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Register a new userRole of Hunds splitting in electronic phase competition in ${rm Pb}_{1-x}{rm Sn}_{x}{rm Te}$
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We study the effect of Hunds splitting of repulsive interactions on electronic phase transitions in the multiorbital topological crystalline insulator Pb$_{1-x}$Sn$_{x}$Te, when the chemical potential is tuned to the vicinity of low-lying Type-II Van Hove singularities. Nontrivial Berry phases associated with the Bloch states impart momentum-dependence to electron interactions in the relevant band. We use a multipatch parquet renormalization group (RG) analysis for studying the competition of different electronic phases, and find that if the dominant fixed-point interactions correspond to antiparallel spin configurations, then a chiral $p$-wave Fulde-Ferrell-Larkin-Ovchinnikov(FFLO) state is favored, otherwise, none of the commonly encountered electronic instabilities occur within the one-loop parquet RG approach.
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$rm CePt_3Si$ is a novel ternary compound exhibiting antiferromagnetic order at $T_N approx 2.2$ K and superconductivity (SC) at $T_c approx 0.75$ K. Large values of $H_{c2} approx -8.5$ T/K and $H_{c2}(0) approx 5$ T indicate Cooper pairs formed out of heavy quasiparticles. The mass enhancement originates from Kondo interaction with a characteristic temperature $T_K approx 8$ K. NMR and $mu$SR measurements evidence coexistence of SC and long range magnetic order on a microscopic scale. Moreover, $rm CePt_3Si$ is the first heavy fermion SC without an inversion symmetry. This gives rise to a novel type of the NMR relaxation rate $1/T_1$ which is very unique and never reported before for other heavy fermion superconductors. Studies of Si/Ge substitution allow us to establish a phase diagram.
We performed systematic angle-resolved photoemission spectroscopy measurements $in$-$situ$ on $T$-${rm La}_{2-x}{rm Ce}_xrm {CuO}_{4pmdelta}$ (LCCO) thin films over the extended doping range prepared by the refined ozone/vacuum annealing method. Electron doping level ($n$), estimated from the measured Fermi surface volume, varies from 0.05 to 0.23, which covers the whole superconducting dome. We observed an absence of the insulating behavior around $n sim$ 0.05 and the Fermi surface reconstruction shifted to $n sim$ 0.11 in LCCO compared to that of other electron-doped cuprates at around 0.15, suggesting that antiferromagnetism is strongly suppressed in this material. The possible explanation may lie in the enhanced -$t$ /$t$ in LCCO for the largest $rm{La^{3+}}$ ionic radius among all the Lanthanide elements.
We study the effect of a uniform external magnetization on p-wave superconductivity on the (001) surface of the crystalline topological insulator(TCI) Pb$_{1-x}$Sn$_{x}$Te. It was shown by us in an earlier work that a chiral p-wave finite momentum pairing (FFLO) state can be stabilized in this system in the presence of weak repulsive interparticle interactions. In particular, the superconducting instability is very sensitive to the Hunds interaction in the multiorbital TCI, and no instabilities are found to be possible for the wrong sign of the Hunds splitting. Here we show that for a finite Hunds splitting of interactions, a significant value of the external magnetization is needed to degrade the surface superconductivity, while in the absence of the Hunds interaction, an arbitrarily small external magnetization can destroy the superconductivity. This implies that multiorbital effects in this system play an important role in stabilizing electronic order on the surface.
We report a polarized neutron scattering study of the orbital-like magnetic order in strongly underdoped ${rm YBa_2Cu_3O_{6.45}}$ and ${rm YBa_2(Cu_{0.98}Zn_{0.02})_3O_{6.6}}$. Their hole doping levels are located on both sides of the critical doping $p_{MI}$ of a metal-insulator transition inferred from transport measurements. Our study reveals a drop down of the orbital-like order slightly below $p_{MI}$ with a steep decrease of both the ordering temperature $T_{mag}$ and the ordered moment. Above $p_{MI}$, substitution of quantum impurities does not change $T_{mag}$, whereas it lowers significantly the bulk ordered moment. The modifications of the orbital-like magnetic order are interpreted in terms of a competition with electronic liquid crystal phases around $p_{MI}$. This competition gives rise to a mixed magnetic state in ${rm YBa_2Cu_3O_{6.45}}$ and a phase separation in ${rm YBa_2(Cu_{0.98}Zn_{0.02})_3O_{6.6}}$.
The ratio of the Zeeman splitting to the cyclotron energy ($M=Delta E_Z / hbar omega_c$), which characterizes the relative strength of the spin-orbit interaction in crystals, is examined for the narrow gap IV-VI semiconductors PbTe, SnTe, and their alloy Pb$_{1-x}$Sn$_x$Te on the basis of the multiband $kcdot p$ theory. The inverse mass $alpha$, the g-factor $g$, and $M$ are calculated numerically by employing the relativistic empirical tight-binding band calculation. On the other hand, a simple but exact formula of $M$ is obtained for the six-band model based on the group theoretical analysis. It is shown that $M<1$ for PbTe and $M>1$ for SnTe, which are interpreted in terms of the relevance of the interband couplings due to the crystalline spin-orbit interaction. It is clarified both analytically and numerically that $M=1$ just at the band inversion point, where the transition from trivial to nontrivial topological crystalline insulator occurs. By using this property, one can detect the transition point only with the bulk measurements. It is also proposed that $M$ is useful to evaluate quantitatively a degree of the Dirac electrons in solids.
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