3:15pm, Wednesday, May 15, 2013 
(2:45~3:15pm, Tea, Coffee, and Cookie)

Low-dimensional or frustrated quantum magnets were revealed to exhibit exotic ground states, magnetic excitations, and quantum phase transitions (QPTs). In the spin-gapped antiferromagnets, the external magnetic field can close the gap in the spectrum, which results in a QPT between a low-field disordered phase and a high-field long-range ordered one. An intriguing finding is that this ordered phase can be approximately described as a Bose-Einstein condensation (BEC) of magnons. In this talk, we show the low-temperature thermal conductivity (k) of several spin-gapped quantum magnets, including the quasi-one-dimensional S=1 chain compound NiCl2-4SC(NH2)2 (DTN), the quasi-one-dimensional ladder compound (CH3)2CHNH3CuCl3 (IPACuCl3), and the layered spin-dimer compound Ba3Mn2O8. It is found that the magnetic excitations can affect the heat transport rather strongly in these materials, particularly at the field-induced QPTs, by either transporting heat or scattering phonons. In addition, we pay attention to a fundamental issue whether the ballistic magnon heat transport (k µ T3), which has actually never been observed in antiferromagnetic materials, can be realized.