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An understanding of the normal state in the high-temperature superconducting cuprates is crucial to the ultimate understanding of the long-standing problem of the origin of the superconductivity itself. This so-called “strange metal” state is thought to be associated with a quantum critical point (QCP) hidden beneath the superconductivity. In electron-doped cuprates—in contrast to hole-doped cuprates—it is possible to access the normal state at very low temperatures and low magnetic fields to study this putative QCP and to probe the T ➔ 0 K state of these materials. We report measurements of the low-temperature normal-state magnetoresistance (MR) of the n-type cuprate system La 2− x Ce x CuO 4 and find that it is characterized by a linear-in-field behavior, which follows a scaling relation with applied field and temperature, for doping ( x ) above the putative QCP ( x = 0.14). The magnitude of the unconventional linear MR decreases as T c decreases and goes to zero at the end of the superconducting dome ( x ~ 0.175) above which a conventional quadratic MR is found. These results show that there is a strong correlation between the quantum critical excitations of the strange metal state and the high- T c superconductivity.
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Anomalous quantum criticality in the electron-doped cuprates
In the physics of condensed matter, quantum critical phenomena and unconventional superconductivity are two major themes. In electron-doped cuprates, the low critical field (H C2 ) allows one to study the putative quantum critical point (QCP) at low temperature and to understand its connection to the long-standing problem of the origin of the high- T C superconductivity. Here we present measurements of the low-temperature normal-state thermopower ( S ) of the electron-doped cuprate superconductor La 2− x Ce x CuO 4 (LCCO) from x = 0.11–0.19. We observe quantum critical S / T versus l n ( 1 / T ) behavior over an unexpectedly wide doping range x = 0.15–0.17 above the QCP ( x = 0.14), with a slope that scales monotonically with the superconducting transition temperature ( T C with H = 0). The presence of quantum criticality over a wide doping range provides a window on the criticality. The thermopower behavior also suggests that the critical fluctuations are linked with T C . Above the superconductivity dome, at x = 0.19, a conventional Fermi-liquid S ∝ T behavior is found for T ≤ 40 K.
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- Award ID(s):
- 1708334
- PAR ID:
- 10096468
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 116
- Issue:
- 13
- ISSN:
- 0027-8424
- Page Range / eLocation ID:
- 5991 to 5994
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1073/pnas.1817653116
