Thermal conductivity of the spin-Peierls compoundCuGeO3

Abstract

The thermal conductivity of the spin-Peierls ͑SP͒ compound CuGeO 3 was measured in magnetic fields up to 16 T. Above the SP transition, the heat transport due to spin excitations causes a peak at ϳ22 K, while below the transition the spin excitations rapidly diminish and the heat transport is dominated by phonons; however, the main scattering process of the phonons is with spin excitations, which demonstrates itself in an unusual peak in at ϳ5.5 K. This low-temperature peak is strongly suppressed with magnetic fields in excess of 12.5 T. RAPID COMMUNICATIONS R2914PRB 58 YOICHI ANDO et al. RAPID COMMUNICATIONS R2916PRB 58 YOICHI ANDO et al.

Low-temperature heat transport of spin-gapped quantum magnets

“…This gap can be suppressed with magnetic fields; above a critical field H c ≈ 12.5 T, the system undergoes a first-order transition to an incommensurate phase [106]. Figure 17 shows the temperature dependence of thermal conductivity of CuGeO 3 single crystal in the temperature range 1.5-40 K. Also shown in this figure are the specific heat data measured on the same crystal in the temperature range 1.8-16 K [105]. The peak of the specific heat is associated with the SP transition [107].…”

“…Hence, the second peak at about 5.5 K can be formed in the thermal conductivity curve. Figure 18 shows the (T) curve in the field range 016 T [105]. With increasing magnetic field, one remarkable feature in this curve is the strong suppression of the 5.5 K peak.…”

“…However, this peak becomes a shoulder at 14 T and it shows a new upturn below 7 K at 16 T. Meanwhile, the position of the 22 K peak is almost unchanged with the change of magnetic field. Since the thermal conductivity at low temperatures is greatly suppressed and the diffusivity still has the 1/T dependence, the authors concluded that phonons are strongly scattered by solitons [105].…”

“…The thermal conductivity of SP systems was firstly studied by Ando et al [105] In this SP material, the size of the spin gap has been found to be  ≈ 23 K [18]. This gap can be suppressed with magnetic fields; above a critical field H c ≈ 12.5 T, the system undergoes a first-order transition to an incommensurate phase [106].…”

“…At higher temperature region, the phonon thermal conductivity  ph approach to be constant. A constant phonon background about 0.4 W/cm· K can be subtracted in the temperature range 15 to 50 K and the remaining contribution approximates  s which has a peak at about 22 K. Below the SP transition temperature, it is reasonable to assume that  is only due to phonons since  s diminishes [105]. The phonons are scattered by both spin excitations and crystal defects.…”