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Universal quantum oscillations in the underdoped cuprate superconductors

Within these last 7 years, quantum oscillation’s measurements in high field facilities in hole doped high temperature superconductors have shed a new light on the low temperature ground state of these fascinating materials. They have established the validity of a generalized Fermi liquid picture for the low temperature normal state, not only in the overdoped part of the phase diagram but also, and more surprisingly in underdoped YBa2Cu3Oy (YBCO). The large Fermi surface (FS) occupying 65% of the first Brillouin zone (FBZ) measured in the overdoped compound in agreement with photoemission measurements and band structure calculations is in sharp contrast to the small Fermi pockets covering only 2% of the FBZ in underdoped YBCO. Combined with negative Hall and Seebeck coefficients, these experimental facts point to a reconstruction of the high temperature FS into electron and hole pockets caused by a competing charge order that breaks the translational symmetry of the crystal, as recently evidenced by high-field NMR, high-field ultrasound velocity measurements and zero field X ray scattering. While this result has been interpreted as a dramatic change of the FS associated with the quintessential CuO2 planes, it may also be attributed to the existence of a non-universal FS piece related to the CuO chains in YBCO. Consequently, it has remained a pivotal open question whether the FS reconstruction has anything to do with aspects of the unidirectional structures, or if it is a universal property of the cuprates. We have settled this issue through the observation of quantum oscillations in the magnetoresistance of a simple tetragonal compound HgBa2CuO4+δ(Hg1201) at p≈0.09 in pulsed magnetic fields of up to 80 T.

Figure 1: Field dependence of the in-plane resistance data for Hg1201 (Tc = 72 K, p = 0.09) in pulsed magnetic fields (up to 80 T) at selected temperatures. Quantum oscillations are clearly observed from the raw data above 60 T. Inset: the derivative of the resistance highlights the oscillations.

Thanks to the long pulse duration of the coilin-coilex system developed by the engineers at the LNCMI-Toulouse, vibrations are significantly reduced and high signal-to-noise ratio can be achieved up to 80 T. Fig. 1 shows the field dependence of the resistance up to 80 T at different temperatures. The oscillatory behaviour is already evident from the raw data at fields above 60 T. To emphasize the quantum oscillations without subtraction of the non-oscillatory component, we also plot the derivative of the data (see inset of Fig. 1). The frequency of the oscillation F = 840 ± 30 T corresponds to a cross-sectional area of the covering about 3% of the FBZ. The quantum oscillations in Y123 and Hg1201 appear approximately in the same doping, temperature and magnetic field range of the phase diagram, with pockets of very similar effective mass and comparable cyclotron frequency. Moreover, the temperature dependence and absolute value of the Hall and Seebeck coefficients are very similar. Remarkably, on cooling, both coefficients sharply decrease below 50 K and finally change sign from positive to negative at low temperature. This supports the scenario of a Fermi-surface reconstruction that leads to a small, closed and coherent electron pocket, and it points to the same underlying mechanism related to the CuO2 plane, because this is the only common structural unit of the two compounds. Small electron pockets can be seen as an universal feature of hole doped cuprates.

Reference: Universal quantum oscillations in the underdoped cuprate superconductors N. Barišić, S. Badoux, M. K. Chan, C. Dorow, W. Tabis, B. Vignolle, G. Yu, J. Béard, X. Zhao, C. Proust & M. Greven Nature Physics 9, 761 (2013)