Lyα emitters with very large Lya equivalent widths, EW₀(Lyα) ≃ 200-400 Å, at <i>z</i> ∼ 2

We present physical properties of spectroscopically confirmed Ly alpha emitters (LAEs) with very large rest-frame Ly alpha equivalent widths EW0(Ly alpha). Although the definition of large EW0(Ly alpha) LAEs is usually difficult due to limited statistical and systematic uncertainties, we identify six LAEs selected from similar to 3000 LAEs at z similar to 2 with reliable measurements of EW0 (Ly alpha) similar or equal to 200-400 angstrom given by careful continuum determinations with our deep photometric and spectroscopic data. These large EW0(Ly alpha) LAEs do not have signatures of AGN, but notably small stellar masses of M star = 10(7-8)M(circle dot) and high specific star formation rates (star formation rate per unit galaxy stellar mass) of similar to 100 Gyr(-1). These LAEs are characterized by the median values of L(Ly alpha) = 3.7 x 10(42) erg s(-1) and M-UV = -18.0 as well as the blue UV continuum slope of beta = -2.5 +/- 0.2 and the low dust extinction E(B -V)(star) = 0.02(-0.02)(+0.04), which indicate a high median Lya escape fraction of f(esc)(Ly alpha) = 0.68 +/- 0.30. This large f(esc)(Ly alpha) value is explained by the low H (I) column density in the interstellar medium which is consistent with full width at half-maximum (FWHM) of the Ly alpha line, FWHM(Ly alpha) = 212 +/- 32 km s(-1), significantly narrower than those of small EW0(Ly alpha) LAEs. Based on the stellar evolution models, our observational constraints of the large EW0 (Ly alpha), the small beta, and the rest-frame He (II) EW imply that at least a half of our large EW0(Ly alpha) LAEs would have young stellar ages of less than or similar to 20 Myr and very low metallicities of Z < 0.02 Z(circle dot) regardless of the star formation history.