References 45 publications

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“…For example Ti 1−x Ta x Se 2 shows metallic-like behavior with dρ/dT > 0 and a superconducting dome, but Ti 1−x Nb x Se 2 gives insulating-like dρ/dT < 0 all the way to room temperature [6,21], even though the Nb and Ta dopants are nominally isoelectronic. The details of how the dopant species interacts with the host matrix are thus highly relevant, as Nb dopants appear to cause substantially more disorder than Ta [21]. In other cases, such as lightlydoped Pd x TiSe 2 [27] and some of the pressure-grown TiSe 2 samples reported by Campbell et al [14], the resistivity shows similar behavior to the iodine vapor transport-grown samples, with a slope-change at T c and a broad peak, but then exhibits a steep upturn in resistivity below 80-100 K, while the Hall coefficient only saturates at a much lower temperature, and at a larger magnitude [14].…”

Section: Discussionmentioning

confidence: 99%

“…While the comparison of such criteria may seem a little mundane, the reliable deter- mination of T c becomes crucial for the construction of phase diagrams based on tuning the properties of TiSe 2 . Superconductivity has been found in TiSe 2 close to the critical point for the suppression of long-range CDW order via pressure [26], charge carrier doping [22], or intercalation [20,21,27]. However, for a full understanding of the interplay of CDW and superconducting orders, it is important to be confident of the determination of the CDW phase boundary, which in some studies has been partially or solely delineated by the analysis of transport measurements.…”

Section: Criteria For the Determination Of Cdw Temperaturementioning

confidence: 99%

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On the origin of the anomalous peak in the resistivity of TiSe2

2019

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Resistivity measurements of TiSe2 typically show only a weak change in gradient at the charge density wave transition at TCDW ≈ 200 K, but more prominently feature a broad peak at a lower T peak ∼ 165 K, which has remained poorly understood despite decades of research on the material. Here we present quantitative simulations of the resistivity using a simplified parametrization of the normal state band structure, based on recent photoemission data. Our simulations reproduce the overall profile of the resistivity of TiSe2, including its prominent peak, without implementing the CDW at all. We find that the peak in resistivity corresponds to a crossover between a low temperature regime with electron-like carriers only, to a regime around room temperature where thermally activated and highly mobile hole-like carriers dominate the conductivity. Even when implementing substantial modifications to model the CDW below the transition temperature, we find that these thermal population effects still dominate the transport properties of TiSe2.Phase transitions such as charge density waves (CDWs) are often first characterized by the observation of anomalies in resistivity measurements. Such phase transitions can influence the resistivity via Fermi surface reconstructions, changes in scattering rates, and/or a loss of free carriers due to the formation of an energy gap. However in TiSe 2 , which exhibits a much-studied CDW-like phase transition at T CDW ≈ 200 K [1, 2], transport measurements show a highly unusual and non-monotonic temperature-dependence. Samples which are close to stoichiometry typically show n-type metallic-like behavior at low temperatures, followed by a prominent broad peak at T peak ∼165 K, distinct from T CDW , beyond which the resistivity decreases with increasing temperature in a semiconductor-like fashion, with a positive Hall coefficient at room temperature [1]. Surprisingly little change occurs at T CDW , with at most a modest change in slope observed at ≈200 K [1, 3], even though the CDW involves changes to the band structure on energy scales as large as 100 meV [4]. The resistivity is known to be highly sensitive to the sample stoichiometry, and the observation of the anomalous broad peak at T peak ∼165 K in resistivity measurements has sometimes been taken as an indicator of sample quality [1,3,5,6]. On the other hand, some studies have interpreted the peak feature as a signature of the role of excitons in the CDW ordering [7][8][9][10][11]. Given the resurgence of interest in TiSe 2 in recent years, it is worthwhile to revisit the long-standing problem of its unusual transport properties [5,[12][13][14], aided by the availability of recent characterizations of its 3D electronic structure by angle-resolved photoemission spectroscopy (ARPES) [15].In this paper, we show that the overall temperaturedependence of the resistivity of TiSe 2 , including the anomalous peak, can be reasonably reproduced without accounting for the CDW at all. Our model is very simple, but it captures the essential ingredien...

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Section: Discussionmentioning

confidence: 99%

Section: Criteria For the Determination Of Cdw Temperaturementioning

confidence: 99%

On the origin of the anomalous peak in the resistivity of TiSe2

2019

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“…TMDs form a large family of materials that have been of significant interest in the past because they exhibit a variety of charge density wave phenomena (CDWs) at low temperatures [16][17][18]. Upon doping or the application of pressure, they give rise to a generic phase diagram that usually includes a superconducting state [19] (figure 1) [20][21][22][23][24][25][26][27][28][29].…”

Section: Introductionmentioning

confidence: 99%

Configurational electronic states in layered transition metal dichalcogenides

et al. 2019

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Mesoscopic irregularly ordered and even amorphous self-assembled electronic structures were recently reported in two-dimensional metallic dichalcogenides (TMDs), created and manipulated with short light pulses or by charge injection. Apart from promising new all-electronic memory devices, such states are of great fundamental importance, since such aperiodic states cannot be described in terms of conventional charge-density-wave (CDW) physics. In this paper, we address the problem of metastable mesoscopic configurational charge ordering in TMDs with a sparsely filled charged lattice gas model in which electrons are subject only to screened Coulomb repulsion. The model correctly predicts commensurate CDW states corresponding to different TMDs at magic filling fractions = / / / / / f 1 3, 1 4, 1 9, 1 13, 1 16.mDoping away from f m results either in multiple neardegenerate configurational states, or an amorphous state at the correct density observed by scanning tunnelling microscopy. Quantum fluctuations between degenerate states predict a quantum charge liquid at low temperatures, revealing a new generalized viewpoint on both regular, irregular and amorphous charge ordering in transition metal dichalcogenides.

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“…1 T -TiSe makes a 2 2 2 CDW order below K and the superconductivity can be induced by suppressing CDW order through, e.g., electric field, doping or pressure [ 160 – 162 ]. Despite multiple ARPES studies and theoretical scenarios to explain the nature of the bulk CDW phase [ 161 – 166 ], the microscopic origin still remains elusive.…”

Section: Arpes Studies On Tmdcmentioning

confidence: 99%

Angle-resolved photoemission spectroscopy for the study of two-dimensional materials

2017

Nano Convergence

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Quantum systems in confined geometries allow novel physical properties that cannot easily be attained in their bulk form. These properties are governed by the changes in the band structure and the lattice symmetry, and most pronounced in their single layer limit. Angle-resolved photoemission spectroscopy (ARPES) is a direct tool to investigate the underlying changes of band structure to provide essential information for understanding and controlling such properties. In this review, recent progresses in ARPES as a tool to study two-dimensional atomic crystals have been presented. ARPES results from few-layer and bulk crystals of material class often referred as “beyond graphene” are discussed along with the relevant developments in the instrumentation.

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Differences in Chemical Doping Matter: Superconductivity in Ti_1–xTa_xSe₂ but Not in Ti_1–xNb_xSe₂

Cited by 47 publications

References 45 publications

On the origin of the anomalous peak in the resistivity of TiSe2

On the origin of the anomalous peak in the resistivity of TiSe2

Configurational electronic states in layered transition metal dichalcogenides

Angle-resolved photoemission spectroscopy for the study of two-dimensional materials

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