Nature of the Bad Metallic Behavior of ${\mathrm{Fe}}_{1.06}\mathrm{Te}$ Inferred from Its Evolution in the Magnetic State

We investigate with angle-resolved photoelectron spectroscopy the changes of the Fermi surface and the main bands from the paramagnetic state to the antiferromagnetic (AFM) state occurring below 72 K in ${\mathrm{Fe}}_{1.06}\mathrm{Te}$. The evolution is completely different from that observed in Fe pnictides, as nesting is absent. The AFM state is a rather good metal, in agreement with our magnetic band structure calculation. On the other hand, the paramagnetic state is very anomalous with a large pseudogap of $\sim 65\mathrm{meV}$ on the electron pocket that closes in the AFM state. We discuss this behavior in connection with spin fluctuations existing above the magnetic transition and the correlations predicted in the spin-freezing regime of the incoherent metallic state.

Figure 1

(a) Sketch of the PM FS for FeTe. (b) Stripe magnetic order in Fe pnictides $Q_{\mathrm{AFM}}=(\pi ,\pi )$. (c) Double stripe magnetic order in FeTe $Q_{\mathrm{AFM}}=(\pi ,0)$. FS map of FeTe in (d) the PM state (80 K) and (e) the AFM state (20 K). It is obtained by integrating the spectral weight around $E_F$ over $\pm 5\mathrm{meV}$, with linear polarization (LP) along $k_x$ and the $h\nu =70\mathrm{eV}$ ($V_0=12.5\mathrm{eV}$ [14] to correspond to $k_z=1$). The insets show the LEED at 100 eV of the $ab$ plane in the corresponding state [20]. Dotted red lines in (a) and (e) indicate the AFM BZ.

Figure 2

(a1)–(a4) Dispersion of the electron pocket in FeTe for the indicated temperatures, along the solid red lines in Figs. 1d, 1e (parallel to $k_x$ and centered at $M$). $h\nu =70\mathrm{eV}$ ($k_z\cong 1$) with LP along $k_x$, which selects orbitals $\mathrm{\text{odd}}/yz$. (b) Thick lines: EDCs at $k_F$ for the electron pocket at different temperatures. Thin lines: Symmetrized EDCs. (c) Temperature dependence of the size of PG [arrows in 2b].

Figure 3

(a1)–(a4) Dispersion of FeTe hole pockets at the BZ center for the indicated temperatures. $h\nu =38\mathrm{eV}$ ($k_z\cong 1$) along $k_x$ with (a) LP along $k_x$, selecting orbitals $\mathrm{\text{odd}}/xz$, and (b) LP in the $yz$ plane ($\mathrm{\text{even}}/yz$). White arrows indicate the positions of the kinks. (a5) Temperature dependence of the top of the inner hole band in (a1)–(a4). (b5) Temperature dependence of $v_F$ for the outer hole band in (b1)–(b4). The same quantities for ${\mathrm{Fe}}_{1.09}{\mathrm{Te}}_{0.78}{\mathrm{Se}}_{0.22}$ are plotted for comparison.

Figure 4

Calculated band structure along the AFM ($\Gamma A$), ferromagnetic ($\Gamma B$), and diagonal ($\Gamma M$) directions [Fig. 1a]. Thin lines: Bands in the PM state. Dotted lines: Bands folded with respect to the AFM BZ boundaries. Thick lines: Bands in the AFM state. The color indicates the dominant orbital character. $d_{XZ}$ and $d_{YZ}$ are defined in axis, corresponding to the AFM order [Fig. 1c].