Majed Abdel-Jawad

A coherent three-dimensional Fermi surface in a high-transition-temperature superconductor

All conventional metals are known to possess a three-dimensional Fermi surface, which is the locus in reciprocal space of the long-lived electronic excitations that govern their electronic properties at low temperatures. These excitations should have well-defined momenta with components in all three dimensions. The high-transition-temperature (high-Tc) copper oxide superconductors have unusual, highly two-dimensional properties above the superconducting transition. This, coupled with a lack of unambiguous evidence for a three-dimensional Fermi surface, has led to many new and exotic models for the underlying electronic ground state. Here we report the observation of polar angular magnetoresistance oscillations in the overdoped superconductor Tl2Ba2CuO6+δ in high magnetic fields, which firmly establishes the existence of a coherent three-dimensional Fermi surface. Analysis of the oscillations reveals that at certain symmetry points, however, this surface is strictly two-dimensional. This striking form of the Fermi surface topography, long-predicted by electronic band structure calculations, provides a natural explanation for a wide range of anisotropic properties both in the normal and superconducting states. Our data reveal that, despite their extreme electrical anisotropy, the high-Tc materials at high doping levels can be understood within a framework of conventional three-dimensional metal physics.

Anisotropic scattering and anomalous normal-state transport in a high-temperature superconductor

The metallic state of high-temperature copper-oxide superconductors, characterized by unusual and distinct temperature dependences in the transport properties1,2,3,4, is markedly different from that of textbook metals. Despite intense theoretical efforts5,6,7,8,9,10,11, our limited understanding is impaired by our inability to determine experimentally the temperature and momentum dependence of the transport scattering rate. Here, we use a powerful magnetotransport probe to show that the resistivity and the Hall coefficient in highly doped Tl2Ba2CuO6+δ originate from two distinct inelastic scattering channels. One channel is due to conventional electron–electron scattering; the other is highly anisotropic, has the same symmetry as the superconducting gap and a magnitude that grows approximately linearly with temperature. The observed form and anisotropy place tight constraints on theories of the metallic state. Moreover, in heavily doped non-superconducting La2−xSrxCuO4, this anisotropic scattering term is absent12, suggesting an intimate connection between the origin of this scattering and superconductivity itself.

Correlation between the superconducting transition temperature and anisotropic quasiparticle scattering in Tl 2 Ba 2 CuO 6+δ

Angle-dependent magnetoresistance measurements are used to determine the isotropic and anisotropic components of the transport scattering rate in overdoped Tl2Ba2CuO6+δ for a range of Tc values between 15K and 35K. The size of the anisotropic scattering term is found to scale linearly with Tc, establishing a link between the superconducting and normal state physics. Comparison with results from angle resolved photoemission spectroscopy indicates that the transport and quasiparticle lifetimes are distinct.

Field-Induced Fermi Surface Reconstruction in Na0.5CoO2

We have performed electrical transport measurements at low temperatures and high magnetic fields in Na0.5CoO2 single crystals. Shubnikov de Haas oscillations corresponding to only 1 % of the area of the orthorhombic Brillouin zone (BZ) were clearly observed, suggesting that most of the original Fermi surface vanished at the charge ordering (CO) transition. In‐plane magnetic fields were found to suppress strongly the CO state. For fields rotated within the conducting planes, we observe angular magnetoresistance oscillations whose periodicity changes from two‐to six‐fold at the transition. This suggests the field‐induced reconstruction of the Fermi surface upon suppression of the CO‐state.

Full Fermi Surface of a High Temperature Superconductor Revealed by Angular Magnetoresistance Oscillations

We report the first observation of polar angular magnetoresistance oscillations in the high-Tc cuprate Tl2Ba2CuO6. These measurements establish the existence of a coherent three-dimensional Fermi surface on the overdoped, superconducting side of the cuprate phase diagram, even in materials with extreme electrical anisotropy. Detailed analysis of the oscillations reveals that c-axis dispersion vanishes at specific symmetry points. This observation has implications for our understanding of a wide range of unusual metallic and superconducting properties of cuprates.