Quantum criticality of Mott transition in organic materials

Furukawa, T.; Miyagawa, Kazuya; Taniguchi, Hiromi; Kato, Reìzo; Kanoda, K.

doi:10.1038/nphys3235

Cited by 127 publications

(203 citation statements)

References 31 publications

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“…In many cases [40][41][42], these nonlocal corrections prove significant only at sufficiently low temperatures. Then our findings should be even quantitatively accurate in the high-temperature incoherent regime, as in the very recent experiments on organic materials [43] for the case of half-filling.…”

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confidence: 99%

Bad-Metal Behavior Reveals Mott Quantum Criticality in Doped Hubbard Models

et al. 2015

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Bad-Metal (BM) behavior featuring linear temperature dependence of the resistivity extending to well above the Mott-Ioffe-Regel (MIR) limit is often viewed as one of the key unresolved signatures of strong correlation. Here we associate the BM behavior with the Mott quantum criticality by examining a fully frustrated Hubbard model where all long-range magnetic orders are suppressed, and the Mott problem can be rigorously solved through Dynamical Mean-Field Theory. We show that for the doped Mott insulator regime, the coexistence dome and the associated first-order Mott metal-insulator transition are confined to extremely low temperatures, while clear signatures of Mott quantum criticality emerge across much of the phase diagram. Remarkable scaling behavior is identified for the entire family of resistivity curves, with a quantum critical region covering the entire BM regime, providing not only insight, but also quantitative understanding around the MIR limit, in agreement with the available experiments.PACS numbers: 71.27.+a,71.30.+h Metallic transport inconsistent with Fermi liquid theory has been observed in many different systems; it is often linked to quantum criticality around some ordering phase transition [1, 2]. Such behavior is notable near quantum critical points in good conductors, for example in heavy fermion compounds [3, 4]. In several other classes of materials, however, much more dramatic departures form conventional metallic behavior are clearly observed, where resistivity still rises linearly with temperature, but it reaches paradoxically large values, well past the MIR limit [5, 6]. This "Bad-Metal" (BM) behavior [7], was first identified in the heyday of high-temperature superconductivity, in materials such as La 2−x Sr x CuO 4 [8]. While the specific copper-oxide family and related high-T c materials remain ill-understood and marred with controversy, it soon became clear that BM behavior is a much more general feature [6] of materials close to the Mott metal-insulator transition (MIT) [9]. Indeed, it has been clearly identified also in various oxides [10, 11], organic Mott systems [12][13][14], as well as more recently discovered families of iron pnictides [15]. Despite years of speculation and debate, so far its clear physical interpretation has not been established.To gain reliable insight into the origin of BM behavior, it is useful to examine an exactly solvable model system, where one can suppress all possible effect associated with the approach to some broken symmetry phase, or those specific to low dimensions and a given lattice structure. This can be achieved by focusing on the "maximally frustrated Hubbard model", where an exact solution can be obtained by solving Dynamical Mean-Field Theory (DMFT) equations [16] in the paramagnetic phase. Although various aspects of the DMFT equation have been studied for more than twenty years, only very recent work [17,18] established how to identify the quantum critical (QC) behavior associated with the interaction-driven Mott transition at ...

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Bad-Metal Behavior Reveals Mott Quantum Criticality in Doped Hubbard Models

et al. 2015

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“…These findings suggest that the spinon metal is likely a good starting point for understanding the spin-liquid behavior observed in these two materials 12,14 . In addition, the pressure-induced Mott transition from the metal to the spin liquid is observed to be either only very weakly first order 20 , or perhaps even continuous [25][26][27] . Motivated by these experiments, we consider a model of interacting electrons on a half-filled triangular lattice "strip" geometry (see Fig.…”

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confidence: 99%

Continuous Mott transition between a metal and a quantum spin liquid

et al. 2015

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More than half a century after first being proposed by Sir Nevill Mott, the deceptively simple question of whether the interaction-driven electronic metal-insulator transition may be continuous remains enigmatic. Recent experiments on two-dimensional materials suggest that when the insulator is a quantum spin liquid, lack of magnetic long-range order on the insulating side may cause the transition to be continuous, or only very weakly first order. Motivated by this, we study a half-filled extended Hubbard model on a triangular lattice strip geometry. We argue, through use of large-scale numerical simulations and analytical bosonization, that this model harbors a continuous (Kosterlitz-Thouless-like) quantum phase transition between a metal and a gapless spin liquid characterized by a spinon Fermi surface, i.e., a "spinon metal". These results may provide a rare insight into the development of Mott criticality in strongly interacting two-dimensional materials and represent one of the first numerical demonstrations of a Mott insulating quantum spin liquid phase in a genuinely electronic microscopic model.

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“…/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.…”

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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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Quantum criticality of Mott transition in organic materials

Cited by 127 publications

References 31 publications

Bad-Metal Behavior Reveals Mott Quantum Criticality in Doped Hubbard Models

Bad-Metal Behavior Reveals Mott Quantum Criticality in Doped Hubbard Models

Continuous Mott transition between a metal and a quantum spin liquid

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

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