Magnetization-Induced Band Shift in Ferromagnetic Weyl Semimetal Co3Sn2S2

Abstract

The discovery of nonmagnetic Weyl semimetals (WSMs) in TaAs compounds has triggered lots of efforts in finding its magnetic counterpart. While the direct observation of the Weyl nodes and Fermi arcs in a magnetic candidate through angle-resolved photoemission spectroscopy is hindered by the complex magnetic domains. The transport features of magnetic WSMs, including negative magnetoresistivity and anomalous Hall conductivity, are not conclusive since these are sensitive to extrinsic factors like defects and disorders in lattice or magnetic ordering. Here, we systematically study the temperature dependent optical spectra of ferromagnetic Co3Sn2S2 experimentally and simulated by first-principles calculations. The many-body correlation effect due to Co 3d electrons leads to renormalization of bands by a factor about 1.33, which is moderate and the description within density functional theory is suitable. As temperature drops down, the magnetic phase transition happens and the magnetization drives the band shift through exchange splitting. The optical spectra can well detect these changes, including the transitions sensitive and insensitive to the magnetization, and those from the bands around the Weyl nodes. The results strongly support that Co3Sn2S2 is a magnetic WSM and the Weyl nodes can be tuned by magnetization with temperature change.PACS numbers: 72.15.-v, 74.70.-b, 78.30.-j Recently, the shandite compound Co 3 Sn 2 S 2 has attracted lots of attentions since it not only shows intrinsic ferromagnetism but also is proposed to have three pairs of Weyl points around the Fermi level in the first Brillouin zone (BZ) [1-3, 5]. For its quasi-two-dimensional crystal structure, low carrier density and strong anomalous Hall effect (AHE), Co 3 Sn 2 S 2 has been thought as a potential candidate to realize the quantum AHE [6,7] in its tow-dimensional (2D) limit [1,8,9]. As a candidate of magnetic Weyl semimetal (WSM) [10], the magnetic ordering states are expected to have interactions with Weyl nodes [2,3], so that the topological properties from WSM can be finely tuned through control of magnetization [2,11]. Actually, it has been found that upon cooling, the magnetization and anomalous Hall conductivity (AHC) of Co 3 Sn 2 S 2 vary accordingly [1, 2] and the first-principles calculations of AHC at different magnetization has shown their intrinsic relationship through the changes in the position of Weyl nodes [2]. To check whether this picture is true or not in realistic samples, here we have performed systematical optical spectra measurements under different temperatures (T s). The advantages of optical spectra measurements over the AHC measurements are as following: First, optical spectrum is * These authors contributed equally to this work. † hmweng@iphy.ac.cn ‡ xgqiu@iphy.ac.cn

Giant magneto-optical responses in magnetic Weyl semimetal Co3Sn2S2

“…3b; two broad peaks are identified at~0.2 and 0.6 eV, as indicated by the open circle and square, respectively. The recent optical study argues that the lower-lying peak at 0.2 eV is mainly the transition among Co 3d orbital in nearly the same spin channel while the higher-lying peak at 0.6 eV is associated with the transition from Co 3d t 2g orbital to e g orbital 31 . Some fine structures discerned in the calculated spectra (Fig.…”

“…Magnetic Weyl semimetal. Co 3 Sn 2 S 2 , a Co-based shandite material, is a ferromagnetic metal with the Curie temperature T C of~175 K 7,8,20,21,[29][30][31] . The crystal structure has a hexagonal lattice belonging to the space group R 3m with forming a kagome network of Co atoms within the Co 3 Sn layer (Fig.…”

Electronic correlations and flattened band in magnetic Weyl semimetal candidate Co3Sn2S2

“…Our results not only reveal the effects of electronic correlations in FM Co 3 Sn 2 S 2 , but also open an avenue for deeply investigating exotic quantum phenomena dominated by flat bands in WSMs. After submission of this work, we became aware of similar optical data about Co 3 Sn 2 S 2 86 .…”

Spin excitations and spin wave gap in the ferromagnetic Weyl semimetal Co3Sn2S2

“…There are three pairs of Weyl nodes in the first Brillouin zone close to the Fermi level (Figure 1(b)), as evidenced by the surface Fermi-arcs and linear bulk band dispersions observed from spectroscopic experiments [11,[17][18][19][20]. With the considerably enhanced Berry curvature from its band structure (Figure 1(c)), a record of large AHC is detected up to 1130 Ω −1 cm −1 accompany by a strong temperature dependence approaching T C [17,38].…”