Dielectric breakdown and current switching effect in the incommensurate layered compound(LaS)1.196VS2

Abstract

A current switching effect of several orders of magnitude was observed in the incommensurate misfit layered compound ͑LaS͒ 1.196 VS 2 . This effect involves correlated vanadium t 2g states in a hexagonal ͓VS 2 ͔ layer. Application of moderate electric fields ͑ϳ50 V/cm͒ induces a dielectric breakdown and restores a metallic state. The large pretransitional nonlinearities are consistent with a Poole-Frenkel mechanism which highlights the role of Coulomb interactions. This behavior and the strong modulation of the vanadium atom positions, revealed by single crystal x-ray structure determination, are in favor of a heterogeneous charge distribution. With respect to recent theoretical works, we suggest that the current switching effect observed in ͑LaS͒ 1.196 VS 2 is related to the breakdown of a remaining Mott insulator state.Transition metal oxides have been extensively studied in the last decades and they have led to a renewed interest in metal insulator transition ͑MIT͒ in correlated electron systems 1 where fascinating properties such as high temperature superconductivity can be encountered. The application of large external fields can affect the ground state of these systems as exemplified by the magnetic field induced MIT observed in manganites and that leads to colossal magnetoresistance. 2 Recently experimental evidence of electric field induced MIT was observed in Mott insulators La 2−x Sr x NiO 4 ͑Ref. 3͒, Sr 2 CuO 3 ͑Ref. 4͒, and Pr 1−x Ca x MnO 3 ͑Ref. 5͒. These important current switching effects may originate from the peculiar charge, spin and/or orbital ordering taking place in these compounds. For example, a field induced stripe depinning was proposed for La 2−x Sr x NiO 4 ͑Ref. 3͒, while a field induced melting of the charge ordered state was proposed in Pr 1−x Ca x MnO 3 ͑Ref. 5͒. Recent theoretical works 6 have shown that a strong enough electric field could break the Mott-insulator phase and explain the MIT. So far, a dielectric breakdown was mainly observed in transition metal oxides that involve e g orbital in a MO 2 square plane. In this paper we report a similar dielectric breakdown for a transition metal sulfide with hexagonal packing and a t 2g orbital. ͑LaS͒ 1.196 VS 2 is a material with partially filled t 2g shells in hexagonal packing. 7 It is a member of the misfit layered chalcogenide family ͑LnX͒ 1+x TX 2 ͑Ln= rare earth; X=S,Se; T=Ti,V,Cr͒ which has been extensively studied during the last decade. 8 These systems have a typical two-dimensional ͑2D͒ structure shown in Fig. 1 where incommensurability occurs along one of the in-plane axes ͑the a direction͒. The mismatch between both sublattices, ͑LnX͒ and ͑TX 2 ͒, is defined by the term 1 + x; its value is equal to the ratio 2a 2 / a 1 ͓a 2 and a 1 being the unit cell parameters of ͑TX 2 ͒ and ͑LnX͒ parts, respectively͔. Band structure calculations indicate that the d bands of the transition element are incompletely filled which should favor a metallic character. 7 In fact, the transport properties strongly depend on the nature of the tra...

Electric‐Pulse‐driven Electronic Phase Separation, Insulator–Metal Transition, and Possible Superconductivity in a Mott Insulator

“…[4,5] This could explain the volatile electric-field-induced MIT observed in systems such as Pr 1-x Ca x MnO 3 , [9] La 2-x Sr x NiO 4 , [10] or (LaS) 1.196 VS 2 . [11] Interestingly, (LaS) 1.196 VS 2 and GaTa 4 Se 8 bear some electronic and structural analogies: both compounds contain transition metal clusters and lie in the vicinity of the metal-insulator transition. This urges us to investigate the effects of electric pulses on the electrical transport properties of GaTa 4 Se 8 crystals.…”

Electrical and optical properties of the mixed-valence misfit-layer compound (YbS)1.25CrS2

“…We find no appreciable influences of a quasi-periodic potential (8a 2 ≈ 5a 1 = 26.55Å) on electrical conduction and the temperature dependence of the resistivity is quite similar to that of bulk samples. However, preliminary experiments under high-electric-field show the dielectric breakdown and the current switching effect as observed in (LaS) 1.196 VS 2 [22] and one-dimensional Mott insulators Sr 2 CuO 3 and SrCuO 2 [23], which may be related with the destruction of Mott-insulator phases by electric field. They will be discussed in another paper in detail.…”

Ultrafast filling of an electronic pseudogap in an incommensurate crystal

“…This is different from the opening of a gap expected in the weak coupling limit of a CDW. As the compound becomes quite insulating in the process [12], we checked at each temperature that there was no shift due to charging effects [23]. In Fig.…”

“…Interestingly, this electronic structure seems to host unconventional behaviors. It has been shown that upon the application of moderate electric fields (≈ 50 V/cm), a current switching leads to a volatile increase of conductivity by 6 orders of magnitude [12]. Such phenomena could be very interesting for applications [13,14].In this paper, we use Angle and Time Resolved Photoelectron Spectroscopy (ARPES and TRPES) to study the interplay of incommensurate distortion, pseudogap and electron-phonon coupling in (LaS) 1.196 VS 2 .…”