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Rosenbaum, Ralph

doi:10.1103/physrevb.44.3599

Cited by 185 publications

(117 citation statements)

References 25 publications

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“…The linear fitting range becomes larger as t increases, suggesting that the low-T transport of the films with t≥85 nm are dominated by the ES-VRH mechanism. For the ES-VRH theory to be valid, the average hopping distance R ES must be larger than the localization length a, and the ratio R ES /a can be calculated according to:and should be larger than unity [25,27]. All R ES /a values for the films with t≥85 nm are larger than 1, satisfying thus the criterion of the ES-VRH model.…”

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confidence: 95%

“…The obtained values of R M /a are listed in Table I. From the fitting, it is also possible to estimate the density of states N(E F ) at the Fermi level and the localization length a according to: [24,27] ( )In (3), it is required to know at least one parameter (either a or N(E F )) for estimating the other one. Based on the reported heat capacity data of bulk SIO [20], we can assume N(E F ) to be ~10 47 /Jm 3 .…”

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Crossover of conduction mechanism in Sr2IrO4 epitaxial thin films

Quindeau

Deniz

et al. 2014

Applied Physics Letters

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High quality epitaxial Sr 2 IrO 4 thin films with various thicknesses (9-300 nm) have been grown on SrTiO 3 (001) substrates, and their electric transport properties have been investigated. All samples showed the expected insulating behavior with a strong resistivity dependence on film thickness, that can be as large as three orders of magnitude at low temperature. A close examination of the transport data revealed interesting crossover behaviors for the conduction mechanism upon variation of thickness and temperature. While Mott variable range hopping (VRH) dominated the transport for films thinner than 85 nm, high temperature (>200 K) thermal activation behavior was observed for films with large thickness (≥85 nm), which was followed by a crossover from Mott to Efros-Shklovskii (ES) VRH in the low temperature range. This low temperature crossover from Mott to ES VRH indicates the presence of a Coulomb gap (~3 meV).Our results demonstrate the competing and tunable conduction in Sr 2 IrO 4 thin films, which in turn would be helpful for understanding the insulating nature related to strong spin-orbitalcoupling of the 5d iridates. In recent years, oxides with the 5d-element Ir have been established as a fertile ground for studying new physics arising from the large relativistic spin-orbit-coupling (SOC) [1][2][3]. So far, a variety of exotic properties related to the strong SOC such as intriguing insulating behavior [3][4][5][6][7][8][9][10] In addition to the newly raised controversy on the insulating nature of SIO, the conduction mechanism of the insulating state has been a long-standing issue. In an early work, variable range hopping (VRH) conduction was reported in single crystalline SIO [3]. A recent study also focusing on SIO single crystals revealed that the conduction well follows the thermal activation mechanism with an energy gap of Δ~107 meV perfectly matching the value of optical measurements [1,12]. Further investigations of the same group showed a VRH dominated conduction in doped SIO even though the doping content was small [19,20]. In Ba 2 IrO 4 (BIO), although it highly resembles SIO in terms of structural and electronic properties, good VRH conduction was observed in the whole measured temperature (T) range. Moreover this type of conduction is robust against carrier doping [6], which is very different from the SIO case. In fact, a close examination of the conduction mechanism in SIO and BIO can provide some more interesting details. While the doped SIO shows 3-dimentional (3D) VRH conduction [19,20] [19], which could probably be related to the SOC. These show intriguing conduction behavior in the single layered iridates, pointing to a rather poor understanding of the conduction mechanism in SIO. Moreover, this issue became even more puzzling in the case of SIO thin films, in which the thermal activation model was frequently used to determine the energy gap of SIO, although a linear fit on a plot of lnρ-1/T is questionable [21,22]. Therefore, it is of high interest and actuality to compreh...

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Crossover of conduction mechanism in Sr2IrO4 epitaxial thin films

Quindeau

Deniz

et al. 2014

Applied Physics Letters

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“…In this case, electrons hop between localized states and the conductance is given by σ ¼ C exp½−ðT 0 =TÞ α , where T 0 depends on the density of localized states and the spread of their wave functions [33]. VRH conductivity can be of either Mott or EfrosShklovskii type, which for a 2D system translates into exponents α ¼ 1=3 and 1=2, respectively [34]. The fit to the data yields an exponent α ¼ 0.57, which is in good agreement with the latter, suggesting the existence of a Coulomb gap.…”

Section: Spin-orbit Semimetal Sriro 3 In the Two-dimensional Limitmentioning

confidence: 99%

Spin-Orbit Semimetal SrIrO3 in the Two-Dimensional Limit

Autieri²,

et al. 2017

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We investigate the thickness-dependent electronic structure of ultrathin SrIrO 3 and discover a transition from a semimetallic to a correlated insulating state below 4 unit cells. Low-temperature magnetoconductance measurements show that spin fluctuations in the semimetallic state are significantly enhanced while approaching the transition point. The electronic structure is further studied by scanning tunneling spectroscopy, showing that 4 unit cells SrIrO 3 is on the verge of a gap opening. Our density functional theory calculations reproduce the critical thickness of the transition and show that the opening of a gap in ultrathin SrIrO 3 is accompanied by antiferromagnetic order.

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“…͑12͒ are in a satisfactory agreement with that determined from the ͑T͒ dependences. The value of T c , the critical temperature where the crossover from Mott-to SE-type conduction occurs, was estimated using different models, namely, Aharony et al ͑T cA ͒, 24 Rosenbaum ͑T cR ͒, 25 and Shlimak et al ͑T cS ͒. 26 It was found that T VSE ജ T cR and T VSE ӷ T cA ͑T cS ͒, where T VSE is the temperature to the transition to SE-VRH conduction.…”

Section: Resultsmentioning

confidence: 99%

Hopping conductivity in p-CuGaSe2 films

Arushanov

Siebentritt²,

Schedel‐Niedrig³

et al. 2006

Journal of Applied Physics

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The results of resistivity measurements on p-type CuGaSe2 films are presented and analyzed within the framework of different hopping conductivity models. Both the Mott [N. Mott and E. A. Davies, Electron Processes in Non-Crystalline Materials (Clarendon, Oxford, 1979); N. F. Mott, Metal-Insulator Transitions (Taylor & Francis, London, 1990)] and the Shklovski-Efros [Electronic Properties of Doped Semiconductors (Springer, Berlin, 1984)] regimes of variable-range hopping are observed. The values of the characteristic and transition temperatures as well as the complete set of parameters describing the properties of the localized holes (the localization radius, the dielectric permeability, the width of the Coulomb gap, and the values of density of states at the Fermi level) are determined.

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Crossover from Mott to Efros-Shklovskii variable-range-hopping conductivity inInxO
Ralph Rosenbaum
¹

Cited by 185 publications

References 25 publications

Crossover of conduction mechanism in Sr2IrO4 epitaxial thin films

Crossover of conduction mechanism in Sr2IrO4 epitaxial thin films

Spin-Orbit Semimetal SrIrO3 in the Two-Dimensional Limit

Hopping conductivity in p-CuGaSe2 films

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Crossover from Mott to Efros-Shklovskii variable-range-hopping conductivity inInxORalph Rosenbaum1

Cited by 185 publications

References 25 publications

Crossover of conduction mechanism in Sr2IrO4 epitaxial thin films

Crossover of conduction mechanism in Sr2IrO4 epitaxial thin films

Spin-Orbit Semimetal SrIrO3 in the Two-Dimensional Limit

Hopping conductivity in p-CuGaSe2 films

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Crossover from Mott to Efros-Shklovskii variable-range-hopping conductivity inInxO
Ralph Rosenbaum
¹