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

Abstract

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...

Strong-coupling charge density wave in monolayer TiSe2

“…In fact, the bottom of the conduction band actually shifts continuously to higher binding energy upon cooling (Fig. 2(i)), which we attribute to a substantial, but essentially trivial chemical potential effect [28,29]. There is no anomaly in the band position at T c , and no evident backfolding of the conduction band spectral weight to the zone centre in the low-temperature state, both pointing to a lack of band hybridisation of this state.…”

“…For the hybridised plot in Fig. 3(b), we fix the Ti displacements at 0.02a, and also allow for a different chemical potential as is observed experimentally [28].…”

Effect of synthesis conditions on the electrical resistivity of TiSe2

“…1. Even though the ρ(T) behavior is qualitatively similar between single-crystalline and polycrystalline samples with a local maximum between 100 and 200 K, at the lower temperatures ρ(T) varies drastically: metallic behavior (dρ/dT > 0) is registered in the single-crystalline sample (dashed line and open circles), explained by either a doped semiconductor picture [26] or partial gapping of the Fermi surface [1], while semiconductor-like behavior (dρ/dT < 0) is found in the polycrystalline sample (solid line). To our knowledge, no systematic study of this discrepancy exists.…”

Mechanisms of electron-phonon coupling unraveled in momentum and time: The case of soft phonons in TiSe 2

“…A layered transition metal dichalcogenide (15), TiSe 2 exhibits a rich phenomenology emerging from carrier-lattice interactions (16)(17)(18).…”