Gap-Opening Transition in Dirac Semimetal <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>ZrTe</mml:mi></mml:mrow><mml:mrow><mml:mn>5</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

We apply $^{125}$Te nuclear magnetic resonance (NMR) spectroscopy to investigate the Dirac semimetal ZrTe$_5$. With NMR field parallel $b$-axis, we observe significant quantum effects. These include an abrupt drop at 150 K in spin-lattice relaxation rate. This corresponds a gap-opening transition carriers, likely indicating onset of excitonic pairing. Below 50 K, see more negative shift for Te$_z$ bridging site repopulation levels with spin polarized carriers these temperatures. is previously reported 3D Hall regime; however, no sign charge density wave as has been proposed.