[Python] Why matplotlib is not graphing correctly?

I have a simple code, to graph the data of the first and second column of a .txt file . However, the graph made by matplotlib (python) is incorrect if I compare it with the one made in excel. Why is this?

Material_A = "C:/Users/Admin/Desktop/2025/Si_refractive index.txt"

Thin_film_Mat_A = np.loadtxt(Material_A,delimiter='\t',skiprows=1)

a_min , a_max = VisualizationRange(lamb_min , lamb_max)
lamb = Thin_film_Mat_A[a_min:a_max +1,0]


#========================== #==========================

# Complex Refractive Index
# Silicon
NA = Thin_film_Mat_A[a_min:a_max +1,1]
NA_normalized = ( NA - min(NA) ) / ( max(NA) - min(NA) )

# Graphic
plt.plot(lamb,NA_normalized)
plt.xlabel("Longitud de onda (nm)")
plt.ylabel("NA (u.a.)")
plt.grid(True)
plt.show()




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