Fluctuation Spectroscopy: A New Approach for Studying Low‐Dimensional Molecular Metals

Müller, Jens

doi:10.1002/cphc.201000814

Cited by 42 publications

(46 citation statements)

References 148 publications

(251 reference statements)

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“…1b by orange and red arrows. Device 1 showed insulating behaviour at low temperature, whereas device 2 showed a small resistance drop at 12 K, followed by a re-entrant percolation transition around 9 K. This behaviour of device 2 indicates that the system is in the partially SC phase where separation between SC and MI phases occurs and the SC fraction is maximized around 9 K. Such a situation has already been investigated in detail for a bulk material by infrared spectroscopy mapping 16 , nuclear magnetic resonance 17 , noise measurement 18 and so on. In our devices, magnetization measurement for another sample (device 3) also showed partial superconductivity and maximization of SC fraction at medium temperature range, which will be described later.…”

Section: Resultsmentioning

confidence: 82%

A strained organic field-effect transistor with a gate-tunable superconducting channel

et al. 2013

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In state-of-the-art silicon devices, mobility of the carrier is enhanced by the lattice strain from the back substrate. Such an extra control of device performance is significant in realizing high-performance computing and should be valid for electric-field-induced superconducting (SC) devices, too. However, so far, the carrier density is the sole parameter for field-induced SC interfaces. Here we show an active organic SC field-effect transistor whose lattice is modulated by the strain from the substrate. The soft organic lattice allows tuning of the strain by a choice of the back substrate to make an induced SC state accessible at low temperature with a paraelectric solid gate. An active three-terminal Josephson junction device thus realized is useful both in advanced computing and in elucidating a direct connection between filling-controlled and bandwidth-controlled SC phases in correlated materials.

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Section: Resultsmentioning

confidence: 82%

A strained organic field-effect transistor with a gate-tunable superconducting channel

et al. 2013

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“…The experiment is described in detail in Ref. [29]. Resistance R and noise power spectral density (PSD) S R have been measured perpendicular to the conducting layers.…”

Section: Experiments Single Crystals Ofmentioning

confidence: 99%

Different electronic transport regimes in the quasi‐two‐dimensional organic conductors κ‐(BEDT‐TTF)₂X

Müller

Brandenburg

Schweitzer

et al. 2012

Physica Status Solidi (b)

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We study the low-frequency dynamical properties of correlated charge carriers in various of the quasi-two-dimensional organic charge-transfer salts k-(BEDT-TTF) 2 X by means of fluctuation (noise) spectroscopy. Close to the critical endpoint of the Mott metal-insulator transition, a pronounced increase of the 1/fnoise level accompanied by a substantial shift of spectral weight to low frequencies indicates a sudden increase of the time scale of the charge fluctuations. For the less correlated, more metallic materials, we find a crossover/transition from hopping transport of more-or-less localized carriers at elevated temperatures to a low-temperature regime, where a metallic coupling of the layers allows for coherent interlayer transport of delocalized electrons.

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“…2 ]Br has been grown as single crystals by electrochemical crystallization [18]. Low-frequency fluctuation spectroscopy measurements have been performed in a five-terminal setup using a bridge-circuit ac technique [19] described in detail in [20]. Resistance R and resistance noise power spectral density (PSD) S R (f ) = 2 |δṼ (f )| 2 /I 2 [21] have been measured perpendicular to the conducting layers, where I is the applied current.…”

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confidence: 99%

Critical Slowing Down of the Charge Carrier Dynamics at the Mott Metal-Insulator Transition

et al. 2015

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We report on the dramatic slowing down of the charge carrier dynamics in a quasi-two-dimensional organic conductor, which can be reversibly tuned through the Mott metal-insulator transition (MIT). At the finite-temperature critical endpoint we observe a divergent increase of the resistance fluctuations accompanied by a drastic shift of spectral weight to low frequencies, demonstrating the critical slowing down of the order parameter (doublon density) fluctuations. The slow dynamics is accompanied by non-Gaussian fluctuations, indicative of correlated charge carrier dynamics. A possible explanation is a glassy freezing of the electronic system as a precursor of the Mott MIT.The Mott metal-insulator transition (MIT), where a charge gap opens due to electron-electron interactions is a key phenomenon in modern condensed-matter physics [1], for which the understanding of various fundamental aspects remains challenging, both theoretically and experimentally [2]. Among them are the nature of the anomalous metallic state and (nano-scale) phase separation in the vicinity of the Mott transition, the understanding of the combined effects of electron-electron interactions and disorder, and the question of universality and critical behavior. In recent years, organic charge-transfer salts have proven an outstanding class of materials with model character for studying these aspects of the Mott MIT [2-5]. These materials κ-(BEDT-TTF) 2 X, composed of the organic donor molecule BEDT-TTF (bis-ethylenedithio-tetrathiafulvalene representing C 6 S 8 [C 2 H 4 ] 2 , abbreviated as ET) and a polymeric anion X, are layered systems with a quasi-twodimensional electronic structure and belong to the very few examples, where the Mott MIT is purely driven by controlling the bandwidth without symmetry breaking [6]. The bandwidth W can be covontrolled either continuously by applying hydrostatic pressure or in discrete steps at ambient pressure by varying the anion X, which mimics changes in the ratio W/U , where U is the effective on-site Coulomb repulsion [7]. Likewise, replacing the eight H-atoms of the ET molecules' C 2 H 4 ethylene endgroups (EEG) in metallic κ-(ET) 2 Cu[N(CN) 2 ]Br (κ-H 8 -Br) by D-atoms (κ-D 8 -Br) results in a chemicallyinduced shift from the metallic towards the Mott insulating state [8]. In the T -p or T -X phase diagram the MIT is represented by an S-shaped, first-order transition line which terminates in a second-order critical point (p cr. /T cr. ), see Fig. 1. Recently, the critical behavior of the charge, spin and lattice degrees of freedom at (p cr. /T cr. ) has been subject of intense research efforts [6,[9][10][11][12][13][14][15]. Despite numerous experimental and theoretical approaches, however, no consensus has been reached on the nature of the Mott criticality in κ-(ET) 2 X and the underlying universality class. Furthermore, an investigation of the critical fluctuations and the dynamic properties of the charge carriers at the critical point, in particular at low frequencies, is still lacking. From general ...

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Fluctuation Spectroscopy: A New Approach for Studying Low‐Dimensional Molecular Metals

Cited by 42 publications

References 148 publications

A strained organic field-effect transistor with a gate-tunable superconducting channel

A strained organic field-effect transistor with a gate-tunable superconducting channel

Different electronic transport regimes in the quasi‐two‐dimensional organic conductors κ‐(BEDT‐TTF)₂X

Critical Slowing Down of the Charge Carrier Dynamics at the Mott Metal-Insulator Transition

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Fluctuation Spectroscopy: A New Approach for Studying Low‐Dimensional Molecular Metals

Cited by 42 publications

References 148 publications

A strained organic field-effect transistor with a gate-tunable superconducting channel

A strained organic field-effect transistor with a gate-tunable superconducting channel

Different electronic transport regimes in the quasi‐two‐dimensional organic conductors κ‐(BEDT‐TTF)2X

Critical Slowing Down of the Charge Carrier Dynamics at the Mott Metal-Insulator Transition

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Different electronic transport regimes in the quasi‐two‐dimensional organic conductors κ‐(BEDT‐TTF)₂X