Giant thermal Hall conductivity from neutral excitations in the pseudogap phase of cuprates
10 Jan 2019
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Grissonnanche Gaël
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Legros Anaëlle
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Badoux Sven
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Lefrançois Etienne
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Zatko Victor
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Lizaire Maude
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Laliberté Francis
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Gourgout Adrien
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Zhou Jianshi
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Pyon Sunseng
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Takayama Tomohiro
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Takagi Hidenori
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Ono Shimpei
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Doiron-Leyraud Nicolas
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Taillefer Louis
The nature of the pseudogap phase of cuprates remains a major puzzle. Although there are indications that this phase breaks various symmetries, there
is no consensus on its fundamental nature...Although Fermi-surface, transport
and thermodynamic signatures of the pseudogap phase are reminiscent of a
transition into a phase with antiferromagnetic order, there is no evidence for
an associated long-range magnetic order. Here we report measurements of the
thermal Hall conductivity $\kappa_{\rm xy}$ in the normal state of four
different cuprates (Nd-LSCO, Eu-LSCO, LSCO, and Bi2201) and show that a large
negative $\kappa_{\rm xy}$ signal is a property of the pseudogap phase,
appearing with the onset of that phase at the critical doping $p^*$. Since it
is not due to charge carriers -- as it persists when the material becomes an
insulator, at low doping -- or magnons -- as it exists in the absence of
magnetic order -- or phonons -- since skew scattering is very weak, we
attribute this $\kappa_{\rm xy}$ signal to exotic neutral excitations,
presumably with spin chirality. The thermal Hall conductivity in the pseudogap
phase of cuprates is reminiscent of that found in insulators with spin-liquid
states. In the Mott insulator LCO, it attains the highest known magnitude of
any insulator.(read more)