arXiv subjects

Nicolas Doiron-Leyraud

Publications and source records attributed to Nicolas Doiron-Leyraud.

24 records · Page 2Linked to original sources

arXiv2008

Linear-T resistivity and change in Fermi surface at the pseudogap critical point of a high-Tc superconductor

A fundamental question of high-temperature superconductors is the nature of the pseudogap phase which lies between the Mott insulator at zero doping and the Fermi liquid at high doping p. Here we report on the behaviour of charge carriers near the zero-temperature onset of that phase, namely at the critical doping p* where the pseudogap temperature T* goes to zero, accessed by investigating a material in which superconductivity can be fully suppressed by a steady magnetic field. Just below p*, the normal-state resistivity and Hall coefficient of La1.6-xNd0.4SrxCuO4 are found to rise simultaneously as the temperature drops below T*, revealing a change in the Fermi surface with a large associated drop in conductivity. At p*, the resistivity shows a linear temperature dependence as T goes to zero, a typical signature of a quantum critical point. These findings impose new constraints on the mechanisms responsible for inelastic scattering and Fermi surface transformation in theories of the pseudogap phase.

cond-mat.supr-con↗

arXiv2008

Electron pockets in the Fermi surface of hole-doped high-Tc superconductors

High-temperature superconductivity occurs as copper oxides 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 underdoped YBa2Cu3Oy and YBa2Cu4O8 was recently shown to include small pockets in contrast with the large cylinder characteristic of the overdoped regime1, 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 YBa2Cu3Oy and YBa2Cu4O8, which reveals that these pockets are electron-like. We propose that electron pockets arise most likely 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 materials 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-Tc superconductors.

cond-mat.supr-con↗

arXiv2008

Quantum oscillations and the Fermi surface in an underdoped high-Tc superconductor

Despite twenty years of research, the phase diagram of high transition- temperature superconductors remains enigmatic. A central issue is the origin of the differences in the physical properties of these copper oxides doped to opposite sides of the superconducting region. In the overdoped regime, the material behaves as a reasonably conventional metal, with a large Fermi surface. The underdoped regime, however, is highly anomalous and appears to have no coherent Fermi surface, but only disconnected "Fermi arcs". The fundamental question, then, is whether underdoped copper oxides have a Fermi surface, and if so, whether it is topologically different from that seen in the overdoped regime. Here we report the observation of quantum oscillations in the electrical resistance of the oxygen-ordered copper oxide YBa2Cu3O6.5, establishing the existence of a well-defined Fermi surface in the ground state of underdoped copper oxides, once superconductivity is suppressed by a magnetic field. The low oscillation frequency reveals a Fermi surface made of small pockets, in contrast to the large cylinder characteristic of the overdoped regime. Two possible interpretations are discussed: either a small pocket is part of the band structure specific to YBa2Cu3O6.5 or small pockets arise from a topological change at a critical point in the phase diagram. Our understanding of high-transition temperature (high-Tc) superconductors will depend critically on which of these two interpretations proves to be correct.

cond-mat.supr-con↗

arXiv2007

Reply to comment by Y. Ando on "Onset of Boson Mode at the Superconducting Critical Point of Underdoped YBa$_2$Cu$_3$O$_y$" by N. Doiron-Leyraud et al

In a recent Comment [arXiv:0711.4654], Y. Ando raises two valid issues in relation to our low-temperature heat transport study of YBa$_2$Cu$_3$O$_y$ across the insulator-to-superconductor boundary: 1) the possible role of twin boundaries in scattering phonons; 2) the best fitting procedure for extracting a fermionic (linear) term from the data. In this Reply, we show that both concerns can be laid to rest by 1) using new data from a tetragonal (twin-free) sample, and 2) using an analysis that does not involve any fitting.

cond-mat.supr-con↗

arXiv2006

Onset of a boson mode at superconducting critical point of underdoped YBa2Cu3Oy

The thermal conductivity $κ$ of underdoped \Y was measured in the $T \to 0$ limit as a function of hole concentration $p$ across the superconducting critical point at $p_{SC}$ = 5.0%. ``Time doping'' was used to resolve the evolution of bosonic and fermionic contributions with high accuracy. For $p \leqslant p_{SC}$, we observe an additional $T^3$ contribution to $κ$ which we attribute to the boson excitations of a phase with long-range spin or charge order. Fermionic transport, manifest as a linear term in $κ$, is seen to persist unaltered through $p_{SC}$, showing that the state just below $p_{SC}$ is a thermal metal. In this state, the electrical resistivity varies as log$(1/T)$ and the Wiedemann-Franz law is violated.

cond-mat.supr-con↗

arXiv2006

Bulk evidence for single-gap s-wave superconductivity in the intercalated graphite superconductor C$_6$Yb

We report measurements of the in-plane electrical resistivity $ρ$ and the thermal conductivity $κ$ of the intercalated graphite superconductor C$_6$Yb to temperatures as low as $T_c$/100. When a field is applied along the c-axis, the residual electronic linear term $κ_0/T$ evolves in an exponential manner for $H_{c1} < H < H_{c2}$. This activated behaviour establishes the order parameter as unambiguously s-wave, and rules out the possibility of multi-gap or unconventional superconductivity in this system.

cond-mat.supr-con↗