Fabric I have created a Dataframe in Notebook using pyspark. now I want to create a Delta PARQUET

Depending on your desired result, there are different methods.  The method you are using will write a parquet file to the Files location.  If you want to create a Delta table, you should use the saveAsTable function with "delta" as the format. 

Keep in mind that table names can only contain alphanumeric characters and underscores.

From the documentation:

# Keep it if you want to save dataframe as CSV files to Files section of the default Lakehouse

df.write.mode("overwrite").format("csv").save("Files/ " + csv_table_name)

# Keep it if you want to save dataframe as Parquet files to Files section of the default Lakehouse

df.write.mode("overwrite").format("parquet").save("Files/" + parquet_table_name)

# Keep it if you want to save dataframe as a delta lake, parquet table to Tables section of the default Lakehouse

df.write.mode("overwrite").format("delta").saveAsTable(delta_table_name)

# Keep it if you want to save the dataframe as a delta lake, appending the data to an existing table

df.write.mode("append").format("delta").saveAsTable(delta_table_name)