2 FIG. 2: Surface and bulk band dispersion. ARPES intensity maps as a function of k$_{x}$ near ¯ Γ (a)-(c) and ¯ M (d)-(f) and their corresponding EDCs, taken using hν = 24 eV, 20 eV and 18 eV photons. The intensity scale of (d)-(f) is a factor of about twenty smaller than that of (a)-(c) due to the intrinsic weakness of the ARPES signal near ¯ M. ARPES spectra along ¯ Γ- ¯ M taken at three different pho- ton energies are shown in Fig. 2. Near ¯ Γ there are two rather linearly dispersive electron like bands that meet exactly at ¯ Γ at a binding energy E$_{B}$ ∼ -0.2 eV. This be- havior is consistent with previous ARPES measurements along the ¯ Γ- ¯ K direction [13] and is thought to come from a pair of spin-split surface bands that become degener- ate at the time reversal invariant momentum (TRIM) ¯ Γ due to Kramers degeneracy. The Fermi velocities of the inner and outer V-shaped bands are 4 . 4 ± 0 . 1 eV · ˚ Aand 2 . 2 ± 0 . 1 eV · ˚ Arespectively as found by fitting straight lines to their MDC peak positions. The surface origin of this pair of bands is established by their lack of depen- dence on hν [Fig. 2(a)-(c)]. A strongly photon energy dispersive hole like band is clearly seen on the negative k$_{x}$ side of the surface Kramers pair, which crosses E$_{F}$ for hν = 24 eV and gives rise to the bulk hole Fermi surface near H [Fig. 1(d)]. For hν ≤ 20 eV, this band shows clear back folding near E$_{B}$ ≈ -0.2 eV indicating that it has completely sunk below E$_{F}$ . Further evidence for its bulk origin comes from its close match to band cal- culations [Fig. 2(a)]. Interestingly, at photon energies such as 18 eV where the bulk bands are far below E$_{F}$ , there remains a uniform envelope of weak spectral inten- Figure 1(c) shows momentum distributions curves (MDCs) of electrons emitted at E$_{F}$ as a function of k$_{x}$ ( ‖ ¯ Γ- ¯ M) for Sb(111). The out-of-plane component of the momentum k$_{z}$ was calculated for different incident photon energies ( hν ) using the free electron final state approximation with an experimentally determined inner potential of 14.5 eV [14]. There are four peaks in the MDCs centered about ¯ Γ that show no dispersion along k$_{z}$ and have narrow widths of Δ k$_{x}$ ≈ 0.03 ˚ A − $^{1}$. These are attributed to surface states and are similar to those that appear in Sb(111) thin films [14]. As hν is increased beyond 20 eV, a broad peak appears at k$_{x}$ ≈ -0.2 ˚ A − $^{1}$, outside the k range of the surface states near ¯ Γ, and eventually splits into two peaks. Such a strong k$_{z}$ disper- description of the exchange correlation potential [17]. sion, together with a broadened linewidth (Δ k$_{x}$ ≈ 0.12 ˚ A − $^{1}$), is indicative of bulk band behavior, and indeed these MDC peaks trace out a Fermi surface [Fig. 1(d)] that is similar in shape to the hole pocket calculated for bulk Sb near H [23]. Therefore by choosing an appropri- ate photon energy (e.g. ≤ 20 eV), the ARPES spectrum along ¯ Γ- ¯ M will have contributions from only the surface states. The small bulk electron pocket centered at L is not accessed using the photon energy range we employed [Fig. 1(d)]. FIG. 1: Experimental separation of bulk from surface electron states in Sb using ARPES. (a) Schematic of the bulk BZ of Sb and its (111) surface BZ. The shaded region denotes the momentum plane in which the following ARPES spectra were measured. (b) LEED image of the in situ cleaved (111) sur- face exhibiting a clear hexagonal symmetry. (c) Select MDCs at the Fermi level taken with photon energies from 14 eV to 26 eV in steps of 2 eV, taken in the TXLU momentum plane. Peak positions in the MDCs were determined by fit- ting to Lorentzians (red curves). (d) Experimental 3D bulk Fermi surface near H (red circles) and 2D surface Fermi sur- face near ¯ Γ (open circles) determined by matching the fitted peak positions from (c) to calculated constant hν contours (black curves). Theoretical hole Fermi surface calculated in [23]. 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