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YbB12 crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Yb is bonded in a 1-coordinate geometry to twenty-four equivalent B atoms. All Yb–B bond lengths are 2.79 Å. B is bonded in a 7-coordinate geometry to two equivalent Yb and five equivalent B atoms. There is one shorter (1.74 Å) and four longer (1.78 Å) B–B bond length.
Abstract The quantum limit in a Fermi liquid, realized when a single Landau level is occupied in strong magnetic fields, gives rise to unconventional states, including the fractional quantum Hall effect and excitonic insulators. Stronger interactions in metals with nearly localized f -electron degrees of freedom increase the likelihood of these unconventional states. However, access to the quantum limit is typically impeded by the tendency of f -electrons to polarize in a strong magnetic field, consequently weakening the interactions. In this study, we propose that the quantum limit in such systems must be approached in reverse, starting from an insulating state at zero magnetic field. In this scenario, Landau levels fill in the reverse order compared to regular metals and are closely linked to a field-induced insulator-to-metal transition. We identify YbB 12 as a prime candidate for observing this effect and propose the presence of an excitonic insulator state near this transition.
YbAlB4 is hexagonal omega structure-derived structured and crystallizes in the orthorhombic Pmmm space group. The structure is three-dimensional. Yb3+ is bonded to twelve B+1.50- atoms to form YbB12 cuboctahedra that share edges with four equivalent YbB12 cuboctahedra, edges with eight equivalent AlB12 cuboctahedra, faces with four equivalent YbB12 cuboctahedra, and faces with four equivalent AlB12 cuboctahedra. There are four shorter (2.57 Å) and eight longer (2.58 Å) Yb–B bond lengths. Al3+ is bonded to twelve B+1.50- atoms to form AlB12 cuboctahedra that share edges with four equivalent AlB12 cuboctahedra, edges with eight equivalent YbB12 cuboctahedra, faces with four equivalent YbB12 cuboctahedra, and faces with four equivalent AlB12 cuboctahedra. There are four shorter (2.48 Å) and eight longer (2.54 Å) Al–B bond lengths. There are two inequivalent B+1.50- sites. In the first B+1.50- site, B+1.50- is bonded in a 9-coordinate geometry to four equivalent Yb3+, two equivalent Al3+, and three B+1.50- atoms. There is two shorter (1.79 Å) and one longer (1.97 Å) B–B bond length. In the second B+1.50- site, B+1.50- is bonded in a 9-coordinate geometry to two equivalent Yb3+, four equivalent Al3+, and three B+1.50- atoms. The B–B bond length is 1.71 Å.
Strong electronic interactions in condensed-matter systems often lead to unusual quantum phases. One such phase occurs in the Kondo insulator YbB12, the insulating state of which exhibits phenomena that are characteristic of metals, such as magnetic quantum oscillations, a gapless fermionic contribution to heat capacity and itinerant-fermion thermal transport. To understand these phenomena, it is informative to study their evolution as the energy gap of the Kondo insulator state is closed by a large magnetic field. Here we show that clear quantum oscillations are observed in the resulting high-field metallic state in YbB12; this is despite it possessing relatively high resistivity, large effective masses and huge Kadowaki–Woods ratio, a combination that normally precludes quantum oscillations. Both quantum oscillation frequency and cyclotron mass display a strong field dependence. By tracking the Fermi surface area, we conclude that the same quasiparticle band gives rise to quantum oscillations in both insulating and metallic states. These data are understood most simply by using a two-fluid picture in which neutral quasiparticles—contributing little or nothing to charge transport—coexist with charged fermions. Overall, our observations of the complex field-dependent behaviour of the fermion ensemble inhabiting YbB 12 provide strong constraints for existing theoretical models.
YbB2 is hexagonal omega structure structured and crystallizes in the hexagonal P6/mmm space group. The structure is three-dimensional. Yb is bonded to twelve equivalent B atoms to form a mixture of face and edge-sharing YbB12 cuboctahedra. All Yb–B bond lengths are 2.73 Å. B is bonded in a 9-coordinate geometry to six equivalent Yb and three equivalent B atoms. All B–B bond lengths are 1.85 Å.
Yb2OsB6 crystallizes in the orthorhombic Pbam space group. The structure is three-dimensional. there are two inequivalent Yb+2.50+ sites. In the first Yb+2.50+ site, Yb+2.50+ is bonded in a 12-coordinate geometry to fourteen B1- atoms. There are a spread of Yb–B bond distances ranging from 2.72–2.87 Å. In the second Yb+2.50+ site, Yb+2.50+ is bonded to twelve B1- atoms to form a mixture of edge and face-sharing YbB12 cuboctahedra. There are a spread of Yb–B bond distances ranging from 2.57–2.60 Å. Os1+ is bonded in a 10-coordinate geometry to ten B1- atoms. There are a spread of Os–B bond distances ranging from 2.36–2.39 Å. There are six inequivalent B1- sites. In the first B1- site, B1- is bonded in a 3-coordinate geometry to four equivalent Yb+2.50+, two equivalent Os1+, and three B1- atoms. There are a spread of B–B bond distances ranging from 1.76–1.81 Å. In the second B1- site, B1- is bonded in a 9-coordinate geometry to four Yb+2.50+, two equivalent Os1+, and three B1- atoms. There is one shorter (1.80 Å) and one longer (1.84 Å) B–B bond length. In the third B1- site, B1- is bonded in a 9-coordinate geometry to four Yb+2.50+, two equivalent Os1+, and three B1- atoms. There is one shorter (1.72 Å) and one longer (1.82 Å) B–B bond length. In the fourth B1- site, B1- is bonded in a 9-coordinate geometry to four Yb+2.50+, two equivalent Os1+, and three B1- atoms. There is one shorter (1.79 Å) and one longer (1.84 Å) B–B bond length. In the fifth B1- site, B1- is bonded in a 9-coordinate geometry to four Yb+2.50+, two equivalent Os1+, and three B1- atoms. In the sixth B1- site, B1- is bonded in a 9-coordinate geometry to six Yb+2.50+ and three B1- atoms. The B–B bond length is 1.86 Å.
Yb2RuB6 crystallizes in the orthorhombic Pbam space group. The structure is three-dimensional. there are two inequivalent Yb2+ sites. In the first Yb2+ site, Yb2+ is bonded in a 12-coordinate geometry to fourteen B1- atoms. There are a spread of Yb–B bond distances ranging from 2.72–2.88 Å. In the second Yb2+ site, Yb2+ is bonded to twelve B1- atoms to form a mixture of edge and face-sharing YbB12 cuboctahedra. There are a spread of Yb–B bond distances ranging from 2.57–2.61 Å. Ru2+ is bonded in a 10-coordinate geometry to ten B1- atoms. There are a spread of Ru–B bond distances ranging from 2.37–2.40 Å. There are six inequivalent B1- sites. In the first B1- site, B1- is bonded in a 3-coordinate geometry to four equivalent Yb2+, two equivalent Ru2+, and three B1- atoms. There are a spread of B–B bond distances ranging from 1.76–1.81 Å. In the second B1- site, B1- is bonded in a 9-coordinate geometry to four Yb2+, two equivalent Ru2+, and three B1- atoms. There is one shorter (1.80 Å) and one longer (1.83 Å) B–B bond length. In the third B1- site, B1- is bonded in a 9-coordinate geometry to four Yb2+, two equivalent Ru2+, and three B1- atoms. There is one shorter (1.71 Å) and one longer (1.80 Å) B–B bond length. In the fourth B1- site, B1- is bonded in a 9-coordinate geometry to four Yb2+, two equivalent Ru2+, and three B1- atoms. There is one shorter (1.79 Å) and one longer (1.84 Å) B–B bond length. In the fifth B1- site, B1- is bonded in a 9-coordinate geometry to four Yb2+, two equivalent Ru2+, and three B1- atoms. In the sixth B1- site, B1- is bonded in a 9-coordinate geometry to six Yb2+ and three B1- atoms. The B–B bond length is 1.83 Å.