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ABSTRACT: Close to optimal doping, the copper oxide superconductors show 'strange metal' behaviour, suggestive of strong fluctuations associated with a quantum critical point. Such a critical point requires a line of classical phase transitions terminating at zero temperature near optimal doping inside the superconducting 'dome'. The underdoped region of the temperature-doping phase diagram from which superconductivity emerges is referred to as the 'pseudogap' because evidence exists for partial gapping of the conduction electrons, but so far there is no compelling thermodynamic evidence as to whether the pseudogap is a distinct phase or a continuous evolution of physical properties on cooling. Here we report that the pseudogap in YBa2Cu3O6+δ is a distinct phase, bounded by a line of phase transitions. The doping dependence of this line is such that it terminates at zero temperature inside the superconducting dome. From this we conclude that quantum criticality drives the strange metallic behaviour and therefore superconductivity in the copper oxide superconductors.
Nature 06/2013; 498(7452):75-7. · 36.28 Impact Factor
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ABSTRACT: Vortices in a type-II superconductor form a lattice structure that melts when
the thermal displacement of the vortices is an appreciable fraction of the
distance between vortices. In an anisotropic high-Tc superconductor, such as
YBa2Cu3Oy, the magnetic field value where this melting occurs can be much lower
than the mean-field critical field Hc2. We examine this melting transition in
YBa2Cu3Oy with oxygen content y from 6.45 to 6.92, and fit the data to a theory
of vortex-lattice melting. The quality of the fits indicates that the
transition to a resistive state is indeed the vortex lattice melting
transition, with the shape of the melting curves being consistent with the
known change in penetration depth anisotropy from underdoped to optimally doped
YBa2Cu3Oy. From the fits we extract Hc2(T = 0) as a function of hole doping.
The unusual doping dependence of Hc2(T =0) points to some form of electronic
order competing with superconductivity around 0.12 hole doping.
09/2012;
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[hide abstract]
ABSTRACT: The electrical resistivity rho_c of the underdoped cuprate superconductor
YBCO was measured perpendicular to the CuO_2 planes on ultra-high quality
single crystals in magnetic fields large enough to suppress superconductivity.
The incoherent insulating-like behavior of rho_c at high temperature,
characteristic of all underdoped cuprates, is found to cross over to a coherent
regime of metallic behavior at low temperature. This crossover coincides with
the emergence of the small electron pocket detected in the Fermi surface of
YBCO via quantum oscillations, the Hall and Seebeck coefficients and with the
detection of a unidirectional modulation of the charge density as seen by
high-field NMR measurements. The low coherence temperature is quantitatively
consistent with the small hopping integral t_perp inferred from the splitting
of the quantum oscillation frequencies. We conclude that the Fermi-surface
reconstruction in YBCO at dopings from p = 0.08 to at least p = 0.15,
attributed to stripe order, produces a metallic state with 3D coherence deep in
the underdoped regime.
07/2011;
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J Chang,
Nicolas Doiron-Leyraud,
Francis Laliberté,
R. Daou,
David LeBoeuf, B. J. Ramshaw,
Ruixing Liang,
D. A. Bonn,
W. N. Hardy,
Cyril Proust,
I. Sheikin,
K. Behnia,
Louis Taillefer
[show abstract]
[hide abstract]
ABSTRACT: The Nernst coefficient of the cuprate superconductor YBa2Cu3Oy was recently
shown to become strongly anisotropic within the basal plane when cooled below
the pseudogap temperature T*, revealing that the pseudogap phase breaks the
four-fold rotational symmetry of the CuO2 planes. Here we report on the
evolution of this Nernst anisotropy at low temperature, once superconductivity
is suppressed by a magnetic field. We find that the anisotropy drops rapidly
below 80 K, to vanish in the T=0 limit. We show that this loss of anisotropy is
due to the emergence of a small high-mobility electron-like pocket in the Fermi
surface at low temperature, a reconstruction attributed to a low-temperature
state that breaks the translational symmetry of the CuO2 planes. We discuss the
sequence of broken symmetries - first rotational, then translational - in terms
of an electronic nematic-to-smectic transition such as could arise when
unidirectional spin or charge modulations order. We compare YBa2Cu3Oy with
iron-pnictide superconductors where the process of (unidirectional)
antiferromagnetic ordering gives rises to the same sequence of broken
symmetries.
03/2011;
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F. Laliberte,
J Chang,
N. Doiron-Leyraud,
E. Hassinger,
R. Daou,
M. Rondeau, B. J. Ramshaw,
R Liang,
D. A. Bonn,
W. N. Hardy,
S. Pyon,
T Takayama,
H Takagi,
I. Sheikin,
L. Malone,
C. Proust,
K. Behnia,
L. Taillefer
[show abstract]
[hide abstract]
ABSTRACT: Quantum oscillations have revealed the presence of a small pocket in the
Fermi surface of the cuprate superconductor YBCO, whose nature and origin are
the subject of much debate. Interpretations include electron and hole pockets;
scenarios include Fermi-surface reconstruction by antiferromagnetism,
d-density-wave order, and stripe order. Here we report quantum oscillations in
the Seebeck and Nernst coefficients of YBCO and show, from the magnitude and
sign of the Seebeck coefficient, that they come from an electron pocket. Using
measurements of the Seebeck coefficient as a function of hole doping p, we show
that the evolution of the Fermi surface in YBCO is the same as in Eu-LSCO, a
cuprate where stripe order (a modulation of spin and charge densities) is well
established. The electron pocket is most prominent where stripe order is
strongest, at p = 1/8. This shows that Fermi-surface reconstruction is a
generic mechanism of underdoped cuprates, intimately related to stripe order.
02/2011;
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F Laliberté,
J Chang,
N Doiron-Leyraud,
E Hassinger,
R Daou,
M Rondeau, B J Ramshaw,
R Liang,
D A Bonn,
W N Hardy,
S Pyon,
T Takayama,
H Takagi,
I Sheikin,
L Malone,
C Proust,
K Behnia,
Louis Taillefer
[show abstract]
[hide abstract]
ABSTRACT: The origin of pairing in a superconductor resides in the underlying normal state. In the cuprate high-temperature superconductor YBa(2)Cu(3)O(y) (YBCO), application of a magnetic field to suppress superconductivity reveals a ground state that appears to break the translational symmetry of the lattice, pointing to some density-wave order. Here we use a comparative study of thermoelectric transport in the cuprates YBCO and La(1.8-x)Eu(0.2)Sr(x)CuO(4) (Eu-LSCO) to show that the two materials exhibit the same process of Fermi-surface reconstruction as a function of temperature and doping. The fact that in Eu-LSCO this reconstruction coexists with spin and charge modulations that break translational symmetry shows that stripe order is the generic non-superconducting ground state of hole-doped cuprates.
Nature Communications 01/2011; 2:432. · 7.40 Impact Factor
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J. S. Bobowski,
J. C. Baglo,
James Day,
P. Dosanjh,
Rinat Ofer, B. J. Ramshaw,
Ruixing Liang,
D. A. Bonn,
W. N. Hardy,
Huiqian Luo,
Zhao-Sheng Wang,
Lei Fang,
Hai-Hu Wen
[show abstract]
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ABSTRACT: We have studied the microwave electrodynamics of single crystal iron-based superconductors Ba$_{0.72}$K$_{0.28}$Fe$_2$As$_2$ (hole-doped, $T_\mathrm{c}$ $\approx $30 K) and Ba(Fe$_{0.95}$Co$_{0.05}$)$_2$As$_2$ (electron-doped, $T_\mathrm{c}$ $\approx$20 K), by cavity perturbation and broadband spectroscopy. SQUID magnetometry was used to confirm the quality and homogeneity of the samples under study. Through cavity perturbation techniques, the temperature dependence of the in-plane London penetration depth $\Delta\lambda(T)$, and therefore the superfluid phase stiffness $\lambda^2(0)/\lambda^2(T)$ was measured. Down to 0.4 K, the data do not show the exponential saturation at low temperatures expected from a singly-, fully-gapped superconductor. Rather, both the electron- and the hole-doped systems seem to be best described by a power law behavior, with $\lambda^2(0)/\lambda^2(T)$ $\sim$ $T^n$ and \emph{n} $\approx$ 2.5. In the three samples we studied, a weak feature near the sensitivity limit of our measurements appears near $T/T_\mathrm{c}$ =~0.04, hinting at a corresponding low energy feature in the superconducting density of states. The data can also be relatively well-described by a simple two-gap s-wave model of the order parameter, but this yields parameters which seem unrealistic and dependent on the fit range. Broadband surface resistance measurements reveal a sample dependent residual loss whose origin is unclear. The data from the \FeAs samples can be made to scale as $\omega^2$ if the extrinsic loss is treated as an additive component, indicating large scattering rates. Finally, the temperature dependence of the surface resistance at 13 GHz obeys a power law very similar to those observed for $\Delta\lambda(T)$. Comment: 11 pages, 11 figures, to be published in Phys. Rev. B
09/2010;
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David LeBoeuf,
Nicolas Doiron-Leyraud,
B. Vignolle,
Mike Sutherland, B. J. Ramshaw,
J. Levallois,
R. Daou,
Francis Laliberté,
Olivier Cyr-Choinière,
Johan Chang,
Y. J. Jo,
L. Balicas,
Ruixing Liang,
D. A. Bonn,
W. N. Hardy,
Cyril Proust,
Louis Taillefer
[show abstract]
[hide abstract]
ABSTRACT: The Hall coefficient R_H of the cuprate superconductor YBa2Cu3Oy was measured
in magnetic fields up to 60 T for a hole concentration p from 0.078 to 0.152,
in the underdoped regime. In fields large enough to suppress superconductivity,
R_H(T) is seen to go from positive at high temperature to negative at low
temperature, for p > 0.08. This change of sign is attributed to the emergence
of an electron pocket in the Fermi surface at low temperature. At p < 0.08, the
normal-state R_H(T) remains positive at all temperatures, increasing
monotonically as T \to 0. We attribute the change of behaviour across p = 0.08
to a Lifshitz transition, namely a change in Fermi-surface topology occurring
at a critical concentration p_L = 0.08, where the electron pocket vanishes. The
loss of the high-mobility electron pocket across p_L coincides with a ten-fold
drop in the conductivity at low temperature, revealed in measurements of the
electrical resistivity $\rho$ at high fields, showing that the so-called
metal-insulator crossover of cuprates is in fact driven by a Lifshitz
transition. It also coincides with a jump in the in-plane anisotropy of $\rho$,
showing that without its electron pocket the Fermi surface must have strong
two-fold in-plane anisotropy. These findings are consistent with a
Fermi-surface reconstruction caused by a unidirectional spin-density wave or
stripe order.
09/2010;
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[show abstract]
[hide abstract]
ABSTRACT: Measurements of quantum oscillations in the cuprate superconductors afford a new opportunity to assess the extent to which the electronic properties of these materials yield to a description rooted in Fermi liquid theory. However, such an analysis is hampered by the small number of oscillatory periods observed. Here we employ a genetic algorithm to globally model the field, angular, and temperature dependence of the quantum oscillations observed in the resistivity of YBa2Cu3O6.59. This approach successfully fits an entire data set to a Fermi surface comprised of two small, quasi-2-dimensional cylinders. A key feature of the data is the first identification of the effect of Zeeman splitting, which separates spin-up and spin-down contributions, indicating that the quasiparticles in the cuprates behave as nearly free spins, constraining the source of the Fermi surface reconstruction to something other than a conventional spin density wave with moments parallel to the CuO2 planes. Comment: 8 pages, 4 figures
04/2010;
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J Chang,
R Daou,
Cyril Proust,
David Leboeuf,
Nicolas Doiron-Leyraud,
Francis Laliberté,
B Pingault, B J Ramshaw,
Ruixing Liang,
D A Bonn,
W N Hardy,
H Takagi,
A B Antunes,
I Sheikin,
K Behnia,
Louis Taillefer
[show abstract]
[hide abstract]
ABSTRACT: The Seebeck and Nernst coefficients S and ν of the cuprate superconductor YBa2Cu3Oy (YBCO) were measured in a single crystal with doping p = 0.12 in magnetic fields up to H = 28 T. Down to T = 9 K, ν becomes independent of field by H 30 T, showing that superconducting fluctuations have become negligible. In this field-induced normal state, S/T and ν/T are both large and negative in the T → 0 limit, with the magnitude and sign of S/T consistent with the small electron-like Fermi surface pocket detected previously by quantum oscillations and the Hall effect. The change of sign in S(T) at T 50 K is remarkably similar to that observed in La2−xBaxCuO4, La2−x−yNdySrxCuO4 and La2−x−yEuySrxCuO4, where it is clearly associated with the onset of stripe order. We propose that a similar density-wave mechanism causes the Fermi surface reconstruction in YBCO.
03/2010;
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J Chang,
R Daou,
Cyril Proust,
David Leboeuf,
Nicolas Doiron-Leyraud,
Francis Laliberté,
B Pingault, B J Ramshaw,
Ruixing Liang,
D A Bonn,
W N Hardy,
H Takagi,
A B Antunes,
I Sheikin,
K Behnia,
Louis Taillefer
[show abstract]
[hide abstract]
ABSTRACT: The Seebeck and Nernst coefficients S and nu of the cuprate superconductor YBa{2}Cu{3}O{y} (YBCO) were measured in a single crystal with doping p=0.12 in magnetic fields up to H=28 T. Down to T=9 K, nu becomes independent of field by H approximately 30 T, showing that superconducting fluctuations have become negligible. In this field-induced normal state, S/T and nu/T are both large and negative in the T-->0 limit, with the magnitude and sign of S/T consistent with the small electronlike Fermi surface pocket detected previously by quantum oscillations and the Hall effect. The change of sign in S(T) at T approximately 50 K is remarkably similar to that observed in La2-xBaxCuO4, La{2-x-y}Nd{y}Sr_{x}CuO{4}, and La{2-x-y}Eu{y}Sr{x}CuO{4}, where it is clearly associated with the onset of stripe order. We propose that a similar density-wave mechanism causes the Fermi surface reconstruction in YBCO.
Physical Review Letters 02/2010; 104(5):057005. · 7.37 Impact Factor
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R Daou,
J Chang,
David Leboeuf,
Olivier Cyr-Choinière,
Francis Laliberté,
Nicolas Doiron-Leyraud, B J Ramshaw,
Ruixing Liang,
D A Bonn,
W N Hardy,
Louis Taillefer
[show abstract]
[hide abstract]
ABSTRACT: The nature of the pseudogap phase is a central problem in the effort to understand the high-transition-temperature (high-T(c)) copper oxide superconductors. A fundamental question is what symmetries are broken when the pseudogap phase sets in, which occurs when the temperature decreases below a value T*. There is evidence from measurements of both polarized neutron diffraction and the polar Kerr effect that time-reversal symmetry is broken, but at temperatures that differ significantly from one another. Broken rotational symmetry was detected from both resistivity measurements and inelastic neutron scattering at low doping, and from scanning tunnelling spectroscopy at low temperature, but showed no clear relation to T*. Here we report the observation of a large in-plane anisotropy of the Nernst effect in YBa(2)Cu(3)O(y) that sets in precisely at T* throughout the doping phase diagram. We show that the CuO chains of the orthorhombic lattice are not responsible for this anisotropy, which is therefore an intrinsic property of the CuO(2) planes. We conclude that the pseudogap phase is an electronic state that strongly breaks four-fold rotational symmetry. This narrows the range of possible states considerably, pointing to stripe or nematic order.
Nature 01/2010; 463(7280):519-22. · 36.28 Impact Factor
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R. Daou,
J Chang,
David LeBoeuf,
Olivier Cyr-Choiniere,
Francis Laliberte,
Nicolas Doiron-Leyraud, B. J. Ramshaw,
Ruixing Liang,
D. A. Bonn,
W. N. Hardy,
Louis Taillefer
[show abstract]
[hide abstract]
ABSTRACT: The nature of the pseudogap phase is a central problem in the quest to understand high-Tc cuprate superconductors. A fundamental question is what symmetries are broken when that phase sets in below a temperature T*. There is evidence from both polarized neutron diffraction and polar Kerr effect measurements that time- reversal symmetry is broken, but at temperatures that differ significantly. Broken rotational symmetry was detected by both resistivity and inelastic neutron scattering at low doping and by scanning tunnelling spectroscopy at low temperature, but with no clear connection to T*. Here we report the observation of a large in-plane anisotropy of the Nernst effect in YBa2Cu3Oy that sets in precisely at T*, throughout the doping phase diagram. We show that the CuO chains of the orthorhombic lattice are not responsible for this anisotropy, which is therefore an intrinsic property of the CuO2 planes. We conclude that the pseudogap phase is an electronic state which strongly breaks four-fold rotational symmetry. This narrows the range of possible states considerably, pointing to stripe or nematic orders. Comment: Published version. Journal reference and DOI added
09/2009;
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J Chang,
R. Daou,
Cyril Proust,
David LeBoeuf,
Nicolas Doiron-Leyraud,
Francis Laliberte,
B. Pingault, B. J. Ramshaw,
Ruixing Liang,
D. A. Bonn,
W. N. Hardy,
H Takagi,
A. Antunes,
I. Sheikin,
K. Behnia,
Louis Taillefer
[show abstract]
[hide abstract]
ABSTRACT: The Seebeck and Nernst coefficients $S$ and $\nu$ of the cuprate superconductor YBa$_2$Cu$_3$O$_y$ (YBCO) were measured in a single crystal with doping $p = 0.12$ in magnetic fields up to H = 28 T. Down to T=9 K, $\nu$ becomes independent of field by $H \simeq 30$ T, showing that superconducting fluctuations have become negligible. In this field-induced normal state, $S/T$ and $\nu/T$ are both large and negative in the $T \to 0$ limit, with the magnitude and sign of $S/T$ consistent with the small electron-like Fermi surface pocket detected previously by quantum oscillations and the Hall effect. The change of sign in $S(T)$ at $T \simeq 50$ K is remarkably similar to that observed in La$_{2-x}$Ba$_x$CuO$_4$, La$_{2-x-y}$Nd$_y$Sr$_x$CuO$_4$ and La$_{2-x-y}$Eu$_y$Sr$_x$CuO$_4$, where it is clearly associated with the onset of stripe order. We propose that a similar density-wave mechanism causes the Fermi surface reconstruction in YBCO. Comment: Final version accepted for publication in Phys. Rev. Lett. New title, shorter abstract, minor revision of text and added references
07/2009;
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David LeBoeuf,
Nicolas Doiron-Leyraud,
Julien Levallois,
R Daou,
J-B Bonnemaison,
N E Hussey,
L Balicas, B J Ramshaw,
Ruixing Liang,
D A Bonn,
W N Hardy,
S Adachi,
Cyril Proust,
Louis Taillefer
[show abstract]
[hide abstract]
ABSTRACT: High-temperature superconductivity in copper oxides occurs when the materials are chemically tuned to have a carrier concentration intermediate between their metallic state at high doping and their insulating state at zero doping. The underlying evolution of the electron system in the absence of superconductivity is still unclear, and a question of central importance is whether it involves any intermediate phase with broken symmetry. The Fermi surface of the electronic states in the underdoped 'YBCO' materials YBa2Cu3O(y) and YBa2Cu4O8 was recently shown to include small pockets, in contrast with the large cylinder that characterizes the overdoped regime, pointing to a topological change in the Fermi surface. Here we report the observation of a negative Hall resistance in the magnetic-field-induced normal state of YBa2Cu3O(y) and YBa2Cu4O8, which reveals that these pockets are electron-like rather than hole-like. We propose that these electron pockets most probably arise from a reconstruction of the Fermi surface caused by the onset of a density-wave phase, as is thought to occur in the electron-doped copper oxides near the onset of antiferromagnetic order. Comparison with materials of the La2CuO4 family that exhibit spin/charge density-wave order suggests that a Fermi surface reconstruction also occurs in those materials, pointing to a generic property of high-transition-temperature (T(c)) superconductors.
Nature 12/2007; 450(7169):533-6. · 36.28 Impact Factor
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J Chang,
R. Daou,
C. Proust,
D. LeBoeuf,
N. Doiron-Leyraud,
F. Laliberté,
B. Pingault, B. J. Ramshaw,
R Liang,
D. A. Bonn,
W. N. Hardy,
H Takagi,
A. Antunes,
I. Sheikin,
K. Behnia,
L. Taillefer
Physical Review Letters, v.104, 057005-1-057005-4 (2010).
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[show abstract]
[hide abstract]
ABSTRACT: The electrical resistivity ρc of the underdoped cuprate superconductor YBa2Cu3Oy was measured perpendicular to the CuO2 planes on ultrahigh quality single crystals in magnetic fields large enough to suppress superconductivity. The incoherent insulating-like behavior of ρc at high temperature, characteristic of all underdoped cuprates, is found to cross over to a coherent regime of metallic behavior at low temperature. This crossover coincides with the emergence of the small electron pocket detected in the Fermi surface of YBa2Cu3Oy via quantum oscillations, the Hall and Seebeck coefficients, and with the detection of a unidirectional modulation of the charge density as seen by high-field nuclear magnetic resonance measurements. The low coherence temperature is quantitatively consistent with the small hopping integral t⊥ inferred from the splitting of the quantum oscillation frequencies. We conclude that the Fermi-surface reconstruction in YBa2Cu3Oy at dopings from p=0.08 to at least p=0.15, attributed to stripe order, produces a metallic state with three-dimensional coherence deep in the underdoped regime.
Phys. Rev. B. 85(22).
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J. Chang,
Nicolas Doiron-Leyraud,
Francis Laliberté,
R. Daou,
David LeBoeuf, B. J. Ramshaw,
Ruixing Liang,
D. A. Bonn,
W. N. Hardy,
Cyril Proust,
I. Sheikin,
K. Behnia,
Louis Taillefer
[show abstract]
[hide abstract]
ABSTRACT: The Nernst coefficient of the cuprate superconductor YBa2Cu3Oy was recently shown to become strongly anisotropic within the basal plane when cooled below the pseudogap temperature T⋆, revealing that the pseudogap phase breaks the fourfold rotational symmetry of the CuO2 planes. Here we report on the evolution of this Nernst anisotropy at low temperature, once superconductivity is suppressed by a magnetic field. We find that the anisotropy drops rapidly below 80 K, to vanish in the T=0 limit. We show that this loss of anisotropy is due to the emergence of a small high-mobility electronlike pocket in the Fermi surface at low temperature, a reconstruction attributed to a low-temperature state that breaks the translational symmetry of the CuO2 planes. We discuss the sequence of broken symmetries—first rotational, then translational—in terms of an electronic nematic-to-smectic transition such as could arise when unidirectional spin or charge modulations order. We compare YBa2Cu3Oy with iron-pnictide superconductors where the process of (unidirectional) antiferromagnetic ordering gives rises to the same sequence of broken symmetries.
Phys. Rev. B. 84(1).
