Modulation in the non-uniformity of the vortex state across the peak effect: evidence via the magnetic quadrupole moment in a very clean crystal of 2H-NbSe<SUB>2</SUB> for H&#x2225;c

The non-uniform magnetic character of the mixed (vortex) state is known to result in a magnetic quadrupolar response of a type-II superconductor. The nucleation of stronger pinned regions coexisting with weaker pinned regions across the peak effect (PE) in a weakly pinned superconductor has been demonstrated using ac scanning Hall bar microscopy by Marchevsky et al. [Nature 409 (2001) 591]. Coexistence of this nature could produce an imprint in the measured quadrupolar response of such samples. We present successful detection of such an imprint across the PE region of a very clean crystal of 2H-NbSe2 for H//c via a well-established procedure of preferentially recording a signal arising from the non-uniformity in the magnetization of the sample in a vibrating sample magnetometer