My wife often contradicts and argues with me. Is that nushuz (marital defiance)?

No — differing in opinion and arguing respectfully is not nushuz; the Prophet's ﷺ own wives answered back to him.
Umar r.a. was once taken aback when his wife answered him back, and she replied that the Prophet's ﷺ wives did the same (narrated by al-Bukhari & Muslim). The Prophet ﷺ dealt with differences of opinion patiently. Nushuz is refusing to fulfil obligations without a Shariah reason, not voicing an opinion. A good husband listens, because a wife often sees what the husband does not — Ummu Salamah r.a. gave the Prophet ﷺ sound advice at Hudaibiyah. Even so, both sides must keep good manners: no insults or shouting. See Rights of husband & wife.