Abstract
The Seebeck coefficient of the cuprate superconductor (LSCO) was measured in magnetic fields large enough to access the normal state at low temperatures, for a range of Sr concentrations from to . For , 0.12, 0.125, and 0.13, decreases upon cooling to become negative at low temperatures. The same behavior is observed in the Hall coefficient . In analogy with other hole-doped cuprates at similar hole concentrations , the negative and show that the Fermi surface of LSCO undergoes a reconstruction caused by the onset of charge-density-wave modulations. Such modulations have indeed been detected in LSCO by x-ray diffraction in precisely the same doping range. Our data show that in LSCO this Fermi-surface reconstruction is confined to . We argue that in the field-induced normal state of LSCO, charge-density-wave order ends at a critical doping , well below the pseudogap critical doping .
- Received 18 November 2015
DOI:https://doi.org/10.1103/PhysRevX.6.021004
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Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Copper-oxide materials known as cuprates act as superconductors at record-high temperatures. The origin of this remarkable phenomenon, discovered three decades ago, remains an outstanding puzzle in condensed-matter physics, largely because cuprates exhibit a number of intriguing electronic phases that are intertwined in ways that we do not yet understand. One of these phases is characterized by modulations in the density of charge carriers, known as a charge density wave. Another fundamental phase of cuprates is the pseudogap phase, which remains unexplained to this day. A key open question is whether the two phases are intimately linked or separate. Here, we use transport experiments on the classic cuprate material to show that these phases are separate.
Prior electrical resistivity measurements on in very high magnetic fields revealed that its pseudogap phase terminates at a critical doping level of in the absence of superconductivity. We measure the thermopower of single crystals of in high magnetic fields (up to 45 T) as a way to track the charge-density-wave order with doping via the profound effect it has on the Fermi surface. We examine a range of Sr concentrations from to . Around , we observe a negative Seebeck coefficient at low temperature, a well-established signature of the charge-density wave in cuprates. As the doping level increases, this signature disappears; we find that the charge-density-wave phase in ends at . The fact that with decreased doping the pseudogap phase sets in well before the charge-density-wave order implies that the origin of the enigmatic pseudogap is independent of charge-density-wave formation.
We expect that our findings will motivate future investigations focusing on the nature of the pseudogap in cuprates.