Electromagnetic properties of viscous charged fluids

Forcella, Davide; Zaanen, Jan; Valentinis, Davide; Marel, D. van der

doi:10.1103/physrevb.90.035143

Cited by 69 publications

(121 citation statements)

References 35 publications

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“…We also note that the agreement is markedly better than the one achieved previously using measurements of ν in the vicinity geometry 12 , and even accommodates the fact that both experimental and theoretical curves in Fig. 3e (inset) deviate from the 1/T 2 dependence expected for the normal Fermi liquid 6,30 . The deviations arise because temperatures ∼50-100 K are not insignificant with respect to the Fermi energy.…”

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confidence: 45%

Superballistic flow of viscous electron fluid through graphene constrictions

et al. 2017

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Electron-electron (e-e) collisions can impact transport in a variety of surprising and sometimes counterintuitive ways 1-6 . Despite strong interest, experiments on the subject proved challenging because of the simultaneous presence of di erent scattering mechanisms that suppress or obscure consequences of e-e scattering 7-11 . Only recently, su ciently clean electron systems with transport dominated by e-e collisions have become available, showing behaviour characteristic of highly viscous fluids 12-14 . Here we study electron transport through graphene constrictions and show that their conductance below 150 K increases with increasing temperature, in stark contrast to the metallic character of doped graphene 15 . Notably, the measured conductance exceeds the maximum conductance possible for free electrons 16,17 . This anomalous behaviour is attributed to collective movement of interacting electrons, which 'shields' individual carriers from momentum loss at sample boundaries 18,19 . The measurements allow us to identify the conductance contribution arising due to electron viscosity and determine its temperature dependence. Besides fundamental interest, our work shows that viscous e ects can facilitate high-mobility transport at elevated temperatures, a potentially useful behaviour for designing graphene-based devices.Graphene hosts a high-quality electron system with weak phonon coupling 20,21 such that e-e collisions can become the dominant scattering process at elevated temperatures, T . In addition, the electronic structure of graphene inhibits Umklapp processes 15 , which ensures that e-e scattering is momentum conserving. These features lead to a fluid-like behaviour of charge carriers, with the momentum taking on the role of a collective variable that governs local equilibrium. Previous studies of the electron hydrodynamics in graphene were carried out using the vicinity geometry and Hall bar devices of a uniform width. Anomalous (negative) voltages were observed, indicating a highly viscous flow, more viscous than that of honey 12,22,23 . In this report, we employ a narrow constriction geometry (Fig. 1a) which offers unique insight into the behaviour of viscous electron fluids. In particular, the hydrodynamic conductance through such constrictions becomes

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confidence: 45%

Superballistic flow of viscous electron fluid through graphene constrictions

et al. 2017

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“…Forcella, Zaanen, Valentinis, and van Der Marel [74] considered electromagnetic properties of viscous charged fluids, finding signatures due to the viscosity such as negative refraction, a frequency-dependent peak in the reflection coefficient, and a strong frequency dependence of the phase. However, they note that these effects may be difficult to observe for viscosities of the order of n .…”

Section: Experimental Determination Of η In Electronic Systemsmentioning

confidence: 99%

Shear viscosity of strongly interacting fermionic quantum fluids

Pakhira

McKenzie

2015

Phys. Rev. B

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Eighty years ago, Eyring proposed that the shear viscosity of a liquid η has a quantum limit η n where n is the density of the fluid. Using holographic duality and the anti-de Sitter/conformal field theory correspondence in string theory, Kovtun, Son, and Starinets (KSS) conjectured a universal bound η s 4πk B for the ratio between the shear viscosity and the entropy density s. Using dynamical mean-field theory, we calculate the shear viscosity and entropy density for a fermionic fluid described by a single-band Hubbard model at half-filling. Our calculated shear viscosity as a function of temperature is compared with experimental data for liquid 3 He. At low temperature, the shear viscosity is found to be well above the quantum limit and is proportional to the characteristic Fermi liquid 1/T 2 dependence, where T is the temperature. With increasing temperature and interaction strength U , there is significant deviation from the Fermi liquid form. Also, the shear viscosity violates the quantum limit near the crossover from coherent quasiparticle-based transport to incoherent transport (the bad metal regime). Finally, the ratio of the shear viscosity to the entropy density is found to be comparable to the KSS bound for parameters appropriate to liquid 3 He. However, this bound is found to be strongly violated in the bad metal regime for parameters appropriate to lattice electronic systems such as organic charge-transfer salts.

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“…Fast momentum relaxation gives the familiar Ohm's law with current locally proportional to the electric field. In the interaction-dominated regime, when particles exchange their momenta at the rates much faster than the disorder collision rates, electrons move in a neatly coordinated way, in many ways resembling the flow of viscous fluids [5][6][7][8][9][10][11][12][13][14][15]. The current-field relation changes drastically in this case [16].…”

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confidence: 99%

Linking Spatial Distributions of Potential and Current in Viscous Electronics

2017

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Viscous electronics is an emerging field dealing with systems in which strongly interacting electrons behave as a fluid. Electron viscous flows are governed by a nonlocal current-field relation which renders the spatial patterns of the current and electric field strikingly dissimilar. Notably, driven by the viscous friction force from adjacent layers, current can flow against the electric field, generating negative resistance, vorticity, and vortices. Moreover, different current flows can result in identical potential distributions. This sets a new situation where inferring the electron flow pattern from the measured potentials presents a nontrivial problem. Using the inherent relation between these patterns through complex analysis, here we propose a method for extracting the current flows from potential distributions measured in the presence of a magnetic field. DOI: 10.1103/PhysRevLett.119.066601 For electron transport in conductors, one can outline two broadly defined scenarios depending on the relative strength of disorder and interactions [1][2][3][4]. In the disorderdominated regime one finds "individualist" behavior of electrons moving in straight lines like pinballs bouncing among impurities. Fast momentum relaxation gives the familiar Ohm's law with current locally proportional to the electric field. In the interaction-dominated regime, when particles exchange their momenta at the rates much faster than the disorder collision rates, electrons move in a neatly coordinated way, in many ways resembling the flow of viscous fluids [5][6][7][8][9][10][11][12][13][14][15]. The current-field relation changes drastically in this case [16].Signatures of viscous flows have been observed in ultraclean GaAs, graphene, and PdCoO 2 [17][18][19][20]. Graphene, in particular, is well suited for studying electron viscosity since low disorder and weak electron-lattice coupling render momentum-conserving two-body (e-e) collisions dominant in a wide range of carrier densities and temperatures. In contrast, momentum-nonconserving umklapp e-e processes are forbidden because of graphene crystal symmetry. Gatetunable and temperature-dependent collision rates help to realize the ballistic and viscous regime in a single sample.Current in an electron fluid is locally proportional to momentum density, but its relation to the electric field is nonlocal since the viscous force is proportional to the velocity Laplacian. As a result, the electric field and current can be quite different vector fields. Unraveling the relation between them is one of the challenges of viscous electronics. In particular, one needs to find ways to reconstruct currents from the potentials, measurable by a variety of experimental techniques. As we will see, while the resulting integral relations are nontrivial, in two dimensions they can be tackled using a powerful framework of complex analysis. This provides a direct link between measured potentials and the current flow patterns.We will see that the currents depend not only on the potentials but also, in...

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Electromagnetic properties of viscous charged fluids

Cited by 69 publications

References 35 publications

Superballistic flow of viscous electron fluid through graphene constrictions

Superballistic flow of viscous electron fluid through graphene constrictions

Shear viscosity of strongly interacting fermionic quantum fluids

Linking Spatial Distributions of Potential and Current in Viscous Electronics

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