Time-reversal and parity violating superconducting state of   Bi_2Sr_2CaCu_20_8
  The time-reversal and parity violating superconducting(SC) phase of Bi2Sr2CaCu2O8 induced by a magnetic field (B), reported by Krishana et al[K. Krishana et al, Science 277, 83 (1997)] over the limited field range of 0.6T < B < 5T, is examined starting with the model free-energy functional predicted by Laughlin [R. B. Laughlin, Physica C 234, 280 (1994)]. On the basis of entropy considerations we show that the passage from the normal to this field-driven SC state at a non-zero temperatures (T) is possible if kBT \leq \Delta 0 where the zero-temperature gap \Delta0 ~ \hbarv/lB, v is the root-mean-square velocity of the d-wave node, and lB = \surd(\hbar/eB) is the magnetic length. The restriction may be construed as setting lower limit on the required field strength at a given temperature. We find that, over the field range mentioned, the specific heat coefficient exhibits \surd B- and the B-linear dependence (Volovick effect). 
Partha Goswami
cond-mat.supr-con