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Exotic high-field phenomena in the S=1/2 frustrated spin ladder BiCu2PO6

Studies on the quasi low-dimensional antiferromagnetic spin systems are stimulated for understanding exotic ground states emerged in these materials. Recently, S =1/2 frustrated two-leg ladder arrangements are realized in BiCu 2 PO 6 [1]. The zig-zag chains formed by the Cu atoms are along the b axis of the crystal, and these chains are coupled each other along the c axis to form a quasi-2D layers with frustrated two-leg ladder structure in the bc plane. Moreover, strong Dzyaloshinskii-Moriya (DM) interaction in this compound breaks triplet degeneracy [2], and the DM interaction may lead exotic high-field phases. Here, we report the anomalous thermal transport and magnetoelectric effect of the BiCu 2 PO 6 under the high magnetic fields.

First, thermal conductivity ( κ ) of this material has been investigated in the static field up to 30 T. While applying the magnetic field along the a axis, suppression of the κ ( T ) and its strong magnetic field dependence are observed below 20 K. This can be interpreted as a resonant scattering of phonon by magnetic excitations that suppresses the phonon heat transport. From the theoretical analysis based on the Boltzmann transport theory and recent inelastic neutron scattering experiment [2], magnetic field dependence of three excitation gaps can be extracted up to 25 T.

Second, electric polarization ( P ) of BiCu 2 PO 6 single crystal has been studied in the pulsed magnetic field up to 60 T. While applying the magnetic field along the b axis, P b starts to appear above the first critical magnetic field ( H c1 ~ 20 T), and the P vector rotates perpendicular to the b axis above the second critical magnetic field ( H c2 ~ 34 T). Calculation of the electric polarization was attempted based on the proposed spin structures at the high-field phases, and the orbital hybridization between metal and ligand ions is considered as a possible microscopic origin of the electric polarization above H c2 .

[1] B. Koteswararao et al ., Phys. Rev. B 76 , 052402 (2007).

[2] K. W. Plumb et al ., arXiv:1408.2528.