Quantum criticality in organic conductors? Fermi liquid versus non-Fermi-liquid behaviour

Dressel, Martin

doi:10.1088/0953-8984/23/29/293201

Cited by 63 publications

(82 citation statements)

References 166 publications

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“…Stimulated by the experimental findings of CO, theoretical studies were conducted on the role of intersite Coulomb interaction in CO [16][17][18], lattice distortion accompanied by CO [19][20][21], the relationship between CO fluctuation and superconductivity (SC) [22], and quantum criticality at the edge of CO [23]. Subsequently, several experimental and theoretical studies have been conducted [24][25][26][27]. Some of these will be introduced from Section 3 on, in relation to the experimental results.…”

Section: Introductionmentioning

confidence: 99%

Infrared and Raman Studies of Charge Ordering in Organic Conductors, BEDT-TTF Salts with Quarter-Filled Bands

Yakushi

2012

Crystals

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This paper reviews charge ordering in the organic conductors, β″-(BEDT-TTF) (TCNQ), θ-(BEDT-TTF) 2 X, and α-(BEDT-TTF) 2 X. Here, BEDT-TTF and TCNQ represent bis(ethylenedithio)tetrathiafulvalene and 7,7,8,8-tetracyanoquinodimethane, respectively. These compounds, all of which have a quarter-filled band, were evaluated using infrared and Raman spectroscopy in addition to optical conductivity measurements. It was found that β″-(BEDT-TTF)(TCNQ) changes continuously from a uniform metal to a chargeordered metal with increasing temperature. Although charge disproportionation was clearly observed, long-range charge order is not realized. Among six θ-type salts, four compounds with a narrow band show the metal-insulator transition. However, they maintain a large amplitude of charge order (Δρ~0.6) in both metallic and insulating phases. In the X = CsZn(SCN) 4 salt with intermediate bandwidth, the amplitude of charge order is very small (Δρ < 0.07) over the whole temperature range. However, fluctuation of charge order is indicated in the Raman spectrum and optical conductivity. No indication of the fluctuation of charge order is found in the wide band X = I 3 salt. In α-(BEDT-TTF) 2 I 3 the amplitude of charge order changes discontinuously from small amplitude at high temperature to large amplitude (Δρ max~0 .6) at low temperature. The long-range chargeordered state shows ferroelectric polarization with fast optical response. The fluctuation of multiple stripes occurs in the high-temperature metallic phase. Among α-(BEDT-TTF) 2 MHg(SCN) 4 (X = NH 4 , K, Rb, Tl), the fluctuation of charge order is indicated only in the X = NH 4 salt. α′-(BEDT-TTF) 2 IBr 2 shows successive phase transitions to the ferroelectric state keeping a large amplitude of charge order (Δρ max~0 .8) over the whole temperature range. It was found that the amplitude and fluctuation of charge order in these compounds is enhanced as the kinetic energy (bandwidth) decreases. OPEN ACCESSCrystals 2012, 2 1292

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Section: Introductionmentioning

confidence: 99%

Infrared and Raman Studies of Charge Ordering in Organic Conductors, BEDT-TTF Salts with Quarter-Filled Bands

Yakushi

2012

Crystals

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“…Several recent optical studies have reported ω 2 and T 2 for M 2 (ω) in a number of different materials. However, in neither of these cases does the coefficient p match the prediction p = 2: p ∼ 1 in URu 2 Si 2 [16], p ∼ 2.4 in the organic material BEDT-TTF [28], and p ∼ 1.5 in underdoped HgBa 2 CuO 4+δ [17]. One possible scenario that has been proposed to explain this discrepancy is the presence of magnetic impurities [13].…”

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Optical Response ofSr2RuO4Reveals Universal Fermi-Liquid Scaling and Quasiparticles Beyond Landau Theory

et al. 2014

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We report optical measurements demonstrating that the low-energy relaxation rate (1/τ) of the conduction electrons in Sr 2 RuO 4 obeys scaling relations for its frequency (ω) and temperature (T ) dependence in accordance with Fermi-liquid theory. In the thermal relaxation regime, 1/τ ∝ (ħ hω) 2 + (pπk B T ) 2 with p = 2, and ω/T scaling applies. Many-body electronic structure calculations using dynamical mean-field theory confirm the low-energy Fermi-liquid scaling, and provide quantitative understanding of the deviations from Fermi-liquid behavior at higher energy and temperature. The excess optical spectral weight in this regime provides evidence for strongly dispersing "resilient" quasiparticle excitations above the Fermi energy. PACS numbers: 78.47.db, 71.10.Ay, 72.15.Lh, 74.70.Pq Liquids of interacting fermions yield a number of different emergent states of quantum matter. The strong correlations between their constituent particles pose a formidable theoretical challenge. It is therefore remarkable that a simple description of low-energy excitations of fermionic quantum liquids could be established early on by Landau [1], in terms of a dilute gas of "quasiparticles" with a renormalized effective mass, of which 3 He is the best documented case [2, 3].Breakdown of the quasiparticle concept can be observed in the transport of metals tuned onto a quantum phase transition, but Fermi-liquid (FL) behavior is retrieved away from the quantum-critical region [4, 5]. The relevance of FL theory to electrons in solids is documented by a number of materials, such as transition metals [6], heavy-fermion compounds [7], and doped semiconductors [8]. Among transition-metal oxides, Sr 2 RuO 4 is a remarkable example which has been heralded as the solid-state analogue of 3 He [9] for at least three reasons: remarkably large and clean monocrystalline samples can be prepared, transport properties display low-temperature FL characteristics [10], and there is evidence for p-wave symmetry of its superconducting phase [11], as in superfluid 3 He.FL theory makes a specific prediction for the universal energy and temperature dependence of the inelastic lifetime of quasiparticles: Because of phase-space constraints imposed by the Pauli principle as well as momentum and energy conservation, it diverges as 1/ω 2 or 1/T 2 [1, 5]. More precisely, the inelastic optical relaxation rate is predicted to vanish according to the scaling law 1/τ ∝ (ħ hω) 2 + (pπk B T ) 2 , with p = 2 [12][13][14]. This leads to universal ω/T scaling of the optical conductivity σ(ω) in the thermal regime ħ hω ∼ k B T [14]. Surprisingly however, despite almost 60 years of research on Fermi liquids, this universal behavior of the optical response, and especially the specific statistical factor p = 2 relating the energy and temperature dependence have not yet been established experimentally [13][14][15][16][17].Here, we report optical measurements of Sr 2 RuO 4 with 0.1 meV resolution [18,19] which reveal this universal FL scaling law [20]. We establish experiment...

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“…Already in a two-fluid picture of a nodal Fermi liquid in parallel to an antinodal liquid, nonuniversal features (for Fermi liquids) are introduced in the optical conductivity, because the properties at the Fermi surface change gradually from Fermi liquid at the nodes (30) to strongly incoherent and pseudogapped at the hot spots near the antinodes (31). In fact, also in other compounds p is found to be different from 2 (32)(33)(34). Recently, Maslov and Chubukov interpreted this as a combination of Fermi liquid scattering and an additional source of elastic scattering from magnetic moments or resonant levels (35).…”

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Spectroscopic evidence for Fermi liquid-like energy and temperature dependence of the relaxation rate in the pseudogap phase of the cuprates

Mirzaei

Stricker

Hancock

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

131

161

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Cuprate high-T c superconductors exhibit enigmatic behavior in the nonsuperconducting state. For carrier concentrations near "optimal doping" (with respect to the highest T c s) the transport and spectroscopic properties are unlike those of a Landau-Fermi liquid. On the Mott-insulating side of the optimal carrier concentration, which corresponds to underdoping, a pseudogap removes quasiparticle spectral weight from parts of the Fermi surface and causes a breakup of the Fermi surface into disconnected nodal and antinodal sectors. Here, we show that the near-nodal excitations of underdoped cuprates obey Fermi liquid behavior. The lifetime τ(ω, T) of a quasi-particle depends on its energy ω as well as on the temperature T. For a Fermi liquid, 1/τ(ω, T) is expected to collapse on a universal function proportional to (h ω) 2 + (pπk B T) 2 . Magnetotransport experiments, which probe the properties in the limit ω = 0, have provided indications for the presence of a T 2 dependence of the dc (ω = 0) resistivity of different cuprate materials. However, Fermi liquid behavior is very much about the energy dependence of the lifetime, and this can only be addressed by spectroscopic techniques. Our optical experiments confirm the aforementioned universal ω-and T dependence of 1/τ(ω, T), with p ∼ 1.5. Our data thus provide a piece of evidence in favor of a Fermi liquid-like scenario of the pseudogap phase of the cuprates.optical spectroscopy | superconductivity | mass renormalization | self energy T he compound HgBa 2 CuO 4+δ (Hg1201) is the single-layer cuprate that exhibits the highest T c (97 K). We therefore measured the optical conductivity of strongly underdoped single crystals of Hg1201 ðT c = 67 KÞ. Here we are interested in the optical conductivity of the CuO 2 layers. We therefore express the optical conductivity as a 2D sheet conductance GðωÞ = d c σðωÞ, where d c is the interlayer spacing. The real part of the sheet conductance normalized by the conduction quantum G 0 = 2e 2 =h is shown in Fig. 1. As seen in the figure, a gap-like suppression below 140 meV is clearly observable for temperatures below T c and remains visible in the normal state up to ∼250 K. This is a clear optical signature of the pseudogap. We also observe the zero-energy mode due to the free charge carrier response, which progressively narrows upon lowering the temperature. In materials where the charge carrier relaxation is dominated by impurity scattering, the width of this "Drude" peak corresponds to the relaxation rate of the charge carriers. Relaxation processes arising from interactions have the effect of replacing the constant (frequency-independent) relaxation rate with a frequencydependent one. The general expression for the optical conductivity of interacting electrons is then Gðω; TÞ = iπK Zω + Mðω; TÞ G 0 :[1]The spectral weight K corresponds to minus the kinetic energy if the frequency integration of the experimental data is restricted to intraband transitions. The effect of electron-electron interactions and coupling to collective mo...

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Quantum criticality in organic conductors? Fermi liquid versus non-Fermi-liquid behaviour

Cited by 63 publications

References 166 publications

Infrared and Raman Studies of Charge Ordering in Organic Conductors, BEDT-TTF Salts with Quarter-Filled Bands

Infrared and Raman Studies of Charge Ordering in Organic Conductors, BEDT-TTF Salts with Quarter-Filled Bands

Optical Response ofSr2RuO4Reveals Universal Fermi-Liquid Scaling and Quasiparticles Beyond Landau Theory

Spectroscopic evidence for Fermi liquid-like energy and temperature dependence of the relaxation rate in the pseudogap phase of the cuprates

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