The new resistance jump: The detection of damage in Nb barrier in MgB2 wires

• A new method for detecting damage in Nb barrier in MgB2 wires.
• The damage is detected by using a four-contact method involving a temperature sweep.
• A new jump in resistance confirms that there is damage in the Nb barrier.
• A damaged Nb barrier do not decrease Tc and Bc2, but do decrease Birr and Itc.

We present a new method for detecting damage to Nb barriers in MgB2 wires by using a four-contact probe. The transport measurements and scanning electron microscope images indicate that a newly identified jump in resistance means that there is damage to the Nb barrier. Damage detection is important for application because it allows us to avoid reactions between the filament and the sheath material, and to develop implementation methods for MgB2 with high critical current density. Our methods for damage detection proposed in this paper are simple, fast, and easy to use.