问如何在mat-datepicker上设置当天

EN

        <form [formGroup]="profileForm" class="event-form w-100-p" fxLayout="column" fxFlex>
 <div fxFlex="1 0 auto" fxLayout="column" fxLayout.gt-xs="row">

                <mat-form-field appearance="outline" class="pr-sm-8" fxFlex="50">
                    <mat-label>Code personnel*</mat-label>
                    <input matInput formControlName="Code_personnel">
                    <mat-error>Code personnel doit composer par 4 chiffres.</mat-error>
                </mat-form-field>

                <mat-form-field appearance="outline" class="pr-sm-8" fxFlex="50">
                    <mat-label>N de tel</mat-label>
                    <input matInput formControlName="N_tel">
                </mat-form-field>

            </div>
<div fxFlex="1 0 auto" fxLayout="column" fxLayout.gt-xs="row">

                <mat-form-field appearance="outline" class="pr-sm-8" fxFlex="100">
                    <mat-label>Date de naissance</mat-label>
                    <input matInput [matDatepicker]="startDatePicker"  formControlName="birthday">
                    <mat-datepicker-toggle matSuffix [for]="startDatePicker"></mat-datepicker-toggle>
                    <mat-datepicker #startDatePicker></mat-datepicker>
                </mat-form-field>

            </div>
        </form>

    </div>

 now;
profileForm = this.fb.group({
    Nom_de_famille: ['' ,Validators.required],//
    Prénom: ['' ,Validators.required],//
    email: ['', [Validators.email,Validators.required]],//
    Code_personnel: ['', Validators.required],//I need here aad the 4 charectres validation
    N_tel: [''],
    birthday: [new Date()],//I have tried that
    adresse: [''],
    lieu:[''],
    CIN:['',Validators.required],
    Genre:[''],
    N_permis:[''],
    Département: ['',Validators.required]
  });
ngOnInit() {  this.now  = formatDate(new Date(), 'yyyy/MM/dd', 'en');
  }