Specific heat of FeSe: Two gaps with different anisotropy in superconducting state

© 2017 Elsevier B.V. We present detailed study of specific heat of FeSe single crystals with critical temperature Tc=8.45 K at 0.4-200 K in magnetic fields 0-9 T. Analysis of the electronic specific heat at low temperatures shows the coexistence of isotropic s-wave gap and strongly anisotropic extended s-wave gap without nodes. It was found two possibilities of superconducting gap parameters which give equally description of experimental data: (i) two gaps with approximately equal amplitudes and weight contribution to specific heat: isotropic δ1=1.7 meV (2δ1/kBTc=4.7) and anisotropic gap with the amplitude δ2max=1.8 meV (2δ2max/kBTc=4.9 and anisotropy parameter m=0.85); (ii) two gaps with substantially different values: isotropic large gap δ1=1.65 meV (2δ1/kBTc=4.52) and anisotropic small gap δ2max=0.75 meV (2δ2max/kBTc=2) with anisotropy parameter m=0.71. These results are confirmed by the field behavior of the residual electronic specific heat γr

Phase transitions and exchange interactions in the SmCr3(BO3)4 crystal

© The Authors, published by EDP Sciences.Spectroscopic investigation and specific heat and magnetic susceptibility measurements of SmCr3(BO3)4 crystals were performed. The spectra of the Sm3+ and Cr3+ ions in samarium chromium borate were calculated and parameters of the exchange interactions between the nearest chromium ions, chromium and samarium ions were determined. Three phase transitions were observed at the temperatures T1= 7.8 ± 0.5 ?, T2 = 6.7 ± 0.5 ?, and T3 = 4.3 ± 0.2 ?, their nature is discussed. The crystal structures with different space symmetry groups R32 and C2/c were found to coexist in SmCr3(BO3)4 single crystal