Observation of a two-dimensional Fermi surface and Dirac dispersion in YbMnSb2

We present the crystal structure, electronic structure, and transport properties of the material YbMnSb2, a candidate system for the investigation of Dirac physics in the presence of magnetic order. Our measurements reveal that this system is a low-carrier-density semimetal with a two-dimensional Fermi surface arising from a Dirac dispersion, consistent with the predictions of density-functional-theory calculations of the antiferromagnetic system. The low temperature resistivity is very large, suggesting that scattering in this system is highly efficient at dissipating momentum despite its Dirac-like nature.

SrCu2(BO3)(2) under pressure: A first-principles study

Frédéric Mila

Using density-functional theory (DFT) band-structure calculations, we study the crystal structure, lattice dynamics, and magnetic interactions in the Shastry-Sutherland magnet SrCu2(BO3)(2) under pressure, concentrating on experimentally relevant pressures up to 4 GPa. We first check that a ferromagnetic spin alignment shortens the nearest-neighbor Cu-Cu distance and reduces the Cu-O-Cu angle compared to the state with the antiferromagnetic spin alignment in the dimers, in qualitative agreement with the structural changes observed at ambient pressure as a function of temperature and applied field. Next, we determine the optimal crystal structures corresponding to the magnetic structures consistent with, respectively, the dimer phase realized at ambient pressure, the Neel ordered phase realized at high pressure, and two candidates for the intermediate phase with two types of dimers and different stackings. For each phase, we performed a systematic study as a function of pressure, and we determined the exchange interactions and the frequencies of several experimentally relevant phonon modes. In the dimer phase, the ratio of the inter- to intradimer couplings is found to increase with pressure, in qualitative agreement with various experiments. This increase is mostly due to the decrease of the intradimer coupling due to the reduction of the Cu-O-Cu angle under pressure. The phonon frequency of the pantograph mode is also found to increase with pressure, in qualitative agreement with recent Raman experiments. In the Neel phase, the frequency of the pantograph mode is larger than the extrapolated value from the dimer phase, again in agreement with the experimental results, and accordingly the intradimer coupling is smaller than the extrapolated value from the dimer phase. Finally, all tendencies inside the candidate intermediate phases are thoroughly worked out, including specific predictions for some Raman active phonon modes that could be used to pin down the nature of the intermediate phase.

AMER PHYSICAL SOC2020

Extremely large magnetoresistance in the "ordinary" metal ReO3

Huancheng Chen, Quansheng Wu, Oleg Yazyev, Shengnan Zhang

The extremely large magnetoresistance (XMR) observed in many topologically nontrivial and trivial semimetals has attracted much attention in relation to its underlying physical mechanism. In this paper, by combining the band structure and Fermi surface (FS) calculations with the Hall resistivity and de Haas-van Alphen (dHvA) oscillation measurements, we studied the anisotropy of magnetoresistance (MR) of ReO3 with a simple cubic structure, an "ordinary" nonmagnetic metal considered previously. We found that ReO3 exhibits almost all the characteristics of XMR semimetals: the nearly quadratic field dependence of MR, a field-induced upturn in resistivity followed by a plateau at low temperatures, and high mobilities of charge carriers. It was found that for magnetic field H applied along the c axis, the MR exhibits an unsaturated H-1.75 dependence, which was argued to arise from the complete carrier compensation supported by the Hall resistivity measurements. For H applied along the direction of 15 degrees relative to the c axis, an unsaturated H-1.90 dependence of MR up to (9.43 x 10(3))% at 10 K and 9 T was observed, which was explained by the existence of electron open orbits extending along the k(x) direction. Two mechanisms responsible for XMR observed usually in the semimetals occur also in the simple metal ReO3 due to its peculiar FS (two closed electron pockets and one open electron pocket), once again indicating that the details of FS geometrical configuration are a key factor for the observed XMR in materials.

AMER PHYSICAL SOC2021

Transport and magnetic properties of BaVSe3

Ana Akrap, Neven Barisic, Helmuth Berger, László Forró, Vladan Stevanovic

We report a comprehensive study of transport, magnetotransport, and magnetic properties of single crystals of BaVSe3. The paramagnetic metal-ferromagnetic metal transition at 43 K was followed as a function of pressure by measuring the electrical resistivity and the thermoelectric power. The exponent of the low-temperature power-law dependence of the resistivity increases with pressure. The effective magnetic moment obtained from magnetic susceptibility in the paramagnetic regime is mu(eff)=1.40 mu(B). The study was completed by band-structure calculations based on density-functional theory both at ambient and high pressures. Transport coefficients of BaVSe3 resemble the high-pressure phase of BaVS3, which suggest that the replacement of sulfur with selenium can be viewed as chemical pressure.

2008

SrCu2(BO3)(2) under pressure: A first-principles study

Frédéric Mila

AMER PHYSICAL SOC2020