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.