  Gapped excitation spectra of Andreev states are studied in one- and
two-dimensional (1D and 2D) normal systems in superconducting contacts subject
to a parallel magnetic field. In the ballistic regime, a specific interplay
between magnetic field spin splitting and the effect of a screening
supercurrent is found to preserve time-reversal symmetry for certain groups of
Andreev states remaining gapped despite the presense of the magnetic field. In
1D wires such states can lead to a fractional thermal magnetoconductance equal
to half of the thermal conductance quantum. In 2D systems the thermal
magnetoconductance is also predicted to remain suppressed well below the
normal-state value in a wide range of magnetic fields.
