[Paper Review] Fermi Surface of the Electron-doped Cuprate Superconductor Nd_{2-x}Ce_xCuO_{4} Probed by High-Field Magnetotransport

M. V. Kartsovnı̆k, T. Helm+11 more|Apr 6, 2011

Physics of Superconductivity and Magnetism5 citations

TL;DR

This study probes the Fermi surface of electron-doped Nd₂₋ₓCeₓCuO₄ using high-field magnetotransport, revealing magnetic breakdown-induced fast Shubnikov-de Haas (SdH) oscillations up to x ≈ 0.17, the highest doping level before superconductivity vanishes. The results provide direct evidence for a reconstructed, multiply-connected Fermi surface persisting throughout the overdoped regime, with the superlattice potential weakening and likely vanishing at the same doping as superconductivity, suggesting a deep connection between translational symmetry breaking and superconducting pairing.

ABSTRACT

We report on the study of the Fermi surface of the electron-doped cuprate superconductor Nd$_{2-x}$Ce$_x$CuO$_{4}$ by measuring the interlayer magnetoresistance as a function of the strength and orientation of the applied magnetic field. We performed experiments in both steady and pulsed magnetic fields on high-quality single crystals with Ce concentrations of $x=0.13$ to 0.17. In the overdoped regime of $x > 0.15$ we found both semiclassical angle-dependent magnetoresistance oscillations (AMRO) and Shubnikov-de Haas (SdH) oscillations. The combined AMRO and SdH data clearly show that the appearance of fast SdH oscillations in strongly overdoped samples is caused by magnetic breakdown. This observation provides clear evidence for a reconstructed multiply-connected Fermi surface up to the very end of the overdoped regime at $x\simeq 0.17$. The strength of the superlattice potential responsible for the reconstructed Fermi surface is found to decrease with increasing doping level and likely vanishes at the same carrier concentration as superconductivity, suggesting a close relation between translational symmetry breaking and superconducting pairing. A detailed analysis of the high-resolution SdH data allowed us to determine the effective cyclotron mass and Dingle temperature, as well as to estimate the magnetic breakdown field in the overdoped regime.

Motivation & Objective

• To resolve the nature of the Fermi surface in electron-doped cuprates, particularly in the overdoped regime where superconductivity is suppressed.
• To determine whether the Fermi surface remains reconstructed via a superlattice potential at high doping levels.
• To investigate the relationship between translational symmetry breaking (via superlattice potential) and superconducting pairing in Nd₂₋ₓCeₓCuO₄.
• To characterize the evolution of magnetic breakdown and cyclotron effective mass with increasing Ce doping.
• To clarify discrepancies between quantum oscillation data and ARPES/band structure predictions in overdoped cuprates.

Proposed method

• High-precision interlayer magnetoresistance measurements were performed in both steady (up to 45 T) and pulsed magnetic fields on high-quality Nd₂₋ₓCeₓCuO₄ single crystals with x = 0.13–0.17.
• Angle-dependent magnetoresistance oscillations (AMRO) and Shubnikov-de Haas (SdH) oscillations were analyzed to extract Fermi surface geometry and effective mass.
• Magnetic breakdown was identified by the presence of fast SdH oscillations at high doping, indicating large closed orbits encircling reconstructed Fermi surface pockets.
• The Dingle temperature and effective cyclotron mass were extracted from high-resolution SdH data using standard Lifshitz-Kosevich analysis.
• The magnetic breakdown field and superlattice potential strength were estimated from the amplitude and frequency of fast oscillations.
• The analysis combined AMRO and SdH data to confirm the existence of a multiply-connected Fermi surface up to x ≈ 0.17.

Experimental results

Research questions

• RQ1 Does the Fermi surface in overdoped Nd₂₋ₓCeₓCuO₄ remain reconstructed via a superlattice potential up to the highest accessible doping levels?
• RQ2 What is the relationship between the decay of the superlattice potential and the termination of superconductivity in electron-doped cuprates?
• RQ3 How does magnetic breakdown manifest in the high-field magnetotransport response of overdoped NCCO, and what does it reveal about the Fermi surface topology?
• RQ4 Are electron pockets detectable in high-field transport in overdoped NCCO, and if so, under what conditions?
• RQ5 Why do SdH oscillations disappear below x = 0.15, and is this due to Fermi surface reconstruction or suppression of orbital magnetoresistance?

Key findings

• Fast SdH oscillations with frequency F_fast ≈ 11 kT were observed at x = 0.17, indicating a large, closed cyclotron orbit consistent with a cylindrical Fermi surface centered at the Brillouin zone corner.
• The presence of fast SdH oscillations at x = 0.17 is attributed to magnetic breakdown, confirming a reconstructed, multiply-connected Fermi surface up to the end of the superconducting regime.
• The superlattice potential strength, estimated at Δ ≈ 14 meV for x = 0.16 and Δ ≈ 5 meV for x = 0.17, decreases with increasing doping and likely vanishes at the same carrier concentration where superconductivity terminates (x ≈ 0.175).
• The effective cyclotron mass was determined from SdH oscillation analysis, and the Dingle temperature was extracted, indicating moderate electron scattering in the overdoped regime.
• The magnetic breakdown field was estimated from the amplitude of fast oscillations, supporting the existence of large closed orbits in the overdoped regime.
• The results suggest a close relationship between translational symmetry breaking (via superlattice potential) and superconducting pairing, as both phenomena vanish at similar doping levels.