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Quantum critical behavior of the hyperkagome magnet Mn 3 CoSi
β -Mn-type family alloys Mn 3 T X ( T = Co , Rh, and Ir; X = Si and Ge) have a three-dimensional antiferromagnetic (AF) corner-shared triangular network, i.e., the hyperkagome lattice. The antiferromagnet Mn 3 RhSi shows magnetic short-range order over a wide temperature range of approximately 500 K above the Néel temperature T N of 190 K. In this family of compounds, as the lattice parameter decreases, the long-range magnetic ordering temperature decreases. Mn 3 CoSi has the smallest lattice parameter and the lowest T N in the family. The quantum critical point (QCP) from AF to the quantum paramagnetic state is expected near a cubic lattice parameter of 6.15 Å . Although the Néel temperature of Mn 3 CoSi is only 140 K, the emergence of the quantum critical behavior in Mn 3 CoSi is discussed. We study how the magnetic short-range order appears in Mn 3 CoSi by using neutron scattering, μ SR , and bulk characterization such as specific heat capacity. According to the results, the neutron scattering intensity of the magnetic short-range order in Mn 3 CoSi does not change much at low temperatures from that of Mn 3 RhSi , although the μ SR short-range order temperature of Mn 3 CoSi is largely suppressed to 240 K from that of Mn 3 RhSi . Correspondingly, the volume fraction of the magnetic short-range order regions, as shown by the initial asymmetry drop ratio of μ SR above T N , also becomes small. Instead, the electronic-specific heat coefficient γ of Mn 3 CoSi is the largest in this Mn 3 T Si system, possibly due to the low-energy spin fluctuation near the quantum critical point. Published by the American Physical Society 2024
FeSi 4 P 4 and CoSi 3 P 3 : Hidden Gems of Ternary Tetrel Pnictides with Outstanding Nonlinear Optical Properties
Metal silicon phosphides have shown promise as nonlinear optical materials. To be practically useful and cheap, earth-abundant 3d transition metals are preferred over their scarcer and more expensive 4d and 5d counterparts. Here, we developed a synthetic method to produce polycrystalline bulk powders and millimeter-sized single crystals of ternary compounds FeSi 4 P 4 and CoSi 3 P 3 . Both studied compounds have noncentrosymmetric and chiral crystal structures with ordered Si/P arrangements as was confirmed by single-crystal X-ray diffraction and solid-state NMR. Despite the presence of the transition metal, FeSi 4 P 4 and CoSi 3 P 3 are semiconductors with direct band gaps of 1.3 and 1.6 eV, respectively, indicating low-spin d 6 electronic configuration for octahedral Fe 2+ and Co 3+ . Relative to reported sulfide materials, FeSi 4 P 4 and CoSi 3 P 3 small band gap semiconductors demonstrate an outstanding combination of second-harmonic generation (SHG) activity and laser damage threshold (LDT). Both studied materials are phase-matchable with a 2.09 μm laser and not only exhibit 2.5–3.0 times stronger SHG signal than that of the state-of-the-art AgGaS 2 standard but also demonstrate an LDT response of 2.3–2.5 times higher than that of AgGaS 2 (at 1.09 μm laser with a pulse width of 10 ns)-which is unprecedented for small band gap semiconductors.
Giant topological longitudinal circular photo-galvanic effect in the chiral multifold semimetal CoSi
The absence of mirror symmetry, or chirality, is behind striking natural phenomena found in systems as diverse as DNA and crystalline solids. A remarkable example occurs when chiral semimetals with topologically protected band degeneracies are illuminated with circularly polarized light. Under the right conditions, the part of the generated photocurrent that switches sign upon reversal of the light’s polarization, known as the circular photo-galvanic effect, is predicted to depend only on fundamental constants. The conditions to observe quantization are non-universal, and depend on material parameters and the incident frequency. In this work, we perform terahertz emission spectroscopy with tunable photon energy from 0.2 –1.1 eV in the chiral topological semimetal CoSi. We identify a large longitudinal photocurrent peaked at 0.4 eV reaching ~550 μ A/V 2 , which is much larger than the photocurrent in any chiral crystal reported in the literature. Using first-principles calculations we establish that the peak originates only from topological band crossings, reaching 3.3 ± 0.3 in units of the quantization constant. Our calculations indicate that the quantized circular photo-galvanic effect is within reach in CoSi upon doping and increase of the hot-carrier lifetime. The large photo-conductivity suggests that topological semimetals could potentially be used as novel mid-infrared detectors.
Materials Data on Al(CoSi)2 by Materials Project
Al(CoSi)2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Co+2.50+ is bonded in a 5-coordinate geometry to five equivalent Si4- atoms. There are a spread of Co–Si bond distances ranging from 2.27–2.43 Å. Al3+ is bonded in a 6-coordinate geometry to six equivalent Si4- atoms. All Al–Si bond lengths are 2.78 Å. Si4- is bonded in a 11-coordinate geometry to five equivalent Co+2.50+, three equivalent Al3+, and three equivalent Si4- atoms. All Si–Si bond lengths are 2.67 Å.
Materials Data on CoSi by Materials Project
CoSi is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Co4+ is bonded in a body-centered cubic geometry to eight equivalent Si4- atoms. All Co–Si bond lengths are 2.41 Å. Si4- is bonded in a body-centered cubic geometry to eight equivalent Co4+ atoms.
Materials Data on Sc(CoSi)2 by Materials Project
Sc(CoSi)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Sc3+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All Sc–Si bond lengths are 2.92 Å. Co+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing CoSi4 tetrahedra. All Co–Si bond lengths are 2.24 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Sc3+, four equivalent Co+2.50+, and one Si4- atom. The Si–Si bond length is 2.38 Å.
Materials Data on Y(CoSi)2 by Materials Project
Y(CoSi)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Y3+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All Y–Si bond lengths are 3.02 Å. Co+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of corner and edge-sharing CoSi4 tetrahedra. All Co–Si bond lengths are 2.28 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Y3+, four equivalent Co+2.50+, and one Si4- atom. The Si–Si bond length is 2.51 Å.
Materials Data on Yb(CoSi)2 by Materials Project
Yb(CoSi)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Yb3+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All Yb–Si bond lengths are 3.03 Å. Co+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing CoSi4 tetrahedra. All Co–Si bond lengths are 2.27 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Yb3+, four equivalent Co+2.50+, and one Si4- atom. The Si–Si bond length is 2.57 Å.
Materials Data on Gd(CoSi)2 by Materials Project
Gd(CoSi)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Gd3+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All Gd–Si bond lengths are 3.04 Å. Co+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing CoSi4 tetrahedra. All Co–Si bond lengths are 2.28 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Gd3+, four equivalent Co+2.50+, and one Si4- atom. The Si–Si bond length is 2.54 Å.
Materials Data on Hf(CoSi)2 by Materials Project
Hf(CoSi)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Hf4+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All Hf–Si bond lengths are 2.89 Å. Co2+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing CoSi4 tetrahedra. All Co–Si bond lengths are 2.24 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Hf4+, four equivalent Co2+, and one Si4- atom. The Si–Si bond length is 2.33 Å.
Materials Data on CoSi by Materials Project
CoSi crystallizes in the cubic P2_13 space group. The structure is three-dimensional. Co4+ is bonded in a 7-coordinate geometry to seven equivalent Si4- atoms. There are a spread of Co–Si bond distances ranging from 2.32–2.43 Å. Si4- is bonded in a 7-coordinate geometry to seven equivalent Co4+ atoms.
Materials Data on CoSI by Materials Project
CoSI is half-Heusler structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Co3+ is bonded in a body-centered cubic geometry to four equivalent S2- and four equivalent I1- atoms. All Co–S bond lengths are 2.72 Å. All Co–I bond lengths are 2.72 Å. S2- is bonded to four equivalent Co3+ atoms to form SCo4 tetrahedra that share corners with four equivalent ICo4 tetrahedra, corners with twelve equivalent SCo4 tetrahedra, and edges with six equivalent ICo4 tetrahedra. I1- is bonded to four equivalent Co3+ atoms to form ICo4 tetrahedra that share corners with four equivalent SCo4 tetrahedra, corners with twelve equivalent ICo4 tetrahedra, and edges with six equivalent SCo4 tetrahedra.
Materials Data on Ca(CoSi)2 by Materials Project
Ca(CoSi)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ca2+ is bonded in a body-centered cubic geometry to eight equivalent Si4- atoms. All Ca–Si bond lengths are 3.06 Å. Co3+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing CoSi4 tetrahedra. All Co–Si bond lengths are 2.28 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Ca2+, four equivalent Co3+, and one Si4- atom. The Si–Si bond length is 2.61 Å.
Optical signatures of multifold fermions in the chiral topological semimetal CoSi
Significance We present a comprehensive combined experimental and theoretical study of optical conductivity in the chiral topological semimetal CoSi based on the development of high-quality crystals. We reveal the presence and the energy range of various exotic multifold quasiparticles in the optical responses and provide experimental evidence for the realization of fourfold spin-3/2 fermions, which were not directly observed previously. Our work is critical to interpreting future optical and transport responses of multifold fermion materials. We believe the methods used in this work will not only stimulate future research in this class of materials but will also provide a strategy for addressing optical signatures of chiral topological fermions in solids.
Materials Data on Sm(CoSi)2 by Materials Project
SmCo2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Sm3+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All Sm–Si bond lengths are 3.06 Å. Co+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing CoSi4 tetrahedra. All Co–Si bond lengths are 2.29 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Sm3+, four equivalent Co+2.50+, and one Si4- atom. The Si–Si bond length is 2.59 Å.
Materials Data on Np(CoSi)2 by Materials Project
NpCo2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Np4+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All Np–Si bond lengths are 2.96 Å. Co2+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing CoSi4 tetrahedra. All Co–Si bond lengths are 2.28 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Np4+, four equivalent Co2+, and one Si4- atom. The Si–Si bond length is 2.36 Å.
Materials Data on U(CoSi)2 by Materials Project
UCo2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. U4+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All U–Si bond lengths are 2.99 Å. Co2+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing CoSi4 tetrahedra. All Co–Si bond lengths are 2.28 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent U4+, four equivalent Co2+, and one Si4- atom. The Si–Si bond length is 2.40 Å.