14 research outputs found
Fermi-surface transformation across the pseudogap critical point of the cuprate superconductor LaNdSrCuO
The electrical resistivity and Hall coefficient R of the
tetragonal single-layer cuprate Nd-LSCO were measured in magnetic fields up to
T, large enough to access the normal state at , for closely
spaced dopings across the pseudogap critical point at .
Below , both coefficients exhibit an upturn at low temperature, which
gets more pronounced with decreasing . Taken together, these upturns show
that the normal-state carrier density at drops upon entering the
pseudogap phase. Quantitatively, it goes from at to at . By contrast, the mobility does not change appreciably, as
revealed by the magneto-resistance. The transition has a width in doping and
some internal structure, whereby R responds more slowly than to the
opening of the pseudogap. We attribute this difference to a Fermi surface that
supports both hole-like and electron-like carriers in the interval , with compensating contributions to R. Our data are in excellent
agreement with recent high-field data on YBCO and LSCO. The quantitative
consistency across three different cuprates shows that a drop in carrier
density from to is a universal signature of the pseudogap
transition at . We discuss the implication of these findings for the
nature of the pseudogap phase.Comment: 11 pages, 12 figure
Hall, Seebeck, and Nernst Coefficients of Underdoped HgBa2CuO4+d: Fermi-Surface Reconstruction in an Archetypal Cuprate Superconductor
Charge density-wave order has been observed in cuprate superconductors whose
crystal structure breaks the square symmetry of the CuO2 planes, such as
orthorhombic YBa2Cu3Oy (YBCO), but not so far in cuprates that preserve that
symmetry, such as tetragonal HgBa2CuO4+d (Hg1201). We have measured the Hall
(R_H), Seebeck (S), and Nernst coefficients of underdoped Hg1201 in magnetic
fields large enough to suppress superconductivity. The high-field R_H(T) and
S(T) are found to drop with decreasing temperature and become negative, as also
observed in YBCO at comparable doping. In YBCO, the negative R_H and S are
signatures of a small electron pocket caused by Fermi-surface reconstruction,
attributed to charge density-wave modulations observed in the same range of
doping and temperature. We deduce that a similar Fermi-surface reconstruction
takes place in Hg1201, evidence that density-wave order exists in this
material. A striking similarity is also found in the normal-state Nernst
coefficient, further supporting this interpretation. Given the model nature of
Hg1201, Fermi-surface reconstruction appears to be common to all hole-doped
cuprates, suggesting that density-wave order is a fundamental property of these
materials
Nernst Effect of stripe ordering LaEuSrCuO
We investigate the transport properties of
LaEuSrCuO (, 0.08, 0.125, 0.15, 0.2) with a
special focus on the Nernst effect in the normal state. Various anomalous
features are present in the data. For and 0.15 a kink-like anomaly is
present in the vicinity of the onset of charge stripe order in the LTT phase,
suggestive of enhanced positive quasiparticle Nernst response in the stripe
ordered phase. At higher temperature, all doping levels except exhibit
a further kink anomaly in the LTO phase which cannot unambiguously be related
to stripe order. Moreover, a direct comparison between the Nernst coefficients
of stripe ordering LaEuSrCuO and superconducting
LaSrCuO at the doping levels and reveals
only weak differences. Our findings make high demands on any scenario
interpreting the Nernst response in hole-doped cuprates
Direct measurement of the upper critical field in a cuprate superconductor
The upper critical field Hc2 is a fundamental measure of the pairing
strength, yet there is no agreement on its magnitude and doping dependence in
cuprate superconductors. We have used thermal conductivity as a direct probe of
Hc2 in the cuprates YBa2Cu3Oy and YBa2Cu4O8 to show that there is no vortex
liquid at T = 0, allowing us to use high-field resistivity measurements to map
out the doping dependence of Hc2 across the phase diagram. Hc2(p) exhibits two
peaks, each located at a critical point where the Fermi surface undergoes a
transformation. The condensation energy obtained directly from Hc2, and
previous Hc1 data, undergoes a 20-fold collapse below the higher critical
point. These data provide quantitative information on the impact of competing
phases in suppressing superconductivity in cuprates.Comment: to appear in Nature Communications; Supplementary Information file
available upon reques
Superconducting Fluctuation investigated by THz Conductivity of LaSrCuO Thin Films
Frequency-dependent terahertz conductivities of LaSrCuO thin
films with various carrier concentrations were investigated. The imaginary part
of the complex conductivity considerably increased from far above a
zero-resistance superconducting transition temperature,
, because of the existence of the fluctuating
superfluid density with a short lifetime. The onset temperature of the
superconducting fluctuation is at most for
underdoped samples, which is consistent with the previously reported analysis
of microwave conductivity. The superconducting fluctuation was not enhanced
under a 0.5 T magnetic field. We also found that the temperature dependence of
the superconducting fluctuation was sensitive to the carrier concentration of
LaSrCuO, which reflects the difference in the nature of the
critical dynamics near the superconducting transition temperature. Our results
suggest that the onset temperature of the Nernst signal is not related to the
superconducting fluctuation we argued in this paper.Comment: J. Phys. Soc. Jpn. in pres
Pseudogap temperature T* of cuprate superconductors from the Nernst effect
International audienceWe use the Nernst effect to delineate the boundary of the pseudogap phase in the temperature-doping phase diagram of hole-doped cuprate superconductors. New data for the Nernst coefficient nu(T) of YBa2Cu3Oy (YBCO), La1.8-xEu0.2SrxCuO4 (Eu-LSCO), and La1.6-xNd0.4SrxCuO4 (Nd-LSCO) are presented and compared with previously published data on YBCO, Eu-LSCO, Nd-LSCO, and La2-xSrxCuO4 (LSCO). The temperature T-nu at which nu/T deviates from its high-temperature linear behavior is found to coincide with the temperature at which the resistivity rho(T) deviates from its linear-T dependence, which we take as the definition of the pseudogap temperature T-star-in agreementwith the temperature at which the antinodal spectral gap detected in angle-resolved photoemission spectroscopy (ARPES) opens. We track T-star as a function of doping and find that it decreases linearly vs p in all four materials, having the same value in the three LSCO-based cuprates, irrespective of their different crystal structures. At low p, T-star is higher than the onset temperature of the various orders observed in underdoped cuprates, suggesting that these orders are secondary instabilities of the pseudogap phase. A linear extrapolation of T-star(p) to p = 0 yields T-star(p -> 0) similar or equal to T-N(0), the Neel temperature for the onset of antiferromagnetic order at p = 0, suggesting that there is a link between pseudogap and antiferromagnetism. With increasing p, T-star(p) extrapolates linearly to zero at p similar or equal to p(c2,) the critical doping belowwhich superconductivity emerges at high doping, suggesting that the conditions which favor pseudogap formation also favor pairing. We also use the Nernst effect to investigate how far superconducting fluctuations extend above the critical temperature T-c, as a function of doping, and find that a narrow fluctuation regime tracks T-c, and not T-star. This confirms that the pseudogap phase is not a form of precursor superconductivity, and fluctuations in the phase of the superconducting order parameter are not what causes T-c to fall on the underdoped side of the T-c dome
Onset field for Fermi-surface reconstruction in the cuprate superconductor YBa 2 Cu 3 O
20 pages and 5 figures in Main text + 9 pages and 6 figures in Supplementary materialQuantum oscillations and negative Hall and Seebeck coefficients at low temperature and high magnetic field have shown the Fermi surface of underdoped cuprates to contain a small closed electron pocket. It is thought to result from a reconstruction by charge order, but whether it is the order seen by NMR and ultrasound above a threshold field or the short-range modulations seen by X-ray diffraction in zero field is unclear. Here we use measurements of the thermal Hall conductivity in YBCO to show that Fermi-surface reconstruction occurs only above a sharply defined onset field, equal to the transition field seen in ultrasound. This reveals that electrons do not experience long-range broken translational symmetry in the zero-field ground state, and hence in zero field there is no quantum critical point for the onset of charge order as a function of doping