Nernst Effect in Poor Conductors and in the Cuprate Superconductors

Alexandrov, A. S.; Zavaritsky, V. N.

doi:10.1103/physrevlett.93.217002

Cited by 41 publications

(57 citation statements)

References 40 publications

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“…In particular, the bipolaron theory accounts for the anomalously large Nernst signal, the thermopower and the insulating-like in-plane low temperature resistance [47,48] as observed [51,64,65,66].…”

Section: Some Normal State Properties Of Cuprates In Fcm a Normmentioning

confidence: 95%

“…Our CTQMC simulations show that with realistic values for the coupling constant, λ ≃ 1, and phonon frequencies, ω ≃ T (a) one can avoid overlap of pairs and get the bose-condensation temperature T c about the room temperature. We believe that the following recipe is worth investigating to look for room-temperature superconductivity [33]: There are strong arguments in favor of 3D bipolaronic BEC in cuprates [3] drawn using parameter-free fitting of experimental T c with BEC T c [41], unusual upper critical fields [42] and the specific heat [43], and, more recently normal state diamagnetism [44], the HallLorenz numbers [45,46], the normal state Nernst effect [47,48], and the giant proximity effect (GPE) [49] as discussed below.…”

Section: And the Mass Renormalization Exponents As Gmentioning

confidence: 99%

“…(15,16) can account for a low value of S tan Θ compared with a large value of e y in some underdoped cuprates [51,65] due to the sign anomaly. Even in the case when localised bosons contribute little to the conductivity their contribution to the thermopower S = ρ(α ext xx − |α l xx |)) could almost cancel the opposite sign contribution of itinerant carriers [47]. Indeed the longitudinal conductivity of itinerant two-dimensional to Fermi statistics with lowering energy across the mobility edge because of the Coulomb repulsion of bosons in localised states [72].…”

Section: Some Normal State Properties Of Cuprates In Fcm a Normmentioning

confidence: 99%

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Bose–Einstein condensation of strongly correlated electrons and phonons in cuprate superconductors

Alexandrov

2007

J. Phys.: Condens. Matter

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Section: Some Normal State Properties Of Cuprates In Fcm a Normmentioning

confidence: 95%

Section: And the Mass Renormalization Exponents As Gmentioning

confidence: 99%

Section: Some Normal State Properties Of Cuprates In Fcm a Normmentioning

confidence: 99%

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Bose–Einstein condensation of strongly correlated electrons and phonons in cuprate superconductors

Alexandrov

2007

J. Phys.: Condens. Matter

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“…(Further, a recent calculation [83] has shown that the qp Nernst signal in the dDW state is actually too small to account for the observed e N .) Finally, in a proposed "bipolaron" model, even the Nernst signal observed below T c has been identified as coming from ("localized") quasiparticles [38]. The extreme view is proposed that H m represents the depairing field [65], so that the condensate is destroyed as soon as ρ becomes non-zero.…”

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%

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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Superconducting Polarons and Bipolarons

Alexandrov¹

2007

Springer Series in Materials Science

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The seminal work by Bardeen, Cooper and Schrieffer (BCS) extended further by Eliashberg to the intermediate coupling regime solved one of the major scientific problems of Condensed Matter Physics in the last century. The BCS theory provides qualitative and in many cases quantitative descriptions of low-temperature superconducting metals and their alloys, and some novel high-temperature superconductors like magnesium diboride. The theory has been extended by us to the strong-coupling regime where carriers are small lattice polarons and bipolarons. Here I review the multi-polaron strong-coupling theory of superconductivity. Attractive electron correlations, prerequisite to any superconductivity, are caused by an almost unretarded electron-phonon (e-ph) interaction sufficient to overcome the direct Coulomb repulsion in this regime. Low energy physics is that of small polarons and bipolarons, which are real-space electron (hole) pairs dressed by phonons. They are itinerant quasiparticles existing in the Bloch states at temperatures below the characteristic phonon frequency. Since there is almost no retardation (i.e. no Tolmachev-Morel-Anderson logarithm) reducing the Coulomb repulsion, e-ph interactions should be relatively strong to overcome the direct Coulomb repulsion, so carriers must be polaronic to form pairs in novel superconductors. I identify the long-range Fröhlich electron-phonon interaction as the most essential for pairing in superconducting cuprates. A number of key observations have been predicted or explained with polarons and bipolarons including unusual isotope effects and upper critical fields, normal state (pseudo)gaps and kinetic properties, normal state diamagnetism, and giant proximity effects. These and many other observations provide strong evidence for a novel state of electronic matter in layered cuprates, which is a charged Bose-liquid of small mobile bipolarons.

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Nernst Effect in Poor Conductors and in the Cuprate Superconductors

Cited by 41 publications

References 40 publications

Bose–Einstein condensation of strongly correlated electrons and phonons in cuprate superconductors

Bose–Einstein condensation of strongly correlated electrons and phonons in cuprate superconductors

Nernst effect in high-Tcsuperconductors

Superconducting Polarons and Bipolarons

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