A multi-component Fermi surface in the vortex state of an underdoped high-Tc superconductor

Abstract

To understand the origin of superconductivity, it is crucial to ascertain the nature and origin of the primary carriers available to participate in pairing. Recent quantum oscillation experiments on high-transition-temperature (high-T(c)) copper oxide superconductors have revealed the existence of a Fermi surface akin to that in normal metals, comprising fermionic carriers that undergo orbital quantization. The unexpectedly small size of the observed carrier pocket, however, leaves open a variety of possibilities for the existence or form of any underlying magnetic order, and its relation to d-wave superconductivity. Here we report experiments on quantum oscillations in the magnetization (the de Haas-van Alphen effect) in superconducting YBa(2)Cu(3)O(6.51) that reveal more than one carrier pocket. In particular, we find evidence for the existence of a much larger pocket of heavier mass carriers playing a thermodynamically dominant role in this hole-doped superconductor. Importantly, characteristics of the multiple pockets within this more complete Fermi surface impose constraints on the wavevector of any underlying order and the location of the carriers in momentum space. These constraints enable us to construct a possible density-wave model with spiral or related modulated magnetic order, consistent with experimental observations.

Chemical potential oscillations from nodal Fermi surface pocket in the underdoped high-temperature superconductor YBa2Cu3O6+x

“…The extracted harmonic signal is similar to that reported in contactless resistivity 9 , magnetic torque performed in pulsed 7 and DC fields 6 , and c-axis conductivity experiments. In the present magnetic torque experiments, the harmonics are further verified to be independent of the thickness of the cantilever, with measurements on two different cantilevers with thicknesses differing by a factor of 5, yielding the same relative size of harmonics, confirming them to be intrinsic to the sample.…”

“…Figure 4a shows a collation of quantum oscillations measured in magnetic torque and contactless resistivity, spanning overall a range 22 T-65 T. An identical beat structure previously revealed to correspond to three closely spaced frequencies (F α = 535(5) T, F γ1 = 440(10) T, F γ2 = 610(20) T) is found, confirming the multiple frequency components earlier reported 3,6,7,9 . A significantly higher F β~1 ,550(50) T frequency earlier reported 6 is also prominently observed in quantum oscillations measured at the lowest temperatures 1 K (to be presented elsewhere). High sensitivity measurements we report here additionally show that the quantum oscillations with this beat structure persist down to 22 T, where the d-wave superconducting gap is well developed.…”

“…From the analysis of the measured second harmonic oscillations, we present the surprising finding that the harmonic content in underdoped YBa 2 Cu 3 O 6 + x (x = 0.56) arises from oscillations of the chemical potential, which are enhanced compared to normal metals by the quasi-two-dimensional topology of the Fermi surface 17,[21][22][23][24] . Oscillatory features corresponding to multiple frequencies in 1/B previously reported 3,6,7,9 are observed: (F α = 535(5) T, F γ1 = 440(10) T, F γ2 = 610(20) T) down to 22 T, and F β = 1,550(50) T at the lowest temperatures 1 K (to be presented elsewhere); yet, we conclude, from the magnitude and phase of the second harmonic with respect to the fundamental oscillations, that the Fermi surface consists chiefly of a single carrier pocket, the multiple frequency components arising from effects of finite c-axis dispersion, bilayer splitting, and magnetic breakdown. The next question relates to the location of this quasi-two-dimensional pocket.…”

“…A lthough high-T c cuprate superconductors have a history spanning a quarter of a century 1,2 , quantum oscillations in these materials have only been measured as recently as a few years ago [3][4][5][6][7][8][9][10][11][12] , by employing high magnetic fields to weaken superconductivity. Interestingly, their advent has signalled a reevaluation of the electronic structure in the normal state of the underdoped cuprates.…”

“…Against this backdrop of contradictory scenarios, an unambiguous interpretation of quantum oscillation results in terms of momentum space location, charge carrier type, and single or multiple surfaces in the case of the underdoped cuprates has remained elusive [3][4][5][6][7][8][9][10] . Quantum oscillations in the case of a fixed chemical potential cannot discern the sign of charge carriers or whether there are single or multiple types of charge carrier present 17 , causing recourse, thus far, to less direct probes such as the Hall effect and thermopower, and calculations of the electronic structure to infer a nodal-antinodal Fermi surface 4,9,[18][19][20] .…”