Impurity effects in unconventional density waves in the unitary limit

Dóra, Balázs; Virosztek, Attila; Maki, Kazumi

doi:10.1103/physrevb.68.075104

Cited by 14 publications

(32 citation statements)

References 35 publications

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“…It has been argued [34] that, if strong antiferromagnetic fluctuations exist in a Fermi liquid, vertex corrections cause the qp current J k to deviate from being normal to the Fermi Surface, and a consequent enhancement of ν. Also, an enhanced qp ν is purportedly obtained in an unconventional d density-wave (dDW) model [35], as well as from paired holes in "anti-phase" domains in an antiferromagnetic state [37].…”

Section: Discussionmentioning

confidence: 99%

“…Nonetheless, acceptance of a vortex origin for e N above T c is by no means unanimous; several models interpreting the Nernst results strictly in terms of quasiparticles have appeared [34,35,36,37,38]. The difficulties may arise because the Nernst experiment is a relatively unfamiliar probe of superconductivity, with a checkered theoretical history [39,40,41,42].…”

Section: Introductionmentioning

confidence: 99%

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Nernst effect in high-Tcsuperconductors

2006

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The observation of a large Nernst signal eN in an extended region above the critical temperature Tc in hole-doped cuprates provides evidence that vortex excitations survive above Tc. The results support the scenario that superfluidity vanishes because long-range phase coherence is destroyed by thermally-created vortices (in zero field), and that the pair condensate extends high into the pseudogap state in the underdoped (UD) regime. We present a series of measurements to high fields H which provide strong evidence for this phase-disordering scenario. Measurements of eN in fields H up to 45 T reveal that the vortex Nernst signal has a characteristic "tilted-hill" profile, which is qualitatively distinct from that of quasi-particles. The hill profile, which is observed above and below Tc, underscores the continuity between the vortex-liquid state below Tc and the Nernst region above Tc. The upper critical field (depairing field) Hc2 determined by the hill profile (in slightly UD to overdoped samples) displays an anomalously weak T dependence, which is consistent with the phase-disordering scenario. We contrast the Nernst results and Hc2 behavior in hole-doped and electron-doped cuprates. Contour plots of eN (T, H) in the T -H plane clearly bring out the continuous extension of the low-T vortex liquid state into the the high-T Nernst region in holedoped cuprates (but not in the electron-doped cuprate). The existence of an enhanced diamagnetic magnetization M that survives to intense H above Tc is obtained from torque magnetometry. The observed M scales accurately like eN above Tc, confirming that the large Nernst signal is associated with local diamagnetic supercurrents that persist above Tc. We emphasize implications of the new features in the phase diagram implied by the high-field results, and discuss several theories.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Nernst effect in high-Tcsuperconductors

2006

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“…Here we have assumed d-wave DW as in high c T cuprates [9][10][11]. Around the nodal points, it is convenient to replace 2 2 cos (2 ) D f by 2 2 v k^, where [18].…”

Section: Quasiparticle Spectrum: the Nersesyan Effectmentioning

confidence: 99%

Unconventional density wave as possible explanation of the Nernst signal in CeCoIn₅

Dóra

Maki

Virosztek

et al. 2005

Physica Status Solidi (b)

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Recently large Nernst effect and Seebeck effect were observed above the superconducting transition temperature 2 3. K in a heavy fermion superconductor CeCoIn 5 . We interpret this large Nernst effect in terms of unconventional density wave (UDW), which appears around 18 T = K. In the presence of magnetic field, Landau levels are formed in UDW, and the transport is dominated by thermally excited quasiparticles across the levels. Our theory describes successfully the available experimental data, and the deduced fitting parameters are in accordance with what is expected in the vicinity of a quantum critical point.

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“…In addition to the high T c cuprates [17], there are reports of large Nernst effects in another organic charge transfer salt α-(BEDT-TTF) 2 KHg(SCN) 4 [23,24], and in inorganic materials such as NbSe 2 [25] and CeCoIn 5 [26], all well removed from superconducting phases. Both α-(BEDT-TTF) 2 KHg(SCN) 4 and NbSe 2 undergo a density wave transition at 8 K and 32 K respectively.…”

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Resonant Nernst Effect in the Metallic and Field-Induced Spin Density Wave States of(TMTSF)2ClO4

et al. 2005

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We examine an unusual phenomenon where, in tilted magnetic fields near magic angles parallel to crystallographic planes, a "giant" resonant Nernst signal has been observed by Wu et al.[Phys. Rev. Lett. 91 56601(2003)] in the metallic state of an organic conducting Bechgaard salt. We show that this effect appears to be a general feature of these materials, and is also present in the field induced spin density wave phase with even larger amplitude. Our results place new restrictions on models that treat the metallic state as an unconventional density wave or as a state with finite Cooper pairing.PACS Numbers (72.15.Jf, 72.15.Gd, 75.30.Fv) 2 The Bechgaard salts, (TMTSF) 2 X (X=PF 6 , ClO 4 , AsF 6 , ReO 4 ,…) continue to attract attention due to the proximity of novel ground states including antiferromagnetic spin density waves (SDW), unconventional superconducting (SC) and metallic states, and magnetic field induced spin density wave (FISDW) states [1,2]. Recently, arguments have been made for the coexistence of the SDW, SC, and metallic states along phase boundaries [3][4][5], for the possibility that the metallic state is an unconventional SDW phase [6], and even for the survival of p-wave Cooper pairing in the metallic state [7].Most studied are (TMTSF) 2 PF 6 (under pressure to remove the ambient pressure SDW phase) and (TMTSF) 2 ClO 4 . These materials are quasi-one-dimensional (Q1D) organic conductors with transfer integrals of order 250, 25, and 0.25 meV for the a, b, and c axis directions respectively. In the SC state, evidence for p-wave pairing exists since the critical field H c2 exceeds the Pauli limit when the field is aligned parallel to the molecular planes [8,9] [12,13]. Here the field is aligned along crystal planes composed of the a-axis and integer combinations of the b and c unit cell parameters. Above a threshold field H th , the FISDW state (with a cascade of subphases) is stabilized due to the quantized nesting of the Q1D Fermi surface [1,15]. Unlike the tan(θ) dependence, the threshold and subphases in the FISDW phase are driven by the field component perpendicular to the conducting ab planes, i.e. the "cosine law" H ⊥ =H cos(θ).In this Letter we examine the longitudinal (Seebeck or TEP) and transverse (Nernst) thermoelectric effects in the metallic and FISDW phases in (TMTSF) 2 ClO 4 (hereafter ClO 4 ). The Nernst effect, an analogue of the Hall effect, is the transverse voltage induced by a temperature gradient in a magnetic field. It has been studied in cuprates due to its sensitivity to the vortex state, where large Nernst signal can be induced by phase slip 3 [16,17]. On the other hand, quasi particles in normal Fermi liquids with one type of charge carriers are known to generate very small Nernst effect because of so called the "Sondheimer cancellation" [18,19]. When more than two types of carriers are involved, the cancellation is not perfect and the Nernst effect can be finite with an order of (e/k B )(T/T F )(ω c τ) where k B T F is the Fermi energy, ω c is the cyclotron...

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Impurity effects in unconventional density waves in the unitary limit

Cited by 14 publications

References 35 publications

Nernst effect in high-Tcsuperconductors

Nernst effect in high-Tcsuperconductors

Unconventional density wave as possible explanation of the Nernst signal in CeCoIn₅

Resonant Nernst Effect in the Metallic and Field-Induced Spin Density Wave States of(TMTSF)2ClO4

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Impurity effects in unconventional density waves in the unitary limit

Cited by 14 publications

References 35 publications

Nernst effect in high-Tcsuperconductors

Nernst effect in high-Tcsuperconductors

Unconventional density wave as possible explanation of the Nernst signal in CeCoIn5

Resonant Nernst Effect in the Metallic and Field-Induced Spin Density Wave States of(TMTSF)2ClO4

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Product

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Unconventional density wave as possible explanation of the Nernst signal in CeCoIn₅